NASA’s Perseverance Mars rover stores rock and soil samples in sealed tubes on Earth’s surface for retrieval on future missions, as shown in this illustration. Credit: NASA/JPL-Caltech
Tucked away at every rock and soil sample collected by NASA‘s Perseverance rover is a potential boon for atmospheric scientists.
NASA’s perseverance Mars Rover is collecting samples on Mars, including rock cores and atmospheric gases, that will eventually be returned to Earth. These samples could provide critical insights into Mars’ atmosphere and its evolution, potentially revealing the presence of microbial life billions of years ago. The gas samples in particular could provide valuable data on trace gases and the planet’s ancient climate, drawing parallels with the atmospheric history of Earth itself and supporting future human missions to Mars.
Mars sample collection
With every rock core that NASA’s Perseverance Mars rover seals into its titanium sample tubes, atmospheric scientists get a little more excited. These samples are being collected for eventual delivery to Earth as part of the Mars Sample Return campaign, twenty-four of which have been taken to date.
Most of these samples consist of rock cores or regolith (broken rock and dust) that can reveal important information about the planet’s history and whether microbial life was present billions of years ago. But some scientists are just as excited about the prospect of studying the “headspace,” or the air in the extra space around the rocky material, inside the tubes.
They want to learn more about Mars’ atmosphere, which is mainly carbon dioxide but may also contain traces of other gases that may have existed since the planet’s formation.
This image shows a crayon-sized rock core inside a sample tube mounted in the drill of NASA’s Perseverance Mars rover. Once the rover seals the tube, air is trapped in the extra space inside the tube — seen here in the small opening (called the headspace) above the rock. Credit: NASA/JPL-Caltech/ASU/MSSS
Insights from Mars’ main space
“The Martian air samples 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 South America. California. “It will help us understand how climates other than ours evolve.”
Among the samples that can be brought to Earth is one tube filled exclusively with gas deposited on the surface of Mars as part of a sample deposit. But much more of the gas in the rover’s collection is in the headspace of rock samples. These are unique because the gas will interact with rocky material in the tubes for years before the samples can be opened and analyzed in laboratories on Earth. What scientists glean from that will provide insight into how much water vapor is floating near Mars’ surface, a factor that determines why ice forms there on the planet and how Mars’ water cycle has evolved over time.
Shown here is a sealed tube containing a sample of the Martian surface collected by NASA’s Perseverance Mars rover after being deposited with other tubes in a ‘sample depot’. Other filled sample tubes are stored in the rover. Credit: NASA/JPL-Caltech
Comparison of trace gases and ancient atmospheres
Scientists also want to better understand trace gases in the Martian air. Most scientifically tempting would be the detection of noble gases (such as neon, argon and xenon), which are so non-reactive that they may have existed unchanged in the atmosphere since they emerged billions of years ago. If collected, 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.
The headspace would also provide a chance to assess the size and toxicity of dust particles – information that will help future astronauts on Mars.
“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 more than a dozen international experts helping 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, a group of planetary researchers, including scientists from NASA, studied the air brought back from the moon by Apollo 17 astronauts some 50 years earlier in a steel container.
“People think the moon has no air, but the atmosphere is very thin and interacts with the rocks on the moon’s surface over time,” says Simon, who studies a variety of planetary samples at Johnson. “This also applies to noble gases that leak from the moon’s interior and collect on the moon’s surface.”
Laboratory techniques for gas analysis
The way Simon’s team extracted the gas for research is similar to what could be done with Perseverance’s air samples. First, they placed the previously unopened container into an airtight enclosure. They then pierced the steel with a needle to draw the gas into a cold trap – essentially a U-shaped pipe extending into a liquid, such as nitrogen, with a low freezing point. By changing the temperature of the liquid, scientists captured some of the gases with lower freezing points at the bottom of the cold trap.
“There are perhaps 25 laboratories in the world that manipulate gas in this way,” Simon said. This approach is not only used to study the origins of planetary materials, but can also be applied to gases from hot springs and gases emitted from the walls of active volcanoes, he added.
Naturally, these sources provide much more gas than Perseverance has in its sample tubes. But if a single tube doesn’t carry enough gas for a given experiment, Mars scientists can combine gases from multiple tubes to get a larger collective sample — another way that free space provides a bonus 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 Martian surface. 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 rock and regolith (broken rock and soil) for possible return to Earth.