In 1976 the Viking Landers conducted soil analyses in Chryse and Utopia Planitias, finding apparent life-like activity but no organic material. Afterwards, it was found that the sensitivity of the pyrolysis experiment was not enough to detect the typical concentrations of life in the Dry Valley soil of the Antarctic. The only organic compound to be detected was acetone, in soil from under a rock. But as it happened, that test chamber had not been used before, and acetone had been used in sterilising the spacecraft before launch, so the results remained ambiguous.
But in 2005 formaldehyde was detected in the atmosphere of Mars, in relatively large quantities. It’s being formed by the action of sunlight on methane, and because methane lasts for only a few hours in the atmosphere, that suggests a great deal is being released from the surface. The orbiters established that the methane and water vapour are being released from the same regions of the surface, such as Solis Planum (formerly Solis Lacus, which Percival Lowell believed to be the capital of the Martian civilisation), and that strongly suggests that there’s volcanic activity underground, or life – or both!
The Phoenix probe was launched successfully on August 4th 2007 in a bid to repeat the mission of Mars Polar Lander, which failed in 2000, to look for evidence of life near the rim of the north polar cap. The object was to search for evidence that liquid water can form from the ice in the soil during the summer, and any organic material in the water which might indicate the presence of life, now or in the past.
Remarkably the probe and its parachute were photographed during the descent, by the Mars Reconnaissance Orbiter whose cameras are comparable to those on spy satellites. The lander, parachute and detached heat shield were then seen on the surface. But as soon as the first photographs from Phoenix itself were released, they confirmed what had been seen from orbit: hexagonal features on the surface, just like those seen on Earth in Arctic regions where the top layer of permafrost melts. There turned out to be ice very near the surface, so close that it had been exposed by the blast of the rocket touchdown. Perchlorate compounds were detected in the soil, causing enough of a stir for Aviation Week to allege that the President had been briefed on more dramatic finds. NASA and JPL denied that, but see below.
By mid-August, the writing was on the wall for the end of the mission: frost had begun to appear around the lander during the hours of near-darkness. At first it was water frost and quickly disappeared as the Sun rose, but as the north polar hood developed over the polar cap and expands in winter the power from the Sun will diminish, while beneath it Phoenix was being buried in carbon dioxide ice. As predicted, Phoenix failed for lack of power as the northern winter advanced: it hadn’t found evidence of past life on Mars, but observations from Earth have now confirmed that methane in the Martian atmosphere, detected by Mars Express, comes from three active areas between Valles Marineris and Syrtis Major; furthermore the emissions are seasonal. Methane isn’t stable in Martian conditions and we knew something had to be replacing it; if it isn’t life below the surface, it could be volcanic activity which might sustain life. But the absence of related gases like sulphur dioxide suggests the release is not volcanic, but may be from actual living organisms. It emerges that Mars has been glaciated over much of its surface twice within the last million years, and to liberate and redistribute so much water there must have been volcanic activity beforehand.
In January 2012, unfortunately, the Russian Phobos-Grunt spacecraft, which was intended to return our first samples from the inner moon of Mars, fell back to Earth. The probe had been trapped in low Earth orbit since its upper stages failed to fire, and only flickers of communication had been achieved because the antennae were masked by the fuel tanks which have failed to separate. The good news is that, despite scare stories on the internet, Phobos-Grunt did not have onboard nuclear batteries like the USA’s Curiosity rover, successfully landed on Mars in 2012 and still hard at work on Gale crater’s central peak. Space expert Jim Oberg correlated reports of Russia’s Mars-96 failure and concluded that it might not have fallen in the Pacific, but come down on land in the Andes. That would be worrying because Mars-96 did have sixteen batteries powered by radioactive isotopes, which could be used to make a dirty bomb if retrieved by the wrong people. But even if Phobos-Grunt had come down in Afghanistan, as it might have, it was a lot less likely to do any serious harm, and in the end it fell at sea.
