September 18

Looking Back at Home

1977 — Voyager 1 Photographs Earth and Moon Together

Image time not established

On September 18, 1977, NASA's Voyager 1 turned its camera back toward the world it had left behind and captured a historic portrait: Earth and the Moon together in a single photographic frame.

Voyager 1 had launched only thirteen days earlier, on September 5, beginning a journey that would take it past Jupiter and Saturn and eventually into interstellar space. When it made the photograph, the spacecraft was already approximately 11.66 million kilometers (7.25 million miles) from Earth.

From that distance, Earth and Moon appeared not as the enormous world beneath our feet and the brilliant object dominating our night sky, but as two small crescents suspended together in darkness.

The illuminated portion of Earth showed eastern Asia, the western Pacific Ocean, and part of the Arctic. Voyager's position placed it roughly above Mount Everest, although Everest itself was on Earth's night side.

Creating the familiar color image required more than a single exposure. Voyager recorded images through different color filters, which were subsequently combined and processed by the Jet Propulsion Laboratory's Image Processing Laboratory. Because Earth was much brighter than the Moon, the lunar image was artificially brightened by a factor of three so that both worlds could be clearly seen together.

Spacecraft had photographed Earth before. Mariner 10 had even photographed Earth and the Moon separately in 1973, and those images were combined into a composite. But Voyager 1's September 18 photograph was different: both Earth and Moon appeared together within the same camera frame.

The photograph anticipated an even more famous Voyager image. On February 14, 1990, from approximately 6.4 billion kilometers (4 billion miles) away, Voyager 1 would turn its camera toward home once again and record Earth as the tiny “Pale Blue Dot.”

But the September 18, 1977 image came first. It offered an early glimpse of something planetary exploration would repeatedly teach us: traveling outward changes the way we see home.

Why It Matters: Voyager 1's portrait was the first spacecraft photograph to show the complete Earth-Moon system together in a single frame. Scientifically, it documented our planetary system from a new perspective. Culturally, it helped establish a tradition of spacecraft looking homeward and showing Earth not as the center of our experience, but as one small world traveling through the universe.

 

Also on This Day

1959 — Vanguard III Begins a Mission to Study the Environment Around Earth

Launch time not established

On September 18, 1959, the United States successfully launched Vanguard III from Cape Canaveral, Florida, aboard the final Vanguard launch vehicle.

The small scientific satellite entered an elliptical Earth orbit carrying instruments designed to investigate Earth's magnetic field, solar X-rays, micrometeorites, radiation, and temperatures in the space environment.

One of its most successful instruments was a proton-precession magnetometer. During approximately 85 days of battery-powered operation, Vanguard III gathered measurements of Earth's magnetic field over a wide range of altitudes. The mission also helped define characteristics of the lower edge of the Van Allen radiation belts and collected information about micrometeorites and the environment surrounding Earth.

Not every experiment worked as intended. Instruments designed to observe solar X-rays and ultraviolet Lyman-alpha radiation were overwhelmed by energetic particles in Earth's radiation belts, preventing useful observations of those phenomena. Even that difficulty provided experience that influenced later space-based astronomy.

Vanguard III was also historically significant because its launch effectively marked the end of the Project Vanguard flight program. Vanguard had begun as the American effort to launch a scientific satellite during the International Geophysical Year. After Sputnik 1 dramatically reached orbit first, Vanguard became associated in the public mind with the early American struggle to catch up in the Space Race. Yet the program ultimately produced successful satellites and valuable scientific and engineering knowledge.

Why It Matters: Vanguard III belonged to the first generation of spacecraft that transformed the region above Earth into a place scientists could directly measure. Its instruments helped investigate Earth's magnetic environment and micrometeorite population while contributing to the developing techniques of scientific satellite research.

1968 — Zond 5 Carries Living Creatures Around the Moon

Closest-approach time not established

On September 18, 1968, the Soviet spacecraft Zond 5 swept around the Moon, carrying an extraordinary collection of passengers—including two Russian steppe tortoises.

Zond 5 had launched on September 14 UTC on a free-return trajectory around the Moon. Along with the tortoises, its biological payload included insects, plants, seeds, bacteria, and other living material. The mission was intended in part to investigate whether living organisms could survive a journey through deep space and back to Earth.

During its September 18 lunar encounter, Zond 5 passed approximately 1,950 kilometers (1,210 miles) above the Moon. The spacecraft also photographed Earth from tens of thousands of kilometers away.

No human being had yet traveled beyond low Earth orbit. Nevertheless, the living organisms aboard Zond 5 were now moving through space beyond the Moon.

Three days later, on September 21, the spacecraft returned to Earth and splashed down in the Indian Ocean. Despite an unusually severe ballistic reentry that subjected its biological passengers to high gravitational forces, the tortoises survived.

They had become the first terrestrial animals to travel around the Moon and return alive.

The mission occurred only three months before Apollo 8 carried Frank Borman, Jim Lovell, and William Anders on humanity's first crewed voyage around the Moon.

Why It Matters: Zond 5 demonstrated that living organisms could survive a circumlunar journey and return to Earth. It also showed how close the Soviet Union had come to achieving a crewed lunar flyby as the United States prepared Apollo 8.

 

The Bigger Picture

September 18 presents three different ways in which leaving Earth changed what humanity could know.

Vanguard III represents measurement. For most of astronomical history, scientists studied the heavens from beneath Earth's atmosphere. Early satellites allowed instruments to enter the environment they were investigating, directly measuring magnetic fields, radiation, particles, and micrometeorites.

Zond 5 represents travel. Nine years after Vanguard III entered Earth orbit, living creatures from Earth were already traveling around the Moon. The enormous distance between observing space and journeying through it was being crossed with astonishing speed.

Then Voyager 1 changed the direction of our gaze.

Its mission was outward-bound. Jupiter and Saturn lay ahead. Yet on September 18, 1977, Voyager looked backward.

The resulting photograph captured something that would become one of the great recurring themes of space exploration: the farther we travel from Earth, the more clearly we sometimes see Earth itself.

From the ground, the Moon appears to travel across our sky while Earth seems immense and stationary beneath us. From Voyager's perspective, both became small worlds sharing the same darkness.

Thirteen years later, Voyager would look home once more and reduce Earth to the Pale Blue Dot.

September 18 therefore reminds us that exploration has two directions. We look outward to understand the universe, and sometimes the universe gives us a new vantage point from which to understand home.

At a Glance

1959 — Launch time not established — Vanguard III launches from Cape Canaveral to investigate Earth's magnetic field, radiation environment, micrometeorites, and other characteristics of near-Earth space.

1968 — Closest-approach time not established — Zond 5 passes approximately 1,950 kilometers above the Moon carrying tortoises and other living organisms on the first successful biological journey around the Moon and back.

1977 — Image time not established — Voyager 1 photographs Earth and the Moon together in a single camera frame from approximately 11.66 million kilometers away, the first spacecraft image of its kind.

September 17

Enterprise Takes Its Name

1976 — NASA Unveils the Space Shuttle Enterprise

Time not established

On September 17, 1976, NASA formally unveiled the first completed Space Shuttle orbiter at the Rockwell International facility in Palmdale, California. The spacecraft bore a name that connected the emerging Shuttle era with one of popular culture's most enduring visions of space exploration: Enterprise.

The orbiter had originally been designated Constitution, with its public rollout deliberately planned for September 17—Constitution Day in the United States. But thousands of fans of the television series Star Trek organized a letter-writing campaign urging the White House to name the spacecraft after the fictional starship Enterprise. President Gerald Ford supported the change, and NASA adopted the name.

The connection became unmistakable at the rollout ceremony. Star Trek creator Gene Roddenberry and members of the original television cast attended as the new orbiter emerged from its assembly building. The Star Trek theme was played during the ceremony.

Enterprise looked like the orbiters that would later travel into space, but it was never equipped for orbital flight. It lacked main engines and many of the systems necessary for a space mission. Instead, NASA built it primarily to test whether the Shuttle's revolutionary reusable spacecraft design could actually fly and land like an airplane.

