Why scientists are intrigued by the air in NASA’s sampling tubes on Mars

Atmospheric scientists are a little more excited about each rock core that NASA’s Perseverance Mars rover seals in its titanium sample tubes, which are collected for possible delivery to Earth as part of the Mars Sample Return campaign. So far, twenty-four people have been caught.

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

They want to know more about the Martian atmosphere, which is composed mainly of carbon dioxide but could also contain traces of other gases that could have existed since the planet’s formation.

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

The value of headspace

Among the samples that could be brought to Earth is a tube filled only with gas deposited on the surface of Mars as part of a sample repository. But much more of the gas collected by the rover is in the headspace of the rock samples. These are unique because the gas will interact with rock materials inside the tubes for years before the samples can be opened and analyzed in laboratories on Earth.

What scientists learn will provide insight into how much water vapor floats near the Martian surface, a factor that determines why ice forms where it does on the planet and how the water cycle of Mars has evolved over time.

Scientists also want to better understand trace gases present in Mars’ air. Most scientifically interesting would be the detection of rare gases (such as neon, argon and xenon), which are so unreactive that they could have been present, unchanged in the atmosphere, since their formation there. billions of years ago.

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

Free space would further provide the 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 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 to decide which samples the rover should collect. “Even scientists who don’t study Mars would be interested because it will provide a better understanding of how planets form and evolve.”

Apollo air samples

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

“People think of the Moon as airless, but it has a very tenuous atmosphere that interacts with rocks on the lunar surface over time,” said Simon, who studies various planetary samples at Johnson. “This includes noble gases escaping from the Moon’s interior and accumulating on the lunar surface.”

The way Simon’s team extracted the gas for study is similar to what could be done with Perseverance’s air samples. First, they place the unopened container in an airtight enclosure. Then they pierced the steel with a needle to extract the gas into a cold trap — essentially a U-shaped pipe that extends into a liquid, like nitrogen, with a low freezing point. By changing the temperature of the liquid, the scientists captured some of the gases with lower freezing points at the bottom of the cold trap.

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

Of course, these sources provide a lot more gas than Perseverance has in its sampling tubes. But if a single tube doesn’t carry enough gas for a particular experiment, Mars scientists could combine gases from multiple tubes to get a larger overall sample — another way headspace can provide additional opportunity to science.