The Mars Sample Return Mission is one of the most ambitious missions ever conceived. Though the samples won’t be returned to Earth until 2033 at the earliest, the Perseverance Rover is busy collecting them right now. Ideally, Perseverance could gather as many samples as we like and ship them all back to Earth. But of course, that’s not possible.
There are limitations, and this means that choosing which samples to return to Earth is an extremely critical task.
Of the thousands of meteorites found on Earth, about 188 have been confirmed to be from Mars. How did they get here? Over the tumultuous history of our Solar System, asteroids have smashed into Mars with such force, the debris was blasted off the planet and then drifted through space, eventually entering Earth’s atmosphere, and surviving the journey to the ground.
Astronomers once thought it was a complex process, with only the most powerful impacts capable of throwing rocks from Mars into space. But new research shows that it takes much less pressure than previously believed, which means there could be more chunks of Mars floating in space and on their way to Earth.
If we think untangling Earth’s complex geological history is difficult, think of the challenge involved in doing the same for Mars. At such a great distance, we rely on a few orbiters, a handful of rovers and landers, and our powerful telescopes to gather evidence. But unlike Earth, Mars is, for the most part, geologically inactive. Much of the evidence for Mars’ long history is still visible on the surface.
That helped scientists identify the source of one of our most well-known meteorites.
Mars is still quite mysterious, despite all we’ve learned about the planet in recent years. We still have a lot to learn about its interior and surface evolution and how changes affected the planet’s history and habitability. Fortunately, an impact on the red planet sent clues to Earth in the form of meteorites.
The geological information contained in these meteorites would be even more valuable if we knew exactly where they came from. A team of researchers say they’ve figured it out.
There are around 61,000 meteorites on Earth, or at least that’s how many have been found. Out of those, about 200 of them are very special: they came from Mars. And those 200 meteorites have been important clues to how Mars formed in the early Solar System.
On Earth, clouds form when enough droplets of water condense out of the air. And those droplets require a tiny speck of dust or sea salt, called a condensation nuclei, to form. In Earth’s atmosphere, those tiny specks of dust are lofted high into the atmosphere where they trigger cloud formation. But on Mars?
For years now, scientists have understood that Mars was once a warmer, wetter place. Between terrain features that indicate the presence of rivers and lakes to mineral deposits that appeared to have dissolved in water, there is no shortage of evidence attesting to this “watery” past. However, just how warm and wet the climate was billions of years ago (and since) has been a subject of much debate.
According to a new study from an international team of scientists from the University of Nevada, Las Vegas (UNLV), it seems that Mars may have been a lot wetter than previous estimates gave it credit for. With the help of Berkeley Laboratory, they conducted simulations on a mineral that has been found in Martian meteorites. From this, they determined that Mars may have had a lot more water on its surface than previously thought.
When it comes to studying the Solar System, meteorites are sometimes the only physical evidence available to researchers. This includes Mars, where meteorites recovered from Earth’s surface have helped to shed light on the planet’s geological past and what kinds of processes have shaped its crust. For geoscientists, they are the best means of determining what Mars looked like eons ago.
Unfortunately for geoscientists, these meteorites have underdone changes as a result of the cataclysmic force that expelled them from Mars. As Dr. Christopher Adcock, an Assistant Research Professor at with the Dept. of Geoscience at UNLV and the lead author of the study, told Universe Today via email:
“Martian meteorites are pieces of Mars, basically they are our only samples of Mars on Earth until there is a sample return mission. Many of the discoveries we have made about Mars came from studying martian meteorites and wouldn’t be possible without them. Unfortunately, these meteorites have all experienced shock from being ejected of the Martian surface during impacts.”
Of the over 100 Martian meteorites that have been retrieved here on Earth, and range in age from between 4 billion years to 165 million years. They are also believed to have come from only a few regions on Mars, and were likely ejecta created from impact events. And in the course of examining them, scientists have noticed the presence of a calcium phosphate mineral known as merrillite.
As a member of the whitlockite group that is commonly found in Lunar and Martian meteorities, this mineral is known for being anhydrous (i.e. containing no water). As such, researchers have drawn the conclusion that the presence of this minerals indicates that Mars had an arid environment when these rocks were ejected. This is certainly consistent with what Mars looks like today – cold, icy and dry as a bone.
