The first comet sample return mission continues to reveal secrets about its icy target, even 18 years after it brought a valuable cargo to Earth for scientists to study.
After launch in 1999, NASA stardust mission It rendezvoused with comet 81P/Wild 2 (81P/ means it is the 81st recognized periodic comet) in 2004, trapping thousands of tiny dust particles in the comet’s tail in a collector made of an ultralight material called “aerogel.” On January 15, 2006, Stardust returned the sample capsule to Earth, which then parachuted to a soft landing in Utah. The transported comet dust particles are still analyzed today.
St. “Almost every Wild 2 particle is unique and has a different story to tell,” said Ryan Ogliore, a professor of physics at Washington University in St. Louis. expression. “Extracting and analyzing these grains is a time-consuming process, but the payoff to science is huge.”
The comet’s name is actually German, pronounced “Vilt 2” in memory of Swiss astronomer Paul Wild, who made his second comet discovery when he found it in 1978.
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Before the Wild 2 sample was returned, scientists suspected that the comet would be composed of particularly primitive material. interstellar dust and particles from sun nebula we created solar system. However, although some interstellar particles have been discovered, the majority of particles studied appear to have been processed in different time periods as well as in different regions of the young solar system. This suggests a fascinating history. The comet may represent a precursor to the chemistry we see in the solar system today.
“Comet Wild 2 includes things we’ve never seen before meteors“And these objects are all perfectly preserved in Wild 2,” Ogliore said.
One noticeable omission in the example relates to dust released from collisions between asteroids; this is believed to have occurred frequently in the disrupted environment of the early solar system. These days, asteroids and protoplanets that had not yet settled into their orbits were tumbling chaotically. The absence of such dust suggests that Wild 2 formed before or in a different location than such rocky asteroids.
Indeed, Wild 2 probably spent most of its life beyond Neptune, in the Kuiper Belt and Scattered Disc, perhaps even orbiting the more distant Oort Cloud. There, hundreds of astronomical units (AU) from the sun, the temperature could not rise above -223 degrees Celsius (-370 degrees Fahrenheit), so liquid water or heat could not chemically alter the comet’s composition.
At some point Wild 2 was nudged through the system, perhaps jolted by the gravity of a passing star, and ended up in a 43-year-long orbit ranging 3.74 billion kilometers (2.3 billion miles) — for comparison, Neptune is 4.3 miles from the Sun. billion kilometers (2.67 billion miles) and 748 million kilometers (464 million miles) from the sun, making it almost the same distance as Jupiter. Then, in 1974, Wild 2 passed within one million kilometers (621,371 miles) of Jupiter; This means that the giant planet’s gravity shifted the comet’s orbit again, shortening it to a 6.2-year orbit ranging from 783 million kilometers (487 million miles). Up to 238 million kilometers (147 million miles) from the sun, which is just beyond the orbit of Mars.
Stardust collected less than a milligram’s worth of comet dust; This is a very small amount, especially compared to 70.3 grams of rock and dust. OSIRIS-REx brought back from asteroid bennu However, despite its small mass, it contains more than 10,000 grains of comet dust larger than a micrometer in size. And new discoveries about Wild 2 will continue to be made, thanks to modern instruments and analysis techniques not yet available in 2005.
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The comet is actually a time capsule from the beginning of the solar system that has been kept in the deep freeze for approximately 4.5 billion years. In the time since Wild 2’s formation, the young solar system has transformed itself into the group of eight planets, numerous dwarf planets, and asteroid and comet belts we see today. Therefore, objects like Wild 2 that have been there throughout the entire process have an important story to tell.
“The comet was a witness to the events that shaped the solar system into the shape we see today,” Ogliore said.
Ogliore’s review article describing findings from Stardust so far was published in the November 2023 issue of the journal. Geochemistry.