With each rock core sealed in its titanium sample tubes by NASA's Perseverance Mars rover, atmospheric scientists find themselves increasingly excited. These samples, which will be delivered to Earth as part of the Mars Sample Return campaign, now total twenty-four.

Most of these samples include rock cores or regolith (broken rock and dust) that may provide significant insights into Mars' history and the potential for ancient microbial life. However, some scientists are equally enthusiastic about the "headspace," or the air in the extra room around the rocky material within the tubes.

Researchers aim to understand more about the Martian atmosphere, primarily composed of carbon dioxide, but possibly containing trace gases that have existed since the planet's formation.

"The air samples from Mars would tell us not just about the current climate and atmosphere, but how it's 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."

The Importance of Headspace
Among the samples potentially returning to Earth is a tube filled solely with gas deposited on the Martian surface. However, most gas within the rover's collection resides in the headspace of rock samples. This gas is unique because it will interact with the rocky material for years before the samples are analyzed on Earth. Scientists anticipate these interactions will reveal how much water vapor exists near the Martian surface, a crucial factor in understanding ice formation and the evolution of Mars' water cycle.

Researchers also seek a deeper understanding of trace gases in Mars' atmosphere. Particularly fascinating would be the detection of noble gases (like neon, argon, and xenon), which are highly nonreactive and may have remained unchanged in the atmosphere for billions of years. These gases could reveal whether Mars originally had an atmosphere. Ancient Mars had a much thicker atmosphere than today, but it is unclear whether this was always the case or developed later. Scientists also have significant questions regarding how the ancient Martian atmosphere compared to early Earth's.

The headspace samples will also help assess the size and toxicity of dust particles, providing vital information for future Mars astronauts.

"The 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 over a dozen international experts that helps decide which samples the rover should collect. "Even scientists who don't study Mars would be interested because it will shed light on how planets form and evolve."

Apollo's Air Samples
In 2021, planetary researchers, including NASA scientists, studied air brought back from the Moon in a steel container by Apollo 17 astronauts fifty years earlier.

"People think of the Moon as airless, but it has a very tenuous atmosphere that interacts with the lunar surface rocks over time," said Simon, who studies a variety of planetary samples at Johnson. "That includes noble gases leaking out of the Moon's interior and collecting at the lunar surface."

The method Simon's team used to extract the gas from the Moon is similar to what could be done with Perseverance's air samples. The unopened container was placed into an airtight enclosure, then pierced with a needle to extract the gas into a cold trap - a U-shaped pipe extending into a low-freezing-point liquid like nitrogen. By altering the liquid's temperature, scientists captured gases with lower freezing points at the bottom of the cold trap.

"There's maybe 25 labs in the world that manipulate gas in this way," Simon said. Besides 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.

Although these sources provide more gas than Perseverance's sample tubes, Mars scientists could combine gases from multiple tubes if a single tube lacks sufficient gas for a particular experiment. This is yet another way the headspace offers a bonus opportunity for scientific study.

Related Links
Mars Sample Return
Mars News and Information at MarsDaily.com
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