What Can Comet 67P Teach Us About the Solar System?

Comet 67P/Churyumov-Gerasimenko (67P)
Bodies like comet 67P/Churyumov-Gerasimenko (67P) comprise the remnants of materials present during the formation of the Solar System. This image mosaic consists of four images taken on January 31, 2015 by Rosetta’s Navigation Camera. Comet image: ESA/Rosetta/NAVCAM.

Thursday, January 18, 2018

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To learn about the Solar System's formation and early evolution in the last 4.5 billion years, we turn to bodies like comets. These celestial bodies offer invaluable clues into the mystery of the Solar System's formation, as they carry with them some of the most pristine material since the birth of the Sun.

Astrochemists like DTM postdoc Anaïs Bardyn study particles from comets to look back into the Solar System's origins. As she delves into the past with her investigations, Bardyn tells us about her most recent results on the chemical composition of comet 67P/Churyumov-Gerasimenko (67P). Using the European Space Agency's Rosetta mission to explore 67P as part of her doctoral studies, her research presents a first-of-a-kind analysis of the comet's chemistry.

Bardyn in a micrometeorites clean room at Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM) Orsay, France, 2013. Photo courtesy Anaïs Bardyn.

What did you learn from your research on 67P?

We reported the global composition of dust particles ejected from comet 67P, as deduced from the COSIMA instrument measurements during the Rosetta mission. We concluded that 67P particles are made of nearly 50 percent organic matter in mass, mixed mostly with non-hydrated minerals.

In addition to providing insight into the conditions of the formation and evolution of the Solar System, comets present an astrobiological interest since they could have played a role in the appearance of life on our planet by bringing in organic molecules and water on the early Earth.

The amount of organic matter in the comet was a pretty exciting result of the study. In a previous publication, we showed that in the solid organic matter of the dust, the carbon is bound in very large macromolecular compounds. Thus, if comets have delivered carbon-rich material to the early Earth, carbon was probably under this complex macromolecular form.

Left: The surface of Rosetta's comet. As the comet approaches the Sun, frozen gases evaporate from below the surface, dragging tiny particles of dust along with them. Right: These dust grains can be captured and examined using the COSIMA instrument. Targets such as this one measuring only a few centimeters act as dust collectors. They retain dust particles of up to 100 microns in size. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA (left), ESA / Rosetta / MPS for COSIMA Team MPS / CSNSM / UNIBW / TUORLA / IWF / IAS / ESA / BUW / MPE / LPC2E / LCM / IMF / UTU / LISA / UOFC / vH & S.

What is the comet's composition like?

Comets like 67P and 1P/Halley are among the most carbon-rich material of our Solar System! The high carbon to silicon elemental abundance measured by COSIMA is close to the value of this same ratio measured in the Sun's visible surface, known as the photosphere. Furthermore, the minerals in 67P dust do not show signatures of alteration by liquid water. These two observations point to a primitive matter, that likely preserved its initial characteristics since the comet accretion during the early stage of the formation of the Solar System, about 4.5 billion years ago!

How did you use the Rosetta spacecraft?

I worked on the COSIMA instrument, a mass spectrometer on board the Rosetta orbiter. During the 2-year mission, COSIMA collected and imaged the dust particles ejected from comet 67P and also analyzed their composition. The instrument collected over 35000 dust particles (with size ranging from 0.1 to 1 millimeter) and analyzed about 250 of them.

Left: Overview of the chemical elements that make up Rosetta's comet. Right: Average mass distribution of organic and mineral substances in Rosetta's comet. Image credit: ESA / Rosetta / MPS for COSIMA Team MPS / CSNSM / UNIBW / TUORLA / IWF / IAS / ESA

How was this space mission different from other cometary dust composition missions?

There are two main differences between the COSIMA measurements and those of previous missions. First, the Rosetta spacecraft followed comet 67P for a period of two years, allowing COSIMA to collect dust particles before, during and after perihelion (the closest distance between the comet's orbit and the Sun). Previous mission were flybys missions and could not spend more than a few hours near the comet. Second, the dust particles were collected at very low velocity (few m/s) on the COSIMA targets and allowed to preserve the dust chemical properties. On the contrary, previous missions collected cometary particles at high velocity impact (6 km/s for Stardust and between 68 and 79 km/s for Giotto and Vega missions).

The Cosmic Dust Sucker at Amundsen-Scott South Pole Station collects cosmic dust, which could include particles remaining from the formation of the Solar System. As a DTM postdoc, Bardyn now analyzes these particles. Photo courtesy Susan Taylor, research scientist at the U.S. Army Cold Regions Research and Engineering Laboratory.

What have you been up to at DTM since you got here?

At DTM, I look for cometary dust in a very cold and isolated place: the South Pole station in Antarctica. Extraterrestrial particles are collected on filters from the clean Antarctic air by the Cosmic Dust Sucker, as some of these particles could originate from comets. Currently, I am looking at the filters to find the particles. Doing this takes time, since the particles are very tiny (about few micrometers). The next step in my research will be to analyze the composition of these particles and compare them with the cometary dust analyzed by the COSIMA instrument.


—Roberto Molar Candanosa