Stardust Burns For Comet

NASA’S Stardust Burns for Comet, Less than a Year Away

Researcher examines a Stardust aerogel tile under a stereo microscope.
Credit: NASA/Ames

The Stardust spacecraft was the first in history to collect samples from a comet and return them to Earth for study. Now the spacecraft is preparing for another visit to a comet.

Just three days shy of one year before its planned flyby of comet Tempel 1, NASA’s Stardust spacecraft has successfully performed a maneuver to adjust the time of its encounter by eight hours and 20 minutes. The delay maximizes the probability of the spacecraft capturing high-resolution images of the desired surface features of the 2.99-kilometer-wide (1.86 mile) potato-shaped mass of ice and dust.

With the spacecraft on the opposite side of the solar system and beyond the orbit of Mars, the trajectory correction maneuver began at 5:21 p.m. EST (2:21 p.m. PST) on Feb. 17. Stardust’s rockets fired for 22 minutes and 53 seconds, changing the spacecraft’s speed by 24 meters per second (54 miles per hour).

Stardust’s maneuver placed the spacecraft on a course to fly by the comet just before 8:42 p.m. PST (11:42 p.m. EST) on Feb. 14, 2011 — Valentine’s Day. Time of closest approach to Tempel 1 is important because the comet rotates, allowing different regions of the comet to be illuminated by the Sun’s rays at different times. Mission scientists want to maximize the probability that areas of interest previously imaged by NASA’s Deep Impact mission in 2005 will also be bathed in the Sun’s rays and visible to Stardust’s camera when it passes by.

“We could not have asked for a better result from a burn with even a brand-new spacecraft,” said Tim Larson, project manager for the Stardust-NExT at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “This bird has already logged one comet flyby, one Earth return of the first samples ever collected from deep space, over 4,000 days of flight and approximately 5.4 billion kilometers (3.4 billion miles) since launch.”

A Wild Encounter

Stardust’s original mission was to collect samples of a comet and return them to Earth. Above, comet particle tracks can be seen in samples of aerogel from Stardust.
Credit: Stardust, JPL, NASA

Launched on Feb. 7, 1999, Stardust passed through the dense gas and dust surrounding the icy nucleus of Wild 2 (pronounced "Vilt-2") on January 2, 2004. As the spacecraft flew through this material, a special collection grid filled with aerogel – a novel sponge-like material that’s more than 99 percent empty space – gently captured samples of the comet’s gas and dust. The grid was stowed in a capsule which detached from the spacecraft and parachuted to Earth on January 15, 2006. Since then, scientists around the world have been busy analyzing the samples to learn the secrets of comet formation and our solar system’s history.

After Stardust flew by Earth to deliver the comet sample, mission controllers placed the still-viable spacecraft on a trajectory toward comet Tempel 1.

Stardust just flew through Wild-2’s dusty gas, but the Deep Impact spacecraft had sent a coffee table-sized impactor to smash into the surface of Tempel 1. This impact occured on July 4, 2005, and instruments on Deep Impact analyzed the immense debris cloud that resulted. Later analysis of the data collected from Deep Impact and other observing telescopes closer to home has revealed the impact cloud contained silicates — crystallized grains even smaller than sand. One of these silicates is a mineral called olivine, found on the glimmering shores of Hawaii’s Green Sands Beach. The cloud also contained clay and carbonate compounds, which was unexpected because they are thought to require liquid water to form.

"How did clay and carbonates form in frozen comets?" asked Carey Lisse of Johns Hopkins University’s Applied Physics Laboratory, Laurel, Md. "We don’t know, but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the Sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body."

Also found were chemicals never seen before in comets, such as iron-bearing compounds and aromatic hydrocarbons, found in barbecue pits and automobile exhaust on Earth. Understanding the composition of comets can help astrobiologists determine whether or not comets could have delivered molecules to the early Earth that were essential for the origin of life.

Second Life

Ice can be found in many places in space, including the surface of comets. This image of the comet Tempel 1 shows icy patches in blue.
Credit: NASA

In January 2007, NASA re-christened the Stardust mission "Stardust-NExT" (New Exploration of Tempel), and the Stardust team began a four-and-a-half year journey to visit the comet where Deep Impact had left such a lasting impression.

“Stardust-NExT will provide scientists the first opportunity to see the surface changes on a comet between successive visits into the inner solar system,” said Joe Veverka, principal investigator of Stardust-NExT from Cornell University, Ithaca, N.Y.

Comet Tempel 1 completes an orbit of the Sun every 5.5 years. “We have theories galore on how each close pass to the Sun causes changes to a comet," said Veverka. "Stardust-NExT should give some teeth to some of these theories, and take a bite out of others.”

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.

While Stardust looks forward to it’s next comet "date" in 2011, the Deep Impact spacecraft’s next match will be taking place later this year. The spacecraft will flyby the comet Hartley 2 on Nov. 4, 2010. After Deep Impact’s date with Tempel 1 ended, NASA used the spacecraft’s telescopes to search for extrasolar planets in distant solar systems.

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