Beginning in 1977, Enterprise was carried aloft atop NASA's modified Boeing 747 Shuttle Carrier Aircraft. Some tests kept the orbiter attached to the aircraft; during others, Enterprise was released in flight so astronauts could glide it independently to a runway landing.

These Approach and Landing Tests provided crucial information about the Shuttle's aerodynamic performance, handling, and landing characteristics. Enterprise was later used for ground testing and fit checks at facilities prepared for operational Shuttle missions.

Although Enterprise never crossed the boundary into space, the orbiters that followed—Columbia, Challenger, Discovery, Atlantis, and Endeavour—built upon what NASA learned from it.

Why It Matters: Enterprise was the pathfinder for the Space Shuttle era. Its testing demonstrated that the unusual winged spacecraft could glide through the atmosphere and land safely after returning from space. Its naming also represents a rare and memorable interaction between science fiction and actual space exploration: a fictional spacecraft inspired the name of a real one that helped prepare humanity's next generation of spacecraft.

Also on This Day

1789 — William Herschel Discovers Saturn's Moon Mimas

Observation time not established

On September 17, 1789, astronomer William Herschel discovered Mimas, one of Saturn's moons, using his enormous 40-foot reflecting telescope at Slough, England.

Herschel had completed the telescope only weeks earlier. Its primary mirror measured approximately 1.2 meters—48 inches—in diameter, making it an extraordinary instrument for its era. The telescope's light-gathering power allowed Herschel to detect objects beyond the reach of smaller instruments.

Mimas is relatively small, only about 396 kilometers (246 miles) across. Its most visually striking feature, unknown to Herschel, is the enormous Herschel crater, named in his honor. At roughly 130 kilometers across, the crater dominates the moon's appearance and gives Mimas its famous resemblance to the fictional Death Star from Star Wars.

Modern observations have revealed that Mimas is much more interesting than its battered, icy exterior initially suggested. Analysis of measurements from the Cassini mission has provided evidence that a global liquid-water ocean may exist beneath its icy crust.

Why It Matters: Herschel's discovery expanded the known Saturnian system and demonstrated the power of increasingly large telescopes to reveal previously unseen worlds. More than two centuries later, spacecraft observations continue to transform those tiny telescopic points of light into complex planetary bodies—and perhaps, in the case of Mimas, ocean worlds.

1857 — Konstantin Tsiolkovsky Is Born

Time unknown

On September 17, 1857, Konstantin Eduardovich Tsiolkovsky was born in Izhevskoye in the Russian Empire.

Long before rockets could reach space, Tsiolkovsky worked out much of the theoretical foundation necessary to make spaceflight possible. A largely self-taught teacher and theorist, he explored concepts involving rockets, orbital travel, space stations, and human journeys beyond Earth.

His landmark 1903 paper, generally translated as “Exploration of Outer Space by Means of Rocket Devices,” described the use of liquid-propellant rockets for spaceflight and presented the mathematical relationship now known as the Tsiolkovsky rocket equation.

That equation relates the change in velocity a rocket can achieve to the velocity of its exhaust and the ratio between its initial and final mass. It expresses one of the fundamental realities of rocketry: a spacecraft must carry propellant to accelerate, but carrying that propellant itself adds mass that must also be accelerated.

Tsiolkovsky also envisioned multistage rockets as a practical way of overcoming this problem. Although he never built the large rockets he imagined, later engineers recognized the importance of his theoretical work.

Why It Matters: Tsiolkovsky helped establish the mathematical and conceptual foundations of astronautics decades before practical spaceflight existed. His career demonstrates that exploration often begins not with a machine but with an idea—and with someone demonstrating that what appears impossible is consistent with the laws of physics.

1962 — NASA Announces Its Second Group of Astronauts

Time not established

On September 17, 1962, NASA announced the selection of nine new astronauts, the second astronaut group in American spaceflight history.

They were Neil Armstrong, Frank Borman, Charles “Pete” Conrad, James Lovell, James McDivitt, Elliot See, Thomas Stafford, Edward White, and John Young.

Unlike the original Mercury Seven, all of whom were military test pilots, the new selection criteria allowed qualified civilian test pilots to apply. Neil Armstrong, a NASA research pilot, became the group's first civilian astronaut.

The nine would play central roles in Gemini and Apollo. Armstrong and Conrad would walk on the Moon. Borman, Lovell, and Anders would make humanity's first voyage around the Moon aboard Apollo 8. Stafford commanded the American spacecraft during the Apollo-Soyuz Test Project. Young eventually walked on the Moon and later commanded the first Space Shuttle mission.

Edward White became the first American to walk in space but later died with Virgil “Gus” Grissom and Roger Chaffee in the Apollo 1 fire. Elliot See died in an aircraft accident in 1966 before making a spaceflight.

Why It Matters: NASA's second astronaut group supplied many of the people who would transform President Kennedy's lunar goal into reality. Their careers linked Mercury-era experimentation with Gemini, Apollo, international cooperation, and eventually the Space Shuttle.

1996 — Shannon Lucid's Record-Setting Stay Aboard Mir Nears Its End

Crew exchange began after docking at 03:13 UTC, September 19

On September 17, 1996, Space Shuttle Atlantis, launched the previous day on STS-79, was approaching Russia's Mir space station carrying astronaut John Blaha, who would replace Shannon Lucid as NASA's long-duration resident aboard Mir.

Lucid had been living aboard the Russian station since March. Launch delays extended her stay well beyond its original schedule. By the time she returned to Earth, she had spent 188 days in space, then the longest spaceflight by an American and the longest by a woman.

September 17 itself was primarily a rendezvous day rather than the crew-exchange milestone—the Shuttle docked with Mir on September 19 UTC. For that reason, this event is better treated as contextual rather than as a principal September 17 anniversary.

 

The Bigger Picture

September 17 offers an especially clear progression from seeing other worlds, to imagining how to reach them, to preparing the people and machines that actually would.

In 1789, William Herschel used one of the largest telescopes ever constructed to discover Mimas. Humanity's relationship with Saturn was entirely observational; even the existence of the little moon had previously been unknown.

In 1857, Konstantin Tsiolkovsky was born. He would spend much of his life thinking about a question that still seemed fantastic: could human beings build machines capable of escaping Earth and traveling through space?

His mathematics said yes.

In 1962, NASA introduced nine astronauts who would help put those principles into practice. Among them was Neil Armstrong, who less than seven years later would become the first human being to step onto another world.

And in 1976, Enterprise emerged from its assembly building. By then, reaching space was no longer an extraordinary experiment undertaken by a handful of pioneering astronauts. NASA was preparing a reusable spacecraft intended to make journeys between Earth and orbit a regular part of human activity.

There is also a delightful cultural thread running through the day. Tsiolkovsky imagined voyages beyond Earth when such ideas belonged largely to speculation. Generations later, Star Trek imagined humans routinely traveling among the stars. Fans of that fictional universe then persuaded their government to give the name Enterprise to a real spacecraft.

September 17 therefore captures one of the recurring patterns in the history of astronomy and space exploration:

We observe what is out there. We imagine reaching it. We determine whether the journey is possible. And eventually, we build the machines and choose the people who will try.

At a Glance

1789 — Observation time not established — William Herschel discovers Mimas, a moon of Saturn, using his newly completed 40-foot telescope.

1857 — Time unknown — Konstantin Tsiolkovsky, future pioneer of astronautics and rocket theory, is born in the Russian Empire.

1962 — Time not established — NASA introduces its second group of nine astronauts, including Neil Armstrong, Frank Borman, Pete Conrad, Jim Lovell, Tom Stafford, Ed White, and John Young.

1976 — Time not established — NASA publicly unveils its first Space Shuttle orbiter, Enterprise, at Palmdale, California.

September 16

A Lifeline in Space

1994 — Astronauts Test a New Way to Rescue Themselves in Space

EVA time: approximately 08:42–15:33 UTC

On September 16, 1994, astronauts Mark C. Lee and Carl J. Meade stepped outside Space Shuttle Discovery during mission STS-64 and deliberately did something spacewalkers normally work very hard to avoid: they floated freely away from their spacecraft.

