Astronomers Probe 'Sandbar' Between Islands of Galaxies

This diagram shows an unusual galaxy with bent jets (see inset). › Full image and caption
› See diagram

Astronomers have caught sight of an unusual galaxy that has illuminated new details about a celestial "sandbar" connecting two massive islands of galaxies. The research was conducted in part with NASA's Spitzer Space Telescope.

These "sandbars," or filaments, are known to span vast distances between galaxy clusters and form a lattice-like structure known as the cosmic web. Though immense, these filaments are difficult to see and study in detail. Two years ago, Spitzer's infrared eyes revealed that one such intergalactic filament containing star-forming galaxies ran between the galaxy clusters called Abell 1763 and Abell 1770.

Now these observations have been bolstered by the discovery, inside this same filament, of a galaxy that has a rare boomerang shape and unusual light emissions. Hot gas is sweeping the wandering galaxy into this shape as it passes through the filament, presenting a new way to gauge the filament's particle density. Researchers hope that other such galaxies with oddly curved profiles could serve as signposts for the faint threads, which in turn signify regions ripe for forming stars.

"These filaments are integral to the evolution of galaxy clusters -- among the biggest gravitationally bound objects in the universe -- as well as the creation of new generations of stars," said Louise Edwards, a postdoctoral researcher at the California Institute of Technology in Pasadena, and lead author of a study detailing the findings in the Dec. 1 issue of the Astrophysical Journal Letters. Her collaborators are Dario Fadda, also at Caltech, and Dave Frayer from the National Science Foundation's National Radio Astronomy Observatory, based in Charlottesville, Virginia.

Blowing in the cosmic breeze

Astronomers spotted the bent galaxy about 11 million light-years away from the center of the galaxy cluster Abell 1763 during follow-up observations with the WIYN Observatory near Tucson, Ariz., and radio-wave observations by the Very Large Array near Socorro, N.M. The WIYN Observatory is named after the consortium that owns and operates it, which includes the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories.

The galaxy has an unusual ratio of radio to infrared light, as measured by the Very Large Array and Spitzer, making it stand out like a beacon. This is due in part to the galaxy having twin jets of material spewing in opposite directions from a supermassive black hole at its center. These jets have puffed out into giant lobes of material that emit a tremendous amount of radio waves.

Edwards and her colleagues noticed that these lobes appear to be bent back and away from the galaxy's trajectory through the filament. This bow shape, the astronomers reasoned, is due to particles in the filament pushing on the gas and dust in the lobes.

By measuring the angle of the arced lobes, Edwards' team calculated the pressure exerted by the filaments' particles and then determined the density of the medium. The method is somewhat like looking at streamers on a kite soaring overhead to judge the wind strength and the thickness of the air.

According to the data, the density inside this filament is indeed about 100 times the average density of the universe. This value agrees with that obtained in a previous X-ray study of filaments and also nicely matches predictions of supercomputer simulations.

Interconnected superclusters

Galaxies tend to bunch together as great islands in the void of space, called galaxy clusters. These galaxy groupings themselves often keep company with other clusters in "superclusters" that loom as gargantuan, gravitationally associated walls of galaxies. These structures evolved from denser patches of material as the universe rapidly expanded after the Big Bang, some 13.7 billion years ago.

The clumps and threads of this primordial matter eventually cooled, and some of it has condensed into the galaxies we see today. The leftover gas is strewn in filaments between galaxy clusters. Much of it is still quite hot -- about one million degrees Celsius (1.8 million degrees Fahrenheit) -- and blazes in high-energy X-rays that permeate galaxy clusters. Filaments are therefore best detected in X-ray light, and one direct density reading of the strands has previously been obtained in this band of frequencies.

But the X-ray-emitting gas in filaments is much more diffuse and weak than in clusters, just as submerged sandbars are extremely hard to spot at sea compared to islands poking above the water. Therefore, obtaining quality observations of filaments is time-consuming with current space observatories.

The technique by Edwards and her colleagues, which uses radio frequencies that can reach a host of ground-based telescopes, points to an easier way to probe the interiors of galaxy-cluster filaments. Instead of laboring to find subtle X-rays clues, astronomers could trust these arced "lighthouse" galaxies to indicate just where cosmic filaments lie.

Knowing how much material these filaments contain and how they interact with galaxy clusters will be very important for understanding the overall evolution of the universe, Edwards said.

