Transit Trivia: Jeremiah Horrocks

The above painting is an artist's conception of the first observed transit of the planet Venus, as predicted and observed by Jeremiah Horrocks in 1639. The portrait is held in the collection of Astley Hall Museum and Art Gallery Chorley and the property of Chorley Council. Image Credit: Because of its age, the image is in the Public Domain.

Kepler's Rudophine Tables proved invaluable to many astronomers, not the least of which was Jeremiah Horrocks (1618 – 1641), an English astronomer, the son of a Liverpool farmer, and a clerk at the local St. Michael's Church in Much Hoole, Lancashire. In the tables, Kepler had predicted transits in 1631 and 1761 and a near miss in 1639. But Horrocks found and corrected an error in Kepler's calculation for the orbit of Venus. He then realized that transits of Venus would occur in pairs that were eight years apart, and so predicted the transit in 1639.

On December 4th, 1639 (November 24th under the Julian calendar, which was then in use in England), Horrocks prepared to observe from Carr House in Much Hoole, near Preston in England. Although he was uncertain of the exact time, Horrocks calculated that the transit would begin at approximately 3:00 PM. The day being Sunday, Horrocks spent much of the time attending to his clerk duties at St. Michael's. It was just as well, for clouds obscured the sun for most of the day, but cleared by about 3:15, when Horrocks was finished with his other obligations. He was able to observe a portion of the event for about 30 minutes until the local sunset. Aside from Horrocks, only one other person observed the transit: English astronomer, mathematician, merchant, and friend to Jeremiah Horrocks, William Crabtree (1610 - 1644). Crabtree  observed from his home in Broughton, near Manchester.

Horrocks understood that looking directly at the sun without proper filtering would cause blindness, a tragedy for anyone, but especially bad for an astronomer. Horrocks therefore focused the image of the sun through a simple refractor telescope and onto a piece of card, where the image could be safely observed.

Horrocks' observations allowed him to make a well-informed guess as to the size of Venus, as well as to make an estimate of the distance between the Earth and the sun. He estimated that distance to be 59.4 million miles (0.639 AU) – about two thirds of the actual distance of 93 million miles (149.6 million km) but a more accurate figure than any suggested up to that time.

The life of Jeremiah Horrocks was indeed impressive. This son of a farmer had managed to study at Cambridge University. He had reviewed, found fault, and corrected the works of earlier greats, including those of Kepler. He correctly predicted a transit of Venus, was one of the first two people to observe the event, and he used his observations to calculate a new distance between Earth and the sun which was the most accurate to that time. And for all of this, Horrocks was only about 21 years old.

In addition, Horrocks determined the orbit of Earth's moon and correctly hypothesized that its shape was elliptical rather than circular. He even suggested that Earth and the sun influenced the moon's orbit, anticipating Isaac Newton's theories on gravity. And Horrocks had begun a detailed study of tides in an attempt to explain the lunar causation of tidal movements. Sadly, Horrocks would not complete this or any other work. He died at his home, from unknown causes, at the age of 22. As his friend William Crabtree expressed, "What an incalculable loss!"

About twenty years later, in 1662, the Polish-Lithuanian astronomer Johannes Hevelius (1611 - 1687) published, at his own expense, the transit work of Jeremiah Horrocks. The treatise was entitled Venus in sole visa (Venus in transit across the Sun). The paper caused great excitement when it was presented to members of the Royal Society. It contained much evidence of Horrocks' enthusiastic and romantic nature, including humorous comments and passages of original poetry. When writing on the century which separated his and the next transit of Venus, Horrocks rhapsodized,

"Oh! then farewell, thou beauteous queen!
Thy sway may soften natures yet untamed,
Whose breasts, bereft of the native fury,
Then shall learn the milder virtues.
We, with anxious mind, follow thy latest footsteps here,
And far as thought can carry us;
My labours now bedeck the monument for future times
Which thou at parting left us. Thy return
Posterity shall witness; years must roll away,
But then at length the splendid sight
Again shall greet our distant children's eyes."

At St. Michael's Church in Much Hoole, a stained glass window on the east wall commemorates Horrocks and his achievement in observing the transit. Nearby, at Carr House, a plaque recognizes the location where Horrocks made his observations.

The next transit of Venus will occur over June 5-6. To learn more, visit these links.

2012 Transit of Venus, NASA/Goddard Space Flight Center: eclipse.gsfc.nasa.gov/OH/transit12.html

Transit of Venus, Sun-Earth Day 2012, NASA: sunearthday.nasa.gov/transitofvenus/
 
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Tiangong-1 Caught by Legault

The above drawing shows the Chinese experimental space station, Tiangong-1 (left), with a Shenzhou spacecraft docked (right). Image Credit: Wikipedia contributor "Craigboy"

On May 11th, French astrophotographer Thierry Legault posted online an image of the sun which included the silhouette of China's experimental space station, Tiangong-1. The spacecraft was passing across the face of the sun near the giant sunspot AR1476.

Tiangong-1 is much smaller than the International Space Station, but it can be seen with the naked eye shining in the night sky as brightly as the stars of the Big Dipper. The image by Legault may be seen online at this URL: legault.perso.sfr.fr/transit_tiangong1_120511.html

Tiangong-1 (meaning “Heavenly Palace 1") is a Chinese space laboratory module which is being used as an experimental test-bed to demonstrate the rendezvous and docking capabilities needed to support a space station complex. The Tiangong-1 spacecraft was launched by a Long March 2F/G rocket on September 29, 2011. Tiangong-1 is part of the Tiangong program, which has the goal of placing a larger, modular station into orbit by 2020. Tiangong-1 will be deorbited in 2013, and replaced over the following decade by the larger Tiangong-2 and Tiangong-3 modules.

Tiangong-1 is expected to be visited by three Shenzhou missions during its two-year operational lifetime. The first of these, the robotic mission Shenzhou 8, successfully docked with the module in November 2011, while the crewed Shenzhou 9 and 10 missions are expected to launch in 2012. Shenzhou 9 is not expected to launch before June.

To learn more about Tiangong-1, visit the following link at NASA’s National Space Science Data Center: nssdc.gsfc.nasa.gov/nmc/masterCatalog.do?sc=2011-053A

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Transit Trivia: Brahe and Kepler

The above image shows a monument dedicated to Tycho Brahe (left) and Johannes Kepler (right). The monument is located in Prague, Czechia. Image Credit: WikiCommons contributor "Mohylek." This image is in the Public Domain.

Danish nobleman and astronomer Tycho Brahe (1546 - 1601) spent much of his life making very careful measurements of the positions of stars and planets. His work yielded data with an accuracy that was not previously possible. Brahe wanted his observations to be the basis of a new and more accurate set of star tables. He trusted this work to his collaborator, whom some considered his competition, the German mathematician, astronomer and astrologer Johannes Kepler (1571 - 1630).

