ALH84001, a controversial meteorite that
was found by a team of meteorite hunters
from the ANSMET
(Antarctic Search for Meteorites)
program, in December 1984.
It weighted almost 5 pounds, and
was shaped like a large potato,
approximately 6 x 4 x 3 inches.
The rock was originally formed from
molten lava, possibly from an ancient
martian volcano. Its planetary
origin was determined from trace gases
found inside it, which match Mars'
atmosphere perfectly. It must have
left Mars from the explosion of
a meteor impact, as no volcanic
eruption could be violent enough to
throw it away fast enough for it
to leave Mars' gravitational field.
(Mars' escape velocity is no less
than 5,000 kilometers (11,000
miles) per second.) It spent the
next 16 million years floating through
space, before succumbing to Earth's
gravitational pull approximately 13,000
years ago.
The reason for the controversy around
ALH84001 is the claims that it contains
evidence of biological life. The first
theories arose in 1996, when small
globules of carbonate minerals
were found, and these must have been
formed by liquid water. Futhermore,
the mineral deposits have been shown
to be much older than than life on
Earth, perhaps as old as 3,6 billion
years old.
Additionally, Doctor David McKay
and his colleagues discovered ropy
tubular structures in the
mineral globules, which they
interpreted as possible fossil
bacteria. However, it has later
been discovered that these bacteria
could have infiltrated the rock while
it was in Antarctica.
Recently, however, renewed evidence
of ancient life on Mars were
presented. NASA researchers
found that the magnetite crystals
embedded in the meteorite are
arranged in long chains, which
they claim could only have been formed
by once-living organisms. Otherwise the
magnetic "chain" would have collapsed
into an iron clump.
Their results are reported in the
February 27 Proceedings of the
National Academy of Sciences.
The full text of their research paper
can be found online:
http://amesnews.arc.nasa.gov/releases/2001/01images/magneticbacteria/bacteria.html