Was Mars once like Earth? Can you imagine the red planet once a verdant green? That might be stretching it a bit, but NASA scientists are on an ambitious hunt for evidence of ancient Martian microbes. What they discover could transform our understanding of life back here on Earth.
Ken Farley, project scientist with NASA’s Mars 2020 mission. He leads the science team and worked with the engineers to design and build the Perseverance rover. Professor of geochemistry at Caltech. (@NASAPersevere)
Dawn Sumner, professor of Earth and planetary sciences at the University of California, Davis. Her work focuses on reconstructing ancient environments on early Earth and Mars, and the early evolution of bacteria. (@sumnerd)
Sweeya Tangudu, part of a team of five that won 4th place in the 2020 Mars Society competition to build a city state for 1 million people on Mars. Her city state was called Phlegra Prime.
Robbie Gitten, aerospace engineer. Part of a team of five that won 4th place in the 2020 Mars Society competition to build a city state for 1 million people on Mars.
Are there signs of life on Mars that don't resemble the definition of life on Earth?
Ken Farley: “I like to say that looking for life on Mars is potentially looking for life as we don't know it. Your suggestion that on Earth we have DNA-based life? Absolutely. It is possible that DNA is a kind of a universal molecule, and life elsewhere would discover the same the same approach. I don't think that's necessarily true.
"And there's reason to believe that even if it is DNA-based, it will be different. It will involve different compounds. And so at the end of the day, the challenge of looking for life, first of all, is to define what life is. And second of all, to figure out how you look for a signal without using the tools that have been honed so carefully over the last decades, which are focused on Earth's life. That may not be universal. So that's a big challenge.”
Can you describe how the Perseverance actually made that touchdown on the red soil of Mars?
Ken Farley: “The skycrane maneuver, which is when we are a few tens of meters off the surface. We have retrorockets firing with the rover mounted on a platform. And we literally winched the rover down to the surface until it touched the ground. And then as soon as we got the signal that it had touched the ground, we cut the cables and the rocket engine bearing stage flew off and crashed, leaving the rover standing by itself on the surface.”
Where is Perseverance right now and why did you choose that particular landing spot location?
Ken Farley: “Perseverance landed in a crater that's about 40 kilometers across called Jezero Crater. And there is very clear evidence that this crater was once filled with a lake. And quite a large lake, 40 kilometers across and hundreds of meters deep. And this was about 3.5 billion years ago. Since that time, Mars' climate has changed completely. There's … no liquid water on the surface of Mars anymore. But at this time, 3.5 billion years ago, we believe this was a very habitable environment.”
What kind of life are we talking about?
Ken Farley: “This is not Earth-like life we are seeking. And that forces us to think a little bit differently. But all we really have to go on is Earth's life. We have an example of what life is like. And 3.5 billion years ago on Earth, that is about the oldest evidence we have of life on Earth. And life at that time was strictly microbial. Life had not evolved into the kind of complex plants and animals that we're familiar with today. That came much, much later. So using Earth as an analogy, we think the most plausible kind of life that might exist that early in the history of the solar system is likely to be microbial.”
Where and how have we identified those ancient microbes as evidence of early life on Earth?
Ken Farley: “The most important thing to understand is that Earth's a very dynamic planet. And there is very little rock record of the very distant past, Earth's history, the time when life presumably originated and got its start. Most of that rock record is gone. There are a few places, including in Western Australia, where there are small slices of rock from that time period.
"And in those rocks that record shallow lakes or seas, microbes were growing and they were actually deforming the mud on which they were growing. And this deformation by the presence of these microbes left a pattern in the rocks, at the scale of inches to feet, that is characteristic of this [microbial] mat of organisms. And very different than the structure that you get from deposition of sediment that is not induced or modified by biology.”
What does Martian climate change actually mean and how did that happen?
Ken Farley: “We know that currently Mars is extremely cold, it's extremely dry, and the surface has nowhere that life as we know it could exist. And one of the great surprises of the several decades of exploration of Mars is that it wasn't always that way. And we see what is really textbook evidence of flowing water on the surface. In the distant past, about 3.5 billion years ago, we see canyons, we see evidence of shorelines on lakes, and a possible ocean that covered part of the planet. And in the case of Jezero Crater where Perseverance landed, we see evidence of a river delta, which is proof positive that there was once a lake in that crater.
"So clearly, climate has changed. Sometime between then and now, we believe it was in the vicinity of between 3 and 3.5 billion years ago that the climate changed. We don't know exactly why. In fact, one of the great questions is how Mars was ever warm enough to host liquid water on its surface. But one of the leading candidates for the explanation of why Mars' climate changed is that it lost its magnetic field. The loss of the magnetic field actually causes a partial loss of the atmosphere. And this simply drives home the point that the way climates work on planets is through greenhouse warming. And when you change the composition or the density of the atmosphere, you change the climate.”
What drives you to want to understand the origins of life both on Mars and here on Earth?
Dawn Sumner: “For me, the study of Mars really helps me value what we have on Earth more. As Ken described earlier, Mars used to be warm enough to have liquid water. It used to be habitable, and it went through this change into this icy, barren rock, as the questioner said, that's a really dramatic planetary scale change. And on Earth, we're going through that due to our own activities with the environmental damage that we're doing.
"It's very difficult to predict what will happen. We can actually use other planets to to try to see what happens when there are changes. What causes a planet to go cold and ... dry. In the case of Earth, we're getting warmer and warmer. Maybe it's a little bit more like Venus, which is super warm. But we need to study planets to understand Earth.”
From The Reading List
New York Times: "NASA’s Perseverance Rover Lands on Mars to Renew Search for Extinct Life" — "NASA safely landed a new robotic rover on Mars on Thursday, beginning its most ambitious effort in decades to directly study whether there was ever life on the now barren red planet."
Scientific American: "NASA’s Perseverance Rover Makes Oxygen on Mars for First Time" — "NASA’s Perseverance rover just notched another first on Mars, one that may help pave the way for astronauts to explore the Red Planet someday."
Slate: "We’re Already Colonizing Mars" — "Sometime in April, the Ingenuity helicopter will take to the Martian air, making it, in NASA’s words, 'the first attempt at powered, controlled flight of an aircraft on another planet.' Or, to put it in more mundane terms, Mars will have become another airport. Of course, many crafts have already landed on Mars—the most recent carrying the rover Perseverance, with the Ingenuity copter nested inside."
Phys.org: "Mars has right ingredients for present-day microbial life beneath its surface, study finds" — "As NASA's Perseverance rover begins its search for ancient life on the surface of Mars, a new study suggests that the Martian subsurface might be a good place to look for possible present-day life on the Red Planet."
This program aired on April 28, 2021.