Number 283, August 27, 1996 by Phillip F. Schewe and Ben Stein
POSSIBLE EVIDENCE FOR LIFE ON MARS has been reported by a team of scientists
studying an ancient rock found in Antarctica in 1984. Minerals in the rock
suggest that it came from Mars, where it was probably ejected by a giant
meteor impact event some millions of years ago. The rock itself, referred
to as ALH84001, was formed billions of years earlier, at a time when Mars
was warmer, wetter, and presumably more hospitable to life. What does the
rock tell us? Team leader, NASA scientist David McKay, says that several
strands of evidence, none of which is conclusive by itself, together point
toward the existence of ancient life forms on Mars. Microscopic inspection
of the rock shows, for example, the presence of organic molecules called
polycyclic aromatic hydrocarbons, which can come from the breakdown of
biological or non-biological sources. Also present in the sample were minerals
sometimes (but not always) associated with bacteria, namely carbonate granules,
magnetite, and pyrrhotite. Finally, sample images show 100-nm-sized ovoid
shapes which, McKay suggests, might be the fossilized creatures themselves.
Various outside scientists have been impressed by the data but skeptical
of a biological interpretation; they argue that non-biological causes could
account for all of the new findings. Meanwhile, government officials, including
President Clinton and NASA administrator Daniel Goldin, have expressed
great interest in this research, and proposals for new Mars-oriented projects
will doubtless receive great attention. (David S. McKay et al., Science,
16 August 1996.)
A TRANS-SOLAR SPACE CRAFT , one sallying forth beyond the outer planets,
would probably need the help of some novel propulsion system, such as the
use of sails which would enable the craft to reach high speeds by patiently
but effectively reflecting sunlight. Under study at NASA, the Thousand
Astronomical Unit mission would have a number of goals. One would be the
closeup study of the Kuiper Belt of asteroids (at a distance of about 40
AU). A second goal would be to locate the heliopause, the zone (at around
110-160 AU) where the outgoing solar wind is halted by the incoming interstellar
wind. Third, at a distance of several hundred AU, a 1-m telescope on the
craft could by triangulation accurately measure distances to stars across
much of the Milky Way. (Currently parallax measurements of distances are
limited by the baseline of the Earth's orbit to stars out to about 200
light years.) Another goal would be the use of the sun as a gravitational
lens for imaging distant objects behind the sun. Moreover, tiny modulations
in the return signal from the craft (3 days' transit for light over a path
of 500 AU) might encode information about passing gravity waves. (Astronomy,
August 1996.)
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