Kepler was able to prepare the new tables using a combination of Brahe's accurate observations, a heliocentric (sun-centered) model of the solar system and Kepler's own discovery that the planets moved in elliptical (not circular) orbits. Following Brahe's death, Kepler faced many obstacles in completing the work. His biggest were Brahe's surviving relatives, who fought Kepler for the publication rights.

In 1623, Kepler at last completed the new tables. However, publication was delayed because of the publishing requirements of Emperor Ferdinand II and because of ongoing negotiations with Brahe's family. In the meantime, religious tension — the root of the ongoing Thirty Years' War — put Kepler and his family in jeopardy. In 1626, Kepler and family moved from Bohemia to Ulm, Upper Austria, where Kepler arranged for the printing of the new tables at his own expense.

Brahe had wanted the tables to be dedicated to his patron, the Bohemian king and Holy Roman emperor Rudolph II. But by the time of their publication in 1627, Rudolf II had died, so instead the tables were dedicated to Emperor Ferdinand II but were still named in honor of Rudolph II.

The Rudolphine Tables (Latin: Tabulae Rudolphinae) included a star catalogue and planetary tables. Most of the calculated positions were accurate to within one minute of arc. In addition, the tables were the first to include corrective factors for atmospheric refraction. In fact, the tables were so accurate that they led to the first observed transits of Mercury (in 1631) and of Venus (in 1639).

The next transit of Venus will occur over June 5-6. To learn more, visit these links.

2012 Transit of Venus, NASA/Goddard Space Flight Center: eclipse.gsfc.nasa.gov/OH/

transit12.html

Transit of Venus, Sun-Earth Day 2012, NASA: sunearthday.nasa.gov/transitofvenus/


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More on Vesta and HED Meteorites

The above image shows three slices of HED-class meteorites. Image Credit: University of Tennessee


This is a follow-up to the recent paper by the NASA Dawn mission team regarding asteroid Vesta and its parentage of the HED family of meteorites. Back on May 11th, a paper by the mission team was posted in the journal Science. In the paper, the team presented evidence that the family of meteorites known as howardite, eucrite and diogenite (HED) originated on asteroid 4 Vesta, and likely left Vesta as a result of the impact which created the large basin near Vesta's south pole.


Above are three nifty slices of HED-class meteorites. They were viewed through a polarizing microscope, where different minerals appear in different colors. The texture of the rocks reveals that they crystallized at different rates. The image on the left comes from a meteorite named QUE 97053 (Antarctica), which is basaltic eucrite. The image in the middle comes from the Moore County (North Carolina) cumulate eucrite. The image on the right comes from a diogenite meteorite named GRA 98108 (Antarctica).


Launched in 2007, NASA's Dawn spacecraft has been studying Vesta since its arrival in July of 2011. The Dawn spacecraft will depart Vesta on August 26 (my birthday) . At that time it will head for its next study target, the dwarf planet Ceres, arriving in 2015.


And now, the mission particulars...


Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. The California Institute of Technology in Pasadena manages JPL for NASA.


For more information about the Dawn mission, visit: www.nasa.gov/dawn and dawn.jpl.nasa.gov .


To read more about the Vesta discoveries, check out the online home page of the journal Science: www.sciencemag.org


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Transit Trivia: Venus and the Ancients

The tablet in the above image is know as the Venus Tablet of Ammisaduqa from the Neo-Assyrian period. The tablet is on display in the British Museum, London. Image Credit: Wikipedia contributor "Fæ"

The celestial body which we now call Venus was known to ancient Indian, Greek, Egyptian, Babylonian and Chinese observers. The early Greeks actually thought they were recording the movements of two different objects — one that appeared in the morning and one that appeared in the evening. Their "evening star" was called Hesperus (in Greek mythology, a son of the dawn goddess Eos) and their "morning star" was called Phosphorus (also a son of Eos and brother to Hesperus) The Greek philosopher and mathematician Pythagoras is credited with realizing these two object were one and the same.

Venus was important to ancient American cultures, in particular for the Maya, who called it Noh Ek, "the Great Star" or Xux Ek, "the Wasp Star"; they embodied Venus in the form of the god Kukulkán (also known as or related to Gukumatz and Quetzalcoatl in other parts of Mexico). In the in the Mayan book which we now call the Dresden Codex, the Maya charted Venus' full cycle.

For their times, these culture made careful records of Venus. But even so, there is no evidence that any of these ancient cultures knew of the transits of Venus across the sun.

The next transit of Venus will occur over June 5-6. To learn more, visit these links.

2012 Transit of Venus, NASA/Goddard Space Flight Center: eclipse.gsfc.nasa.gov/OH/transit12.html

Transit of Venus, Sun-Earth Day 2012, NASA: sunearthday.nasa.gov/transitofvenus/

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MRO Detects Dune Movement

The above animation present two alternating images of the same area of Martian sand dunes taken three years apart. The animation shows the movement of the dunes. If you have problems seeing the animation, visit this link: http://www.nasa.gov/mission_pages/MRO/news/mro20120509.html Image Credit: NASA/JPL-Caltech/Univ. of Arizona/JHU-APL


Images from NASA's Mars Reconnaissance Orbiter have revealed that movement in sand dune fields on the planet Mars occurs on a surprisingly large scale, about the same as in dune fields on Earth.


The discovery is unexpected for three reasons: (1) the Red Planet has a much thinner atmosphere than Earth, (2) the atmosphere is only about one percent as dense, and (3) the atmosphere's high-speed winds are less frequent and weaker than Earth's.


We know from other Mars missions that the planet has its share of dust storms -- just talk to the Mars Exploration Rover mission team. Even so, researchers have debated for years whether the sand dunes observed on Mars were mostly fossil features related to past climate, or were they were currently active. In the past two years, researchers used the High Resolution Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter (MRO) to detect and report sand dune movement.


The researchers now report that entire dunes as thick as 200 feet (61 meters) are moving as coherent units across the Martian landscape. Their study was published online May 9th by the journal Nature.


Researchers analyzed before-and-after images using a new software tool developed at the California Institute of Technology (Caltech) in Pasadena, California. The tool measured changes in the position of sand ripples, revealing that the ripples move faster the higher up they are on a dune.


The study examined images taken in 2007 and 2010 of the Nili Patera sand dune field located near the Martian equator. By correlating the ripples' movement to their position on the dune, the analysis determined the entire dunes are moving. This allows researchers to estimate the volume, or flux, of moving sand.


The study adds important information about the pace at which blowing sand could be actively eroding rocks on Mars. Using the new information about the volume of sand that is moving, scientists estimate rocks in Nili Patera would be worn away at about the same pace as rocks near sand dunes in Antarctica, where similar sand fluxes occur.


