[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Monica Grady: Visitors from outer space (4 of 4)

Ron wrote:

> Dr. Monica Grady is one of the world's top exobiologists - meaning
> she studies life outside Earth. She is also the meteor curator at
> London's Natural History Museum. In this interview, she tells
> EcoWatch reporter Chris Jeavens the biggest finds are sometimes
> right under our noses.

Focus: Visitors From Outer Space (Astronomy Now, November 1997, pp.
45-47):

Around four particles of extraterrestrial material lands on Earth per
hour, per square kilometre. Much can be learned from these meteorites
(by Monica Grady).

Meteorites ftom other planets

In addition to meteorites from the asteroid belt, there are currently
nineteen meteorites from the Moon(*) in the world's collections. Lunar
meteorites can be compared directly with samples brought to Earth by the
Apollo and Luna missions between 1969 and 1976.
The surface of the Moon is covered in craters caused by impacting
bodies. If the impactor arrives with the requisite velocity and on a
favourable trajectory, then the force of the impacts will be sufficient
to eject material from the surface with a velocity great enough to
overcome the Moon's gravity and be launched into space. Subsequently the
material goes into orbit in interplanetary space, and some of it
eventually lands on the Earth as a meteorite. In the same way, rocks
have come to us from Mars: we have twelve meteorites that have been
ejected by impact from the surface of our neighbouring planet (**).
How do the Martian meteorites differ from 'ordinary' meteorites from the
asteroid belt? And how is it known that they come from Mars?
Firstly, the Martian meteorites do not have the ancient age of 4600
million years shown by other meteorites: they might be as young as 180
million years. In other words, they crystallised from a planetary-sized
body that was still molten inside, long after the formation of the
asteroids, so they cannot come from the asteroid belt.
In order to confirm the Martian origin, this group of meteorites must be
compared with the planet Mars itself. Much is known about the
composition of Mars' atmosphere and surface from data from two NASA
missions to the planet: the Viking probes of 1976, and the recent
Pathfinder landing. In 1979, the eight kilogram stone meteorite
EETA79001 was found in the Elephant Moraine region of Victoria Land in
Antarctica. EETA79001 contains numerous dark patches of glass,
distributed throughout the meteorite in pockets. This glass was made by
localised melting during the event when the rock was thrown off its
parent's surface by an impact. When the glass is analysed in the
laboratory, trapped gases are released. These gases have the same
composition as Mars' atmosphere, which demonstrate the meteorite's
Martian origin.
The study of Martian meteorites has been given a great deal of publicity
since the summer of 1996, when a second Antarctic Martian meteorite
achieved notoriety. ALH 84001 is a 1.9 kg basalt that contains patches
of carbonate throughout its entire mass. The carbonates are orange, and
rimmed with light and dark layers, indicating a change in composition of
the mineral grains, brought about by changes in the conditions (fluid
composition, ambient temperature, acidity) under which they were
deposited. The carbon and oxygen in the carbonates indicate that the
grains were produced at low temperatures from Martian atmospheric carbon
dioxide dissolved in water, probably just below the surface of Mars,
when water circulated through it.
Scientists from NASA think they might have found evidence for fossilised
Martian bacteria inside these carbonate patches, showing that life might
have existed on another planet, although the claim is controversial and
disputed by many other scientists. Even if the current evidence for past
life on Mars is found to be incorrect, it is clear from the study of
meteorites from Mars that we can learn about events that have taken
place on our neighbouring planet, when it had a thicker atmosphere and
could support running water.

(*) Calcalong Creek - Dar al Gani 262 - Dar al Gani 400 - ALHA81005 -
EET 87521 - EET 96008 - MAC 88104 - MAC 88105 - QUE 93069 - QUE 94269 -
QUE 94281 - Asuka 881757 - Yamato 791197 - Yamato 793169 - Yamato 793274
- Yamato 82192 - Yamato 86032.

(**) Meanwhile there are 14:

Yamato 793605 - ALH 84001 - ALHA77005 - EETA79001 - LEW 88516 -
QUE 94201 - Chassigny - Governador Valadares - Lafayette - Nakhla -
Shergotty - Zagami - Dar al Gani 489 - Dar al Gani 476

The importance of meteorites

Meteorites are a diverse set of extraterrestrial materials, representing
planetary and solar system material in its many forms. By studying
meteorites, processes that have taken place as our Solar System evolved
can be studied. We can also learn about the evolution of other stars
that contributed to our solar neighbourhood. Without meteorites and
comets, it is likely that life would not have evolved on Earth; studying
Martian meteorites might possibly allow us to study the primitive
beginnings of life on another planet. But meteorites are not only
associated with the seeds of life: they are also instrumental in
influencing evolutionary pathways, as a consequence of catastrophic
impact and associated environmental changes.

Monica M. Grady is a research specialist in meteorites in the
Department of Mineralogy at the Natural History Museum.


Best wishes,

Bernd

----------
Archives located at:
http://www.meteoritecentral.com/list_best.html

For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------