NASA's EPOXI flyby reveals new insights into comet features

NASA's EPOXI mission spacecraft successfully flew past comet Hartley 2 at 7 a.m. PDT (10 a.m. EDT) Thursday, Nov. 4. Scientists say initial images from the flyby provide new information about the comet's volume and material spewing from its surface.

"Early observations of the comet show that, for the first time, we may be able to connect activity to individual features on the nucleus," said EPOXI Principal Investigator Michael A'Hearn of the University of Maryland, College Park. "We certainly have our hands full. The images are full of great cometary data, and that's what we hoped for."

EPOXI is an extended mission that uses the already in-flight Deep Impact spacecraft. Its encounter phase with Hartley 2 began at 1 p.m. PDT (4 p.m. EDT) on Nov. 3, when the spacecraft began to point its two imagers at the comet's nucleus. Imaging of the nucleus began one hour later.

"The spacecraft has provided the most extensive observations of a comet in history," said Ed Weiler, associate administrator for NASA's Science Mission Directorate at the agency's headquarters in Washington. "Scientists and engineers have successfully squeezed world-class science from a re-purposed spacecraft at a fraction of the cost to taxpayers of a new science project."

Images from the EPOXI mission reveal comet Hartley 2 to have 100 times less volume than comet Tempel 1, the first target of Deep Impact. More revelations about Hartley 2 are expected as analysis continues.

Initial estimates indicate the spacecraft was about 700 kilometers (435 miles) from the comet at the closest-approach point. That's almost the exact distance that was calculated by engineers in advance of the flyby.

"It is a testament to our team's skill that we nailed the flyby distance to a comet that likes to move around the sky so much," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "While it's great to see the images coming down, there is still work to be done. We have another three weeks of imaging during our outbound journey."

The name EPOXI is a combination of the names for the two extended mission components: the Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). The spacecraft has retained the name "Deep Impact." In 2005, Deep Impact successfully released an impactor into the path of comet Tempel 1.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, manages the EPOXI mission for NASA's Science Mission Directorate. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., in Boulder, Colo.

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

Deep impact spacecraft successfully flies by comet Hartley 2

The University of Maryland-led EPOXI mission successfully flew by comet Hartley 2 at 10 a.m. EDT Nov. 3, 2010, and the spacecraft has begun returning images. Hartley 2 is the fifth comet nucleus visited by any spacecraft and the second one visited by the Deep Impact spacecraft.

Scientists and mission controllers are studying never-before-seen images of Hartley 2 appearing on their computer terminal screens. See images at: http://epoxi.umd.edu/

"We are all holding our breath to see what discoveries await us in the observations near closest approach," said University of Maryland astronomer Michael A'Hearn, one of the originators of science team leader for both the Deep Impact mission and its follow on mission EPOXI.

At approximately 10 a.m. EDT, the spacecraft passed within 700 kilometers (435 miles) of the comet. Minutes after closest approach, the spacecraft's High-Gain Antenna was pointed at Earth and began downlinking vital spacecraft health and other engineering data stored aboard the spacecraft's onboard computer during the encounter. Twenty minutes later, the first images of the encounter made the 37 million kilometer (23 million mile) trip from the spacecraft to NASA's Deep Space Network antenna, appearing moments later on the mission's computer screens.

"The mission team and scientists have worked for this day," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's good to see Hartley 2 up close."

A Deeper Impact on Planetary Science

With the latest EPOXI mission data on Hartley 2, the Deep Impact spacecraft is adding to an already extensive scientific legacy. Launched in January 2005, the spacecraft made scientific history and world-wide headlines when it smashed a probe into comet Tempel 1 on July 4th of that year. Following the conclusion of that mission, a Maryland-led team of scientists won approval from NASA to fly the Deep Impact spacecraft to a second comet.

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). During the EPOCh phase of EPOXI, the Deep Impact spacecraft provided information on possible extrasolar planets and was one of three spacecraft to find for the first time clear evidence of water on Moon. A study accepted for publication in The Astrophysical Journal and just released by NASA, provides "colorful" findings on Earth and other planets in our solar system that someday may help identify earthlike worlds around other stars.

The overall objective of the flyby of Hartley 2 is the same as that for the Deep Impact mission's trip to Tempel 1: to learn more about the origin and history of our solar system by learning more about the composition and diversity of comets. Comets contain material from the early days of the solar system before the planets formed. "If we understand the comets really well it will tell us how the planets got made," explained A'Hearn. "That's why we choose comets to study."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., 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 and eight other members of the EPOXI science team. 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.

Primordial dry ice fuels comet jets

One of the biggest comet findings coming out of the amazing images and data taken by the University of Maryland-led EPOXI mission as it zipped past comet Hartley 2 last week is that dry ice is the 'jet' fuel for this comet and perhaps many others.

Images from the flyby show spectacular jets of gas and particles bursting from many distinct spots on the surface of the comet. This is the first time images of a comet have been sharp enough to allow scientists to link jets of dust and gas with specific surface features. Analysis of the spectral signatures of the materials coming from the jets shows primarily CO2 gas (carbon dioxide) and particles of dust and ice.

