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

-