The Spitzer observations were made before it ran out of its liquid coolant in May 2009 and began its warm mission.

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 Caltech, also in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer.

NASA Funds High School Student Robotics Program

NASA funds a nationwide high school robotics competition that provides students the opportunity to engage with engineers and technology experts for hands-on, realistic exposure to engineering and technical professions.

NASA is providing up to $20 million over the next five years to support a national program to inspire student interest in science, technology and mathematics with a focus on robotic technology.

The funding is part of a cooperative agreement with the Foundation for Inspiration and Recognition of Science and Technology (FIRST), a nonprofit organization in Manchester, N.H. FIRST provides students the opportunity to engage with government, industry and university experts, including those at NASA's Jet Propulsion Laboratory, Pasadena, Calif., for hands-on, realistic exposure to engineering and technical professions.

"This is the largest NASA-funded student program geared toward robotics activities," said NASA Administrator Charles Bolden. "For the next five years, approximately 25,000 students across the country will not only learn from our nation's best and brightest, but also compete and have fun at the same time."

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View my last 3 blog postings...

• Saturn Then and Now: 30 Years Since Voyager Visit
• Cassini Sees Saturn on a Cosmic Dimmer Switch
• NASA Study Shows Role of Melt in Arctic Sea Ice Lo...

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Saturn Then and Now: 30 Years Since Voyager Visit

Ed Stone, project scientist for NASA's Voyager mission, remembers the first time he saw the kinks in one of Saturn's narrowest rings. It was the day the Voyager 1 spacecraft made its closest approach to the giant ringed planet, 30 years ago. Scientists were gathering in front of television monitors and in one another's offices every day during this heady period to pore over the bewildering images and other data streaming down to NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Stone drew a crude sketch of this scalloped, multi-stranded ring, known as the F ring, in his notebook, but with no explanation next to it. The innumerable particles comprising the broad rings are in near-circular orbits about Saturn. So, it was a surprise to find that the F ring, discovered just a year before by NASA's Pioneer 11 spacecraft, had clumps and wayward kinks. What could have created such a pattern?

"It was clear Voyager was showing us something different at Saturn," said Stone, now based at the California Institute of Technology in Pasadena. "Over and over, the spacecraft revealed so many unexpected things that it often took days, months and even years to figure them out."

The F ring curiosity was only one of many strange phenomena discovered in the Voyager close encounters with Saturn, which occurred on Nov. 12, 1980, for Voyager 1, and Aug. 25, 1981, for Voyager 2. The Voyager encounters were responsible for finding six small moons and revealing the half-young, half-old terrain of Enceladus that had to point to some kind of geological activity.

Images from the two encounters also exposed individual storms roiling the planet's atmosphere, which did not show up at all in data from Earth-based telescopes. Scientists used Voyager data to resolve a debate about whether Titan had a thick or thin atmosphere, finding that Titan was shrouded in a thick haze of hydrocarbons in a nitrogen-rich atmosphere. The finding led scientists to predict there could be seas of liquid methane and ethane on Titan's surface.

"When I look back, I realize how little we actually knew about the solar system before Voyager," Stone added. "We discovered things we didn't know were there to be discovered, time after time."

In fact, the Voyager encounters sparked so many new questions that another spacecraft, NASA's Cassini, was sent to probe those mysteries. While Voyager 1 got to within about 126,000 kilometers (78,300 miles) above Saturn's cloud tops, and Voyager 2 approached as close as about 100,800 kilometers (62,600 miles), Cassini has dipped to this altitude and somewhat lower in its orbits around Saturn since 2004.

Because of Cassini's extended journey around Saturn, scientists have found explanations for many of the mysteries first seen by Voyager. Cassini has uncovered a mechanism to explain the new terrain on Enceladus – tiger stripe fissures with jets of water vapor and organic particles. It revealed that Titan indeed does have stable lakes of liquid hydrocarbons on its surface and showed just how similar to Earth that moon really is. Data from Cassini have also resolved how two small moons discovered by Voyager – Prometheus and Pandora – tug on the F ring to create its kinked shape and wakes that form snowballs.

"Cassini is indebted to Voyager for its many fascinating discoveries and for paving the way for Cassini," said Linda Spilker, Cassini project scientist at JPL, who started her career working on Voyager from 1977 to 1989. "On Cassini, we still compare our data to Voyager's and proudly build on Voyager's heritage."