Scientists calculate that if someone stood in the Nili Patera dunes and measured out a one-yard (one-meter) width, they would see more than two cubic yards (1,500 liters) of sand pass by in an Earth year, about as much as in a child's sand box.


Scientists will use the information to understand broader mysteries on Mars, like why so much of the surface appears heavily eroded, how that occurred, and whether it is a current process or it was done in the past. Scientists can now point to sand flux as a mechanism capable of creating significant erosion today on the Red Planet.


And now the instrument particulars...


The HiRISE camera provides unprecedented resolution in studying the Martian landscape. NASA's Jet Propulsion Laboratory, Pasadena, California, a division of Caltech, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate in Washington. Lockheed Martin Space Systems, Denver, built the spacecraft. HiRISE is operated by the University of Arizona and was built by Ball Aerospace & Technologies Corp., Boulder, Colorado.


For related images and more information about Mars Reconnaissance Orbiter, visit the mission home page: www.nasa.gov/mro


To learn more about the study, visit the online home page of the journal Nature: www.nature.com


For more on NASA' Exploring Mars Program, visit the program home page: mars.jpl.nasa.gov


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Transit Trivia: Predicting Patterns

The duration of a transit of Venus is usually measured in hours (the transits of 2004 and 2012 last about six hours). Before modern astronomy, observations of transits of Venus helped scientists measure the distance between the Sun and the Earth using the method of parallax.


Transits of Venus are the rarest of all predictable astronomical phenomena and currently occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. Before 2004, the last pair of transits of Venus were in December 1874 and December 1882. The first of the latest pair of transits occurred on June 8, 2004 and the other will occur on June 6, 2012.  Following that, the next pair of transits will be in December 2117 and December 2125.


The pattern repeats every 243 years because 243 sidereal orbital periods of the Earth (365.25636 days, which is slightly different from the tropical year) is 88757.3 days, and 395 sidereal orbital periods of Venus (224.701 days) is 88756.9 days. Thus, after this time both Venus and Earth have returned to very nearly the same point in each of their respective orbits. This period of time corresponds to 152 synodic periods of Venus.


The pattern of 105.5, 8, 121.5 and 8 years is not the only pattern that is possible within the 243-year cycle. Prior to 1518, the pattern of transits was 8, 113.5 and 121.5 years, and prior to 546, transits always took place 121.5 years apart. The current pattern will continue until 2846, when it will be replaced by a pattern of 105.5, 129.5 and 8 years. Thus, the 243-year cycle is relatively stable, but the number of transits and their timing within the cycle will vary over time.


The safest way to observe the event in 2012 would be to project the image of the Sun, as seen through a telescope, onto a screen. Nevertheless, the event can also be seen with free eyes using special stained glasses. If observing with Welder’s glasses, a grade of at least 14 should be used. Observing the Sun without filters can cause a temporary or permanent loss of visual function, as it can damage and even destroy retinal cells.

For more on the June 2012 Transit of Venus, visit these links.

2012 Transit of Venus, NASA/Goddard Space Flight Center: eclipse.gsfc.nasa.gov/OH/transit12.html

Transit of Venus, Sun-Earth Day 2012, NASA: sunearthday.nasa.gov/transitofvenus/

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JunoCam Certifies With the Dipper

Above is an image, taken by NASA's Juno spacecraft of the asterism known in the U.S. as the "Big Dipper." Image Credit: NASA/JPL-Caltech/SWRI/MSSS


The above image is an asterism -- a grouping of stars that is not an official constellation, but is still familiar to observers. The grouping is called different names by different people. For example, it is called the "Big Dipper" (US), the "Plough" (UK), the "Great Cart" (Germany), and "Seven Ploughs" (Malaysia).


Whatever the name, these stars have long been, for northern hemisphere observers, a welcome and familiar introduction to the heavens. Now, these stars are helping the Juno mission team make sure that Juno's camera is ready to do its job.


Launched on August 5, 2011, the solar-powered Juno spacecraft is about 380 million miles (612 million kilometers) into its five-year, 1,905-million-mile (3,065-million-kilometer) journey to Jupiter.  Once there, the spacecraft will orbit the planet's poles 33 times and use its nine instruments to image and probe beneath the gas giant's obscuring cloud cover to learn more about Jupiter's origins, structure, atmosphere and magnetosphere, and look for a potential solid planetary core.


The instrument tasked with taking closeups of Jupiter's atmosphere is the JunoCam. But it would be four-and-a-half years until JunoCam's CCD (charged-coupled device) actually saw Jupiter. So the mission planners needed something on which to certify the instrument and they decided on this familiar grouping of stars. On March 21, JunoCam took the image seen above. The Juno team was thrilled by the result and is confident that the instrument is ready for Jupiter.


You can view the full test image online at: photojournal.jpl.nasa.gov/catalog/PIA15653


Juno's name comes from Greek and Roman mythology. The god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife, the goddess Juno, was able to peer through the clouds and reveal Jupiter's true nature.


And now, the mission particulars...


NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. JunoCam was developed and is operated by Malin Space Science Systems in San Diego. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is a division of the California Institute of Technology in Pasadena.  


Learn more about Juno online at www.nasa.gov/juno and missionjuno.swri.edu .


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Transit Trivia: Coming June 5-6

Above are three close-up images from a transit of the planet Venus across the face of the sun. The top image shows Venus on the eastern limb of the Sun. The faint ring around the planet comes from the scattering of its atmosphere, which allows some sunlight to show around the edge of the otherwise dark planetary disk. The faint glow on the disk is an effect of the TRACE telescope. The bottom left image is in the ultraviolet, and the bottom right image is in the extreme ultraviolet. The three images were captured by NASA's Sun-observing TRACE spacecraft. Image Credit: NASA/LMSAL 

The next transit of the Planet of Venus across the face of the sum will occur over Tuesday-Wednesday, June 5-6. In astronomy, a transit occurs when a smaller celestial body passes across the face of a larger celestial body from the point of view of the observer.

From Earth, there are only two regularly occurring transits of celestial bodies across the sun -- one by the planet Mercury and the other by the planet Venus. In truth, a third celestial body crosses the sun, but that is the moon and it completely covers the sun when the alignment is right. But because these events cover so much of the sun, and in some cases all of the sun, these occurrences are more precisely called occultations (coverings) rather than transits (crossings).

For reasons which we will get into later, transits of Venus occur in pairs that are just a few years apart. The last transit occurred June 8, 2004. The second of the pair occurs over June 5/6. After that, the next pair will in December 2117 and December 2125.

For more on the June 2012 Transit of Venus, visit these links.

