Sampling Stardust on Sunday
|Artist rendering of pickup scene, Utah Test Range
Credit: NASA/JPL, U. Wash
The Stardust spacecraft is fast approaching, zooming toward Earth at 4 miles per second. By Sunday, January 15, the spacecraft will be close enough to drop off its payload of cometary and interstellar dust.
The sample return capsule should enter the Earth’s atmosphere at 4:57 a.m. EST (2:57 am MST). Anyone awake in Nevada, Utah, and central California up to central Oregon should be able to see the Stardust capsule as a 30-second streak of light in the night sky.
The capsule will hurtle toward the ground at over 28,000 miles per hour, with parachutes slowing the 101-pound capsule as it descends toward the Utah Test and Training Range. The Stardust capsule’s parachutes are similar in design to those on the Genesis capsule, which crashed into the Utah desert in 2004 when its parachutes failed to deploy. It was later determined that a sensor for the Genesis parachutes had been installed backward. Stardust managers say extensive tests have convinced them their sample return capsule will not meet a similar fate. But even if something does go wrong with Stardust’s parachutes, Tom Duxbury, Stardust program manager at the Jet Propulsion Laboratory in Pasadena, California, says the capsule would survive.
"We have a smaller and more rugged return capsule than Genesis," says Duxbury. "Our collector grid is a very thick aluminum, very hard. The aerogel is a very robust material; we’ve tested it, and pounded it into the ground at more than a few 100 Gs and it survived just fine. So even with a hard landing we believe we will recover most if not all of our science."
After landing at about 5:12 a.m. EST, the capsule will be collected by a helicopter crew and flown to a clean room at the Michael Army Airfield for initial processing. Then the capsule will be shipped to the Johnson Space Center in Houston, Texas, where scientists will unload an ice-cube sample tray containing over 130 aerogel tiles. These tiles should be embedded with hundreds of thousands of cometary particles and bits of interstellar dust. Each particle may be no larger than the width of a human hair, and scientists expect to be able to slice each of these miniscule pieces into hundreds of samples for study.
|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.
The Stardust spacecraft launched in 1999, and it traveled halfway to Jupiter in order to fly within 150 miles of the nucleus of comet Wild 2.
Although 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. The comet spent most of its lifetime in this cold outer region and therefore preserved most of its original dust and gases. Scientists think the Kuiper Belt is a remnant of the solar system’s original building blocks, so samples from Wild 2 could help us better understand the evolution of the solar system and the Earth.
"Virtually all of the atoms in our bodies and in the Earth were in interstellar grains – stardust grains – before the solar system formed," says Donald Brownlee, Stardust principal investigator from the University of Washington in Seattle. "We’re using this comet as a library that picked up records of the formation of our solar system, and has been storing them far from the sun at very low temperatures for four and a half billion years."
Stardust is scheduled to release its sample return capsule at 12:57 a.m. EST on January 15. If there is a problem with the spacecraft and the scientists decide not to release the capsule on Sunday, they will have another opportunity three years later. The Stardust spacecraft will continue to orbit the sun, and on its next approach to Earth scientists could again attempt to release the capsule.