This consisted of placing the synthetic whitlockite sample inside a projectile, then using a helium gas gun to accelerate it up to speeds of 700 meters per second (2520 km/h or 1500 mph) into a metal plate – thus subjecting it to intense heat and pressure. The sample was then examined using the Berkeley Lab’s Advanced Light Source (ALS) and the Argonne National Laboratory’s Advanced Photon Source (APS) instruments.
“When we analyzed what came out of the capsule, we found a significant amount of the whitlockite had dehydrated to the mineral merrillite,” said Adcock. “Merrillite is found in many meteorites (including Martian). The means it is possible the rocks meteorites are made from originally started life with whitlockite in them in an environment with more water than previously thought. If true, it would indicate more water in the Martian past and the early Solar System.”
Not only does this find raise the “water budget” for Mars in the past, it also raises new questions about Mars’ habitability. In addition to being soluble in water, whitlockite also contains phosphorous – a crucial element for life here on Earth. Combined with recent evidence that shows that liquid water still exists on Mars’ surface – albeit intermittently – this raises new questions about whether or not Mars had life in the past (or even today).
But as Adcock explained, further experiments and evidence will be needed to determine if these results are indicative of a more watery past:
“As far as life goes, our results are very favorable for the possibility – but we need more data. Really we need a sample return mission or we need to go there in person – a human mission. Science is closing in on the answers to a number of big questions about our solar system, life elsewhere, and Mars. But it is difficult work when it all has to be done from far away.”
And sample returns are certainly on the horizon. NASA hopes to conduct the first step in this process with their Mars 2020 Rover, which will collect samples and leave them in a cache for future retrieval. The ESA’s ExoMars rover is expected to make the journey to Mars in the same year, and will also obtain samples as part of a sample-return mission to Earth.
These missions are scheduled to launch the summer of 2020, when the planets will be at their closest again. And with crewed missions to the surface planned for the following decade, we might see the first non-meteorite samples of Mars brought back to Earth for analysis.
Could this meteorite show evidence of ancient water and life on Mars? That’s one possibility raised in a new paper led by NASA and including members of a team who made a contentious claim about Martian microfossils in another meteorite 18 years ago.
“This is no smoking gun,” stated lead author Lauren White, who is based at NASA’s Jet Propulsion Laboratory, of the findings released this week. “We can never eliminate the possibility of contamination in any meteorite. But these features are nonetheless interesting and show that further studies of these meteorites should continue.”
The new, peer-reviewed work focuses on tunnels and microtunnels the scientists said they found in a meteorite called Yamato 00593. The meteorite is about 30 pounds (13.7 kilograms) and was discovered in Antarctica in 2000. The structures were found deep within the rock, NASA stated, and “suggest biological processes might have been at work on Mars hundreds of millions of years ago.”
Scientists believe the 1.3-billion-year-old rock left Mars about 12 million years ago after an impact threw it off the surface. It reached Antarctica 50,000 years ago and after it was found in 2000, was analyzed and believed to be a “nakhlite”, or a kind of Martian meteorite. “Martian meteoritic material is distinguished from other meteorites and materials from Earth and the moon by the composition of the oxygen atoms within the silicate minerals and trapped Martian atmospheric gases,” NASA stated.
There are two things in the meteorite that caught the attention of scientists. One is the aforementioned tunnels and microtunnels, which they say are similar to those altered by bacteria in basalt on Earth. The second is tiny, carbon-enriched spherules (in the nanometer to micrometer range) between layers in the rock — structures similar to another Martian meteorite (Nakhla) that struck Egypt in 1911. In that case, the rock was recovered quickly after landing and still had the same spherules, the researchers noted.
The authors said it’s possible that these structures could be explained by other mechanisms besides life, but said the similarities to what they have found on Earth “imply the intriguing possibility that the Martian features were formed by biotic activity.”
The research team includes NASA’s David McKay (who died a year ago), Everett Gibson and Kathie Thomas-Keptra. In 1996, these same scientists (then led by McKay) found “biogenic evidence” in a meteorite called Allen Hills 84001, but other science teams have disagreed with the findings. There have been a lot of papers about this particular meteorite, and you can read more about the controversy in this 2011 Universe Today article.