But Voyager left a few mysteries that Cassini has not yet solved. For instance, scientists first spotted a hexagonal weather pattern when they stitched together Voyager images of Saturn's north pole. Cassini has obtained higher-resolution pictures of the hexagon – which tells scientists it's a remarkably stable wave in one of the jet streams that remains 30 years later – but scientists are still not sure what forces maintain the hexagon.

Even more perplexing are the somewhat wedge-shaped, transient clouds of tiny particles that Voyager discovered orbiting in Saturn's B ring. Scientists dubbed them "spokes" because they looked like bicycle spokes. Cassini scientists have been searching for them since the spacecraft first arrived. As Saturn approached equinox, and the sun's light hit the rings edge-on, the spokes did reappear in the outer part of Saturn's B ring. But Cassini scientists are still testing their theories of what might be causing these odd features.

"The fact that we still have mysteries today goes to show how much we still have to learn about our solar system," said Suzanne Dodd, Voyager's project manager, based at JPL. "Today, the Voyager spacecraft continue as pioneers traveling toward the edge of our solar system. We can't wait for the Voyager spacecraft to enter interstellar space – true outer space – and make more unexpected discoveries."

Voyager 1, which was launched on Sept. 5, 1977, is currently about 17 billion kilometers (11 billion miles) away from the sun. It is the most distant spacecraft. Voyager 2, which was launched on Aug. 20, 1977, is currently about 14 billion kilometers (9 billion miles) away from the sun.

The Voyagers were built by JPL, which continues to operate both spacecraft. Caltech manages JPL for NASA. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages Cassini for NASA. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

More Voyager information is available at http://www.nasa.gov/voyager and http://voyager.jpl.nasa.gov .

More Cassini information is available at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Cassini Sees Saturn on a Cosmic Dimmer Switch

This false-color composite image, constructed from data obtained by NASA's Cassini spacecraft, shows Saturn's rings and southern hemisphere. › Full image and caption

Like a cosmic lightbulb on a dimmer switch, Saturn emitted gradually less energy each year from 2005 to 2009, according to observations by NASA's Cassini spacecraft. But unlike an ordinary bulb, Saturn's southern hemisphere consistently emitted more energy than its northern one. On top of that, energy levels changed with the seasons and differed from the last time a spacecraft visited Saturn in the early 1980s. These never-before-seen trends came from a detailed analysis of long-term data from the composite infrared spectrometer (CIRS), an instrument built by NASA's Goddard Space Flight Center in Greenbelt, Md., as well as a comparison with earlier data from NASA's Voyager spacecraft. When combined with information about the energy coming to Saturn from the sun, the results could help scientists understand the nature of Saturn's internal heat source.

"The fact that Saturn actually emits more than twice the energy it absorbs from the sun has been a puzzle for many decades now," said Kevin Baines, a Cassini team scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and a co-author on a new paper about Saturn's energy output. "What generates that extra energy? This paper represents the first step in that analysis."

The research, reported this week in the Journal of Geophysical Research-Planets, was led by Liming Li of Cornell University in Ithaca, N.Y. (now at the University of Houston).

"The Cassini CIRS data are very valuable because they give us a nearly complete picture of Saturn," Li said. "This is the only single data set that provides so much information about this planet, and it's the first time that anybody has been able to study the power emitted by one of the giant planets in such detail."

The planets in our solar system lose energy in the form of heat radiation in wavelengths that are invisible to the human eye. The CIRS instrument picks up wavelengths in the thermal infrared region, far enough beyond red light where the wavelengths correspond to heat emission.

"In planetary science, we tend to think of planets as losing power evenly in all directions and at a steady rate," Li said. "Now we know Saturn is not doing that." (Power is the amount of energy emitted per unit of time.)

Instead, Saturn's flow of outgoing energy was lopsided, with its southern hemisphere giving off about one-sixth more energy than the northern one, Li explains. This effect matched Saturn's seasons: during those five Earth-years, it was summer in the southern hemisphere and winter in the northern one. (A season on Saturn lasts about seven Earth-years.) Like Earth, Saturn has these seasons because the planet is tilted on its axis, so one hemisphere receives more energy from the sun and experiences summer, while the other receives less energy and is shrouded in winter. Saturn's equinox, when the sun was directly over the equator, occurred in August 2009.

