Re: Mas sobre la vida en Marte

["Felix Ares" <fares@...>]

----------
> From raticulin
From: Santiago Arteaga <arteaga en cs.umd.edu>
> To: Escepticos. <escepticos en correo.dis.ulpgc.es>
> Subject: Mas sobre la vida en Marte
> Date: viernes 28 de marzo de 1997 23:02
> 
> 
>         No se si me estoy poniendo un poco pesado, pero es que           
> encuentro el tema interesante... otro analisis que "demuestra" que
> el meteorito nunca estuvo caliente desde el momento en que se formo,
> es mas, no estuvo demasiado caliente ni siquiera durante la caida...

La parte interior. N la superficial. ?No?
> 
>         Santi
> 
> 
> -------------------------------------
> 
> sci.space.news (moderated) #9605 (0 + 5 more)                            
 [1]
> From raticulin
From: Andrew Yee <ayee en nova.astro.utoronto.ca>
> [1] Caltech Geologists Find New Evidence That Martian Meteorite Could
Have
> +   Harbored Life (Forwarded)
> Date: Thu Mar 27 19:15:57 EST 1997
> 
> California Institute of Technology
> Pasadena, CA
> 
> Contact: Robert Tindol
> (818) 395-3631
> tindol en caltech.edu
> 
> Embargoed for Release at 4 p.m. Thursday, March 13, 1997
> 
> Caltech Geologists Find New Evidence That Martian Meteorite Could Have
> Harbored Life
> 
> PASADENA -- Geologists studying Martian meteorite ALH84001 have found new
> support for the possibility that the rock could once have harbored life.
> 
> Moreover, the conclusions of California Institute of Technology
researchers
> Joseph L. Kirschvink and Altair T. Maine, and McGill University's
Hojatollah
> Vali, also suggest that Mars had a substantial magnetic field early in
its
> history.
> 
> Finally, the new results suggest that any life on the rock existing when
it
> was ejected from Mars could have survived the trip to Earth.
> 
> In an article appearing in the March 13 issue of the journal Science, the
> researchers report that their findings have effectively resolved a
> controversy about the meteorite that has raged since evidence for Martian
> life was first presented in 1996. Even before this report, other
scientists
> suggested that the carbonate globules containing the possible Martian
> fossils had formed at temperatures far too hot for life to survive. All
> objects found on the meteorite, then, would have to be inorganic.
> 
> However, based on magnetic evidence, Kirschvink and his colleagues say
that
> the rock has certainly not been hotter than 350 degrees Celsius in the
past
> four billion years -- and probably has not been above the boiling point
of
> water. At these low temperatures, bacterial organisms could conceivably
> survive.
> 
> "Our research doesn't directly address the presence of life," says
> Kirschvink. "But if our results had gone the other way, the
high-temperature
> scenario would have been supported."
> 
> Kirschvink's team began their research on the meteorite by sawing a tiny
> sample in two and then determining the direction of the magnetic field
held
> by each. This work required the use of an ultrasensitive superconducting
> magnetometer system, housed in a unique, nonmagnetic clean lab facility.
The
> team's results showed that the sample in which the carbonate material was
> found had two magnetic directions -- one on each side of the fractures.
> 
> The distinct magnetic directions are critical to the findings, because
any
> weakly magnetized rock will reorient its magnetism to be aligned with the
> local field direction after it has been heated to high temperatures and
> cooled. If two such rock fragments are attached so that their magnetic
> directions are separate, but are then heated to a certain critical
> temperature, they will have a uniform direction.
> 
> The igneous rock (called pyroxenite) that makes up the bulk of the
meteorite
> contains small inclusions of magnetic iron sulfide minerals that will
> entirely realign their field directions at about 350 degrees C, and will
> partially align the field directions at much lower temperatures. Thus,
the
> researchers have concluded that the rock has never been heated
substantially
> since it last cooled some four billion years ago.
> 
> "We should have been able to detect even a brief heating event over 100
> degrees Celsius," Kirschvink says. "And we didn't."
> 
> These results also imply that Mars must have had a magnetic field similar
in
> strength to that of the present Earth when the rock last cooled. This is
> very important for the evolution of life, as the magnetic field will
protect
> the early atmosphere of a planet from being sputtered away into space by
the
> solar wind. Mars has since lost its strong magnetic field, and its
> atmosphere is nearly gone.
> 
> The fracture surfaces on the meteorite formed after it cooled, during an
> impact event on Mars that crushed the interior portion. The carbonate
> globules that contain putative evidence for life formed later on these
> fracture surfaces, and thus were never exposed to high temperatures, even
> during their ejection from the Martian surface nearly 15 million years
ago,
> presumably from another large asteroid or comet impact.
> 
> A further conclusion one can reach from Kirschvink's work is that the
inside
> of the meteorite never reached high temperatures when it entered Earth's
> atmosphere. This means, in effect, that any remaining life on the Martian
> meteorite could have survived the trip from Mars to Earth (which can take
as
> little as a year, according to some dynamic studies), and could have
ridden
> the meteorite down through the atmosphere by residing in the interior
cracks
> of the rock and been deposited safely on Earth.
> 
> "An implication of our study is that you could get life from Mars to
Earth
> periodically," Kirschvink says. "In fact, every major impact could do
it."
> 
> Kirschvink's suggested history of the rock is as follows:
> 
> The rock crystallized from an igneous melt some 4.5 billion years ago and
> spent about half a billion years on the primordial planet, being
subjected
> to a series of impact-related metamorphic events, which included
formation
> of the iron sulfide minerals.
> 
> After final cooling in the ancient Martian magnetic field about four
billion
> years ago, the rock would have had a single magnetic field direction.
> Following this, another impact crushed parts of the meteorite without
> heating it, and caused some of the grains in the interior to rotate
relative
> to each other. This led to a separation of their magnetic directions and
> produced a set of fracture cracks. Aqueous fluids later percolated
through
> these cracks, perhaps providing a substrate for the growth of Martian
> bacteria.
> 
> The rock then sat more or less undisturbed until a huge asteroid or comet
> smacked into Mars 15 million years ago. The rock wandered in space until
> about 13,000 years ago, when it fell on the Antarctic ice sheet.
> 
> 
> ---
> Andrew Yee
> ayee en nova.astro.utoronto.ca