2012 Transit of Venus, NASA/Goddard Space Flight Center: eclipse.gsfc.nasa.gov/OH/transit12.html

Transit of Venus, Sun-Earth Day 2012, NASA: sunearthday.nasa.gov/transitofvenus/

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Curiosity Driving School in the Mojave

The above image shows the stripped-down rover used for test-driving in the Mojave Desert. Image Credit: NASA/JPL-Caltech

This passed week, team members of NASA's Mars Science Laboratory mission took a test rover to Dumont Dunes in California's Mojave Desert. No, no. It wasn't for joyriding. Well, it wasn't only for joyriding. They did it on order to improve their knowledge of the best way to operate the actual Curiosity rover, which is en route to Mars and scheduled for an August landing.

The test rover had a full-scale version of Curiosity's mobility system, but it was otherwise stripped down so that it weighed about the same on Earth as Curiosity will weigh in the lesser gravity of Mars.

What the team members learned in their tests on windward and downwind portions of the dunes will be used in making decisions about driving Curiosity on the dunes near a mountain in the center of Gale Crater. Of course, the mission team must first put the Curiosity rover safely on Mars. The landing methods are new and innovative, but much innovation is needed on order to progress toward eventual human missions to the Red Planet.

And now, the mission particulars...

Launched November 26, 2011, NASA's Mars Science Laboratory spacecraft and Curiosity rover are on track for landing the evening of August 5, 2012, PDT (early on August 6, Universal Time and EDT) to begin a two-year prime mission. Researchers plan to use Curiosity to study layers in Gale Crater's central mound, Mount Sharp. The mission will investigate whether the area has ever offered an environment favorable for microbial life.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for the NASA Science Mission Directorate, Washington.

More information about Curiosity is online at www.nasa.gov/msl and mars.jpl.nasa.gov/msl .  You can follow the mission on Facebook at: www.facebook.com/marscuriosity  and on Twitter at: www.twitter.com/marscuriosity .

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Venus Transit May Help Exoplanet Studies

The above image, taken by the Hubble Space Telescope, shows the Moon's Crater Tycho. Image Credit: NASA, ESA, and D. Ehrenreich (Institut de Planétologie et d'Astrophysique de Grenoble (IPAG)/CNRS/Université Joseph Fourier)

The mottled landscape surrounding the impact crater Tycho is among the most violent-looking places on our Moon. But astronomers didn't aim NASA's Hubble Space Telescope to study Tycho. The above image was taken in preparation to observe the transit of Venus across the sun's face on June 5-6. What astronomers learn from the transit may help in the search for habitable extra-solar planets (exoplanets).

Hubble has no filtering precautions, so it cannot look directly at the sun. Instead, astronomers are planning to point the telescope at Earth's moon, using it as a mirror to capture reflected sunlight and isolate the small fraction of the light that passes through Venus's atmosphere. Imprinted on that small amount of light are the fingerprints of the planet's atmospheric makeup. These observations will mimic a technique that is already being used to sample the atmospheres of giant planets outside our solar system which pass in front of their stars -- like Spitzer did with 55 Cancri e.

In the case of the Venus transit observations, astronomers already know the chemical makeup of the Venus atmosphere, and that it does not show signs of life on the planet. But all of this knowledge is a good thing, because the Venus transit lets astronomers test whether this observing technique detects the familiar chemical signature of Venus. If it does, they have a chance of detecting the very faint fingerprints of a distant Earth-like planet, even one that might be habitable for life, that transits its own star. Venus is an excellent proxy because it is similar in size and mass to our planet.

And now, the mission particulars...

The Hubble Space Telescope (HST) was carried into orbit by the Space Shuttle Discovery in April 1990. HST is a 2.4-meter (7.9 ft) aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared. The telescope is named after the astronomer Edwin Hubble. HST was built by NASA, with contributions from the European Space Agency (ESA), and is operated by the Space Telescope Science Institute. The HST is one of NASA's Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. The HST mission websites are: hubble.nasa.gov and asd.gsfc.nasa.gov/archive/hubble and hubblesite.org

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Super-Earth Exoplanet Confirmed

The above image is an artist's conception of the exoplanet 55 Cancri e orbiting Cancri A, a yellow dwarf star. Image Credit: Spitzer/NASA/JPL-Caltech

NASA's Spitzer Space Telescope has confirmed that a known planet beyond our solar system (an extra-solar planet, or exoplanet) is in fact a rocky planet like our Earth, but much larger. The planet is not habitable, but the detection is a historic step in the search for Earth-type planets.

The planet, called 55 Cancri e, falls into a class of planets called super Earths, which are more massive than our home world but less massive than giant planets like Neptune. The planet is about twice as big and eight times as massive as Earth. It orbits the bright star 55 Cancri. And the orbital period is very short -- only 18 hours.

Previously, Spitzer and other telescopes were able to study the planet by analyzing how the light from 55 Cancri changed as the planet passed in front of the star. But in the new study, Spitzer measured how much infrared light was reflected from the planet. The results reveal the planet is likely dark in appearance, and its sun-facing side is more than 2,000 Kelvin (3,140 degrees Fahrenheit), hot enough to melt metal.

The new information is consistent with a prior theory that 55 Cancri e is a water world: a rocky core surrounded by a layer of water in a "supercritical" state where it is both liquid and gas, and topped by a blanket of steam.

Some suggest that 55 Cancri e might be similar to placing the planet Neptune very close to our sun. The resulting world would have most of its atmosphere boiled away, leaving a large, rocky core and a remnant atmosphere that is super-heated on top, with some areas below cool enough for liquid water to exist.

The 55 Cancri system is relatively close to Earth, at a distance of 41 light-years. It has five known planets, with 55 Cancri e the closest to the star and tidally locked, so one side always faces the star. Spitzer discovered that the sun-facing side is extremely hot, indicating the planet probably does not have a substantial atmosphere to carry the sun's heat to the unlit side.

For the record, 55 Cancri is located in the constellation of Cancer, the Crab, and it is a double star system. Cancri A is a spectral type G8V yellow dwarf star and Cancri B is a spectral type M3.5-4V red dwarf star. Cancri A has an apparent magnitude of 5.95, making it visible through binoculars. Cancri B is of 13th-magnitude brightness and only visible through larger instruments, such as telescopes. All five planets orbit Cancri A. The celestial coordinates for 55 Cancri (technically, the 55 Cancri A coordinates) are RA 08h 52m 35.8s, Dec +28 degrees 19 minutes 51 seconds.

And now, the Spitzer mission particulars...

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology (Caltech) in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit: www.nasa.gov/spitzer and spitzer.caltech.edu . More information about exoplanets and NASA's planet-finding program is at planetquest.jpl.nasa.gov .

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OCO-2 is Coming Together

The above image is an artist's conception of OCO-2 in Earth orbit. Image Credit NASA/JPL-Caltech

Here is a pre-flight update on NASA's Orbiting Carbon Observatory-2 (OCO-2), which may launch as early as the summer of 2014. The Jet Propulsion Laboratory has completed work on the spacecraft's science instrument -- the heart of the OCO-2 spacecraft.

