by The first comet return mission is still revealing secrets about its icy target – even 18 years after bringing precious cargo to Earth for scientists to discus.
After launching in 1999, NASA’s Stardust Mission rendezvoused with the comet named 81P/Wild 2 (81P/ means that it is the 81st periodic comet to be identified) in 2004, capturing thousands of tiny dust particles from 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 descended toward a soft landing in Utah. The dust particles carried by comets are still being analyzed today.
“Almost every Wild 2 particle is unique and has a different story to tell,” said Ryan Ogliore, an associate professor of physics at Washington University in St. Louis. statement. “Removing and analyzing these grains is a time-consuming process, but the scientific rewards are great.”
The comet’s name is German and is pronounced “Vilt 2” after the Swiss astronomer Paul Wild who made his second comet discovery when he discovered it in 1978.
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Before the Wild 2 sample was returned, scientists suspected that the comet would be composed of primordial matter, specifically interstellar dust and particles from the solar nebula who founded our Solar system. Although some interstellar particles have been discovered, however, most of the particles studied appear to have been processed during different periods of time and in different regions of the young solar system. This hints at a fascinating history. The comet could be a precursor to the chemistry we see in the solar system today.
“Comet Wild 2 has things we’ve never seen before meteoriteslike unusual carbon-iron assemblages, and the precursors to undulating spheres that make up the most common type of meteorite,” Ogliore said.
A notable absence from the sample is dust ejected from collisions between asteroids, which are believed to have occurred frequently in the turbulent environment of the early solar system. During these days, asteroids and protoplanets fell very chaotically, not yet settled in their orbits. The absence of this type of dust suggests that Wild 2 formed before such rocky asteroids or elsewhere.
In fact, Wild 2 probably spent most of its life orbiting Neptune, in the Kuiper Belt and Scattered Disk, or perhaps even in the Oort Cloud beyond. Out there, hundreds of astronomical units (AU) from the sun, the temperature would not get above -223 degrees Celsius (-370 degrees Fahrenheit), so liquid water or heat could not have chemically changed the composition of the comets.
At some point, Wild 2 was ejected from the system, possibly engulfed by the gravity of a running star and ended up on an elongated 43-year orbit that ranged from 3.74 billion kilometers (2.3 billion miles.) — for comparison, Neptune It is 4.3 billion kilometers (2.67 billion miles) from the sun — and 748 million kilometers (464 million miles) from the sun, going almost on par with Jupiter. Then, in 1974, Wild 2 passed within one million kilometers (621,371 miles) of Jupiter, meaning the giant planet’s gravity changed the comet’s orbit again, shortening it to a 6.2-year long orbit from 783 million kilometers (487 million miles ). from the sun 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, which is tiny, especially compared to the 70.3 grams of rocks and dust that OSIRIS-REx brought back from the asteroid Bennu in 2023. However, despite the small mass, it is still responsible for more than 10,000 cometary dust grains greater than a micrometer in size. And thanks to modern instruments and analytical techniques that were not even available in 2005, new discoveries will continue to be made about Wild 2 .
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The comet is essentially a time capsule from the beginning of the solar system that has been kept in a deep freeze for the better part of 4.5 billion years. In the time since the formation of Wild 2, the young solar system has transformed itself into the grouping of eight planets, many dwarf planets and asteroid belts and comets that we see today. So, things like Wild 2 have an important story to tell.
“The comet witnessed the events that shaped the solar system into what we see today,” Ogliore said.
Ogliore’s review article describing Stardust’s findings to date was published in the November 2023 issue of the journal. Geochemistry.
