May atmospheric samples from Mars inform us extra in regards to the Purple Planet than floor samples?

NASA is actively working over the next few years to bring back surface samples from Mars that it hopes will help us better understand whether life once existed on the Red Planet's surface billions of years ago. But what about atmospheric samples? Could these give scientists better information about Mars' history? That's the goal of a recent study presented at the 55th Lunar and Planetary Science Conference, where a team of international researchers examined the significance of the returned atmospheric samples from Mars and how they could tell us about the Red Planet's formation and evolution.

Here, Universe Today discusses this research with the study's lead author, Dr. Edward Young, professor in the Department of Earth, Planetary and Space Sciences at UCLA, and study co-author Dr. Timothy Swindle, professor emeritus at the University of Arizona's Lunar & Planetary Laboratory. They cover the motivation behind the study, how to obtain atmospheric samples, current or planned missions, follow-up studies, and whether they believe there was ever life on the Red Planet. So what was the motivation for the study?

Dr Young tells Universe Today: “We learn a lot about the formation of a planet from its atmosphere and rocks. In particular, isotope ratios of certain elements can determine the processes that led to the planet's formation.”

Photo credit: European Space Agency

Dr Swindle adds: “There are two basic motivations. First, we plan to bring back all these rock samples and we want to know how they interacted with the atmosphere, but we can't find that out without knowing the composition of the atmosphere in detail. So we need an atmospheric sample to know what the rocks might have exchanged elements and isotopes with. But we would also like a sample of the Martian atmosphere to answer some fundamental questions about processes that have taken place or are taking place on Mars. For example, Martian meteorites contain trapped atmospheric noble gases such as krypton and xenon. But it appears that these meteorites contain at least two different 'atmospheric' components.”

For the study, researchers suggested several benefits of returning a Martian atmosphere sample to Earth. These include atmospheric samples contained in the sample tubes of NASA's Perseverance (Percy) rover and insights into possible solar damage inside Mars, evolutionary trends in atmospheric composition, the nitrogen cycle, and methane sources on Mars. For Percy's atmospheric sample, also known as Sample #1 “Roubion,” the study notes that this sample was obtained after Percy attempted to collect a rock core sample but collected atmospheric gases instead. In addition, the study suggests that the sample tube will not leak while waiting for its return to Earth, and that the gases present in the sample will be ideal for analysis even after it returns to Earth. But aside from the sample from the Percy rover, how else could a Martian atmosphere sample be obtained?

“At least two other ideas have been proposed for taking a sample of the Martian atmosphere,” Dr. Swindle tells Universe Today. “One is to fly a spacecraft through the Martian atmosphere, take a sample, and then bring it back to Earth. The other is to have a sample return 'canister' (it doesn't have to be any bigger than a Perseverance tube) that has valves and a (Mars) air compressor. You could land it on the Martian surface, open the valve to the atmosphere, turn on the compressor, and take a sample containing hundreds or thousands of times as much Martian atmosphere as a simply sealed volume with no compression, as Perseverance has done and hopefully will do again.”

Dr. Swindle and Dr. Young both mention the Sample Collection for Investigation of Mars (SCIM) mission, proposed in 2002 by a team of NASA and academic researchers with the goal of collecting atmospheric samples at an altitude of 40 kilometers (25 miles) above the Martian surface and returning them to Earth for further analysis. Unfortunately, although SCIM was selected as a semi-finalist for the 2007 Mars Scout Program, it was not selected for further development, and both Dr. Young and Dr. Swindle tell Universe Today that there are currently no atmospheric sampling missions planned other than sampling for the Percy rover. What follow-up studies to this research are currently underway or planned?

Dr. Swindle and Dr. Young both mention that due to the small size of the sample tubes, they are trying to collect small amounts of atmospheric gas. Dr. Swindle told Universe Today, “A big question right now is how well a sealed Perseverance tube can contain an atmospheric sample. How good is the seal? Could the tube leak in a hard landing? Would some molecules of the Martian atmosphere stick to the coating of the tubes? There has been some activity on all of these questions, and so far the answers have all been good – it looks like these Perseverance tubes could work well, even though they weren't really designed to collect atmospheric samples.”

As mentioned, collecting and returning an atmospheric sample from Mars could help scientists better understand the formation and evolution of the Red Planet. Today's Mars is a very cold and dry world with an atmosphere that is only a fraction of Earth's. Liquid water cannot exist on its surface, nor does it experience active volcanism. However, in recent decades, significant evidence from landers, rovers, and orbiters suggests that billions of years ago, after Mars formed, it looked very different. This included an active interior that generated a magnetic field that protected the surface from harmful solar and cosmic radiation, a much denser atmosphere replenished by active volcanism, and flowing liquid water, all of which may have led to the existence of some life forms on the surface.

However, given Mars' small size (half the size of Earth), this means that its internal heat cooled much more quickly (possibly over millions of years), causing volcanism to become dormant and the magnetic field generated by the activity inside to weaken. The latter led to damaging solar and cosmic radiation leaching the atmosphere and causing the liquid water on the surface to evaporate into space. So do Dr Young and Dr Swindle believe there was ever life on Mars, and will we ever find it?

Dr. Young tells Universe Today: “I really don't know. I think microbial life at some point in the past or even now is a reasonable hypothesis, but we don't have enough information.”

Dr Swindle also expressed uncertainty as to whether life ever existed on Mars, but explained to Universe Today: “If not, why did life begin so early on Earth but not on Mars, which had a similar climate at the time? If so, how similar is it to life on Earth? Since Earth and Mars are constantly exchanging rocks due to impacts, the question is whether life on Earth is related to life on Mars. If it did exist, it will be difficult to find. But an atmospheric sample could help. For example, there appears to be methane in the Martian atmosphere. Most, but not all, of the methane in Earth's atmosphere is biological in origin, and analyzing the relative ratios of carbon or hydrogen isotopes is one of the best ways to find out.”

When will we get an atmospheric sample from Mars and what will we learn from it about the formation and evolution of the Red Planet in the coming years and decades? Only time will tell, and that's why we do science!

As always, keep doing science and keep looking up!

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