Early on Tuesday, May 9, a truck carrying the instrument left Pasadena. Later that afternoon it reached Orbital Science Corporation's Satellite Manufacturing Facility in Gilbert, Arizona. And later this month, the instrument will be integrated with the Orbital-built OCO-2 spacecraft bus, which arrived in Gilbert on April 30.

OCO-2 is the latest mission in NASA's study of the global carbon cycle and NASA's first mission dedicated to studying atmospheric carbon dioxide. Carbon dioxide is the most significant human-produced greenhouse gas and the principal human-produced driver of climate change.

The original OCO mission was lost shortly after launch on February 24, 2009, when the Taurus XL launch vehicle carrying it malfunctioned and failed to reach orbit. If all continues on schedule, OCO-2 will launch from Vandenberg Air Force Base, California, as early as the summer of 2014.

And now, the mission particulars...

OCO-2 is managed by JPL for NASA's Science Mission Directorate, Washington. Orbital Sciences Corporation, Dulles, Virginia, built the spacecraft and provides mission operations under JPL's leadership. The California Institute of Technology in Pasadena manages JPL for NASA.

For more information on OCO-2, visit: oco.jpl.nasa.gov and www.nasa.gov/oco .

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Dawn: Protoplanet and HED Parent

The above image shows the mineral distribution in the southern hemisphere of asteroid Vesta. The image was made from data obtained by NASA's Dawn spacecraft. Image Credit: NASA/JPL-Caltech/UCLA/INAF/MPS/DLR/IDA

A very interesting paper on asteroid 4 Vesta was published May 11th in the journal Science. The paper is authored by members of NASA's Dawn mission team. Launched in 2007, the Dawn spacecraft has been studying Vesta since its arrival in July of 2011.

The new paper supports the thinking that Vesta is a protoplanet left over from the earliest epoch of our solar system's formation. This is based on a comparison of Dawn's Vesta data with analyses of the howardite-eucrite-diogenite (HED) class of meteorites and the general agreement that HED meteorites came from a parent body with a differentiated -- layered -- internal structure.

The Dawn mission team has been studying a giant impact basin at Vesta's south pole. The team reasons that the creation of the basin would have been quite sufficient to produce the Vesta family of asteroids as well as the HED class of meteorites. This is supported by Dawn's spatially resolved mineralogy of the Vesta surface, which reflects the composition of the HED meteorites and confirms that Vesta's crust was formed by the melting of a chondritic parent body.

Vesta's mass, volume, and gravitational field are consistent with a core having an average radius of 107 to 113 kilometers. This indicates there must have been sufficient internal melting to separate the iron from other present materials so that the iron could gather in Vesta's core and the other materials could layer based upon their relative densities.

In short, Dawn's results confirm pre-mission theories that Vesta's structure became differentiated during its formation. In addirion, they support the  identification of HED meteorites as "children" of asteroid 4 Vesta.

The Dawn spacecraft will depart Vesta on August 26 (my birthday) . At that time it will head for its next study target, the dwarf planet Ceres, arriving in 2015.

And now, the mission particulars...

Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. The California Institute of Technology in Pasadena manages JPL for NASA.

For more information about the Dawn mission, visit: www.nasa.gov/dawn and dawn.jpl.nasa.gov .

To read more about the Vesta discoveries, check out the online home page of the journal Science: www.sciencemag.org

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Comparing Black Hole Activity to Star Formation

The above image is an artistically modified image of the local galaxy Arp 220, located 250 Mly (77 Mpc) from Earth. The original image was taken by the Hubble Space Telescope and helps to illustrate the results of the Herschel Space Observatory. Image Credit: NASA/JPL-Caltech

The Herschel Space Observatory has shown astronomers that galaxies with the most powerful, active black holes at their cores produce fewer stars than galaxies with less active black holes. The results are the first to demonstrate that black holes suppressed galactic star formation when the universe was less than half its current age. The Herschel mission is lead by the European Space Agency (ESA) with important contributions by NASA. The results of the study are in a paper that is published in this week's issue of the journal Nature.

Based on evidence to date, astronomers believe that supermassive black holes, weighing as much as millions of suns, reside in the hearts of all large galaxies. When gas falls upon them, the material is accelerated and heated around the black hole, releasing great amounts of energy. It is thought that earlier in the history of the universe, these giant, luminous black holes, called active galactic nuclei, were often much brighter and more energetic. In addition, astronomers think that star formation was livelier at that time.

But this new study of nearby galaxies suggest that active black holes can squash star formation. The revved-up, central black holes likely heat up and disperse the galactic reservoirs of cold gas needed to create new stars. These studies have only provided "snapshots" in time, however, leaving the overall relationship of active galactic nuclei and star formation unclear, especially over the cosmic history of galaxy formation.

The researchers compared their infrared readings with X-rays streaming from the active central black holes in the survey's galaxies, measured by NASA's Chandra X-ray Observatory. At lower intensities, the black holes' brightness and star formation increased in sync. However, star formation dropped off in galaxies with the most energetic central black holes. Astronomers think inflows of gas fuel new stars and supermassive black holes. Feed a black hole too much, however, and it starts spewing radiation into the galaxy that prevents raw material from coalescing into new stars.

And now, the mission particulars...

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and important participation by NASA. NASA's Herschel Project Office is based at JPL. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at Caltech, supports the United States astronomical community. Caltech manages JPL for NASA.

To learn more about the study, visit the online home page of the journal Nature: www.nature.com

For NASA's Herschel website, visit www.nasa.gov/herschel . For ESA's Herschel website, visit www.esa.int/SPECIALS/Herschel .

Follow this link for more information about NASA's Chandra X-ray Observatory: chandra.harvard.edu

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More From Sunspot AR1476

The above image shows an active region, source of at least half a dozen solar flares and numerous other small bursts of plasma over about 36 hours (Apr. 29 - May 1, 2012). The bright active region, viewed in extreme ultraviolet light by Solar Dynamics Observatory. Image Credit: , must have had a tangled magnetic field for it to erupt so frequently. None of the flares were major, but they made for a nifty movie. Image Credit: NASA/SDO/Goddard Spaceflight Center

Meanwhile, back on the sun...

It seems the huge sunspot AR1476, which has already produced M-class solar flares, appears to be on the verge of producing something even stronger. The sunspot's 'beta-gamma-delta' magnetic field has sufficient energy for X-class flares, which are the most powerful kind.

To review, a solar flare is an explosion on the sun that occurs when the energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. Flares produce a burst of radiation across the electromagnetic spectrum, from radio waves to X-rays and gamma-rays.

