February 6, 2022
Sunday, February 6, 2022
The evidence is clear now isn’t it, that there was life on Mars? That’s what I first thought when reading about the latest findings from the Curiosity rover that has been exploring Gale Crater since 2012. After over 40 years of looking for life (past or present) on Mars, why can’t the Curiosity team say they’ve done it but instead have to be such a killjoy?
“Extraordinary claims require extraordinary evidence.” This is one of those annoyingly true statements by Carl Sagan about the scientific method. It’s why the team analyzing the results from the Curiosity rover have to be so darn cautious interpreting the data.
Of the 30 samples collected by Curiosity since it landed in 2012, 24 were heated in the Sample Analysis at Mars (SAM) instrument to release methane and measure the carbon isotopes. Isotopes of an element have the same chemical properties but different nuclear properties. Carbon comes in three flavors or isotopes each with six protons in the nucleus: Carbon-12 has six neutrons in the nucleus; Carbon-13 has seven neutrons in the nucleus; and Carbon-14 has eight neutrons in the nucleus. Carbon-12 makes up 99% of the carbon atoms, Carbon-13 makes up 1%, and Carbon-14 makes up 1 in a trillion carbon atoms. Carbon-14 is radioactive and it is the one we use for radiocarbon dating.
One characteristic of a biosignature (ideal sign of ancient life) is chemical compounds that are essential and unique to cellular processes. Life is exceedingly choosy about the chemical building blocks it uses. That is good because that "pickiness" helps us distinguish a genuine biological remnant from a specimen produced by something else. Carbon-12 is the lightest form of carbon, so life enhances the amount of Carbon-12 in its reactions. Therefore, biological remnants will have a deficit of Carbon-13 compared to ordinary geological remains.
In ten of the samples that had the carbon isotopes measured, there was a significant deficit of Carbon-13. Those ten samples were collected in six different locations. Now, it will actually take a constellation of biosignatures to make a case for ancient life. Besides unusual carbon isotope ratios, there will need to be enhanced ratios of hydrocarbons, chemical changes from metabolism, microfossils, molds, or casts in the rocks from microbes, and possibly macro structures such as stromatolites and microbial mats.
Notice how careful the team has been. They didn’t announce their discovery after the first or second or even third measurements. They waited until they’d collected TEN measurements in six different locations over about a decade’s time. No YouTube announcements touting a “fact” of Martian life. Nothing announced to the public until after the paper had gone through the peer-review process and was accepted for publication.
The Curiosity team went a step further of questioning the Carbon-13 deficit by proposing two other ways of producing the Carbon-13 deficit, though they are probably less likely than a biological explanation. Ultraviolet light interacting with the carbon dioxide and/or sulfur dioxide in Mars’ atmosphere could have produced carbon-containing (organic) molecules with a deficit of Carbon-13. Another less-likely possibility involves our solar system passing through an interstellar dust cloud. Some interstellar dust grains we’ve collected have greatly reduced Carbon-13 amounts. The dust would have settled on glaciers that later melted. Further observations will enable the team to discard one or two of the Carbon-13 possibilities—more drillings are needed!
But let’s say a team finds the constellation of biosignatures in the future and publishes their results in a peer-reviewed journal. Will that mean past Martian life is an accepted fact? Not really. Just because something is published in a peer-reviewed journal does not make it be the final word, the absolute whole truth. There are plenty of times when something published in a peer-reviewed journal is found to be incorrect. Before a paper is published, the peer reviewer(s) (also called "referee") will examine the analytical methods and logical reasoning of the author(s) to catch any errors and maybe suggest an alternative interpretation of the data. After the paper is published, other research teams will examine the claims, trying to reproduce the data or collecting new data that refutes the original conclusions or finding errors of logic missed by the first peer reviewers. The peer review process involves checking and re-checking, validating any claims and preventing the psychological traps of confirmation biases (the tendency to interpret or "cherry-pick" new evidence as confirmation of one's existing beliefs or theories).
Closer to home, the James Webb Space Telescope successfully reached its destination 1.5 million kilometers from Earth. All of the components are successfully deployed. For the next few months, the 18 individual mirrors will be carefully aligned to act as one large mirror and the science instruments will be calibrated. Hopefully, by the first part of May, we should receive the first images.
The hunt continues for intermediate mass black holes that bridge the gap between the stellar mass black holes less than 100 times the mass of the sun and the supermassive black holes that are millions to billions of times the mass of the sun. We need to find ones in the gap to help us figure out how the supermassive black holes got so big, so quickly.
The latest announcement is of a 100,000 solar-mass black hole in a globular cluster called B023-G078 inside of the Andromeda Galaxy but like the handful of announcements of other intermediate mass black holes, that pesky peer review process shows that the data could be plausibly explained as a clustering of smaller compact objects. However, the data say it’s more likely to be an intermediate mass black hole. Further work will be done to try to disprove the other explanations and build the case for the intermediate mass black hole explanation. Astronomers are used to being patient and going through the critical analysis of a thorough peer review process.
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