In the study, Saturn's seasons looked Earth-like in another way: in each hemisphere, its effective temperature, which characterizes its thermal emission to space, started to warm up or cool down as a change of season approached. The effective temperature provides a simple way to track the response of Saturn's atmosphere to the seasonal changes, which is complicated because Saturn's weather is variable and the atmosphere tends to retain heat. Cassini's observations revealed that the effective temperature in the northern hemisphere gradually dropped from 2005 to 2008 and started to warm up again by 2009. In the southern hemisphere, the effective temperature cooled from 2005 to 2009.

The emitted energy for each hemisphere rose and fell along with the effective temperature. Even so, during this five-year period, the planet as a whole seemed to be slowly cooling down and emitting less energy.

To find out if similar changes were happening one Saturn-year ago, the researchers looked at data collected by the Voyager spacecraft in 1980 and 1981 and did not see the imbalance between the southern and northern hemispheres. Instead, the two regions were much more consistent with each other.

Why wouldn't Voyager have seen the same summer-versus-winter difference between the two hemispheres? One explanation is that cloud patterns at depth could have fluctuated, blocking and scattering infrared light differently.

"It's reasonable to think that the changes in Saturn's emitted power are related to cloud cover," says Amy Simon-Miller, who heads the Planetary Systems Laboratory at Goddard and is a co-author on the paper. "As the amount of cloud cover changes, the amount of radiation escaping into space also changes. This might vary during a single season and from one Saturn-year to another. But to fully understand what is happening on Saturn, we will need the other half of the picture: the amount of power being absorbed by the planet."

Scientists will be doing that as a next step by comparing the instrument's findings to data obtained by Cassini's imaging cameras and infrared mapping spectrometer instrument. The spectrometer, in particular, measures the amount of sunlight reflected by Saturn. Because scientists know the total amount of solar energy delivered to Saturn, they can derive the amount of sunlight absorbed by the planet and discern how much heat the planet itself is emitting. These calculations help scientists tackle what the actual source of that warming might be and whether it changes.

Better understanding Saturn's internal heat flow "will significantly deepen our understanding of the weather, internal structure and evolution of Saturn and the other giant planets," Li said.

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., a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA Goddard, where the instrument was built.

More Cassini information is available at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Source http://www.jpl.nasa.gov/news/news.cfm?release=2010-380

NASA Study Shows Role of Melt in Arctic Sea Ice Loss

A mosaic of satellite images shows the movement of fragmented ice away from ice edges, which scientists use to track the loss of multiyear ice due to melt. › Larger image

A NASA analysis of satellite data has quantified, for the first time, the amount of older and thicker "multiyear" sea ice lost from the Arctic Ocean due to melting.

Since the start of the satellite record in 1979, scientists have observed the continued disappearance of older "multiyear" sea ice that survives more than one summer melt season. Some scientists suspected that this loss was due entirely to wind pushing the ice out of the Arctic Basin -- a process that scientists refer to as "export." In this study, Ron Kwok and Glenn Cunningham at NASA's Jet Propulsion Laboratory in Pasadena, Calif., used a suite of satellite data to clarify the relative role of export versus melt within the Arctic Ocean.

Kwok and Cunningham show that between 1993 and 2009, a significant amount of multiyear ice -- 1,400 cubic kilometers (336 cubic miles) -- was lost due to melt, not export.

"The paper shows that there is indeed melt of old ice within the Arctic basin and the melt area has been increasing over the past several years," Kwok said. "The story is always more complicated -- there is melt as well as export -- but this is another step in calculating the mass and area balance of the Arctic ice cover."

The results have implications for understanding how Arctic sea ice gets redistributed, where melt occurs in the Arctic Ocean, and how the ocean, ice and atmosphere interact as a system to affect Earth's climate. The study was published in October 2010 in Geophysical Research Letters.

Scientists track the annual cycle of Arctic sea ice coverage as it melts through the summer to reach a minimum extent each September, before refreezing through fall and winter. Much of that ice is seasonal, meaning that it forms and melts within the year.

But multiyear ice that survives more than one season has also been declining, as noted in previous work by Joey Comiso of NASA's Goddard Space Flight Center in Greenbelt, Md., who shows a loss of about 10 percent per decade since the beginning of the satellite record in 1979. Scientists want to know where this loss is occurring.

