The rover Spirit reached the 1000 sol mark on Mars, meaning it had been operating for 1000 Martian days, which is about 910 sols longer than the rover team had hoped for. In fact, considering that its computer crashed within a day or two of landing, its lasted about 998 sols longer than expected at that point. Fortunately, engineers corrected the problem (they had left a pile of files in read-only-memory, so the computer ran out of space as it gathered data; as a system administrator who is constantly fighting with users, especially engineers, about server space usage, I wasn't the least bit surprised).
About half way around the planet, Opportunity has passed the 900 sol mark and is scoping out a new crater to explore. The little-rovers-that-could join the ranks of other NASA successes like Galileo (despite its balky antenna, it operated for about seven years longer than anyone thought it would), Cassini (which sends one amazing image after another back), and its Martian friend, the Mars Global Observer. They have been joined by the the Mars Reconnaissance Orbiter, which has already sent back incredible images, including a lovely snap that shows Opportunity quite clearly. All this effort has one purpose, whether stated or not: To try to determine if life ever existed on Mars.
Of course, the situation would be clarified in a moment if, one sunny day, we got a picture back from a rover that showed a Martian insect crawling around on the lens, or maybe a six-legged giraffe walking across the landscape. However, if any life is to be found on Mars, it seems most likely to be of the microbial type. But that sort of thing is very hard to find. We know because we've tried.
In 1976, the Viking missions went to Mars, landing on June 19 and September 3, respectively. They did pretty well, too, with Viking 2 lasting 4 years and Viking 1 sending back souvenir photos until 1982. Both of them had equipment on board to sample the Martian soil for the presence of microbial life. The equipment consisted of three experiments:
- One added soil to a “soup”; if the soup was chemically broken down, it could indicate that something in the soil was metabolizing with the food in the soup.
- In the second test, gases were added to the soil; if the gases combined with the soil, it would be indicative of photosynthesizing microbes generating organic matter.
- The third test, a gas chromatograph mass spectrometer (GCMS), would check heated soil samples for released organic compounds.
That didn't mean, however, that there had never been little creepy-crawlies on the red planet. In 1984, a meteorite, prosaically named ALH84001 was found in Antarctica. After sitting around wherever interesting meteorites reside while waiting to be examined, some scientists determined it was actually a piece of Mars and looked into it very deeply. They decided they had found evidence of microbial activity (including a fossilized microbe) in the rock. The news was a sensation and was met with a lot of natural skepticism. As time went on, most of the weight of opinion went against the team, deciding that what was find in the meteorite was simply normal geological goings on. Alternatively, others felt that the meteorite had been contaminated by terrestrial bugs.
In 2001, another review of the rock determined that it had magnetite trails that would be indicative of bacterial activity. But, this finding, following on the original hoopla, seemed to get lost. So, the evidence for current and past life on Mars seemed to be non-existent. But, sometimes a new look at old data can be revealing.
A study has been done on another Martian meteorite that seems to have microscopic tracks, similar to tracks seen in rocks on Earth that are only formed by bacteria. The team studying the tracks has tried to extract DNA from the tracks, as they would be able to in terrestrial rocks. This could mean that there's some other cause for the tracks that we don't understand or that the DNA has been destroyed. However, the bacterial tracks , if that's what they are, would have been set down 600 million years ago, which would make it unlikely for the DNA to have survived.
Of course, such bacterial activity would have required water, the finding of which is the holy grail of Martian exploration. There may not be much water available now, but analysis of rover data indicates now that Mars was covered with a planet-wide ocean. It's not clear how much life, if any, might have been in that ocean, but the data seems to indicate that the conditions could have been favorable to the formation of at least a limited amount of living organisms.
That may be a slim hope, but another interesting development is a finding concerning the GCMS methodology used on the Viking landers. It turns out that the GCMS has been found to be insufficiently sensitive to detect life in Mars-like soils found here on Earth. It would be easy to be critical of the original concept, but keep in mind that it took 30 years to find this out. It took the mineral analysis capabilities of the current rovers to determine the true nature of Martian dirt. Once that was done, someone had to take the initiative to see how the original Viking experiments would have worked against such soil.
Bottom line? Viking 1 and 2 may have detected current microbial life on the planet.
We keep finding out that conditions on other planets and moons are different from what we expected. Titan doesn't have oceans of methane, but Europa probably has an ocean of water. There are volcanoes and geysers where we didn't expect such things. Venus is ridiculously hot with an incredibly dense atmosphere while Mars is very cold with a thin atmosphere – and no canals.
But, life may be out there, although it could be harder to find than we thought. Then again, we may have found it already.
Cosmos, Carl Sagan, Random House, 1980
Mars Meteorite: Proof of Life?
Debunking the Martian Meteorite
Mars Meteorite Similar To Bacteria-etched Earth Rocks
Viking landers may have missed Martian life
Soil minerals point to planet-wide ocean on Mars