They were testing a new device called the Simplified Aid for EVA Rescue, better known as SAFER.

SAFER was conceived as an emergency rescue system. Astronauts performing extravehicular activity normally remain connected to their spacecraft by safety tethers. But engineers had to consider a frightening possibility: What would happen if a spacewalker somehow became completely untethered and began drifting away?

Without some means of propulsion, the astronaut might have no way to return.

SAFER provided an answer. The compact unit was worn like a backpack over the astronaut's spacesuit and used small jets of compressed nitrogen controlled by the astronaut. Unlike the much larger Manned Maneuvering Unit used during several Shuttle flights in 1984, SAFER was not intended primarily as a vehicle for routine untethered maneuvering. It was an emergency system—a kind of life jacket for space.

During their six-hour, 51-minute spacewalk, Lee and Meade took turns flying the device untethered near Discovery. They maneuvered above and around the Shuttle's payload bay while evaluating SAFER's controls and handling characteristics. The tests demonstrated that an astronaut who accidentally became separated from a spacecraft could potentially maneuver back to safety.

The technology subsequently became part of normal spacewalking safety procedures. Astronauts conducting spacewalks outside the International Space Station wear SAFER units as an emergency backup should their tethers fail.

Why It Matters: SAFER addressed one of the most dangerous conceivable emergencies during a spacewalk: an astronaut drifting helplessly away from the spacecraft. The September 16 test transformed an emergency-rescue concept into demonstrated technology and helped make future extravehicular activity safer.

 

Also on This Day

1978 — A Total Lunar Eclipse Crosses Earth's Shadow

Greatest eclipse: 19:04:12 UTC

On September 16, 1978, the Moon passed completely through the darkest portion of Earth's shadow, producing a total lunar eclipse.

The eclipse began when the Moon entered Earth's penumbral shadow at approximately 16:22 UTC. The partial phase began around 17:21 UTC, and totality began at approximately 18:25 UTC.

At 19:04:12 UTC, the eclipse reached its greatest phase. Totality lasted approximately 78 minutes and 39 seconds, ending around 19:44 UTC. The Moon finally left Earth's penumbral shadow at approximately 21:46 UTC.

A lunar eclipse occurs because Earth moves directly between the Sun and the Moon. During totality, the Moon does not normally disappear completely. Sunlight passing through Earth's atmosphere is refracted into Earth's shadow, while shorter blue wavelengths are scattered more efficiently. The remaining reddish light can illuminate the lunar surface, producing the familiar copper or red appearance of a totally eclipsed Moon.

The September 1978 eclipse had an umbral magnitude of approximately 1.327, meaning the Moon passed deeply enough into Earth's umbra that its entire disk was immersed in the central shadow.

Why It Matters: Lunar eclipses are among the most accessible demonstrations of celestial mechanics. Long before spacecraft existed, observations of Earth's curved shadow crossing the Moon helped reinforce the understanding that Earth is spherical. Modern eclipse predictions also demonstrate the remarkable precision with which the motions of Earth, Moon, and Sun can be calculated.

1996 — Atlantis Launches on the First American Crew Exchange at Mir

08:54:49 UTC

On September 16, 1996, at 08:54:49 UTC, Space Shuttle Atlantis lifted off from Kennedy Space Center on mission STS-79, beginning the fourth Shuttle docking mission with the Russian space station Mir.

The mission represented an important development in American-Russian cooperation in space. Astronaut John Blaha traveled aboard Atlantis to begin a long-duration stay on Mir, while astronaut Shannon Lucid, already aboard the Russian station, would return to Earth aboard the Shuttle.

Lucid had arrived at Mir in March. Delays in launching STS-79 extended her mission to 188 days, establishing at the time both a new American space-duration record and a world record for a woman.

STS-79 also carried the first double SPACEHAB module, providing additional room for equipment and supplies. During the docked portion of the mission, the Shuttle and Mir crews transferred thousands of pounds of water, supplies, experiments, and equipment between the two spacecraft.

The launch itself had encountered unusual delays. Atlantis had been rolled back from its launch pad twice because of threats from Hurricanes Bertha and Fran—the first time a Shuttle had undergone two hurricane-related rollbacks during a single processing cycle.

Why It Matters: STS-79 conducted the first exchange of American long-duration crew members aboard Mir. The Shuttle-Mir program required American and Russian flight controllers, engineers, astronauts, and cosmonauts to learn how to operate together for extended periods—a body of experience that helped prepare both nations for their partnership aboard the International Space Station.

2015 — A Sounding Rocket Fires a Record 44 Rocket Engines

Time not established

On September 16, 2015, a NASA Black Brant XI sounding rocket launched from Andøya, Norway, carrying the Charged Aerosol Release Experiment II, or CARE II.

The flight investigated dusty plasmas—mixtures containing electrically charged particles and small grains of matter that occur naturally in portions of Earth's upper atmosphere and elsewhere in space.

But the mission also achieved an unusual engineering record.

During the flight, 44 rocket engines were fired, earning recognition from Guinness World Records for the greatest number of rocket engines fired during a single flight. Only three provided the principal propulsion for launching the vehicle. Four others served as spin motors, while many of the remaining motors were used to create the artificial exhaust cloud required for the scientific experiment.

The mission is a useful reminder that not all significant space research requires an orbital spacecraft. Sounding rockets can carry experiments above most of Earth's atmosphere for relatively brief flights, allowing scientists to investigate phenomena that are difficult or impossible to reproduce at ground level.

Why It Matters: CARE II combined an unusual engineering achievement with scientific investigation of the upper atmosphere. Sounding rockets remain an important—and comparatively economical—bridge between laboratory research on Earth and longer-duration experiments conducted in orbit.

 

The Bigger Picture

September 16 reminds us that exploring space requires more than simply finding ways to travel farther from Earth.

The 1978 lunar eclipse represents astronomy in one of its oldest forms: watching the predictable motions of celestial bodies from the ground and learning about the geometry of our solar system.

The 1994 SAFER experiment addressed a very different problem. Once humans began leaving their spacecraft to work in the vacuum of space, engineers had to devise ways of protecting them when something went wrong.

Two years later, STS-79 demonstrated another essential development: cooperation. The United States and Russia, whose earlier space programs had developed largely as rivals, were exchanging crew members aboard Mir and learning how to conduct long-duration missions together.

And the CARE II mission reminds us that even in an era of sophisticated planetary probes and enormous orbital laboratories, relatively small sounding rockets continue to make valuable contributions to space science.

Together, these events illustrate four complementary aspects of humanity's relationship with space: observing it, learning to survive in it, learning to work together within it, and continuing to devise new ways to study it.

The history of space exploration is therefore not simply a succession of destinations. It is also the story of gradually acquiring the knowledge, technologies, safeguards, and partnerships necessary for human beings to operate beyond their home world.

At a Glance

1978 — 19:04:12 UTC — A total lunar eclipse reaches greatest eclipse; totality lasts approximately 78 minutes and 39 seconds.

1994 — Approximately 08:42–15:33 UTC — Astronauts Mark Lee and Carl Meade conduct an STS-64 spacewalk and perform the first in-space tests of the SAFER emergency maneuvering system.

1996 — 08:54:49 UTC — Space Shuttle Atlantis launches on STS-79, beginning the first American long-duration crew exchange at Russia's Mir space station.

2015 — Time not established — NASA's CARE II sounding-rocket mission launches from Norway and fires 44 rocket engines during the flight, establishing a world record.

September 15

Farewell to Cassini

2017 — Cassini Plunges into Saturn

10:31–10:32 UTC — spacecraft event time

On September 15, 2017, NASA's Cassini spacecraft entered the atmosphere of Saturn, deliberately bringing one of the most scientifically productive planetary missions in history to an end.

Cassini had left Earth nearly twenty years earlier, on October 15, 1997. After a journey of almost seven years, it entered orbit around Saturn on July 1, 2004, and began an extraordinary thirteen-year exploration of the planet, its rings, its magnetic environment, and its diverse family of moons.

