of the meteorites—ALH84001—that proved to come from Mars. It looked in no way extraordinary, resembling a brownish potato. When the microchemistry was examined, certain species of organic molecules were discovered, chiefly polycyclic aromatic hydrocarbons (PAHs). These are not in themselves all that remarkable. Structurally they resemble the hexagonal patterns on bathroom tiles with a carbon atom at each vertex. PAHs are known in ordinary meteorites, in interstellar grains, and are suspected on Jupiter and Titan. They do not by any means indicate life. But thePAHs were arranged so that there were more of them deeper in the Antarctic meteorite, suggesting that this was not contamination from Earthly rocks (or automobile exhaust), but intrinsic to the meteorite. Still, PAHs in uncontaminated meteorites do not indicate life. Other minerals sometimes associated with life on Earth were also found. But the most provocative result was the discovery of what some scientists are calling nanofossils—tiny spheres attached one to another, like very small bacterial colonies on Earth. But can we be sure that there are no terrestrial or Martian minerals that have a similar form? Is the evidence adequate? For years I’ve been stressing with regard to UFOs that extraordinary claims require extraordinary evidence. The evidence for life on Mars is not yet extraordinary enough.
But it’s a start. It points us to other parts of this particular Martian meteorite. It guides us to other Martian meteorites. It suggests the search for quite different meteorites in the Antarctic ice field. It hints that we search not just for other deeply buried rocks obtained from or on Mars, but for much shallower rocks. It urges upon us a reconsideration of the enigmatic results from the biology experiments on
Viking
, some of which were argued by a few scientists to indicate the presence of life. It suggests sending spacecraft missions to special locales on Mars which may have been the last to surrender their warmth and wetness. It opens up the entire field of Martian exobiology.
And if we are so lucky as to find even a simple microbe on Mars, we have the wonderful circumstance of two nearby planets, each with life on it in the same early epoch. True, maybe life was transported by meteorite impact from one world to another and does not indicate independent origins on each world. We should be able to check that by checking the organic chemistry and morphology of the life-forms uncovered. Maybe life arose on only one of these worlds, but evolved separately on both. Wethen would have an example of several billion years of independent evolution, a biological bonanza available in no other way.
And if we are most lucky, we will find really independent life-forms. Are they based on nucleic acids for their genetic coding? Are they based on proteins for their enzymatic catalysis? What genetic code do they use? Whatever the answers to these questions, the entire science of biology is the winner. And whatever the outcome, the implication is that life may be much more widespread than most scientists had thought.
In the next decade there are vigorous plans by many nations for robot orbiters, landers, roving vehicles, and subsurface penetrator spacecraft to be sent to Mars to lay the groundwork for answering these questions; and—maybe—in 2005 a robotic mission to return surface and subsurface samples from Mars to Earth.
2. Is Titan a Laboratory for the Origin of Life? Titan is the big moon of Saturn, an extraordinary world with an atmosphere ten times denser than the Earth’s and made mainly of nitrogen (as here) and methane (CH 4 ). The two U.S.
Voyager
spacecraft detected a number of simple organic molecules in the atmosphere of Titan—carbon-based compounds that have been implicated in the origin of life on Earth. This moon is surrounded by an opaque reddish haze layer, which has properties identical to a red-brown solid made in the laboratory when energy is
But it’s a start. It points us to other parts of this particular Martian meteorite. It guides us to other Martian meteorites. It suggests the search for quite different meteorites in the Antarctic ice field. It hints that we search not just for other deeply buried rocks obtained from or on Mars, but for much shallower rocks. It urges upon us a reconsideration of the enigmatic results from the biology experiments on
Viking
, some of which were argued by a few scientists to indicate the presence of life. It suggests sending spacecraft missions to special locales on Mars which may have been the last to surrender their warmth and wetness. It opens up the entire field of Martian exobiology.
And if we are so lucky as to find even a simple microbe on Mars, we have the wonderful circumstance of two nearby planets, each with life on it in the same early epoch. True, maybe life was transported by meteorite impact from one world to another and does not indicate independent origins on each world. We should be able to check that by checking the organic chemistry and morphology of the life-forms uncovered. Maybe life arose on only one of these worlds, but evolved separately on both. Wethen would have an example of several billion years of independent evolution, a biological bonanza available in no other way.
And if we are most lucky, we will find really independent life-forms. Are they based on nucleic acids for their genetic coding? Are they based on proteins for their enzymatic catalysis? What genetic code do they use? Whatever the answers to these questions, the entire science of biology is the winner. And whatever the outcome, the implication is that life may be much more widespread than most scientists had thought.
In the next decade there are vigorous plans by many nations for robot orbiters, landers, roving vehicles, and subsurface penetrator spacecraft to be sent to Mars to lay the groundwork for answering these questions; and—maybe—in 2005 a robotic mission to return surface and subsurface samples from Mars to Earth.
2. Is Titan a Laboratory for the Origin of Life? Titan is the big moon of Saturn, an extraordinary world with an atmosphere ten times denser than the Earth’s and made mainly of nitrogen (as here) and methane (CH 4 ). The two U.S.
Voyager
spacecraft detected a number of simple organic molecules in the atmosphere of Titan—carbon-based compounds that have been implicated in the origin of life on Earth. This moon is surrounded by an opaque reddish haze layer, which has properties identical to a red-brown solid made in the laboratory when energy is
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