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The Viking Landers, 25 Years Later
bavid314 writes: "CNN has a decent story looking back on Viking I and Viking II. For someone who wasn't alive at the time of the landings, it provides a good synopsis. Furthermore, it evokes the question of why recent missions fail to include biological experiments to test for the presence of life."
Try getting an organic chemist to say "silicon-based life" with a straight face.
IANAOC, but the short answer is that while you can substitute silicon for carbon on paper, the properties of silicon are different enough to make this impossible in practice. For instance, the silicon equivalent of methane (CH4) is silane (SiH4) which spontaneously burns on contact with oxygen. Silicon-to-silicon bonds are weaker, so making large compounds is difficult; smaller silicon compounds (e.g. SiO2) are often stable and unreactive.
That doesn't exclude other forms of silicon-based life, but chances are any life that is out there is carbon-based (though not necessarily the same as carbon-based life as we know it.)
This is roughly the insight that led to the Gaia hypothesis.
James Lovelock came up with the idea when he was hired to do some life-detectors for Viking. His reasoning went along the lines of:
- 'Life' can be taken to refer to a property of a system that allows it to stay in a non-equilibrium chemical state. (bear with me)
- 'life' achieves this by interaction with its environment.
- This interaction therefore leaves the environment in a non-equilibrium chemical state - for instance the Earth's atmosphere wouldn't contain 20% oxygen in the presence of lots of reducing agents unless something is actively producing fresh oxygen.
- therefore a nice test for life on, e.g., Mars is to look at the chemical composition of the atmosphere and see if it's chemically stable in isolation. Which, disappointingly perhaps, it is.
The nice bit about this approach, I thought, is that it uses a sufficiently generic definition of life that it avoids the carbon-centric issue. As long as you go along with his 'life' definition.The really hairy conceptual leap from there is the full-on Gaia hypothesis which roughly says that if 'life' is defined as above, then the whole Earth might be treatable as 'life' since it's out of chemical equilibrium. Take it or leave it - Lovelock refuses to refer to Gaia as other than a Hypothesis.
Good piece or Gordian-knot cutting by Lovelock, I thought.
TomV
It's interesting how they regard the Viking probes as something gigantic and powerful(and, importantly, successful) as opposed to recent probes that are smaller and cheaper. But I don't think that smaller and cheaper is worse... it obviously reduces the impact in case of a failure. Moreover, I would reason that the instruments used in modern probes are lighter, cheaper, sturdier, smaller, more powerful versions of the ones used on the big old probes. And they made significant advances in a ton of other areas, they know more about where to look for failures, they have more powerful computers, transcievers (DSN I guess) and so on... so why is the faster/cheaper/smaller approach showing itself as a failure?
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The Vikings were great spacecraft, there's no doubt about that, and the things that they discovered about Mars have been invaluble to planetary scientists over the past 25 years. However, the biology experiments on board the landers were just poorly thought out crap.
Prior to the Viking lander touchdowns, the only spacecraft to touch down on mars was the Soviet Mars 3 mission which landed safely in 1971, only to have its computer lock up 30 seconds later such that no data was ever sent from the surface (D'oh!). All that was known about the surface was that which could be learned from orbiting spacecraft -- geomorphology, aeronomy, and the like, but certainly no chemistry. By sending generic rudimentary biology experiments to Mars without any knowledge of the chemical environment they would be operating in NASA set itself up for the rash of uninterpretable data that those experiments returned. In addition, the biology experiments for Mars were designed by astronomers, not biologists, and their focus reflects this.
This failure has an important lesson to teach us about planetary exploration: don't get ahead of yourself. Before we can go searching for life, we need to do some basic science, learning about how a planet works before blindly looking for our version of life everywhere. Despite this, every NASA Mars press release mentions how Mars Odyssey, or MGS, or whatever new spacecraft will be looking for life, and that's too bad. At least the spacecraft themselves are better thought out, sent to address specific scientific problems and to teach us more about the planet Mars so that someday we CAN go look for life, but this time, we'll do it RIGHT.
Well, similarly, I see no reason why Mars wouldn't be teeming with life that's not carbon-based. A more definite answer to that question (and a nice exercise in interstellar navigation and precision landing) could be obtained by landing a probe right next to one of the Viking probes and seeing if some of the materials they were made of have been chewed at, or consumed, at a rate that's not explainable by natural phenomena.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
Hard to believe that it's already been 25 years since Leif Erickson and his Viking pals first came to North America.
Of course, they landed way up in what is now the Canadian great white north, so it is not too surprising that no signs of life were found.
Look at all the Mars stuff happening - Mars in the Media, and the immediately recent Mars opposition and new hubble shots, the killer success of the surveyor mission, the probes heading there right now, the rover mission and others.
NASA should be pimping the hell out of it. The existence of extraterrestrial life, even microbes, is a question of enormous magnitude. It is truly a question of biblical proportions. NASA's work on Mars could perhaps unravel one of the greatest mystery humans face. It will be very interesting to discover what is returned to Earth in the Mars soil samples returning to Earth in 2005. You can check out the strategy paper NASA issued on researching Mars exobiology.
The ultimate mystery!
The US government is afraid of finding out that life on Mars is more intelligent than life on Earth.
Phoenix
I am me. Insightful, isn't it?