Why scientists are interested in the air in NASA’s Mars test tubes

Atmospheric scientists get a little more excited with each rock core NASA’s Perseverance Mars rover seals its titanium tubes with samples being collected for eventual delivery to Earth as part of the Mars Sample Return campaign. Twenty-four have been taken so far.

Most of these samples consist of rock cores or regolith (broken rock and dust), which could reveal important information about the planet’s history and whether microbial life was present billions of years ago. But some scientists are equally excited by the prospect of studying the “head space,” or air in the extra room around the rocky material in the tubes.

They want to learn more about the Martian atmosphere, which is mostly carbon dioxide but could also contain trace amounts of other gases that may have been around since the planet’s formation.

“Air samples from Mars will tell us not only about the current climate and atmosphere, but also how it has changed over time,” said Brandi Carrier, a planetary scientist at NASA’s Jet Propulsion Laboratory in Southern California. “It will help us understand how climates different from our own evolve.”

Headspace value

Among the samples that could be brought to Earth is one tube filled entirely with gas stored on the surface of Mars as part of a sample repository. But much more of the gas in the rover’s collection is in the upper space of the rock samples. These are unique because the gas will interact with the rock material inside the tubes for years before the samples can be opened and analyzed in laboratories on Earth.

What scientists get from them will provide insight into how much water vapor floats near the surface of Mars, one of the factors that determines why ice forms on the planet and how the Martian water cycle has evolved over time.

Scientists also want to better understand trace gases in the air on Mars. Most scientifically impressive would be the detection of noble gases (such as neon, argon, and xenon) that are so unreactive that they may have been in the atmosphere unchanged since their formation billions of years ago.

If these gases were captured, they could reveal whether Mars began with an atmosphere. (Ancient Mars had a much denser atmosphere than today, but scientists aren’t sure if it was always there or if it developed later). There are also big questions about how ancient the planet’s atmosphere is compared to early Earth.

In addition, Headspace would provide the ability to assess the size and toxicity of dust particles—information that will help future astronauts on Mars.

“Gas samples have a lot to offer Mars scientists,” said Justin Simon, a geochemist at NASA’s Johnson Space Center in Houston who is part of a group of more than a dozen international experts helping decide which samples the rover should collect. “Even scientists who don’t study Mars will be interested because it will shed light on how planets form and evolve.”

Apollo air samples

In 2021, a group of planetary researchers, including NASA scientists, studied air brought back from the Moon in a steel container by Apollo 17 astronauts some 50 years earlier.

“People think the moon is airless, but it has a very thin atmosphere that interacts with rocks on the lunar surface over time,” said Simon, who studies various planetary samples at Johnson. “This includes rare gases that escape from the interior of the moon and collect on the lunar surface.”

The way Simon’s team extracted the gas for study is similar to what can be done with Perseverance’s air samples. First, they put the previously unopened container into an airtight seal. They then pierced the steel with a needle to draw the gas into the cryogenic paste—essentially a U-shaped tube that extends into a low-freezing liquid like nitrogen. By changing the temperature of the liquid, the researchers trapped some gases with lower freezing points at the bottom of the cold trap.

“There are maybe 25 labs in the world that manipulate the gas in this way,” Simon said. In addition to being used to study the origin of planetary materials, the approach can be applied to gases from hot springs and gases emitted from the walls of active volcanoes, he added.

Of course, these sources provide much more gas than Perseverance has in its tubes. But if one tube doesn’t carry enough gas for a particular experiment, Mars scientists could combine gases from multiple tubes to get a larger aggregate sample—another way overhead space offers a bonus opportunity for science.