Solar flares are classified, from lowest to highest, as A, B, C, M and X according to the peak flux (in watts per square meter, W/m^2) of 100 to 800 picometer X-rays near Earth, as measured on the GOES spacecraft. The five categories break down as follows.

A-class: Peak flux of less than 10^-7 Watts/square meter. A-class flares produce no noticeable consequences on Earth.

B-class: Peak flux ranges from 10^-7 to 10^-6 Watts/square meter. B-class flares produce no noticeable consequences on Earth.

C-class: Peak flux ranges from 10^-6 to 10^-5 Watts/square meter. C-class flares produce few noticeable consequences
on Earth.

M-class: Peak flux ranges from 10^-5 to 10^-4 Watts/square meter. M-class flares  can cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare.

X-class: Peak flux is greater than 10^-4 Watts/square meter. X-class flare are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms.

Within each category are nine subdivisions of strength. For example, C1 to C9, M1 to M9, and so on. On July 14, 2000, the sun produced a X6 flare which triggered a major radiation storm around Earth and was nicknamed the Bastille Day event.

REMEMBER: Never look directly at the sun without proper filtering equipment.

To learn more about the sun and to stay current on solar activity, visit the mission home page of Solar Dynamics Observatory (SDO), sdo.gsfc.nasa.gov

...and the mission home page of the Solar and Heliospheric Observatory (SOHO), sohowww.nascom.nasa.gov

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Willie Nelson Has Nothing on Opportunity

The above image, showing Greeley Haven, was taken by the rear hazard-avoidance camera of the Opportunity rover near the end of its first post-winter drive. The shadow on the foreground was made by Opportunity's solar array. Image Credit: NASA/JPL-Caltech

After 130 sols at its winter parking spot, Greeley Haven, the Mar Exploration Rover Opportunity is on the road, again! It has been eight Earth-years and over 34.36 kilometers (21.35 miles) since landing on the Red Planet, and Opportunity isn't showing any signs of slowing down. On May 8, Opportunity made its first move of the season, driving about 12 feet (3.67 meters).

There is quite a bit of dust built up on Opportunity's solar array. So until the wind blows some of it away, Opportunity will be investigating areas that don't have a southward slope. This strategy will ensure that Opportunity is positioned to receive sufficient sunlight for regularly recharging its batteries. Even so, there are plenty "sunny" targets of interest for the Opportunity mission team.

To learn more about Opportunity, as well as NASA's ongoing exploration of the planet Mars, visit NASA's Mars Exploration Program home page: mars.jpl.nasa.gov

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Dawn News Conference Thursday

This Thursday (May 10) at 11 AM PDT (2 PM EDT), NASA will host a news conference to present a new analysis of asteroid Vesta, using data from the Dawn mission. NASA will broadcast the event live on NASA Television and streamed on the NASA website.  For NASA TV streaming video, downlink and scheduling information, visit: www.nasa.gov/ntv .  

The news conference will also be streamed live on Ustream with a moderated chat available at: www.ustream.com/nasajpl2 . Questions may also be asked via Twitter using the hashtag #asknasa .

The briefing panelists are: Carol Raymond, Dawn deputy principal investigator, NASA's Jet Propulsion Laboratory, Pasadena, California; Harry McSween, chair, Dawn surface composition working group, University of Tennessee, Knoxville; Vishnu Reddy, Dawn framing camera team member, Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, and the University of North Dakota, Grand Forks; David O'Brien, Dawn participating scientist, Planetary Science Institute, Tucson, Arizona; and Maria Cristina De Sanctis, Dawn co-investigator and visible and infrared mapping spectrometer team lead, Italian National Institute for Astrophysics, Rome.

To learn more about the Dawn mission, visit these links: www.nasa.gov/dawn and dawn.jpl.nasa.gov .

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Titan's Methane Abundance is Considered

Above is a false-color image showing a thin, detached haze layer (purple line) that appears to float above Titan's main atmospheric haze. The image was taken July 3, 2004, by narrow-angle camera aboard the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute 

In the April 20th issue of the Astrophysical Journal, two papers are presented which review the methane production on Saturn’s largest moon, Titan, and attempt to estimate how long this process has been going on. Titan hides behind a thick, smoggy atmosphere. Scientists describe it as one of the most complex chemical environments in the solar system — cranking out hydrocarbons that rain down on Titan's icy surface and cloak it in soot. With a brutally cold surface temperature of around minus 270 degrees Fahrenheit (minus 170 degrees Celsius), the hydrocarbons form lakes of liquid methane and ethane.
Methane gas is the most important raw ingredient in Titan's chemical factory. This molecule is composed of one carbon atom and four hydrogen atoms. It should not last long because it's being continuously destroyed by sunlight and converted to more complex molecules and particles. But scientists are certain just how long they last, hence the two new papers.

The papers used data collected by two instruments on NASA's Cassini spacecraft in orbit around Saturn and one instrument on the European Space Agency's Huygens probe that landed on Titan's surface in January 2005. All three instruments were built at NASA's Goddard Space Flight Center in Greenbelt, Maryland. One paper uses infrared signatures (spectra) of methane from Cassini's composite infrared spectrometer to estimate how much "heavy" methane containing rare isotopes is present in Titan's atmosphere.

Isotopes are versions of an element with different weights, or masses. For example, carbon 13 is a heavier (and rare) version of the most common type of carbon, called carbon 12. Occasionally, a carbon-13 atom replaces a carbon-12 atom in a methane molecule. Because methane made with carbon 12 is slightly lighter, the chemical reactions that convert it to more complex hydrocarbons happen a bit faster. This means carbon-12 methane gets used up at a slightly faster rate than heavy carbon-13 methane, so the concentration of heavy methane in Titan's atmosphere increases slowly. By modeling how the concentration of heavy methane changes over time, the scientists predicted how long Titan's chemical factory has been running.
Scientists estimate that methane has a maximum age of 1.6 billion years, or about a third the age of Titan. But if methane escapes from the top of the Titan atmosphere, as some previous work has suggested, the age may be shortened to as little as 10 million years, which would be compatible with the observations of the Cassini mission.

Both scenarios assume that methane entered the atmosphere in one burst of outgassing, probably from the restructuring of Titan's interior as heavier materials sank towards the center and lighter ones rose toward the surface. But if the methane has been continuously replenished from a source, then its isotopes would always appear 'fresh' and the scientists can't restrict the age in their model. Possible sources include methane clathrates, basically a methane molecule inside a "cage" or lattice of ice molecules. Methane clathrates are found in the frigid depths of Earth's oceans, and some scientists think there could be an ocean of liquid water mixed with ammonia (acting as antifreeze) beneath Titan's water-ice crust. If this is so, methane might be released from its clathrate cages during the eruptions of proposed 'cryovolcanoes' of water-ammonia slurry, or more simply could slowly seep out through fractures in the crust.

