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August 2, 2024
This article is longer than typical articles featured in the Journal. Consequently, the text sizing and line spacing have been adjusted.
Last week, the Perseverance rover stumbled upon a rock that now serves as exciting evidence to support the idea that ancient life once existed on Mars. Following an abundance of findings on Mars over the past two decades, this rock showcased 3 different characteristics that have never been spotted together before. While the rock’s “veins” and the calcium sulfate minerals (formed as a precipitate when reacting with H2O) found in them indicated that the rock had once interacted with liquid water, Perseverance also detected organic molecules (more on “veins” and organic molecules later). Additionally, the rover’s Planetary Instrument for X-Ray Lithochemistry (PIXL) discovered something unique: white spots on the rock surrounded by a black outline that had iron and phosphate traces. While they could’ve been created through natural geological processes, such as magma or volcanic activity that formed the olivine they found in the rock’s veins in addition to CaSO4, NASA hopes that the spots were caused by the same chemical reaction which is associated with microbial life on Earth.
Image Courtesy of NASA JPL
"Leopard Spots" = white spots with black outlines
Image Courtesy of NASA JPL
However, this hasn’t been the only interesting discovery so far. Around the same time, the other rover, Curiosity, spotted yellow-green crystals in a crushed rock that its wheels had broken while cruising the Martian surface. The unexpected find of pure sulfur (Mars was known to have sulfates such as gypsum, but pure sulfur was a surprising find) can further support that Mars experienced hot/cold springs and volcanic processes in its early history, considering pure sulfur naturally forms from these geological processes on Earth. However, the actual cause that led to a field of rocks with pure sulfur inside has still not been answered.
NASA, now, is so quickly capable of deciphering small details in these new Martian rocks to understand if their presence can say something about the habitability of a region on Mars. From understanding the veins of various rocks and what they can explain, to having a concrete understanding of Mars’s past to make educated assumptions and predictions of mysterious findings, scientists have come a long way in understanding the red planet. So what major findings has NASA’s rovers uncovered in the past two decades (and did they show any clues of past or current Martian life)?
One of the first major finds was in 2001, when NASA’s Mars Odyssey Orbiter utilized its Gamma Ray Spectrometer and its neutron detectors to presumably find water ice beneath the surface of Mars by detecting hydrogen atoms. For some background, cosmic rays are subatomic particles created through astronomical bodies or events that travel through space and interact with other astronomical objects. Earth is not affected by cosmic ray collisions due to its atmosphere deflection. But this isn’t the same case for Mars. Whenever cosmic rays collided with the Martian surface, the orbiter observed some neutrons being absorbed by supposed hydrogen atoms beneath the surface, causing a release of gamma rays to be returned. Later, NASA studied patterns in which neutrons were absorbed by tracking regions that lacked neutrons, concluding the presence of water ice inside of Mars through hydrogen absorption.
In the image on the right, the large blue contour represents a lack of neutrons detected, which is the region that is now assumed to have water ice beneath Mars. The surrounding red and yellow contours highlight areas that the Odyssey orbiter found significantly larger amounts of neutrons, indicating a lesser presence of hydrogen atoms. In 2008, the Phoenix Mars lander studied various samples by slightly digging into the Martian surface, ultimately confirming the presence of water ice on Mars.
A secondary image on the right shows a mapping of where scientists believe most of the water ice on Mars currently lies beneath the surface (presumptions made from newer data), hoping that future missions to the red planet will consider this when determining regions for astronaut landing and shelter.
Image Courtesy of NASA
Image Courtesy of NASA
Image Courtesy of NASA JPL
Since the Odyssey’s interesting observation, further evidence, such as geological findings through hydrated minerals and rock carvings, has confirmed that H2O had existed and continues to be prevalent on the planet (i.e. fusion of H2O ice and CO2 ice beneath the surface, not necessarily pure liquid H2O). For instance, one prime example of geological evidence dates back to 2007 when the Spirit rover’s broken wheel unintentionally revealed a patch of white soil that contained 90% pure silica. According to Steven Ruff who was a faculty researcher at ASU during the discovery of the silica, "On Earth, the only way to have this kind of silica enrichment is by hot water reacting with rocks." Therefore, the silica suggested the possibility of steam vents or hot springs in the earlier history of Mars–both of which could help harbor microorganisms.
Another instance caught NASA’s eyes in 2015 when the Mars Reconnaissance Orbiter (MRO) showed “recurring slope lineae,” as if you poured a cup of water on your mini sand castle, and it dried leaving downward trails (sorry, terrible way to describe it). Hydrated salts were detected with these darker-shaded streaks, suggesting its recent formation by water. However, the proposal was disproven two years later as it was concluded by other researchers that dry sands/grains created the dark streaks.
Image Courtesy of NASA JPL
Another finding that excited the community near the same time was the presence of large amounts of manganese-oxide in Gale Crater which were found (by Curiosity) in sedimentary rocks that contributed to the Murray Formation. The plentiful amounts of magnesium-oxide suggested that a large source of oxygen must’ve been present for an oxidation process of manganese.
