Could MMX collect organic material from Phobos?

Organics have been found in a 4-billion-year-old Martian meteorite, supporting the idea that water once flowed over Mars’s surface. Further hints to the red planet’s habitable past may be collected by the MMX spacecraft, having been deposited on the surface of Phobos during Mars’s history.

Summary

Research led by Dr. Mizuho Koike (now Assistant Professor at Hiroshima University) with Professor Tomohiro Usui’s group here at ISAS, JAXA has revealed organics in the carbonate minerals of a Martian meteorite. The nitrogen-bearing molecules are inherent to Mars and have been preserved for over 4 billion years.

The preservation of these organics requires the molecules to become trapped in near-surface minerals due to a reaction with water in Mars’s Noachian age (4.1 – 3.7 billion years ago) and then left undisturbed until today. This supports a more ‘Earth-like’ environment for early Mars, with a wet, organic-rich environment.

Data on this tantalising past is currently quite limited, due to the sparse sampling of Martian meteorites that arrived on Earth from this early epoch. But surface material from Mars over its evolution is expected to have been deposited on its much closer moons. This will be collected by the Martian Moon eXploration (MMX) mission, when the spacecraft gathers a sample from Phobos. The next decade will therefore reveal much about Martian organics and the possible habitability of our neighbouring planet.

This study is published online in Nature Communications on April 24th, 2020.

More about this discovery

Organics are carbon-containing molecules, many of which are used by life on Earth. This makes Martian organics a hot topic for understanding how life on a planet could begin. Although recent Martian exploration has found evidence for the presence of organic material on Mars, little remains known about its origin, distribution, preservation or the possible relationship with any biological activity. New discoveries of organic formation are therefore key pieces in the jigsaw puzzle of Mars’s past.

This discovery of preserved organic material was found in Martian meteorite Allan Hills (ALH) 84001 that was discovered in Antarctica in 1984. The meteorite was previously known to contain inorganic carbonate minerals that must have solidified from water near the surface of Mars around 4 billion years ago (Figure 1). The carbonates host trace impurities that provide direct clues to the conditions that existed on Noachian Mars, with the type of molecule determined by past chemistry caused by either geology or biology activity in that era.

However, previous studies that examined these carbonates used a ‘destructive’ analysis, meaning that a small sample of the meteorite was destroyed in order to examine its composition. The problem with this technique is that contamination from Antarctica can become mixed with the Martian sample, making it difficult to trace only Martian history.

In this study, the authors performed the first successful in-situ study of nitrogen in the Martian carbonate sample, which kept the sample whole (and therefore contaminants separate) during the analysis. Nitrogen is an essential element for life on Earth, and types of molecules formed with Nitrogen help trace the conditions and potential habitability of the planet. This technique identified molecules containing nitrogen by looking at the absorption of X-rays by nitrogen atoms, which absorb at slightly different energies depending on the type of molecule (Figure 2).

The team found the nitrogen in the sample was in organic molecules and distinct from contaminants from Earth, confirming that these organics were most likely to be from Noachian Mars. There was also no inorganic nitrate; molecules formed from nitrogen and oxygen that oxidize (or ‘rust’) the surface rocks on Mars to create the characteristic red. This suggests Noachian Mars was not a red planet at all, but a wet, organic-rich world.

The present-day Martian surface is too harsh an environment for most organics to survive. However, past organic molecules can potentially be preserved in near-surface minerals as they react with water. The nitrogen-baring organics discovered in the Allan Hills meteorite were probably incorporated into the carbonates as they solidified out from water in the Noachian age and were then preserved just below the surface of Mars before being ejected into space during an impact to journey to Earth (Figure 3).

The original source for these organics is still unknown. There are two possibilities: delivery from outside of Mars or in-situ synthesis on Mars itself. Shortly after formation, Mars would have been showered in carbonaceous meteorites (rock fragments from asteroids such as Ryugu), comets, and/or dust particles. Organics material was likely trapped in this material, having formed in water on larger asteroids or comets and provided Mars’s early organic content. On the other hand, volcanic activity on early Mars may have produced ammonia (NH4) which could have led to the production of nitrogen-baring organics on Mars (Figure 3).

In either scenario, these findings support the idea that Mars was once not the ‘red planet’ but had a more ‘Earth-like’ environment.

A journey to the Martian moons

The discovery of Noachian materials in a Martian meteorite is a rare find. Most Martian meteorites are relatively young (500 – 170 million years old) and do not come from the Noachian age where water may have run on Mars. Only two meteorites (this example, ALH 84001, and NWA 7034) are known to contain Noachian materials. Moreover, even these valuable rocks suffered from severe contamination from terrestrial water and organics during their long residences on Antarctic ice or the Sahara Desert. This makes it quite difficult to retrieve Martian history from such limited samples.

While our research team succeeded to reduce the contamination on the meteorite by analytical techniques, we ultimately need to reach truly contamination-free, fresh Martian materials.

One of the problems with examining Martian meteorites on Earth is that the interplanetary journey and entry through our atmosphere is extremely tough. Most material will not survive the journey, especially softer rocks that formed in water and are most likely to contain organic material. However, the two Martian moons are much closer to Mars and expected to be coated with Martian material, including the matter too fragile to be delivered to Earth as meteorites.

This material will be collected by the MMX spacecraft when it gathers a sample from the surface of Phobos. Within that container, we may find the key to Mars’s past.

Further reading:

Journal paper: In-situ preservation of nitrogen-bearing organics in Noachian Martian carbonates.

DOI: 10.1038/s41467-020-15931-4

Authors: Mizuho Koike^1*, Ryoichi Nakada², Iori Kajitani^1,3, Tomohiro Usui^1,4, Yusuke Tamenori⁵, Haruna Sugahara¹, and Atsuko Kobayashi^4,6
(*corresponding)

Affiliations:

1. Department of Solar System Sciences, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan.
2. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). 200 Monobe, Nankoku, Kochi 783-8502, Japan.
3. Department of Earth and Planetary Science, The University of Tokyo. 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
4. Earth-Life Science Institute, Tokyo Institute of Technology. 2-12-1 Ookayama, Meguro, Tokyo 152-8550, Japan.
5. Spectroscopy and Imaging Division, Japan Synchrotron Radiation Research Institute. 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
6. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.