"Previously it was thought that water vapor from water ice was the propulsive force behind jets of material coming off of the body, or nucleus, of the comet," said University of Maryland Astronomy Professor Jessica Sunshine, who is deputy principal investigator for the EPOXI mission. "We now have unambiguous evidence that solar heating of subsurface frozen carbon dioxide (dry ice), directly to a gas, a process known as sublimation, is powering the many jets of material coming from the comet. This is a finding that only could have been made by traveling to a comet, because ground based telescopes can't detect CO2 and current space telescopes aren't tuned to look for this gas," Sunshine said.

Sunshine and other members of the EPOXI science team are meeting all this week at the University of Maryland to analyze the very large amount of data from the closest approach, and new data continues to come down at a rate of some 2000 images a day.

The Deep Impact spacecraft that flew past comet Hartley 2 has three instruments -- two telescopes with digital color cameras and an infrared spectrometer. The spectrometer measures the absorption, emission and reflection of light (spectroscopic signature) that is unique to each molecular compound. This allows Maryland scientists to determine the composition of the material on the comet's surface, in the jets, and in the coma, or cloud of particles around it. They have found that water and carbon dioxide dominate the infrared spectrum of comet Hartley 2's environment and that organics, including methanol, are present at lower levels.

This is no surprise to scientists. But what is surprising is that there is a lot more carbon dioxide escaping this comet than expected. "The distribution of carbon dioxide and dust around the nucleus is much different than the water distribution, and that tells us that the carbon dioxide rather than water takes dust grains with it into the coma as it leaves the nucleus, said Assistant Research Scientist Lori Feaga. "The dry ice that is producing the CO2 jets on this comet has probably been frozen inside it since the formation of the solar system."

From Deep Impact to Hartley 2

According to University of Maryland Research Scientist Tony Farnham, findings from the team's 2005 Deep Impact mission to comet Tempel 1, though less conclusive, nonetheless indicate that the Hartley 2 findings that super-volatiles (CO2) and not water drive the activity, probably are a common characteristic of comets. "Tempel 1 was most active before perihelion when its southern hemisphere, the hemisphere that appeared to be enhanced in CO2, was exposed to sunlight," said Farnham, a member of both the Deep Impact and EPOXI science teams. "Unlike our Hartley encounter, during the flyby with Tempel 1, we were unable to directly trace the CO2 to the surface, because the pole was in darkness during encounter."

The Maryland scientists devised the plan to reuse the Deep Impact spacecraft and travel to a second comet in order to learn more about the diversity of comets and the processes that govern them. This became the EPOXI mission on which the spacecraft has flown to comet Hartley 2.

The spacecraft's images show that Hartley 2 has an elongated nucleus, 2 kilometers in length and 0.4 kilometers wide at the narrow neck. Hartley 2 is only the 5th cometary nucleus ever seen and exhibits similarities and differences to the bodies or nuclei of other comets. Mission Principal Investigator and science team leader Michael A'Hearn, a University of Maryland professor of astronomy, said the mission has provided, and continues to provide, a tremendous wealth of data about Hartley 2 and the team expects to announce more science findings in the coming weeks.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Maryland.

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NASA's Stardust spacecraft burns for another comet flyby

Eighty-six days out from its appointment with a comet, NASA's Stardust spacecraft fired its thrusters to help refine its flight path. The Stardust-NExT mission will fly past comet Tempel 1 next Valentine's Day (Feb. 14, 2011). It will perform NASA's second comet flyby within four months.

"One comet down, one to go," said Tim Larson, project manager for both the Stardust-NExT mission and the EPOXI mission -- which successfully flew past comet Hartley 2 on Nov. 4.

The trajectory correction maneuver, which adjusts the spacecraft's flight path, began at 2 p.m. EST (11:00 a.m. PST) on Nov. 20. The Stardust spacecraft's rockets fired for 9 seconds, consumed about 41 grams (1.4 ounces) of fuel and changed the spacecraft's speed by all of 0.33 meters per second (about 0.7 miles per hour). The maneuver was designed to target a point in space 200 kilometers (124 miles) from comet Tempel 1.

Launched on Feb. 7, 1999, Stardust became the first spacecraft in history to collect samples from a comet (comet Wild 2), and return them to Earth for study. While its sample return capsule parachuted to Earth in January 2006, mission controllers were placing the still viable spacecraft on a path that would allow NASA the opportunity to re-use the already-proven flight system if a target of opportunity presented itself. In January 2007, NASA re-christened the mission "Stardust-NExT" (New Exploration of Tempel), and the Stardust team began a four-and-a-half year journey for the spacecraft to comet Tempel 1. This will be the second exploration of Tempel 1 by a spacecraft (Deep Impact).

Along with the high-resolution images of the comet's surface, Stardust-NExT will also measure the composition, size distribution and flux of dust emitted into the coma, and provide important new information on how Jupiter family comets evolve and how they formed 4.6 billion years ago.

Stardust-NExT is a low-cost mission that will expand the investigation of comet Tempel 1 initiated by NASA's Deep Impact spacecraft. JPL, a division of the California Institute of Technology in Pasadena, manages Stardust-NExT for the NASA Science Mission Directorate, Washington, D.C. Joe Veverka of Cornell University, Ithaca, N.Y., is the mission's principal investigator. Lockheed Martin Space Systems, Denver, built the spacecraft and manages day-to-day mission operations.

For more information about Stardust-NExT, visit: http://stardustnext.jpl.nasa.gov .