The second Titan paper also models the time-evolution of methane. In this work, the concentration of the heavy methane is determined from measurements by Cassini's ion and neutral mass spectrometer, which counts molecules in the atmosphere of different masses (weights). Measurements made by the Huygens gas chromatograph mass spectrometer, which also counts molecules of different masses, were used to constrain the impact of escape on the heavy methane in the atmosphere.

Scientists compute that, even if methane has been replenished from the interior over time to match or exceed the amounts fed into the atmospheric chemical factory, the process must have been running for a maximum of one billion years. If the process had started any earlier, they would expect see a build-up of methane in the lakes on the Titan surface and in the atmosphere beyond what they observe today.

And now, the mission particulars…

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington.

To read more on these papers, visit the Astrophysical Journal: iopscience.iop.org/0004-637X

To learn more about the Cassini-Huygens mission and spacecraft, visit: saturn.jpl.nasa.gov  and  www.nasa.gov

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The Sombrero is a Twofer

The above image is an infrared view of the Sombrero galaxy, recorded by NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech

Some galaxies are plump and round. Others are a slender disk like our spiral Milky Way. But it seems that the Sombrero galaxy is both. Scientists have drawn this conclusion from new observations made using NASA's Spitzer Space Telescope. The galaxy, which is a round elliptical galaxy with a thin disk embedded inside, is one of the first known to exhibit characteristics of the two different types. Scientists think these findings will lead to a better understanding of galaxy evolution, a topic that is still poorly understood.

Formally known as NGC 4594, the Sombrero galaxy is located 28 million light-years away in the constellation Virgo. The galaxy was discovered in 1767 by Pierre Mechain. From Earth, we can see the thin edge of its flat disk and a central bulge of stars, making the galaxy resemble a wide-brimmed hat. Astronomers do not know whether the Sombrero's disk is shaped like a ring or a spiral, but they agree it belongs to the disk class.

Being an infrared telescope, Spitzer captures a different view of the galaxy than visible-light telescopes. In visible light, the galaxy appears to be immersed in a glowing halo, which scientists had thought was relatively light and small. But in the infrared, a different view emerges. Spitzer sees old stars through the dust and reveals the halo has the right size and mass to be a giant elliptical galaxy.

It is tempting to think the giant elliptical swallowed a spiral disk. However, astronomers say this is highly unlikely because that process would have destroyed the disk structure. One scenario they propose is that a giant elliptical galaxy was inundated with gas more than nine billion years ago. Early in the history of our universe, networks of gas clouds were common, and they sometimes fed growing galaxies, causing them to bulk up. The gas would have been pulled into the galaxy by gravity, falling into orbit around the center and spinning out into a flat disk. Stars would have formed from the gas in the disk.

The above scenario poses lots of questions. For example: How did the disk shape survive inside a massive elliptical? And how unusual is this process of formation? Researchers say the answers could help them piece together how other galaxies evolve. Another galaxy, called Centaurus A, appears also to be an elliptical galaxy with a disk inside it. But its disk does not contain many stars. Astronomers speculate that Centaurus A could be at an earlier stage of evolution than the Sombrero and might eventually look similar.

The findings also answer a mystery about the number of globular clusters in the Sombrero galaxy. Globular clusters are spherical nuggets of old stars. Ellipticals typically have a few thousand, while spirals contain a few hundred. The Sombrero has almost 2,000, a number that makes sense now but had puzzled astronomers when they thought it was only a disk galaxy.

The details on this study are being published in the Monthly Notice of the Royal Astronomical Society. The paper was posted online April 23rd. To read the paper, click on the following link: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2012.20925.x/abstract

And now, the Spitzer mission particulars…

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit these links: spitzer.caltech.edu and www.nasa.gov/spitzer

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Punching Holes in the F Ring

The above six images, obtained by NASA's Cassini spacecraft, show trails that were dragged out from Saturn's F ring by objects about a half mile (1 kilometer) in diameter. Scientists have seen more than 500 of these kinds of trails in over 20,000 images collected by Cassini from 2004 to 2011. The trails seen in this set are typical of the entire collection. From left to right in the top row, the trails in these images are 18, 85 and 96 miles long (29, 136 and 155 kilometers long). In the bottom row from left to right, the trails are 43, 129 and 32 miles long (69, 207 and 51 kilometers long). Image Credit: NASA/JPL-Caltech/SSI/QMUL

It seems that scientists were studying images from the Cassini spacecraft and discovered strange half-mile-sized (kilometer-sized) objects punching through parts of Saturn's F Ring and leaving glittering trails behind them. Folks are calling these trails "mini-jets" and they appear to answer some elusive questions about the F Ring. The results were presented during this year's meeting of the European Geosciences Union, which was held April 22 through 27 in Vienna, Austria.

The F Ring is the outermost discrete ring of Saturn and perhaps the most active ring in the solar system. Its features change a bit every few hours. The F ring It is located 3,000 km beyond the outer edge of the A Ring. It was discovered in 1979 by the Pioneer 11 imaging team. It is very thin, just a few hundred kilometers wide, and is held together by two shepherd moons, Prometheus and Pandora, which orbit inside and outside the ring.

Scientists knew that relatively large objects like the Saturnian moon Prometheus (as long as 92 miles, or 148 kilometers, across) could create channels, ripples and snowballs in the F Ring. But scientists didn't know what happened to these snowballs after they were created. Some were surely broken up by collisions or tidal forces in their orbit around Saturn, but now scientists have evidence that some of the smaller ones survive, and their differing orbits mean they go on to strike through the F ring on their own.

These small objects appear to collide with the F Ring at gentle relative speeds — something on the order of about 4 mph (2 meters per second). The collisions drag glittering ice particles out of the F ring with them, leaving a trail typically 20 to 110 miles (40 to 180 kilometers) long. Murray's group happened to see a tiny trail in an image from Jan. 30, 2009 and tracked it over eight hours. The long footage confirmed the small object originated in the F ring, so they went back through the Cassini image catalog to see if the phenomenon was frequent.

According to scientists, these mini-jets are so tiny that it took quite a bit of time and luck to find them. It is reported that they went through 20,000 images and were thrilled to find 500 examples of these rogues during just the seven years Cassini has been at Saturn.

In some cases, the objects traveled in packs, creating mini-jets that looked quite exotic, like the barb of a harpoon. Other new images show grand views of the entire F Ring, showing the swirls and eddies that ripple around the ring from all the different kinds of objects moving through and around it.

And now, the mission particulars...

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colo. JPL is a division of the California Institute of Technology, Pasadena.