"The decline of the multiyear ice cover of the last several decades has not been quantitatively explained," Kwok said.

To investigate the loss of multiyear ice, Kwok and Cunningham looked at a 17-year span of data from 1993 to 2009 from a range of polar-observing satellites and instruments, including NASA's Quick Scatterometer (QuikScat); the Ice, Cloud and land Elevation Satellite (ICESat); the Advanced Microwave Scanning Radiometer (AMSR); and the European Space Agency's European Remote Sensing (ERS)-1 and -2 satellites. Some instruments track ice coverage, while others track motion and concentration.

The team collected satellite images and tracked pixels of multiyear ice from April 1, prior to the onset of seasonal melt, and into the summer. Pixels that deviated away from images of the ice edge were considered lost to melt.

The team compared summertime melt of multiyear ice in the Beaufort Sea with estimates of ice lost from the Arctic basin through the Fram Strait -- a major passage through which ice can exit the Arctic Ocean. The comparison revealed how much multiyear ice was lost to export and how much was lost to melt.

They found that over the 17-year period, an area of 947,000 square kilometers (365,639 square miles), or about 32 percent of the decline in multiyear sea ice area, was lost in the Beaufort Sea due to melt.

A similar calculation using thickness estimates from NASA's ICESat from 2004 to 2009 show a volume loss of 1,400 cubic kilometers (336 cubic miles), or about 20 percent of the total loss by volume.

How and where multiyear ice is lost has impacts on the Arctic system. For example, more loss by melt means more freshwater remains in local Arctic waters rather than being transported southward.

"These results also show that thick multiyear sea ice is not immune to melt in the Pacific sector of the Arctic Ocean in today's climate," Kwok said.

The additional freshwater from melt in the Pacific sector, which encompasses the area of study, could contribute to the freshening of the Beaufort Gyre and potentially influence circulation, but the degree of that influence remains uncertain.

Not all of the multiyear ice loss is accounted for, however. Ice loss through Fram Strait and from melt from 2005 to 2008 accounts for just 52 percent of total ice loss. The team suggests that melt in other Arctic regions and outflow through other passages besides Fram Strait could account for the difference.

Since its launch in 1999, QuikScat, developed and managed by JPL, has advanced Earth science research and helped improve environmental predictions using measurements of global radar backscatter from Earth's ocean, land and ice surfaces. QuikScat data help scientists better understand and predict the processes that drive our climate, such as ocean circulation and the global water cycle. In addition to its numerous weather forecasting and climate research applications, QuikScat data also help monitor changes in Arctic sea ice and icebergs, as well as snow and soil moisture changes on land. For more on QuikScat, visit: http://winds.jpl.nasa.gov/index.cfm.

For more information, see:

› Missing 'Ice Arches' Contributed to 2007 Arctic Ice Loss

› NASA Satellite Reveals Dramatic Arctic Ice Thinning

› Satellites Show Arctic Literally on Thin Ice

NASA Spacecraft on Final Approach Toward Comet

EPOXI navigation team members and engineers were in mission control for the final flight-path maneuver before the spacecraft's planned Nov. 4 flyby of comet Hartley 2. › Larger image

The EPOXI mission spacecraft has refined its path toward a Nov. 4 flyby of comet Hartley 2, successfully performing its final maneuver today at 8 a.m. PDT (11 a.m. EDT). The spacecraft burned its engines for 6.8 seconds, changing the spacecraft's velocity by 1.4 meters per second (3 miles per hour).

"I've worked the Stardust flyby of comet Wild 2 and the Deep Impact encounter with comet Tempel 1, and I have never seen a comet flit around the sky like this one," said mission navigator Shyam Bhaskaran of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We needed to make this burn to re-locate the spacecraft for the 700-kilometer [about 435 miles] flyby distance."

Part of the reason Hartley 2 is hard to pin down is because the small comet is very active.

"Hartley 2 is one-seventh the size of comet Tempel 1, but it releases almost the same amount of material into the space environment," said EPOXI Principal Investigator Mike A'Hearn of the University of Maryland. "These jets can act as thrusters and actually make small changes to the comet's orbit around the sun."

