In a most informative article, David. F. Coppedge contrasts known facts as to why Mars might be lifeless with science writing that relentlessly attempts to paint it as hopeful.
Coppedge: The paper in Geophysical Research Letters by I.B. Smith et al., “A Solid Interpretation of Bright Radar Reflectors Under the Mars South Polar Ice” (GRL, 15 July 2021, DOI: 10.1029/2021GL093618) says that clay is a sufficient material to account for the observations. The water interpretation is problematic, because “the amount of dissolved salt and heat required to maintain liquid water at this location is difficult to reconcile with what we know about Mars.”
Christopher Mason: There is a chance, however, that if we do detect signs of life on Mars, it could have come from Earth in the first place. Ever since the first two Soviet probes landed on the Martian surface in 1971, followed by the US Viking 1 lander in 1976, there likely have been some fragments of microbial, and maybe human DNA, on the Red Planet.
National Geographic: Utopia Planitia, thought to be the site of an ancient sea, has sedimentary layers that could contain evidence of past water. Even more exciting, these layers of rock could contain traces of any past life on Mars, says James Head III, a planetary scientist at Brown University.
Normally, we could dismiss all this as wishful thinking — except there are the extremophiles on Earth, representing every domain of life.
Researchers: The raging megaflood — likely touched off by the heat of a meteoritic impact, which unleashed ice stored on the Martian surface — set up gigantic ripples that are tell-tale geologic structures familiar to scientists on Earth.
Some see this as evidence that the universe is teeming with life on numberless planets. But what if we find fossil bacteria on Mars with genetics eerily similar to the ones we have on Earth? That could end up undermining such claims. But we shall see.
Siegel: It’s the ultimate nightmare of astrobiologists: that there’s a fascinating history of life to uncover on another world, but we’ll contaminate it with our own organisms before we ever learn the true history of life on that world.
Speculations about space aliens isn’t. It may take a while to find out if there was ever life on Mars but maybe we’ll really know something this time.
Sheldon: The point is that we don’t expect to find nitrate and ammonia in the soil of Mars, not unless some nitrogen fixing bacteria put it there recently, because over time it will all come out of the soil as N2 gas. Claiming that the process goes the other way, from N2 in atmosphere to nitrates in soils, goes backwards, from high entropy to low entropy.
Standish: If the nitrogen cycle isn’t established within a certain time, nitrogen will be removed from the atmosphere and the surface will become rich in nitrate (bad) or, in a reducing atmosphere, ammonia (really bad). The bottom line is that there are speculations that probably get around this, but it is one more needle that has to be threaded for chemical evolution to produce the first life, or a problem for the first life to quickly take care of.
Researcher: Findings suggest that structure alone is not sufficient to confirm whether or not microscopic life-like formations are fossils. More research will be needed to say exactly how they were formed…
Maybe this is the closest we’ll ever really get to extraterrestrial life. Go there and grow stuff.
Life on Mars would be a lot of fun but one suspects it’ll never live up to the hype.
Levin: When the Viking Molecular Analysis Experiment failed to detect organic matter, the essence of life, however, NASA concluded that the LR had found a substance mimicking life, but not life. Inexplicably, over the 43 years since Viking, none of NASA’s subsequent Mars landers has carried a life detection instrument to follow up on these exciting results.