However, in a research paper years later titled “Formation of manganese oxides on early Mars due to active halogen cycling,” scientists claimed that the manganese-oxide didn’t have to be generated due to oxygen on Mars, and instead proved that an oxidation reaction of manganese wouldn’t be possible in Mars’s past or current atmospheric conditions given the abundance of CO2. What they did uncover, however, was that halogens (Group 17/7A) such as chlorine (specifically chlorate) and bromine (specifically bromate), both of which are more ample on Mars than Earth, were able to oxidize manganese–with the help of water–faster than oxygen could have done it.
Image Courtesy of NASA
These two retracted claims truly show how much mystery still surrounds our understanding of Mars, and the presence of methane perfectly sums this up. After being first recorded by Curiosity in 2012, the methane detection started showing some strange things. The rover suddenly recorded spikes in methane concentrations in the atmosphere, as shown in the image. The spikes also followed a seemingly seasonal pattern. However, these weren’t the oddest observations...
In 2016 when the ESA launched their ExoMars Trace Gas Orbiter, their readings came back with no detections of methane in the Martian atmosphere. However, it was confirmed years later that both the rover and the orbiter were accurate. ESA’s data of methane concentration were during the daytime because their orbiter was powered by sunlight; however, Curiosity dealt with tasks all day and conducted methane concentration tests in the nighttime. So what causes the difference? Essentially, nighttime atmospheric conditions on Mars were calmer, allowing methane to clump together near the surface. In the daytime, the Sun created an atmosphere of hot air and cold air shifts that essentially mixed the methane in the atmosphere, diluting its concentration due to a larger denominator.
But even though scientists have figured out this occurrence, scientists are still puzzled by some of methane’s behaviors on the red planet. For one, how exactly is methane being produced on Mars? And if the production is constant, why isn’t there increasingly greater methane concentrations in the atmosphere if it’s supposed to last 300+ years there?
Image Courtesy of NASA JPL
But getting back on track, an even larger find (and even stronger evidence for potential past life on Mars) was the detection of boron a little less than a decade ago. Just like RNA came before DNA in the early growth of life on Earth, the possibility for Mars to be capable of supporting the presence of RNA molecules raised huge hopes that life would have existed in its past. When exploring the Gale Crater, the Curiosity rover’s ChemCam found boron in the “veins” of Martian mudstone, shown with the green on the image to the left.
The veins highlighted that such rocks had been influenced by water. Additionally, Los Alamos National Laboratory's Patrick Gasda states that the presence of boron indicates that the lake of Gale Crater “wasn’t overly acidic.” Because of this, it’s possible that bacteria could have potentially grown and lived in it. Now it’s important to note that because of the presence of water, boron was able to form borates. Borates are essential in preventing RNA from decomposing in water by stabilizing the ribose in RNA. While this discovery might not seem significant, it is the proof that scientists needed to confirm the possibility of RNA molecules even being capable of existing on Mars.
But Curiosity has done much more than find boron. Starting in 2015, it also started finding organic molecules. These organic molecules were detected in the Gale Crater’s Sheepbed mudstone samples that were heated up by Curiosity’s “Sample Analysis at Mars” technology. One interesting molecule detected in 2018 upon the release of these organic molecules were thiophenes.
Thiophenes can be found in life and through fossils on Earth, such as the Asteraceae plant family that can produce thiophenes as a defense against bacterial or fungal pathogens, or from coal/crude oil which can originate from past life; because of this, thiophenes became an interesting topic of conversation for their presence on Mars. In one paper, “Thiophenes on Mars: Biotic or Abiotic Origin?,” by Jacob Heinz and Dirk Schulze-Makuch, speculations are made on the most realistic possibilities of thiophenes on Mars. They start off with abiotic reasoning, mentioning that thiophenes have been found in meteorites, and that their discovery on Mars likely traced to this. The thiophenes could’ve also been created through a chemical reaction of organic molecules and sulfur compounds. However, the authors also proposed biological claims for the presence of thiophenes. Heinz and Schulze-Makuch argue that the abundance of sulfates on Mars in comparison to sulfur must’ve been caused by a process involving bacteria, called bacterial sulfate reduction, in which sulfates would be turned into sulfides which would react with organic molecules to form thiophenes. However, there continues to be no leads on thiophenes and their significance to Mars habitability.
Image Courtesy of NASA JPL
The Perseverance rover has also found organic molecules in the Jezero Crater in addition to its most recent discovery covered in the first article. While the rovers are capable of holding samples (often drilled out from rocks) inside of itself, the Perseverance rover has started leaving samples on the Martian surface in well-identifiable regions for future pickup by NASA.
Perseverance is one of the first steps toward the establishment of the Mars Sample Return initiative, which would exponentially increase our understanding about Mars (as Perseverance’s carefully selected samples are intended to be studied in laboratories on Earth to gauge a better understanding of ancient life in Martian rocks). Currently, NASA has devised a plan to launch a Mars Ascent Vehicle to the red planet which would collect all the samples and send them back up to orbit so they can get back to Earth via a secondary spacecraft. The plan seems pretty extreme, and it is.
So until we can figure out how to safely transport these samples back to Earth for more research, all eyes are on the Mars rovers.
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