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

NASA’s Perseverance Mars rover stores rock and soil samples in sealed tubes on the planet’s surface for retrieval on future missions, as shown in this illustration. Image source: NASA/JPL-Caltech

Hidden with every rock and soil sample collected by NASAThe Perseverance rover is a potential boon for atmospheric scientists.

NASA’s perseverance Mars The rover collects samples from Mars, including rock cores and atmospheric gases, to eventually return to Earth. These samples may provide important insights into the Martian atmosphere and its evolution, perhaps revealing the presence of microbial life billions of years ago. Gas samples, in particular, could provide valuable data on trace gases and the planet’s ancient climate, which compares with the history of Earth’s atmosphere and helps inform future manned missions to Mars.

Mars sample collection

With each rocky core that NASA’s Perseverance Mars rover seals into its titanium sampling tubes, atmospheric scientists become more excited. These samples are collected for eventual delivery to Earth as part of the Mars Sample Return Campaign twenty four taken so far.

Most of these samples consist of rock cores or rock debris (broken rocks 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 thrilled by the prospect of studying the “headspace,” or the air in the extra chamber around the rocky material, in the tubes.

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

Perseverance Mars Rover Sample Headspace

This image shows a rock core the size of a piece of chalk in a sample tube located inside the drilling instrument of NASA’s Perseverance Mars rover. Once the rover closes the tube, air will be trapped in the extra space in the tube, seen here in the small gap (called the “headspace”) above the rock. Image source: NASA/JPL-Caltech/Arizona State University/MSSS

Insights from Mars Headspace

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

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Among the samples that could be brought to Earth is only one tube filled with gas deposited on the surface of Mars as part of a sample repository. But a much larger amount of the gas in the rover’s array lies within the core space of the rock samples. It is unique because the gas will interact with rocky material inside the tubes for years before samples are opened and analyzed in laboratories on Earth. What scientists extract from them will give an idea about the amount of water vapor swirling near the surface of Mars, which is one of the factors that determine why ice forms where it does on the planet and how the water cycle on Mars evolved over time.

Sealed sample tube from the Perseverance Mars rover

Seen here is a sealed tube containing a sample of the Martian surface collected by NASA’s Perseverance Mars rover, after depositing it with other tubes in a “sample repository.” Other filled sample tubes are stored inside the rover. Image source: NASA/JPL-Caltech

Comparison of trace gases and ancient atmospheres

Scientists also want to better understand trace gases in the Martian air. Even more scientifically exciting would be the discovery of noble gases (such as neon, argon, and xenon), which are so unreactive that they may have been present in the atmosphere, unchanged, since their formation billions of years ago. If these gases are captured, they could reveal whether Mars started out with an atmosphere. (Ancient Mars had a thicker atmosphere than it does 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.

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In addition, the headspace will provide an opportunity to evaluate 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 scientists from NASA, studied air brought from the Moon in a steel container by Apollo 17 Astronauts about 50 years ago.

“People think the Moon is airless, but its atmosphere is very fragile and interacts with lunar surface rocks over time,” said Simon, who studies a variety of planetary samples at Johnson. “This includes noble gases escaping from the Moon’s interior and collecting on the Moon’s surface.”

Laboratory techniques for gas analysis

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 previously unopened container into an airtight container. They then punctured the steel with a needle to extract the gas and placed it in a cold trap, a U-shaped tube extending into a liquid, such as nitrogen, with a low freezing point. By changing the temperature of the liquid, scientists were able to capture some gases with lower freezing points at the bottom of the cold trap.

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

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Naturally, these sources provide much more gas than Perseverance provides in its sample tubes. But if a single tube doesn’t hold enough gas for a given experiment, Mars scientists can combine gases from multiple tubes to get a larger combined sample — another method that provides an additional opportunity for science.

NASA’s Perseverance Mars Rover

NASA’s Perseverance rover, part of the Mars 2020 mission, is an advanced mobile laboratory designed to explore the surface of Mars. The rover was launched on July 30, 2020, and landed on Mars on February 18, 2021, in Jezero Crater. Perseverance’s primary mission is to search for signs of ancient life and collect samples of rocks and regolith (broken rocks and soil) for possible return. to ground.

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