|Comet Wild 2 imaged just after flyby. The image highlights the remarkably rugged surface of the comet, which in close-up stereo views shows hardened impact craters, cliffs, and mesas in the landscape.
In January 2004, after a turbulent journey through the coma of comet Wild 2, the Stardust spacecraft embarked on a long, silent pilgrimage back to Earth. Very soon now, Stardust will swing back into our neighborhood to deliver its payload of cometary dust samples.
Stardust will drop its sample return capsule into Earth's atmosphere on January 15, 2006, and the capsule will hurtle toward the ground at over 28,000 miles per hour. Parachutes will help slow down the descent of the 101-pound capsule, allowing it to make a "soft landing" at the U.S. Air Force Utah Test and Training Range at 5:12 a.m. EST.
At least, that's the plan. There has been some concern about the capsule's parachutes ever since the Genesis mission mishap. When the parachutes on the Genesis capsule failed to deploy, it slammed down into the Utah desert at 193 miles per hour, breaking open the capsule, shattering the contents and contaminating the samples of solar wind. Stardust's parachutes have some of the same design elements as Genesis, but mission scientists say they have confidence that the parachutes on the Stardust capsule will work properly.
"We took the lessons we learned in Genesis, and we went through a very rigorous and extensive process of looking at the Stardust sample return capsule -- digging up the blueprints, going through all the testing that was done pre-launch," says Ed Hirst, Stardust mission system manager at the Jet Propulsion Laboratory (JPL) in Pasadena, California. "The specific Genesis mishap that has been proven, we're convinced that that is not going to happen on Stardust."
|Artist rendering of pickup scene, Utah Test Range
Credit: NASA/JPL, U. Wash
"Our return capsule is quite small but extremely rugged," adds Tom Duxbury, Stardust project manager at JPL. "In the event that a chute doesn't open or we might land hard, we know that we can very well finish the rest of our science opportunities."
If all goes well, Stardust's sample return capsule will be opened in a clean room at Johnson Space Center in Houston, Texas. Mission scientists say the clean room is needed to ensure the pristine samples don't become contaminated, rather than out of any concern that the samples might be a danger to Earth.
"Each year we have 30 to 40,000 tons of primitive material from comets and asteroids that lands on Earth, and this is about one particle per square meter per day," says Don Brownlee, Stardust principal investigator from the University of Washington in Seattle. "So during the course of our seven-year mission, there was more comet dust collected in your backyard than what we're bringing home."
Stardust launched in 1999, and it has traveled 2.88 billion miles -- halfway to Jupiter and back. Although the comet Wild 2 now moves between the orbits of Jupiter and Mars, it originally formed in the Kuiper Belt on the outskirts of the solar system. It spent most of its lifetime in this cold outer region, preserving most of its original dust and gases. (Comets that travel close to the sun lose their volatile materials over time, since the heat causes the material to boil off into space.)
Scientists think the Kuiper Belt is a remnant of the solar system's original building blocks. Dust samples from Wild 2, therefore, could help us better understand the evolution of the solar system and the Earth.
"There's some evidence that the oceans didn't primarily come from comets; they probably came from inner solar system objects (like asteroids)," says Brownlee. "But nonetheless, we would like to know the role of comets in affecting the prebiotic Earth. It took about seven-tenths of a billion years for life to show up on Earth. And when it first formed in here, the source of organic molecules it assembled from were either made on Earth or they were delivered from space."
The Stardust spacecraft flew within 150 miles of Wild 2's nucleus. A tray of silicon-dioxide aerogel was exposed during this treacherous flight, allowing dust streaming off the comet to become embedded in the ultra low-density material. The anticipated thousands of comet samples in the aerogel collector should each be much smaller than the diameter of a human hair.
|Micron-sized dust particles similiar to those trapped in the silica aerogel.
After Stardust drops off the sample capsule, it will resume an orbit around the sun. Andy Dantzler, director of NASA's solar system division, says that on January 3 NASA will release details about the spacecraft's resources for anyone who might want to use it for future projects.
Brownlee says it's unlikely that the spacecraft will ever collide with a planet or the Sun over the years, but ultimately it will be ejected out of the solar system.
"We have a crew onboard of over a million people -- their names are etched in a little silicon chip," says Brownlee. "As an astrobiology-type person, I'm intrigued by the thought that those names and that spacecraft will far outlive the Earth. When the Sun becomes a red giant and scorches the Earth, that spacecraft and those names will still be floating around the galaxy somewhere."
Related Web Pages
The Pause before the Crash
July Fourth: Crashing the Party
Comet Blaster Blasts Off
Deep Impact Mission Page
Cometary Big Dig
Live Webcam of Stardust Mission
Early Wild Success for Stardust
Telescopes for Stardust
Harpooning a Comet
Two-Way Asteroid Trip Takes Off
Tale of a Comet
We Are All Made of Stars
Winter Boon From Deep Space