By 2017, Cassini's supply of maneuvering propellant was nearing exhaustion. Mission planners faced an unusual problem created in part by Cassini's own discoveries. The spacecraft had revealed that Enceladus possesses a subsurface ocean and ejects water-rich material through enormous plumes, while observations of Titan had revealed lakes and seas of liquid hydrocarbons and an extraordinarily complex organic environment.

Scientists did not want an uncontrolled Cassini eventually crashing into one of these worlds and potentially contaminating an environment of astrobiological interest with terrestrial microorganisms. NASA therefore chose to dispose of the spacecraft safely by sending it into Saturn itself.

Cassini's final phase became known as the Grand Finale. Beginning in April 2017, the spacecraft made 22 daring passages through the previously unexplored region between Saturn and its innermost ring. These final orbits allowed Cassini to make measurements that could not have been attempted earlier in the mission.

Then came September 15.

At approximately 10:31 UTC, Cassini began encountering Saturn's atmosphere. Its attitude-control thrusters fired increasingly hard as the spacecraft struggled to keep its high-gain antenna pointed toward Earth. About a minute later, the thrusters reached full capacity. Atmospheric forces overwhelmed Cassini's ability to maintain its orientation, its antenna turned away from Earth, and the spacecraft's signal disappeared. Moments later, Cassini broke apart and burned in Saturn's atmosphere.

But observers on Earth did not know immediately that Cassini was gone. Saturn was so distant that Cassini's radio signals required approximately 83 minutes to cross the solar system. The final signal reached NASA's Deep Space Network station in Canberra, Australia, at about 11:55 UTC.

Cassini continued gathering and transmitting scientific measurements during its descent. Instead of storing its final observations for later transmission—which would have been impossible—the spacecraft sent data directly to Earth as it sampled Saturn's upper atmosphere.

It was doing science until almost the final moment of its existence.

Why It Matters: Cassini transformed our understanding of the Saturn system. Among its many discoveries, it revealed active jets and evidence for a global subsurface ocean at Enceladus, explored Titan's methane-and-ethane lakes and seas, studied Saturn's extraordinarily complex rings and atmosphere, and observed interactions among the planet, rings, moons, and magnetosphere. Its intentional destruction also established an important principle of planetary protection: exploration carries a responsibility to protect potentially habitable environments for future scientific investigation.

 

Also on This Day

1857 — Astronomer Anna Winlock Is Born

Time unknown

On September 15, 1857, Anna Winlock was born in Cambridge, Massachusetts. She would become an astronomer and one of the earliest women employed as a scientific computer at the Harvard College Observatory.

Winlock was the daughter of astronomer Joseph Winlock, director of the Harvard College Observatory. After her father's death in 1875 left the family in financial difficulty, she approached the observatory seeking work. She became one of the women whose painstaking mathematical calculations and analysis of astronomical observations contributed substantially to Harvard's research.

Her work included reducing observations made with the observatory's meridian circle and helping produce astronomical catalogues. She became particularly associated with the Harvard Zones, observations used in compiling an extensive catalogue of stars near the celestial poles. She also performed calculations concerning asteroids.

Winlock's career preceded the better-known generation of women at Harvard—including Williamina Fleming, Antonia Maury, Annie Jump Cannon, and Henrietta Swan Leavitt—whose work became fundamental to modern stellar astronomy.

Why It Matters: Anna Winlock represents an often-overlooked part of astronomical history. Long before women were routinely admitted to professional scientific careers, women working as astronomical computers performed the calculations, measurements, and cataloguing upon which major observatories depended. Their work helped transform enormous quantities of observations into usable astronomical knowledge.

1938 — James Christy Is Born

Time unknown

On September 15, 1938, American astronomer James W. Christy was born in Milwaukee, Wisconsin.

Four decades later, while working at the U.S. Naval Observatory, Christy would make a discovery that fundamentally changed astronomers' understanding of Pluto.

In 1978, Christy was examining photographic plates of Pluto when he noticed that the distant object appeared slightly elongated. Rather than dismissing the irregularity as a flaw in the photographic image, he examined additional plates and discovered that the elongation appeared in different positions according to a repeating pattern.

Christy correctly concluded that Pluto had a previously unknown companion.

The object was subsequently named Charon. The discovery allowed astronomers to determine the orbital characteristics of the Pluto-Charon system much more accurately and ultimately led to substantially improved estimates of Pluto's mass and size.

Decades later, when NASA's New Horizons spacecraft flew through the Pluto system in 2015, Charon was revealed as a remarkable world in its own right, with enormous canyons, varied terrain, and evidence of a complicated geological history.

Why It Matters: Christy's discovery transformed Pluto from an apparently solitary distant object into a complex planetary system. It also demonstrates a recurring lesson in astronomy: important discoveries sometimes begin when a scientist notices an apparent imperfection and asks whether it might actually be telling us something about the universe.

1966 — Gemini XI Returns from a Record-Setting Mission

13:59:35 UTC

On September 15, 1966, at 13:59:35 UTC, astronauts Charles “Pete” Conrad Jr. and Richard F. Gordon Jr. splashed down in the western Atlantic Ocean, completing the ambitious Gemini XI mission.

During their three days in space, Conrad and Gordon had demonstrated several capabilities that would soon be essential for Apollo.

Gemini XI achieved rendezvous and docking with an Agena target vehicle during its first orbit, demonstrating how rapidly two spacecraft could meet in space. Gordon performed two extravehicular activities, and the docked Gemini-Agena combination used the Agena's engine to climb to an altitude of approximately 1,374 kilometers (854 miles)—a human altitude record at the time.

The astronauts also experimented with connecting Gemini and Agena by a tether and creating a small amount of artificial gravity by rotating the two spacecraft around their common center of mass.

After completing 44 Earth orbits, Gemini XI performed an automatically controlled reentry and landed only a few kilometers from its planned recovery point. Conrad and Gordon were recovered by the USS Guam.

Why It Matters: Gemini XI demonstrated techniques—rendezvous, docking, maneuvering two joined spacecraft, extravehicular activity, and precision reentry—that helped prepare NASA for Apollo. Gemini's achievements sometimes stand in the shadow of the Moon landings that followed, but Apollo depended upon skills developed and tested during these demanding missions.

2006 — Cassini Photographs Saturn from Its Shadow

Observation sequence began September 15 UTC

Eleven years before Cassini's mission ended on September 15, the same spacecraft used an extraordinary alignment to produce one of the most revealing views ever made of Saturn's rings.

On September 15, 2006, Cassini passed into Saturn's shadow, placing the enormous planet between the spacecraft and the Sun. With Saturn blocking the Sun's intense glare, Cassini could look back toward the planet and its rings under lighting conditions impossible to reproduce from Earth.

Over nearly three hours, Cassini's wide-angle camera obtained 165 images that were later assembled into a spectacular panoramic mosaic. The spacecraft remained in Saturn's shadow for roughly twelve hours, giving its instruments an exceptional opportunity to study extremely faint material in and around the ring system.

The backlighting revealed delicate structures normally overwhelmed by sunlight, contributing to the identification and study of previously unknown faint rings. The resulting panorama also contained something almost inconspicuously small: Earth, visible as a tiny point of light beyond Saturn's rings.

Why It Matters: The observation demonstrated how profoundly viewing geometry can affect astronomical discovery. By placing Saturn between itself and the Sun, Cassini saw structures that otherwise remained nearly invisible. It also produced one of the great visual reminders of planetary exploration: our enormous home world reduced to a tiny point of light seen from the vicinity of Saturn.

 

The Bigger Picture

September 15 offers an unusual opportunity to see the history of astronomy and space exploration as a continuous story.

Anna Winlock represents the painstaking work of measuring and cataloguing the sky. Astronomy advanced because generations of observers and computers transformed individual observations into organized knowledge.

James Christy represents discovery through careful observation. By recognizing that a small irregularity in images of Pluto was real rather than accidental, he revealed another world.

