Are we alone in the universe? This is one of the most important questions that science tries to answer for us. Building on previous discoveries, the Perseverance rover helps answer that question. If it found evidence that life once existed on Mars, a planet that was once warmer and wetter but is now very inhospitable, there’s a good chance that life could be abundant around the world. Perseverance is currently wandering alongside an ancient river delta on Mars, taking samples and using its instruments to scan the various rock deposits. Here on Earth, river deltas are teeming with life. They are also places where signs of past life—organic compounds—concentrate in layers of sediment and rock as they accumulate over time. So if life did develop on Mars a long time ago, a river delta like the one in Jezero Crater is about the best place to look for the same signs of life. This map of the western edge of Jezero Crater shows the path of the Perseverance rover since the start of its mission in February 2021 (white line) and the rover’s current position (red star). Credit: NASA When the rover collected two of its last samples, from Skinner Ridge and Wildcat Ridge, it sent back some exciting results. While the rocks look quite different, they both formed in a habitable environment. That is, conditions at the time and place where these rock deposits were laid down were friendly to life as we know it. However, the fine grain structure and lighter color of the Wildcat Ridge sample made it particularly interesting. These two abrasion patches show the Skinner Ridge rock sample (left), which is made of larger rounded grains that are bonded together, and the Wildcat Ridge rock sample (right), which is smooth and fine-grained. Both are exactly the kind of rocks NASA is looking for potential biosignatures. Credit: NASA “In the distant past, the sands, silts and salts that now make up the Wildcat Ridge sample were deposited under conditions where life could potentially have thrived,” Perseverance project scientist Ken Farley of Caltech said in a NASA press release. By scanning the Wildcat Ridge scour pad using SHERLOC, Scanning Habitable Environments with Raman and Luminescence for organics and chemicals, Perseverance identified a treasure trove of organic compounds. “At Wildcat Ridge, we detected signals that we believe come from a class of organic matter called aromatics, which are stable molecules composed of carbon, hydrogen, and sometimes other elements, with a ring structure,” Sunanda Sharma, SHERLOC scientist at NASA . Jet Propulsion Laboratory, said during a press briefing on these results on Thursday. “These signals were present at almost every point, in every scan. They’re also some of the brightest we’ve seen so far on the mission, and they’re about seven times brighter than what we saw at Thorton Gap, which is the scrape patch at Skinner Ridge,” Sharma explained. According to Sharma, these aromatics were found along with sulfate minerals. Similar conditions have been found here on Earth, where sulfates tend to preserve organic compounds. This suggests that these Martian organics and sulfates were deposited and concentrated in this delta location as the lake in the Jezero crater dried up. “This makes these samples and this set of observations some of the most interesting we’ve made so far on the mission and fulfills some of the excitement the team had as we approached the delta front,” Sharma said. This discovery confirms that Perseverance was definitely sent to the right place on Mars, with the right set of tools, to conduct its search for signs of ancient life. This composite image of the delta front puts the rover’s most recent samples in context, showing the locations of the Wildcat Ridge and Skinner Ridge sampling areas. The insets show mosaic views from the rover each after drilling a sample from the rock. Credit: NASA/Scott Sutherland But what’s the really exciting part of all this? Perseverance’s SHERLOC instrument detected signs of organic matter in these rocks. While the rover has already found organic compounds in other areas of the crater, the Wildcat Ridge sample showed the strongest detection of organics yet!
Signs of life? It can…
What Perseverance found here are “potential biosignatures.” Finding organic compounds in rock samples is not a definitive sign of life. For something to be an “organic” compound simply means that the molecules contain carbon atoms (and usually hydrogen, oxygen, and other elements such as nitrogen, phosphorus, and sulfur). While many organic compounds are part of or produced by biological life forms, some are formed through geological processes. Thus, detection of organics alone is not a definitive sign of life. To find “definitive biosignatures”—absolutely convincing evidence that life once existed on Mars—will have to wait. “The fact that organic matter was found in such a sedimentary rock—known for preserving fossils of ancient life here on Earth—is significant. However, as capable as our instruments at Perseverance are, further inferences about what is contained in Wildcat Ridge sample will have to wait until it returns to Earth for in-depth study as part of the agency’s Mars Sample Return campaign,” Farley explained in the NASA press release.
Mars sample return
So, how long do we have to wait? Lori Glaze, the director of NASA’s Planetary Science Division, presented the timeline of the Mars Sample Return campaign during Thursday morning’s briefing. “The Earth Return Orbiter, which will carry the samples back to Earth, is expected to launch in 2027 under our current plan,” Glaze said. “The Sample Return Lander will launch a few months later, in the spring of 2028.” This artist’s rendering shows the different elements of the Mars Sample Return campaign, with the lander (bottom right), the sample retrieval drone (center, left), the Mars Ascent Vehicle (top right), and the Earth Return Orbiter (top ), all working together with tenacity to complete the mission. Credit: NASA/JPL-Caltech When the Sample Return Lander arrives, it will use two Ingenuity-like drone helicopters to collect the sample tubes from where Perseverance dropped them to the surface. Meanwhile, the rover will also drive to the lander’s location to add its remaining samples to the return payload. As Glaze explained, these samples will be launched into orbit around Mars sometime in the 2030s and will make the journey on the Earth Return Orbiter to arrive here on Earth in 2033. With direct access to these samples and the most advanced laboratories on Earth, scientists can confirm the source of the organic compounds and perhaps bring us one step closer to knowing if extraterrestrial life really exists.