On Thursday, Nov. 4, the spacecraft will fly past the comet, with closest approach expected about 7 a.m. PDT [10 a.m. EDT]. This flyby will mark the fifth time in history that a spacecraft has been close enough to image the heart of the comet, more commonly known as the nucleus.

EPOXI is an extended mission that uses the already "in-flight" Deep Impact spacecraft to explore distinct celestial targets of opportunity. The name EPOXI itself is a combination of the names for the two extended mission components: the extrasolar planet observations, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). The spacecraft will continue to be referred to as "Deep Impact."

JPL, a division of the California Institute of Technology in Pasadena, manages the EPOXI mission for NASA's Science Mission Directorate, Washington. The University of Maryland, College Park, is home to the mission's principal investigator, Michael A'Hearn. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md., is the science lead for the mission's extrasolar planet observations. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

For more information about EPOXI, visit: http://www.nasa.gov/epoxi and http://epoxi.umd.edu/.

View my last 3 blog postings...

• The Man Behind Comet Hartley 2
• NASA's Comet Mission May Face Multiple Jets Nov. 4...
• NASA Spacecraft Preps for Comet Flyby

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The Man Behind Comet Hartley 2

Malcolm Hartley of the Anglo-Australian Observatory, Siding Spring, New South Whales, Australia. › Larger image

Over the last 40 years, Malcolm Hartley has done just about every possible job for Siding Spring Observatory's UK Schmidt telescope in New South Wales, Australia. The British-born, Scottish-educated Hartley has logged time as the 1.2 meter (3.9 foot) telescope's observer, processor, copier, hypersensitization expert, and quality controller.

On the afternoon of March 16, 1986, Hartley's job was that last one -- quality control. In that role, he was the first to view each 36-by-36 centimeter (14-by-14 inch) photographic glass plate after it had been exposed to the night sky. Checking for imperfections on one of the previous evening's 60-minute illuminations, Hartley came upon something that wasn't supposed to be there.

"Back then, the observations came in as negatives -- stars and other objects in the sky appeared black on a clear background," said Hartley. "I noticed a dark haze around a trail. Trails indicate something that is traveling fast through the sky, but asteroids don't have a haze. So I thought it might be a comet."

Hartley double-checked his sighting a couple of nights later, then submitted his findings to the Minor Planet Center in Cambridge, Mass. A couple of days after that, the center issued a brief circular informing the astronomical world of the discovery of comet Hartley 2.

"I was very happy for a couple of days," said Hartley."Every scientist wants to discover something and it's a fantastic feeling. There was even a mention in the local paper, the Coonabarabran Times."

On the world's stage, having a comet named after you is certainly unique. But not so much in the small town of Coonabarabran -- which they say comes from the local Aboriginal word for 'inquisitive person.' It is the closest town to the Warrumbungle Range and Siding Spring Mountain and the Anglo-Australian Observatory.

"There are several other colleagues at Siding Springs who have discovered comets," Hartley said. "Robert McNaught has discovered over 50, and I don't think he's ever been mentioned in the Times. It's a rural farming community, and while there are amateur astronomers in the area, finding comets is not really a big deal."

Hartley went on to discover or co-discover 10 comets with the UK Schmidt telescope, and with each, he would feel an initial rush of excitement. But in 2002, the Anglo-Australian Observatory retrofitted its Schmidt to perform multi-object spectroscopy, essentially halting all astrophotography with the telescope and ending any future possibility for comet discovery. Hartley, who never was directly tasked with finding comets, continued to work the telescope's galaxy surveys. Comets, it seemed, had become little more than a historical footnote in his career. That is, until he got a call from a science magazine.

"At the beginning of last year, a reporter emailed and said that the EPOXI mission changed its target and now it was going to go to Hartley 2," said Hartley. "I didn't even know Hartley 2 was one of the two comets under consideration."

Hartley 2 was definitely on NASA's very short list of potential comet targets. The only problem with Hartley 2 was it would take more than two years of extra deep-space cruising to get there. So the only other candidate on the short list, the similar-sized comet Boethin, was selected. That is, until it disappeared. Scientists theorize that comet Boethin had broken into non-traceable fragments. This situation left NASA's short list as a list of one -- comet Hartley 2.

So Malcolm Hartley did what anybody would do who has a namesake comet that was just selected as a target for a NASA comet flyby, after the previous selection had disappeared. He thanked the reporter, logged off his computer and wondered what "his comet" would look like. Whatever that was going to be, Hartley was sure he would find out from the comfort of his living room. Then NASA called.

