Photo credit: NASA/JPL-Caltech
Back in September, an announcement was made about an important discovery on Mars. This BBC headline was fairly typical:
“Life on Mars? ‘Leopard-spot’ rocks could be biggest clue yet”
This got a lot of news coverage, and much of it was exaggerated. Many people probably got the impression that we had found life on Mars, or some kind of evidence for it.
But what was actually found?
Much ado about not very much
The paper in Nature that triggered all this was far more subdued than most of the media reports.
In the paper, the authors analyzed mudstone samples taken by the Perseverance rover on Mars. Turns out that the mudstones contain some minerals — the little dots in the photo above that some have said look like leopard spots — that seem to be the product of redox (reduction-oxidation) chemistry.
On Earth, these minerals can be produced by microbial activity. The authors considered several non-biological explanations for the Martian minerals, but concluded that they were unlikely.
The paper did not say that this was definitive evidence for life. The authors didn’t even spend much time discussing the idea. (Outside of the footnotes, the word “biosignature” only appears three times in the eleven-page paper.)
And this was quite appropriate. Redox reactions are common in chemistry. True, some are related to life (for example, when your body breaks down glucose to make energy). But many others are completely unrelated to life (for example, when iron rusts).
So, the authors didn’t make overreaching claims about these minerals being evidence for life. Instead, they concluded by stating that further analysis was necessary.
But if all you saw was the media reports, this is probably not the impression you would have received.
Not our first rodeo. Or even the second, or third…
This isn’t the first time that media reports have overhyped a potential “biosignature” discovery.
Remember the announcement of a biosignature on Venus? That claim was overturned later.
It’s not even the first time this happened for Mars. Remember the 1996 announcement of “fossilized bacteria” in Martian meteorite ALH84001? That was discarded too.
It’s not even the second time for Mars. Some readers will remember the Viking 1 and Viking 2 landers in 1976, and the initial claims that the LR (‘Labeled Release’) experiment found live microorganisms in Martian soil.
Premature “evidence for life” announcements aren’t even limited to our Solar System. For example, just a few months before the “leopard spot” announcement, a new analysis challenged previous claims about potential biosignatures in the atmosphere of K2-18b. (This is an exoplanet orbiting the red dwarf star K2-18, roughly 125 light years away from Earth.)
This new find on Mars isn’t any more impressive than the others were.
However, it is more potentially more expensive. Multiple researchers have recommended that NASA dedicate a future mission to retrieving the leopard-spot samples from Perseverance, and bringing them back to Earth for analysis.
This would cost tens of billions of dollars, just to get a closer look at some dried, dead mud.
We can hope that those entrusted with public funds will dedicate those funds to something more scientifically useful.
Addendum: life on Mars is impossible today
The next time you hear a claim about potential life on Mars, remember that the surface of Mars is extremely hostile to life. Lethal levels of UV radiation, perchlorate chemicals, and other nasty environmental factors will kill unprotected microorganisms in a matter of seconds.
So, scientists looking for “potential biosignatures” have to believe that Mars was much different in the past, with a much thicker atmosphere, a robust global magnetic field (to retain the atmosphere), large oceans, and more, including the absence of all the nasty things that would kill life now.
But the planet we see today isn’t like that.
Science is based on observations, and the past is not observable — we can only make observations in the present. And extrapolating today’s observations back to billions of years ago requires all sorts of unverifiable and often highly questionable assumptions (not to mention a worldview that includes billions of years, which contradicts numerous lines of evidence for a young Solar System).
So all claims about what Mars could have been like way back then, are speculation rather than science. The planet we see today is deadly.