Gemini XI represents learning how to operate in space. Rendezvous, docking, spacewalking, maneuvering, and controlled reentry were skills humanity had to master before astronauts could attempt voyages to the Moon.

And then there is Cassini, appearing twice on this date.

On September 15, 2006, Cassini hid in Saturn's shadow and looked outward, using an extraordinary perspective to reveal the planet's rings as they had never been seen before.

Exactly eleven years later, on September 15, 2017, the same spacecraft turned toward Saturn for the last time and disappeared into the world it had spent thirteen years exploring.

There is something fitting in that coincidence. Astronomy begins with looking carefully. Space exploration allows us to carry that act of looking to places our ancestors could never reach. And eventually every mission ends, leaving behind its observations for others to study.

September 15 therefore reminds us that exploration is not simply about reaching distant places. It is about seeing what was previously unseen, preserving what we learn, and passing that knowledge to those who come next.

At a Glance

1857 — Time unknown — Astronomer Anna Winlock is born in Cambridge, Massachusetts; she later becomes one of the earliest women employed as a scientific computer at Harvard College Observatory.

1938 — Time unknown — Astronomer James W. Christy is born; four decades later he will discover Charon, Pluto's largest moon.

1966 — 13:59:35 UTC — Gemini XI splashes down in the Atlantic after a mission that demonstrated rendezvous, docking, EVA, high-altitude flight, and other techniques important to Apollo.

2006 — Observation sequence began September 15 UTC — Cassini enters Saturn's shadow and conducts an extraordinary series of backlit observations of the planet and its rings.

2017 — Approximately 10:31–10:32 UTC — Cassini enters Saturn's atmosphere and loses attitude control, ending nearly twenty years in space and thirteen years of exploration at Saturn.

2017 — Approximately 11:55 UTC, Earth-received time — Cassini's final radio signal reaches the Deep Space Network in Canberra, Australia, approximately 83 minutes after the spacecraft's destruction at Saturn.

September 14

Around the Moon and Back

1968 — Zond 5 Begins a Historic Journey

21:42:10 UTC

On September 14, 1968, at approximately 21:42:10 UTC, the Soviet Union launched Zond 5 from Site 81 at the Baikonur Cosmodrome aboard a Proton-K rocket. The spacecraft was placed first into Earth orbit and then sent toward the Moon on a free-return trajectory.

Zond 5 was a version of the Soyuz 7K-L1 spacecraft being developed as part of the Soviet effort to send cosmonauts around the Moon. No people were aboard this flight, but the spacecraft carried an unusual collection of living passengers—including two Russian steppe tortoises, along with insects, plants, microorganisms, and other biological specimens. Scientists hoped to learn more about how living organisms would respond to a journey beyond Earth's immediate environment.

Four days later, on September 18, Zond 5 swept around the Moon, passing approximately 1,950 kilometers (1,210 miles) above its surface. The spacecraft then headed back toward Earth. On September 21, it reentered Earth's atmosphere and splashed down in the Indian Ocean, where Soviet recovery vessels retrieved it. The tortoises and other biological specimens survived the journey.

The mission achieved an extraordinary milestone: living creatures from Earth had traveled around the Moon and returned safely. It also demonstrated important technologies required for human lunar missions, including navigation across hundreds of thousands of kilometers and high-speed atmospheric reentry after returning from the Moon.

The timing was particularly significant. Only three months later, in December 1968, Apollo 8 astronauts Frank Borman, Jim Lovell, and William Anders would become the first humans to travel around the Moon.

Why It Matters: Zond 5 demonstrated that a spacecraft could travel from Earth, pass around the Moon, and return living passengers safely to Earth. It represented an important technological bridge between robotic lunar exploration and human voyages to the Moon.

 

Also on This Day

1712 — Giovanni Domenico Cassini Dies

Time unknown

On September 14, 1712, the influential Italian-born French astronomer Giovanni Domenico Cassini died in Paris.

Cassini was one of the outstanding observational astronomers of the seventeenth century. Among his achievements, he discovered four moons of Saturn—Iapetus, Rhea, Tethys, and Dione—and identified the prominent division between Saturn's A and B rings that still bears his name: the Cassini Division.

He also made important observations of Jupiter and Mars and contributed to efforts to determine the scale of the solar system.

Centuries later, his name would travel to Saturn aboard the Cassini spacecraft, the NASA-European Space Agency-Italian Space Agency mission that entered orbit around Saturn in 2004 and transformed our knowledge of the planet, its rings, and its remarkable family of moons.

Why It Matters: Cassini helped establish planetary astronomy as the careful study of other worlds as physical places with measurable characteristics. His discoveries remain part of the language of astronomy more than three centuries after his death.

1926 — J. L. E. Dreyer Dies

Time unknown

On September 14, 1926, Danish-born astronomer Johan Ludvig Emil Dreyer, usually known as J. L. E. Dreyer, died in Oxford, England, at age 74.

Dreyer's most enduring contribution was the New General Catalogue of Nebulae and Clusters of Stars, published in 1888 and universally known as the NGC. The catalogue contained 7,840 objects, with thousands more subsequently included in Dreyer's supplementary Index Catalogues.

His system remains part of the working vocabulary of astronomy. Familiar objects continue to be identified by their NGC numbers: the Andromeda Galaxy is NGC 224, the Orion Nebula is NGC 1976, and the Whirlpool Galaxy is NGC 5194.

Dreyer was also an important historian of astronomy. He wrote about the development of astronomical thought and devoted considerable scholarly attention to the life and observations of Tycho Brahe.

Why It Matters: Dreyer helped organize the deep sky. His catalogues gave generations of astronomers a common system for identifying thousands of objects beyond the solar system—a system that remains in widespread use today.

1958 — Mohr Sounding Rockets Reach the Upper Atmosphere

Time unknown

On September 14, 1958, three experimental sounding rockets designed by German engineer Ernst Mohr were successfully launched near Cuxhaven, West Germany. Their dart-like payloads reached an altitude of approximately 50 kilometers (31 miles).

The achievement followed unsuccessful launch attempts in June. Mohr's single-stage, solid-fueled rocket accelerated a narrow payload dart that separated after burnout and continued upward because of its more efficient aerodynamic shape. The successful September flights reached their intended altitude.

Fifty kilometers is below the 100-kilometer Kármán line commonly used to define the boundary of space, but sounding rockets occupy an important place in the history of space science. They allow instruments to investigate portions of Earth's atmosphere that are too high for balloons while avoiding the complexity and expense of placing a spacecraft into orbit.

Why It Matters: Mohr's experiments formed part of the postwar development of sounding-rocket technology—an important scientific tool for studying Earth's upper atmosphere and the environment approaching space.

 

The Bigger Picture

September 14 brings together three stages in humanity's effort to understand and eventually travel beyond Earth.

Cassini represents observation. With increasingly capable telescopes, astronomers discovered that the planets were not simply wandering points of light but complex worlds surrounded by rings and moons.

Dreyer represents organization. As telescopes revealed thousands of objects beyond the solar system, astronomy required systematic catalogues so that scientists could identify, compare, and communicate what they observed.

The sounding rockets of 1958 represent experimentation beyond the ground. Astronomical and atmospheric instruments increasingly could be carried above the dense lower atmosphere.

And Zond 5 represents exploration. Only ten years after the Mohr rocket experiments reached 50 kilometers above Earth, another spacecraft departed Earth altogether and began a journey of hundreds of thousands of kilometers around the Moon and back.

The progression captures much of the story at the heart of On This Day in Astronomy and Space: humanity observed the heavens, learned to map and understand them, developed machines capable of rising above Earth, and eventually began sending those machines to other worlds.

At a Glance

1712 — Time unknown — Giovanni Domenico Cassini, pioneering observer of Saturn and its moons, dies in Paris.

1926 — Time unknown — J. L. E. Dreyer, compiler of the New General Catalogue (NGC), dies in Oxford.

1958 — Time unknown — Ernst Mohr's experimental sounding rockets successfully reach approximately 50 kilometers above West Germany.

