NASA’s Mars rover Perseverance stores rock and soil samples in sealed tubes on the planet’s surface for collection on future missions, as seen in this image. Image credit: NASA/JPL-Caltech
Hidden with every rock and soil sample taken by NASAThe Perseverance rover is a potential blessing for atmospheric researchers.
NASA’s Endurance Mars Rover collects samples on Mars, including rock cores and atmospheric gases, to eventually be returned to Earth. These samples could provide important insights into the Martian atmosphere and its evolution, and potentially prove the existence of microbial life billions of years ago. The gas samples in particular could provide valuable data on trace gases and the planet’s climate in ancient times, draw parallels with Earth’s atmospheric history, and aid future manned missions to Mars.
Mars sample collection
Atmospheric scientists get a little more excited with each rock core that NASA’s Perseverance Mars rover seals into its titanium sample tubes. These samples are being collected for eventual return to Earth as part of the Mars Sample Return campaign. So far, 24 samples have been collected.
Most of these samples consist of rock cores or regolith (broken rock and dust), which provide important information about the planet’s history and whether microbial life was present billions of years ago. But some scientists are equally excited about the prospect of studying the “headspace,” or air in the extra space around the rock material in the tubes.
They want to learn more about Mars’ atmosphere, which consists mainly of carbon dioxide but may also contain traces of other gases that may have been present since the planet’s formation.
This image shows a rock core the size of a piece of chalk in a sample tube in the drill on NASA’s Perseverance Mars rover. Once the rover seals the tube, air becomes trapped in the extra space in the tube – seen here in the small gap (called “headspace”) above the rock. Image credit: NASA/JPL-Caltech/ASU/MSSS
Insights from the Martian Headspace
“The 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 (JPL) in Southern California. “They will help us understand how climates different from our own evolve.”
Among the samples that could be brought to Earth is a tube filled solely with gas deposited on the Martian surface as part of a sample dump. But a far greater portion of the gas in the rover’s collection is in the open space of rock samples. These are unique because the gas will interact with the rock material in the tubes for years before the samples can be opened and analyzed in labs on Earth. What scientists learn from them will shed light on how much water vapor is floating near the Martian surface, a factor that determines why ice forms where it does on the planet, and how Mars’ water cycle has evolved over time.
A sealed tube containing a sample of the Martian surface collected by NASA’s Perseverance Mars rover is shown here after it was placed in a “sample repository” with other tubes. Other filled sample tubes are stored in the rover. Image credit: NASA/JPL-Caltech
Comparison of trace gases and atmospheres of earlier times
Scientists also want to better understand the trace gases in Mars’ air. The most scientifically exciting would be the discovery of noble gases (such as neon, argon and xenon) that are so unreactive that they could have been present in the atmosphere unchanged since it formed billions of years ago. If discovered, these gases could shed light on whether Mars originally had an atmosphere. (Ancient Mars had a much denser atmosphere than today, but scientists aren’t sure if it was always there or evolved later.) There are also big questions about how the planet’s atmosphere was in ancient times compared to that of early Earth.
The headspace would also provide the ability to assess the size and toxicity of dust particles – information that would help future astronauts on Mars.
“The gas samples have a lot to offer Mars researchers,” said Justin Simon, a geochemist at NASA’s Johnson Space Center in Houston. He is part of a group of more than a dozen international experts who will help decide which samples the rover should collect. “Even scientists who don’t study Mars would be interested because it will provide insight into how planets form and evolve.”
Apollo’s air samples
In 2021, a group of planetary scientists, including NASA scientists, studied the air that the Apollo 17 astronauts brought back from the moon in a steel container about 50 years earlier.
“People think the moon is airless, but it has a very thin atmosphere that interacts with the rocks on the lunar surface over time,” said Simon, who studies various planetary samples at Johnson. “These include noble gases that escape from the interior of the moon and collect on the lunar surface.”
Laboratory techniques for gas analysis
The way Simon’s team extracted the gas for study was similar to what might be done with Perseverance’s air samples. First, they placed the previously unopened container in an airtight container. Then they pierced the steel with a needle to extract the gas into a cold trap – essentially a U-shaped tube extending into a liquid, such as nitrogen, with a low freezing point. By changing the temperature of the liquid, the scientists trapped some of the lower freezing point gases at the bottom of the cold trap.
“There are maybe 25 labs 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 could also be applied to gases from hot springs and those emitted from the walls of active volcanoes, he added.
Of course, these sources provide much more gas than Perseverance has in its sample tubes. But if a single tube doesn’t contain enough gas for a particular experiment, Mars researchers could combine gases from multiple tubes to get a larger total sample—another way in which open space offers additional opportunities for science.
NASA’s Mars rover Perseverance
NASA’s Perseverance rover, part of the Mars 2020 mission, is an advanced mobile laboratory for exploring the Martian surface. Perseverance launched on July 30, 2020, and landed in the Jezero Crater on Mars on February 18, 2021. Its primary mission is to search for signs of ancient life and collect rock and regolith (broken rock and soil) samples for possible return to Earth.