Why are scientists fascinated by the air in NASA’s Mars sample tubes?

Atmospheric scientists get a little more excited with each rock core NASA’s Mars rover seals in titanium sample tubes, collected for final delivery to Earth as part of the Mars Sample Return Campaign. Twenty-four cases have been taken so far.

Most of these samples contain rock or rock cores (broken rock and dust) that may reveal important information about the planet’s history and whether microbial life existed billions of years ago. But some scientists are just as excited by the prospect of studying the “headspace,” or extra room air around the rock material, in the tubes.

They want to learn more about Mars’ atmosphere, which is mostly carbon dioxide but can contain small amounts of other gases that may have existed since the planet formed.

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

The value of the original space

Among the samples that could be brought back to Earth is a tube filled only with gas deposited on the Martian surface as part of the sample repository. But far more than the gas in the Mars rover complex is located in the space above the rock samples. These are unique because the gas will interact with the rock material inside the pipes for years before the samples are opened and analyzed in laboratories on Earth.

What scientists get from them provides insight into the amount of water vapor near the surface of Mars, a factor that determines why the ice is where it is 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 tempting are the discoveries of noble gases (such as neon, argon, and xenon), which are so unreactive that they may have existed unchanged in the atmosphere since their formation billions of years ago.

If these gases are captured, they could reveal whether Mars began with an atmosphere. (Ancient Mars had a much thicker 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 the planet’s ancient atmosphere compares to that of early Earth.

The headspace also provides an opportunity to assess the size and toxicity of dust particles — information that will help future astronauts on Mars.

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

Apollo air samples

In 2021, a team of planetary researchers, including NASA scientists, studied air returned from the moon in a steel container by the Apollo 17 astronauts some 50 years earlier.

“People think of the moon as airless, but it has a very weak atmosphere that interacts with lunar surface rocks over time,” says Simon, who studies a variety of planetary samples at Johnson. “It consists of noble gases that leak out from inside the moon and accumulate on the surface of the moon.”

The way Simon’s team extracted the gas for study is similar to what can be done with Perseverance’s air samples. First, the unopened container is placed in a closed container. The steel was then pierced with a needle to extract the gas in a cold trap—essentially a U-shaped tube that extends into a low-freezing liquid like nitrogen. By changing the temperature of the liquid, the scientists obtained 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. He added: In addition to being used to study the origin of planetary materials, this approach can also be applied to gases from hot springs and gases emitted from the walls of active volcanoes.

Of course, these sources offer much more gas than the Perseverance in their sample tubes. But if a single tube doesn’t carry enough gas for a particular experiment, Mars scientists can combine gases from multiple tubes to get a larger overall sample—another way the core space offers a great opportunity for science.