1968 — 21:42:10 UTC — Zond 5 launches from Baikonur on the historic mission that will carry living organisms around the Moon and safely back to Earth.

September 13

 Humanity Reaches Another World

1959 — Luna 2 Reaches the Moon

22:02:04 UTC

On September 13, 1959, at approximately 22:02:04 UTC, the Soviet spacecraft Luna 2 struck the Moon, becoming the first human-made object to reach the surface of another celestial body.

Launched from the Soviet Union the previous day, Luna 2 was placed on a direct trajectory toward the Moon. After traveling through space for roughly a day and a half, the spacecraft impacted the lunar surface in the region between Mare Imbrium and Mare Serenitatis, near the crater Autolycus. NASA places the impact roughly 160 miles from the site where Apollo 15 astronauts would land twelve years later.

Luna 2 was not merely intended to demonstrate that the Moon could be reached. The spacecraft carried scientific instruments for investigating cosmic rays, radiation, magnetic fields, and the space environment. Its measurements found no significant lunar magnetic field or radiation belts comparable to Earth's. The spacecraft also carried metallic spheres bearing Soviet emblems, which were intended to scatter upon impact.

The achievement came less than two years after Sputnik 1 inaugurated the Space Age. Sputnik demonstrated that humans could place an artificial object into orbit around Earth. Luna 2 crossed another threshold: something built by human hands had now traveled from Earth to another world.

Why It Matters: Luna 2 transformed reaching another celestial body from an aspiration into an accomplished fact. Every successful planetary landing and impact mission that followed—from the Moon and Mars to asteroids and comets—belongs to a history whose first physical contact with another world occurred on September 13, 1959.

 

Also on This Day

1850 — John Russell Hind Discovers 12 Victoria

Time unknown

On the evening of September 13, 1850, English astronomer John Russell Hind discovered the asteroid 12 Victoria while observing at George Bishop's Observatory in London.

Hind was comparing his observations in the constellation Pegasus with a recently prepared star chart when he noticed an object that did not belong among the mapped stars. He correctly recognized it as a previously unknown member of the solar system.

Victoria was only the twelfth asteroid known to astronomy. When the first asteroid, Ceres, had been discovered in 1801, astronomers had no idea that the region between Mars and Jupiter contained a vast population of small worlds. Discoveries such as Victoria gradually revealed the true nature of what we now call the asteroid belt.

The asteroid's name produced an interesting nineteenth-century controversy. Officially, Hind named it for Victoria, the Roman goddess of victory, but the name also honored Britain's reigning Queen Victoria. Some American astronomers objected because the developing convention discouraged naming asteroids after living people, and the alternative name Clio appeared for a time in American publications.

Hind eventually discovered ten asteroids, becoming one of the most successful asteroid hunters of his generation.

Why It Matters: The discovery of Victoria was part of a profound change in humanity's picture of the solar system. What had once seemed to consist principally of the Sun, planets, and their moons was increasingly understood to contain a much larger and more diverse population of smaller worlds.

1985 — An F-15 Destroys a Satellite in Orbit

Time not established

On September 13, 1985, U.S. Air Force Major Wilbert D. “Doug” Pearson climbed rapidly in a specially modified F-15A Eagle and launched an ASM-135A anti-satellite missile toward an object hundreds of kilometers above him.

The target was Solwind P78-1, an aging scientific satellite that had been used to study the Sun. The missile released a miniature kinetic-kill vehicle that homed in on the satellite and destroyed it through a high-speed collision. The test marked the first—and ultimately only—time the ASM-135 system destroyed an actual satellite in orbit.

The achievement demonstrated something technologically extraordinary and strategically troubling: a weapon carried by an aircraft in Earth's atmosphere could successfully strike an object traveling at orbital velocity high above the planet.

The test also illustrated another danger. Destroying a satellite at orbital velocity created a cloud of debris. Such fragments can remain in orbit and pose collision hazards to other spacecraft, making destructive anti-satellite testing an enduring concern in the increasingly crowded environment around Earth.

Why It Matters: The 1985 test demonstrated that space had become more than a realm of scientific discovery and peaceful exploration. It had also become strategically important enough to be treated as a potential arena of military conflict—and showed that actions in space could leave consequences long after an individual mission ended.

 

The Bigger Picture

September 13 presents three remarkably different moments in humanity's changing relationship with the universe.

In 1850, John Russell Hind stood at a telescope and discovered another small world orbiting the Sun. Astronomy was still fundamentally an activity conducted from Earth: humans looked outward and gradually learned what populated the heavens.

In 1959, that relationship changed. Luna 2 did something no telescope could do. Humanity sent a machine across the gulf between Earth and Moon and physically touched another celestial body for the first time.

By 1985, human activity had expanded into near-Earth space so extensively that satellites had become important not only for science and communication but also for national security—and nations were developing technologies capable of destroying them.

These events reveal both the promise and the responsibility that accompany technological progress. We discovered other worlds, learned how to reach beyond our own, and eventually confronted the consequences of bringing human competition into space with us.

September 13 therefore tells more than a story of technological advancement. It reminds us that our increasing ability to reach the universe also raises an enduring question: What will humanity choose to do with the power to operate there?

At a Glance

1850 — Time unknown — John Russell Hind discovers asteroid 12 Victoria at George Bishop's Observatory in London.

1959 — 22:02:04 UTC — Luna 2 impacts the Moon, becoming the first human-made object to reach another celestial body.

1985 — Time not established — An ASM-135A missile launched from an F-15 destroys the Solwind P78-1 satellite, the first satellite destroyed by a weapon launched from an aircraft.

Europa Clipper Mission Teleconference

 On Monday, September 9, NASA will hold a media teleconference to provide an update on the Europa Clipper mission, that will study whether Jupiter’s moon Europa could be hospitable to life. The teleconference will occur after a key decision point meeting earlier that day regarding next steps for the mission. The teleconference can be watched here: https://www.nasa.gov/live/

If you would like information on the Europa mission and the spacecraft, I have a book for you! The book is called Journey to Europa: The NASA Europa Clipper Mission, and it is available in Kindle and paperback form. Click on the image below to check it out!

-

Potential Sign of Life on Venus

Artist's concept of the thick clouds that obscure Venus’ surface. Image Credit: ESO/M. Kornmesser & NASA/JPL/Caltech

An international team of astronomers have confirmed that the cloud tops of Venus contain traces of phosphine, a gas that is produced by microbial life. The gas is also produced by some Earth-based industrial processes. That said, no known non-biological processes can create phosphine in the conditions found on Venus.

The find raises two intriguing possibilities: One, the possibility that Venus may harbor life in its clouds. And two, the phosphine could be the result of some unknown chemical process, which would be an enticing subject of scientific study.

You may read the full article at Astronomy.com

-

Martian Clay Found

The Curiosity rover selfie is composed of 57 individual images taken by the rover's Mars Hand Lens Imager (MAHLI), a camera on the end of the rover's robotic arm. The images are stitched together into a panorama, and the robotic arm is digitally removed. Image credit: NASA/JPL-Caltech/MSSS

NASA's Mars Curiosity rover confirmed that the region it's exploring, called the "clay-bearing unit," prooved to be an accurate name. Two samples the rover recently drilled at rock targets called "Aberlady" and "Kilmarie" have revealed the highest amounts of clay minerals found during the mission. Both drill targets appear in a new selfie taken by the rover on May 12, 2019, the 2,405th Martian day, or sol, of the mission.

The region is located on the side of lower Mount Sharp and stood out to NASA orbiters before Curiosity landed in 2012. Clay often forms in water, which is essential for life; Curiosity is exploring Mount Sharp to see if it had the conditions to support life billions of years ago. The rover's mineralogy instrument, called CheMin (Chemistry and Mineralogy), provided the first analyses of rock samples drilled in the clay-bearing unit. CheMin also found very little hematite, an iron oxide mineral that was abundant just to the north, on Vera Rubin Ridge.

