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Comet offers a rare chance to study the origins of the solar system



Artistic concept of the Stardust spacecraft flying from Comet 81P / Wild. Credit: NASA / JPL

In order to better understand the early history of the solar system, more comet samples are urgently needed, say researchers analyzing comet dust brought to Earth by NASA's Stardust mission in 2006.

Dust particles originate from Comet 81

P / Wild (also known as Wild 2) and date back to the dawn of the solar system, with references to its earliest history.

"The Future of Stardust Science", a paper published in June 2017 in the journal Meteoritics & Planetary Science summarizes the approximately 150 scientific publications based on Stardust science. It makes an important point beyond the limits of our knowledge of the early protosolar disk of gas and dust from which the solar system was formed. That is, Wild 2 and other Kuiper Belt comets – those originating from the Neptune orbit – are poorly represented in our samples of extraterrestrial material.

In contrast, asteroids in our collections are represented by meteorites and have been well documented for more than a century, while the material of the moon was collected and brought to scientists for analysis by the Apollo astronauts.

Andrew Westphal, an elderly member of the Stardust team and an astrophysicist at the University of California, Berkeley, urged researchers to seek out more Kuiper belt material that can be studied on Earth because of its unique provenance.

A glimpse of the capsule of Stardust, after successfully falling back to earth under the parachute. in 2006. Credit: NASA

"The further one digs further and further in the solar system, the more primitive material is taken," says Westphal, the main author of the work. "Especially if you get a sample of a comet, you get a sample [that has been] for 4.6 billion years in the freezer."

About 10 percent of a typical comet-belt comet is unaltered interstellar material. Part of this material consists of pre-solar grains – circumstellar dust grains condensed in the outflows (emissions) of other stars long before the formation of the solar system. However, most of the interstellar material was thought to be formed in the interstellar medium

Little Information on Water

The determination of whether liquid water was ever present in Wild 2 is also an important target of comet researchers. Astronomical evidence shows that cometary water can have variable ratios of deuterium to hydrogen (D to H) and that the average ratio differs from that of water on Earth. A famous example of this is comet 67P / Churyumov-Gerasimenko, which was examined from 2014 to 2016 in the Rosetta mission of the European Space Agency. Other cometary D / H ratios were measured with ground-based telescopes.

If comets In their waters they have a different ratio of D to H than the water of the earth. This probably means that comets have not released most of the water to the surface. Instead, investigators speculate that it was asteroids that brought the water but needed more research from both asteroids and comets to confirm the hypothesis.

A possible interstellar dust trace (circled) in Stardust's airgel collector. Credit: UC Berkeley / Andrew Westphal

Unfortunately, no "volatile substances" – molecules with low boiling points such as water – survived at 6.1 kilometers per second (3.8 miles per second or 13.680 miles per second) in the airgel and aluminum foil collectors of the spaceship hour). , This situation has made it difficult to advance science on comet D to H ratios.

"The rocks survived, but no water was preserved," says Westphal. "However, some rare organic substances retained their D / H ratios."

The researchers also searched for phyllosilicates, which are clays that preserve water in them, but to date Stardust studies have not revealed phyllosilicates

There might be another opportunity to study the material of a comet , NASA's proposed Comet Rendezvous, Sampling, Investigation and Return (CORSAIR) mission was developed to collect Comet 88P / Howell materials, including organic matter, that could offer more implications for astrobiology. If the mission is approved, these samples would return to Earth in the 2030s.


Further information:
Researchers present list of comets 67P / Churyumov-Gerasimenko ingredients

Further information:
A. J. Westphal al. The Future of Stardust Science, Meteoritics & Planetary Science (2017). DOI: 10.1111 / Maps.12893


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