"I've never been involved with a space mission," said Hartley. "I had never visited JPL or any NASA facility for that matter. So this is all new to me. I am very grateful you have asked me to come and witness this. It is an experience very few people have had before."

Exactly once before -- of all the approximately 3,800 known comets, four have been imaged closeup by spacecraft. And of those four, only Swiss astronomer Paul Wild (pronounced "Vilt") was alive to see his comet visited. And while Wild witnessed the launch of NASA 's Stardust spacecraft from Cape Canaveral, Fla., in 1999, he watched the close-up images of his comet from the comfort of his living room in 2003. (Wild passed away in 2008). Hartley will see his comet from JPL's mission control room.

"When I discovered the comet in 1986, I never envisaged that I would come to the location where the mission was run, to see it up-close and personal," said Hartley, who was a boy when JPL was starting up.

Not surprisingly, the 63-year-old astrophotographer also has some thoughts on the mission to his comet.

"You went to Tempel 1, but then you reconfigured the spacecraft for the extended mission," said Hartley. "That's pretty clever stuff that you've done. That's the kind of science that's really interesting. To be able to do something extra on top of the successful mission you mounted at Tempel 1, it's really special."

EPOXI is an extended mission that utilizes the already "in-flight" Deep Impact spacecraft to explore distinct celestial targets of opportunity. The term EPOXI is a combination of the names for the two extended mission components: the Extrasolar Planet Observations and Characterization (EPOCh), and the Hartley 2 flyby, called the Deep Impact eXtended Investigation (DIXI). For more information about EPOXI, visit: http://www.nasa.gov/epoxi and http://epoxi.umd.edu.

JPL, a division of the California Institute of Technology in Pasadena, manages the EPOXI mission for NASA.

View my last 3 blog postings...

• NASA's Comet Mission May Face Multiple Jets Nov. 4...
• NASA Spacecraft Preps for Comet Flyby
• Space Buckyballs Thrive, Finds NASA Spitzer Telesc...

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NASA's Comet Mission May Face Multiple Jets Nov. 4

The Deep Impact spacecraft's High- and Medium-Resolution Imagers (HRI and MRI) have captured multiple jets emanating from comet Hartley 2 turning on and off while the spacecraft is 8 million kilometers (5 million miles) away from the comet. The movies from HRI and MRI show the progression of two jets during a 16-hour time period.

Two movies derived from images taken by the two cameras aboard NASA's EPOXI mission spacecraft show comet Hartley 2 is, as expected, quite active, and it provides information on the nucleus's rotation. The spacecraft has been imaging Hartley 2 almost daily since Sept. 5, in preparation for its scheduled Nov. 4 flyby of the comet.

"The comet brings us new surprises every day," said Michael A'Hearn, EPOXI principal investigator from the University of Maryland, College Park. "The data we have received to this point have been tremendous. It is forcing us to rethink what we know about cometary science, and we are still days away from encounter."

On Oct. 26, the spacecraft's two cameras, a High-Resolution Imager (HRI), and a Medium-Resolution-Imager (MRI), caught two jets firing off the comet's surface over a 16-hour period. The spacecraft captured these images from a distance of about 8 million kilometers (5 million miles) away. The data lead mission scientists to believe that both jets originate from similar latitudes on the comet's nucleus.

"These movies are excellent complements of one and other and really provide some excellent detail of how a comet's jets operate," said A'Hearn. "Observing these jets from EPOXI provides an entirely different viewpoint from what is available for Earth-based observers and will ultimately allow a proper three-dimensional reconstruction of the environment surrounding the nucleus."

The name EPOXI is a combination of the names for the two extended mission components: the extrasolar planet observations, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). The spacecraft will continue to be referred to as "Deep Impact." The Deep Impact mission successfully deployed a projectile into the path of comet Tempel 1 in 1995. The spacecraft is being "recycled" for the comet Hartley 2 flyby.

JPL manages the EPOXI mission for NASA's Science Mission Directorate, Washington. The University of Maryland, College Park, is home to the mission's principal investigator, Michael A'Hearn. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md., is the science lead for the mission's extrasolar planet observations. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

For more information about EPOXI visit http://www.nasa.gov/epoxi and http://epoxi.umd.edu/.

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