Other than proof that there was a significant amount of water once in Gale Crater, what these new findings mean for the region is still up for debate. It's likely that the rocks in the area formed as layers of mud in ancient lakes - something Curiosity also found lower on Mount Sharp. Water interacted with sediment over time, leaving an abundance of clay in the rocks there.

Amid this new drilling and analyzing, Curiosity took a break to watch some clouds - all in the name of science. The rover used its black-and-white Navigation Cameras (Navcams) to snap images of drifting clouds on May 7 and May 12, 2019, sols 2400 and 2405. They're likely water-ice clouds about 19 miles (31 kilometers) above the surface.

The mission's team has been trying to coordinate cloud observations with NASA's InSight lander, located about 373 miles (600 kilometers) away, which recently took its own cloud images. Capturing the same clouds from two vantage points can help scientists calculate their altitude.

More information about Curiosity is at: https://mars.nasa.gov/msl/

More information about Mars is at: https://mars.nasa.gov/

-

Happy Birthday, Pioneer 10!

Pioneer 10 was launched March 2, 1972. Shown, artist rendering of Pioneer 10 flyby of Jupiter. Image credit, NASA.

March 2 marks a birthday, of sorts, for NASA's Pioneer 10 mission. On this day in 1972, the spacecraft was launched on the first mission to the planet Jupiter.

Originally designated Pioneer F, the spacecraft weighed 258 kilograms (569 pounds), completed the first mission to the planet Jupiter and, later, became the first of five artificial objects to achieve the escape velocity that will allow them to leave the Solar System. The project was conducted by the NASA Ames Research Center in California, and the space probe was manufactured by TRW Inc.

The spacecraft was launched on March 2, 1972 by an Atlas-Centaur expendable vehicle from Launch Complex 36A at Cape Canaveral, Florida. Between July 15, 1972, and February 15, 1973, it became the first spacecraft to traverse the asteroid belt. Photography of Jupiter began November 6, 1973, at a range of 25,000,000 kilometers (16,000,000 mi), and a total of about 500 images were transmitted. The closest approach to the planet was on December 4, 1973, at a range of 132,252 kilometers (82,178 mi). During the mission, the on-board instruments were used to study the asteroid belt, the environment around Jupiter, the solar wind, cosmic rays, and eventually the far reaches of the Solar System and heliosphere.

Pioneer 10 crossed the orbit of Saturn in 1976 and the orbit of Uranus in 1979. On June 13, 1983, the craft crossed the orbit of Neptune, the outermost planet, and so became the first human-made object to leave the proximity of the major planets of the Solar System. The mission came to an official end on March 31, 1997, when it had reached a distance of 67 AU from the Sun, though the spacecraft was still able to transmit coherent data after this date.

After March 31, 1997, Pioneer 10's weak signal continued to be tracked by the Deep Space Network to aid the training of flight controllers in the process of acquiring deep space radio signals. There was an Advanced Concepts study applying chaos theory to extract coherent data from the fading signal.

The last successful reception of telemetry was received from Pioneer 10 on April 27, 2002; subsequent signals were barely strong enough to detect, and provided no usable data. The final, very weak signal from Pioneer 10 was received on January 23, 2003 when it was 12 billion kilometers (80 AU) from Earth. Further attempts to contact the spacecraft were unsuccessful. A final attempt was made on the evening of March 4, 2006, the last time the antenna would be correctly aligned with Earth. No response was received from Pioneer 10. NASA decided that the RTG units (the spacecraft's power generators) had probably fallen below the power threshold needed to operate the transmitter. Hence, no further attempts at contact were made.

To learn more about Pioneer 10 and the NASA Pioneer missions, visit these sites.

NASA Pioneer Missions

Web Archive of the NASA Pioneer Mission Home Page

-

Phoenix Mars Lander Is a Bit Dusty

The above animation "blinks" between two images: One taken May 25, 2008, the other taken December 21, 2017. Both show the landing site for NASA's Phoenix Mars Lander. The later image shows the result of dust layering. Image credit: NASA/JPL-Caltech/Univ. of Arizona

A late 2017 image of NASA's Phoenix Mars mission, which landed nearly a decade ago in the norther regions of Mars, shows that dust has covered some marks of the landing.

The Phoenix lander itself, plus its back shell and parachute, are still visible in the image taken December 21, 2017, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. But an animated-blink comparison with an image from about two months after the May 25, 2008, landing shows that patches of ground that had been darkened by removal of dust during landing events have become coated with dust again.

In August 2008, Phoenix completed its three-month mission studying Martian ice, soil and atmosphere. The lander worked for two additional months before reduced sunlight caused energy to become insufficient to keep the lander functioning. The solar-powered robot was not designed to survive through the dark and cold conditions of a Martian arctic winter.

Both images in the animation were taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. The one with three patches of darker ground -- where landing events removed dust -- was taken on July 20, 2008. The one with a more even coating of pale dust throughout the area was taken on December 21, 2017. Both image cover an area roughly 300 meters wide at 68 degrees north latitude, 234 degrees east longitude.

The University of Arizona, Tucson, led the Phoenix mission and also operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colorado. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, managed the Phoenix Mars Lander Project and manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington. Lockheed Martin Space, Denver, built both the Phoenix and Mars Reconnaissance Orbiter spacecraft.

For more information on the Phoenix Mars Lander, the Mars Reconnaissance Orbiter mission and NASA's Mars exploration program, check out these site.

Phoenix Mars Lander Mission

Mars Reconnaissance Orbiter Mission

NASA's Mars Exploration Program

-

The Rings of Saturn Viewed Planet-Side and the Final Days of Cassini

On August 20, NASA's Cassini spacecraft completed another pass between Saturn and its rings. The below animation shows the ring system from above (sunlit side) and then below (shadow side). All of the ring system is seen. But due to the angle, the rings and the ring divisions appear foreshortened (squeezed together). Also, the inner C ring looks larger in the foreground.

Saturn's ring system as seen during the Cassini pass between the rings and Saturn on August 20, 2017. Image Credit: NASA/JPL-Caltech/Space Science Institute

The Grand Finale is Nearly Complete

The spacecraft is quickly approaching its  mission-ending dive into the atmosphere of Saturn on September 15. An April 22 gravitational assist from Saturn's moon Titan put the craft on its final path. But several mission milestones remain before then.

The spacecraft is expected to lose radio contact with Earth within about one to two minutes after beginning its descent into Saturn's upper atmosphere. But on the way down, eight of Cassini's 12 science instruments will be operating. In particular, the spacecraft's ion and neutral mass spectrometer (INMS), which will be directly sampling the atmosphere's composition, potentially returning insights into the giant planet's formation and evolution. On the day before, September 14, other Cassini instruments will make detailed, high-resolution observations of Saturn's auroras, temperature, and the vortices at the planet's poles. Cassini's imaging camera will take it's last views on September 14 and then be shut down. Below are some highlights from the final days of Cassini.

September 9 -- Cassini will make the last of 22 passes between Saturn itself and its rings -- closest approach is 1,044 miles (1,680 kilometers) above the clouds tops.

September 11 -- Cassini will make a distant flyby of Saturn's largest moon, Titan. Even though the spacecraft will be at 73,974 miles (119,049 kilometers) away, the gravitational influence of the moon will slow down the spacecraft slightly as it speeds past. A few days later, instead of passing through the outermost fringes of Saturn's atmosphere, Cassini will dive in too deep to survive the friction and heating.

September 14 -- Cassini's imaging cameras take their last look around the Saturn system, sending back pictures of moons Titan and Enceladus, the hexagon-shaped jet stream around the planet's north pole, and features in the rings.

September 14 (5:45 p.m. EDT / 2:45 p.m. PDT) -- Cassini turns its antenna to point at Earth, begins a communications link that will continue until end of mission, and sends back its final images and other data collected along the way.

September 15 (4:37 a.m. EDT / 1:37 a.m. PDT) -- The "final plunge" begins. The spacecraft starts a 5-minute roll to position INMS for optimal sampling of the atmosphere, transmitting data in near real time from this point to end of mission.