Just before the Curiosity rover’s landing on Mars, I reviewed Rod Pyle’s book “Destination Mars: New Explorations of the Red Planet” (Prometheus Books, 2012) for the online critical magazine Concatenation. In recommending the book, I drew attention to an astonishing revelation near the end. To begin with, the slant put on the findings of the Phoenix mission, analysing soil and ice near the north polar cap, is much more positive for the search for life than most media coverage suggested. When the Phoenix lander found perchlorates in the Martian soil, the general response seemed to be that they made the existence of life still less likely. But according to Peter Smith of the University of Arizona, “it turns out that chlorine in perchlorate form is very stable, very soluble in water, and… lowers the freezing point of water, so if you concentrate perchlorate, you get a very low freezing point in brines, and life could survive in those brines. Second, there are microbes on Earth that live on perchlorate. They use it as an energy source.”
What’s truly jaw-dropping, however, are the revelations in Pyle’s August 2011 interview with Dr. Chris McKay of NASA Ames Research Centre. The cited source is a Discovery News release which is still available online: evidently the findings were published in the Journal of Geophysical Research, December 2010, but I didn’t see any fanfare about them at the time.To understand their significance, you have to appreciate the 35 years of controversy over the Gas Chromatograph Mass Spectrometer results from the Viking landers in 1976. Despite the possible but ambiguous indications of biological activity in the other experiments, the GCMS detector failed to find organic compounds in the soil; hence the famous quote from Dr. Gerald Soffen, “All the signs suggest that life exists on Mars, but we can’t find any bodies.” Subsequent tests indicated that Viking’s GCMS would have been insufficiently sensitive to detect organic compounds on the surface in Antarctica’s Dry Valleys, although microorganisms are prolific below the ground and inside the rocks. At times the discussion has become heated enough for claims that there’s a conspiracy to promote the Viking results as wholly negative.
Immediately after the Phoenix discovery, McKay reran the Viking experiments using perchlorate-enriched soil from the Atacama desert, and produced perfectly matching results. In the presence of perchlorate, organic compounds in the desert soil broke down when heated to produce the compounds detected by Viking. And if that wasn’t enough, the same results were found with soil from the Dry Valleys. Inferring the presence of organic compounds in the Viking samples doesn’t prove that there is or was life on Mars, but it demolishes the generalisation that the Vikings proved there was no life. The Discovery release begins with a statement from McKay that there was no justification for testing with perchlorates until they were detected on Mars, and ends with one from a colleague saying the 20-year gap in Mars exploration might never have happened if these results had been available at the time.
Back in 1976, Viking 2 was intended to land on a dune field in Utopia Plantitia, to obtain the greatest possible contrast with the Viking 1 site in Chryse. In the event it landed among rock ejecta from the crater Mie, and the two sites were extremely similar, although Utopia was further north and it was hoped that it would collect more water vapour in the Martian spring. (It did collect frost in the winter.) China’s Zhurong lander has now set down on a much more open section of Utopia, and what it finds will be awaited with interest. Zhurong’s carrier Tianwen-1 is now in orbit, joining a small fleet of spacecraft including ESA’s Mars Express, NASA’s Mars Reconnaissance Orbiter, MAVEN, and the veteran Mars Odyssey (20 years on station), India’s MOM, the United Arab Emirates’ Hope, and Europe’s Trace Gas Orbiter, the communications relay for the Rosalind Franklin lander scheduled for launch in August to October 2022, after delays caused by issues with its supersonic parachute.
As the Perseverance lander begins exploration on the river delta in Jezero crater, preceded by reconnaissance flight of the Ingenuity Mars helicopter, it will begin to collect and cache samples to be picked up by a European rover called ‘Fetch’, and eventually returned to Earth. Plans for more advanced missions are on the table. Now that cameras of spy-satellite resolution are available for planetary exploration, both MRO and its counterpart Lunar Reconnaissance Orbiter have been finding ‘skylights’, which are deep holes formed by roof collapses in underground lava tubes. These can run for many miles and there’s still argument about whether Hadley Rille on the Moon is one that’s collapsed along its length, though the Apollo 15 astronauts didn’t think so. But they could be shelters for life, or sites for future bases, protected from cosmic radiation. Within days of the Curiosity landing, a study contract was awarded for a vehicle to investigate them, under NASA’s NIAC Innovative Advanced Concepts programme (‘Astrobotic Wins Contract to Develop Moon Cave Explorer’, Pittsburgh, PA, August 21 2012), and after the success of Ingenuity we can expect to hear more about the skylight explorers before long.
Also in this series: