Viking 1 despatched again this shade picture of a sundown on Mars August 21, 1976. Credit score: NASA/JPL
This 12 months marks 100 years for the reason that births of two pioneers within the seek for life on Mars. Joan Oró and Gilbert V. Levin have been a part of NASA’s Venture Viking, which delivered twin spacecraft to Mars in 1976. Every consisted of an orbiter and a lander probe, carrying a collection of scientific devices designed to search for life on Mars.
Whereas each Oró and Levin labored immediately on devices for Viking, that they had very completely different interpretations of the mission’s scientific findings. I used to be lucky to satisfy each throughout the early 2000s. I talked with them extensively concerning the experiments carried out by the 2 landers —Viking Lander 1, which touched down at a web site referred to as Chryse Planitia on July 20 (precisely 7 years after people first landed on the Moon) and Viking Lander 2, which set down at Utopia Planitia about 4,000 miles (6,500 kilometers) away on September 3.
Probably the most perplexing Viking outcomes was from an instrument referred to as the labeled launch (LR) experiment, as a result of it produced seemingly constructive outcomes for all times at each touchdown websites. Viking’s different devices (and scientific consensus) disagreed, however Levin, the LR’s principal investigator, was nonetheless calling it a constructive outcome some three a long time after the experiment had come to an finish. He remained satisfied that he’d found life on Mars for the remainder of his life.
Studying the rocks
Born October 26, 1923, in Lleida, Catalonia, Spain, Joan Oró was a biochemist whose work targeted on the origins of life. His analysis occurred largely on the College of Houston. In 1959, Oró demonstrated that adenine — considered one of a handful of nitrogenous bases that DNA and RNA use to hold genetic info — might kind from easier chemical substances within the absence of biology. Six years prior, in a well-known experiment on the College of Chicago, graduate pupil Stanley Miller and chemist Harold Urey had demonstrated abiotic (with out biology) synthesis of assorted biologically necessary chemical substances below circumstances thought to have characterised the early Earth. Oró’s achievement continued this path towards understanding how life might need begun.
Practically a half century later, I used to be doing analysis in that very same college division, linked with my astrobiology coaching primarily based at NASA’s Johnson House Middle. Once I met Oró within the early 2000s, he was a Professor Emeritus, spending a part of the 12 months in Houston and half in Barcelona, work he continued till his loss of life in 2004. Throughout considered one of his visits in Houston, I interviewed Oró about an instrument he labored on referred to as the fuel chromatograph mass spectrometer (GCMS), which examined the regolith at each Viking touchdown websites to find out its make-up, particularly whether or not it contained any natural supplies — the constructing blocks of life.
It’s within the air
Born April 23, 1924, Gil Levin developed his instrument for many years earlier than the Viking launch. I met him at a convention of the Mars Society across the flip of the twenty first century. At that time, not solely was he nonetheless publishing papers explaining the rationale behind his perception within the experiment’s outcomes, however he had developed an improved model of the experiment. He even launched the instrument on a Russian mission to Mars, however the spacecraft failed. For the remainder of his life, till his loss of life in 2021 on the age of 97, Levin saved making an attempt to get his improved LR onto a Mars mission, however NASA by no means permitted it.
Working as an engineer within the late Forties and 50s, Levin was recruited to work on detection of micro organism in environmental water samples, utilizing a way through which small natural compounds — potential meals for any micro organism — have been equipped to water samples. Metabolism by the micro organism would produce fuel, inflicting seen bubbles. However for the reason that course of took so lengthy, bubbles would typically seem too late to assist public well being purposes.
Levin modified the gear to make use of carbon-14, a radioactive isotope of carbon, as a marker for any liberated fuel. That method, metabolism of the meals by microorganisms can be revealed lengthy earlier than any bubbles can be seen. This in the end led Levin to develop the instrument to ship to Mars on Venture Viking.
Many natural molecules are chiral, that means that they’ll happen in two mirror-image types (like your proper and left palms). Whereas abiotic reactions produce each types equally, life on Earth requires “left-handed” molecules over their right-handed mirror picture. Scientists don’t perceive why, however life’s choice for leftie molecules is properly established.
So Levin proposed sending the LR instrument with left-handed and right-handed “snacks” for potential microorganisms. Identical to with water samples, they might search for carbon-14 as an indication that the snacks had been consumed. If this occurred with substrates of 1 mirror picture, however not with the opposite, it could point out life, as a result of nonbiological processes don’t discriminate between left- and right-handed.
However as a consequence of weight restrictions for the devices, Levin wanted to downsize the LR and have only one combination of vitamins. And so, as an alternative of chirality, the experiment needed to be managed with warmth, obtainable from an oven included with different devices.
On this model of the experiment, scientists assumed that top temperatures would destroy microbial life, because it does on Earth. So if fuel have been detected from solely the unheated pattern, that will point out organic exercise. At each touchdown websites, that’s what really occurred: Gasoline was liberated from unheated martian regolith samples after they acquired the nutrient liquid, however not from samples that have been heated (sterilized) previous to testing.
The battle
However Oró’s chemistry instrument, the GCMS, appeared to detect no natural compounds in that very same regolith. If there was life, the place have been the lifeless our bodies? That’s how astronomer and science communicator Carl Sagan defined it on the unique Cosmos tv sequence. The obvious lack of natural matter within the martian regolith made many of the science staff, together with Oró, favor a speculation put forth by the principal investigator of a distinct Viking biology experiment, Vance Oyama. He thought that Levin’s fuel launch had come from hydrogen peroxide current within the regolith.
It was a simplified speculation that doesn’t actually have any extra proof than the organic interpretation does, though within the years following, different scientists got here up with a sophisticated mannequin through which completely different chemical substances within the regolith might need precipitated the constructive LR outcomes together with the noticed variations between the heated and unheated samples. Through the years, the interpretation of the Viking GCMS discovering would come below scrutiny for different causes, however in my interview of Oró across the 12 months 2000, he stated it went “poof.”
I discovered neither Levin’s nor Oró’s rationalization notably convincing, however throughout the years that I used to be speaking with Levin, studying his papers, and infrequently presenting work in the identical conferences and classes the place he introduced, I discovered his improved LR instrument thought intriguing. He needed to ship it again to Mars with the flexibility to check the regolith individually with left-handed versus right-handed natural molecules. That is nonetheless a superb thought for distinguishing organic from nonbiological chemical adjustments.
As we glance to Mars and different worlds, I hope that chirality shall be at middle stage after we are prepared, hopefully quickly, to ship extra devices to Mars, designed to look immediately for the exercise of life.