For information about Cassini, visit: www.nasa.gov/cassini and saturn.jpl.nasa.gov

New images and movies of the mini-jets and other peculiar F ring behavior are available at: www.nasa.gov/mission_pages/cassini/whycassini/cassini20120423.html

To learn more about the 2012 meeting of the European Geosciences Union, visit this link: www.egu2012.eu

To learn more about the NASA Pioneer 10 and 11 missions, visit this link: science.nasa.gov/missions/pioneer-10-11/

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Super Moon 2012

The above image shows moonrise over a metropolitan area. Image Credit: Bill Watson (WillyFlyBoy), http://pictureontario.ca/blog/ .

This weekend, May 5 and 6, the rising full moon will be a perigee moon — a moon that reaches the closest point in its orbit at the time of its full phase. Because of its apparent increase in size and brightness, a perigee full moon has been nicknamed a "super moon." This weekend’s super moon will appear as much as 14 percent bigger and 30 percent brighter than other full moons of 2012. The moon will officially become full Saturday (May 5) at 11:35 PM EDT. The last super moon occurred March 19th 2011. Next month’s full moon comes close, but occurs one day after perigee. The next super moon will occur June 23rd, 2013.

The key to getting the most out of a super moon lies in looking to the sky at the right time. Look at the moon as it rises over the horizon and it will likely appear enormous, especially if seen behind objects in the foreground. For reasons still not understood by astronomers or psychologists, a low-hanging moon looks unnaturally large when it shines through trees, buildings and other foreground objects. A super moon amplifies this effect.

Some have long thought the full moon was to blame for misfortune, accidents, crime and chaos. The Latin word for “moon” — Luna — is the root of the word "lunacy." There was even wild speculation last year that the perigee moon contributed to the magnitude 9.0 earthquake that crushed the coast of Japan the week before.

It is true that during a full moon, when the moon is opposite the sun in our sky, the opposing gravitational pull from these bodies causes the high and low tides to be more extreme than normal. And a perigee moon does increase this affect even more. However, the effect of perigee full moons is much too small to influence Earth's seismic activity. In addition, there is no scientific evidence to date which supports the belief that lunar phases influence our mental faculties.

To read more on super moons, check out this NASA Science News article: http://science.nasa.gov/science-news/science-at-nasa/2012/02may_supermoon/

To see a video on this weekend’s event, follow this link: http://www.youtube.com/watch?v=kOplwuMTyS4

To keep up with future moon perigees and lunar phases, check out John Walker’s Lunar Perigee and Apogee Calculator at Fourmi Labs: http://www.fourmilab.ch/earthview/pacalc.html

Extra, Extra! Get your Handouts Here!....

In related news, I had a great time this passed May 1st evening as I helped with the sidewalk telescopes event for the families of a local home school. Thanks, again, to friend and fellow amateur astronomer Craig MacDougal for the invitation to participate. To download a PDF copy of my “Exploring the Moon” handout from the event, click the following link: http://tiny.cc/JMTSSA002-20120501

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Near-Earth Objects, Part Eight

Frequently Asked Questions For Impact Risk Assessment

How is an orbit calculated? 

An asteroid's orbit is computed by finding the elliptical path about the sun that best fits the available observations of the object. That is, the object's computed path about the sun is adjusted until the predictions of where the asteroid should have appeared in the sky at several observed times match the positions where the object was actually observed to be at those same times. As more and more observations are used to further improve an object's orbit, we become more and more confident in our knowledge of where the object will be in the future.

How far into the future does Sentry search for impacts? 

100 years.

Why do your first calculations of an orbit often look more threatening than later ones?

Because orbits stemming from very limited observation sets are more uncertain it is more likely that such orbits will "permit" future impacts. However, such early predictions can often be ruled out as we incorporate more observations and reduce the uncertainties in the object's orbit. Most often, the threat associated with a specific object will decrease as additional observations become available, and so objects will be posted to, and later removed from, our Impact Risk Page. The Palermo Scale values will typically start out at less negative values when the object's orbit is most uncertain and evolve to more negative values (and eventually off the list) as more and more observations allow the object's orbit to be continually improved.

On the other hand, in the unlikely case where a particular potential impact event persists until the orbit is relatively well constrained, the impact probability and associated risk will tend to increase as observations are added. This is not too paradoxical: If an asteroid is indeed going to come very near the Earth then a collision cannot be ruled out early on. The impact probability will tend to grow as the orbit is refined and alternative and safer trajectories are eliminated. Eventually, the impact probability will drop (usually quite abruptly) to zero or, if the asteroid is really on a collision trajectory, it will continue to grow until it reaches 100%.

How soon after the discovery is a search for potential collisions initiated? 

When the discovery of a new NEA is announced by the Minor Planet Center (MPC), Sentry automatically (usually within an hour or two) prioritizes the object for an impact risk analysis. If the prioritization analysis indicates that the asteroid cannot pass near the Earth or that its orbit is very well determined then the computationally intensive nonlinear search for potential impacts is not pursued. If, on the other hand, a search is deemed necessary then the object is added to a queue of objects awaiting analysis. Its position in the queue is determined by the estimated likelihood that potential impacts may be found.

How often do these results change? 

NEA orbits and close approach tables are continuously and automatically updated whenever new observations are made available, generally within a couple of hours of the release of the information. Whenever an NEA orbit is updated the object is re-prioritized and, if appropriate, it is re-queued for a new potential impact search. This process is ongoing - taking place anytime, day and night, seven days a week.

Why isn't 1950 DA listed on the Risk Page? 

1950 DA is an asteroid for which there is some possibility of impact in March of the year 2880. The case is extraordinary because the current orbit of 1950 DA is very precisely known, which allows us to explore centuries into the future, much farther than is usually possible. The Sentry automatic monitoring system is tailored for objects with poorly determined orbits and it searches for potential impacts only over the next 100 years.

Why are the results published by NEODyS not the same as those published by Sentry? 

The differences between the two systems are generally not substantial, and in some sense they are reassuring. Independent systems using different software and theoretical approaches are not expected to produce the same results from statistical searches. Experience has shown that there is excellent agreement between the two systems for the more serious potential collision detections.

One of the differences between the two systems stems from different approaches to computing the impact probability. This computation is rough by its very nature, and different techniques may be used; impact probabilities different by a factor of ten or so are not extraordinary.

Another important variation is that Sentry uses a different sampling strategy, one that should detect nearly all potential impacts with probability greater than 10^-8 (1 in 100 million), and does not expend much effort pursuing less likely cases, although it may find some anyway. In any case, nothing with impact probability below 10^-10 (1 in 10 billion) is published by Sentry. In contrast, NEODyS may not detect as many potential impacts at probabilities below 10^-6 (1 in 1 million), but in certain cases it can detect very low probability events that Sentry does not.


To be continued...

NASA's Near-Earth Object (NEO) Program coordinates NASA-sponsored efforts to detect, track and characterize potentially hazardous asteroids and comets that could approach the Earth. To learn more, visit the home page of NASA's Near-Earth Object Program: http://neo.jpl.nasa.gov/

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