September 15 (7:53 a.m. EDT / 4:53 a.m. PDT) -- Cassini enters Saturn's atmosphere. Its thrusters fire at 10 percent of their capacity to maintain directional stability, enabling the spacecraft's high-gain antenna to remain pointed at Earth and allowing continued transmission of data.

September 15 (7:54 a.m. EDT / 4:54 a.m. PDT) -- Cassini's thrusters are at 100 percent of capacity. Atmospheric forces overwhelm the thrusters' capacity to maintain control of the spacecraft's orientation, and the high-gain antenna loses its lock on Earth. At this moment, expected to occur about 940 miles (1,510 kilometers) above Saturn's cloud tops, communication from the spacecraft will cease, and Cassini's mission of exploration will have concluded. The spacecraft will break up like a meteor moments later.

A Very Long Mission at Saturn

As Cassini completes its 13-year tour of Saturn, its Grand Finale -- which began in April -- and final plunge are just the last beat. Following a four-year primary mission and a two-year extension, NASA approved an ambitious plan to extend Cassini's service by an additional seven years. Called the Cassini Solstice Mission, the extension saw Cassini perform dozens more flybys of Saturn's moons as the spacecraft observed seasonal changes in the atmospheres of Saturn and Titan. From the outset, the planned endgame for the Solstice Mission was to expend all of Cassini's maneuvering propellant exploring, then eventually arriving in the ultra-close Grand Finale orbits, ending with safe disposal of the spacecraft in Saturn's atmosphere.

Mountains of New Data on the Saturn System

Since its launch in 1997, the findings of the Cassini mission have revolutionized our understanding of Saturn, its complex rings, the amazing assortment of moons and the planet's dynamic magnetic environment. The most distant planetary orbiter ever launched, Cassini started making astonishing discoveries immediately upon arrival and continues today. Icy jets shoot from the tiny moon Enceladus, providing samples of an underground ocean with evidence of hydrothermal activity. Titan's hydrocarbon lakes and seas are dominated by liquid ethane and methane, and complex pre-biotic chemicals form in the atmosphere and rain to the surface. Three-dimensional structures tower above Saturn's rings, and a giant Saturn storm circled the entire planet for most of a year. Cassini's findings at Saturn have also buttressed scientists' understanding of processes involved in the formation of planets.

Why End the Mission?

The spacecraft is running low on the rocket fuel used for adjusting its course. If left unchecked, this situation would eventually prevent mission operators from controlling the course of the spacecraft.

Two moons of Saturn, Enceladus and Titan, have captured news headlines over the past decade as Cassini data revealed their potential to contain habitable – or at least "prebiotic” – environments.

In order to avoid the unlikely possibility of Cassini someday colliding with one of these moons, NASA chose to safely dispose of the spacecraft in the atmosphere of Saturn. This will ensure that Cassini cannot contaminate any future studies of habitability and potential life on Enceladus and Titan.

For more information about the Saturn system and the Cassini mission, click on the links below.

NASA Cassini Mission

NASA Saturn/Cassini Mission Coverage

-

Asteroid 3122 Florence Close Approach September 1

On September 1, asteroid 3122 Florence will become the largest asteroid to fly by Earth since near-Earth asteroids were discovered a century ago.

Asteroid 3122 Florence will pass by Earth on September 1, 2017, at a distance of about 4.4 million miles. Image Credit: NASA/JPL-Caltech

Measurements made by the Spitzer Space Telescope and NEOWISE asteroid-hunting instrument suggest that Florence is around 2.7 miles (5 km) in diameter. The asteroid will pass 4.4 million miles from Earth, about 18 times the distance from the Earth to the moon.

Many known asteroids have passed closer to Earth than Florence will, but those were estimated to be smaller. NASA has tracked near-Earth objects since 1998.

Background on Florence

The body called Florence was first detected March 2, 1981 by American astronomer Schelte “Bobby” Bus from Australia’s Siding Spring Observatory. The discovery was provisionally labeled 1981 ET₃. In 1993, it was acknowledged as asteroid discovery number 3122 and was named 3122 Florence in honor of Florence Nightingale (1820-1910), the founder of modern nursing.

3122 Florence is a stony asteroid of the Amor group, classified as near-Earth object and potentially hazardous asteroid (PAH). It orbits the sun at a distance of 1.0–2.5 AU once every 2 years and 4 months (859 days). Its orbit has an eccentricity of 0.42 and an inclination of 22° with respect to the ecliptic. The PHA classification is due to both the body’s absolute magnitude (H ≤ 22) and its minimum orbit intersection distance (MOID ≤ 0.05 AU).

Observing Opportunity

For visual astronomers, 3122 Florence will be clearly visible in the night sky beginning August 27. On September 1, 3122 Florence will pass 0.04723 AU (7,066,000 km; 4,390,000 mi) from Earth, brightening to apparent magnitude 8.5, when it will be visible in small telescopes for several nights as it moves through the constellations Piscis Austrinus, Capricornus, Aquarius and Delphinus.

NEO Close Approaches in 2017

Florence is just one of a few bodies passing Earth this year. In January, asteroid 2017 AG₁₃ snuck up on astronomers. The body was between 36 and 111 feet wide and passed Earth at half the distance to the moon. Another asteroid in the same size range, 2012 TC₄, is scheduled to pass roughly one-fourth the distance to the moon—between 4,200 miles and 170,000 miles—on October 12, 2017.

Earth-Based Radar Observing

The size and proximity of Florence make it a perfect target for ground-based radio telescope observations. Radar imaging is planned at NASA's Goldstone Solar System Radar in California and at the National Science Foundation's Arecibo Observatory in Puerto Rico. The resulting radar images will show the real size of Florence and could reveal surface details as small as about 30 feet (10 meters).

NEO Tracking Continues

Currently, NASA is tracking 1,826 near-Earth objects classified as Potentially Hazardous Asteroids, which have some risk of striking Earth in the future. Among those are several larger than Florence, including 1999 JM₈ at 4.3 miles across, 4183 Cuno at 3.5 miles across and 3200 Phaeton at 3.2 miles across. None have come as close as Florence. Florence won’t make a closer pass until around the year 2500.

More information about asteroids and near-Earth objects can be found at:

NASA Center for Near Earth Object Studies

NASA Asteroid Watch

For more information about NASA's Planetary Defense Coordination Office, visit:

NASA Planeterary Defense Coordination Office

-

Journey to the Shadow, No. 14

New friend Scott Wargo made this video of totality during the August 21 eclipse, as seen from our Greenwood, South Carolina location. I've already shared this link on some sites, so apologies if you have already seen this. Just trying to be thorough. Enjoy. http://bit.ly/2wakOKK

-

Journey to the Shadow, No. 13

Friend Craig MacDougal made this 13-minute YouTube video to capture the sights and sounds of the August 21 eclipse. Watch the Walmart as the sky grows erily darker and folks get more excited, see the darkness and hear the shouting during totality, and then watch how the world seems to quickly return to normal afterward. Did it really happen? I'm pretty sure it did! http://bit.ly/2w3PmPZ

-

Journey to the Shadow, No. 12

August 21, 2017

I have no photos from totality. But I have memories. Wow! Amazing. It was so otherworldly. The corona had the look of a Star Fleet delta shield with a solar prominence thrown in. The experience was so worth the trip. I will be scanning the recordings for the eclipse as it appeared when I saw it with my own eyes. We broke camp about 30 minutes after the end of totality. We are making our way back home with the rest of humanity. ETA, sometime after midnight Eastern Time.

-

Journey to the Shadow, No. 11

August 21, 2017

More observers collected as we got closer to totality. One family had some guests, a missionary family back from Niger. We had some fun with a pinhole projector.

-

Journey to the Shadow, No. 10

August 21, 2017

As we waited through the partial phase, Craig played a little Frisbee to pass the time.

-

Journey to the Shadow, No. 9

August 21, 2017

We met up with Craig's friends in Greenwood. We are camped in a shaded area by the parking lot of a Super Walmart. Partly cloudy, but we still consider it a great spot. Also, we aren't relocating again. And so we wait.

-