[meteorite-list] Meteorites: Friend or Foe? (Monica Grady Interview - Part 2)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Nov 9 12:31:56 2006
Message-ID: <200611091731.JAA12088_at_zagami.jpl.nasa.gov>

http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=2139

Meteorites: Friend or Foe?
Astrobiology Magazine
November 9, 2006

Summary: In this interview, Monica Grady discusses the varieties
of dust and meteorites that have fallen to Earth, and explains what they
tell us about the history of the solar system and its potential for life.


Meteorites: Friend or Foe?

Monica Grady, a professor of planetary and space science at the Open
University in the UK, is one of the world's meteorite experts.
Monica Grady, meteorite expert.

In addition to studying the finer details of these rocks from space that
fall to Earth -- such as learning the geochemistry of meteorites
originating from Mars -- she is also interested in the broader
implications of her findings, and uses her research to learn more about
the possibility of life elsewhere in the universe.

In part two of this interview with Astrobiology Magazine, Grady
discusses the varieties of dust and meteorites that have fallen to
Earth, and explains what they tell us about the history of the solar
system and its potential for life.

Read part one <http://www.astrobio.net/news/article2136.html> of this
interview.

------------------------------------------------------------------------
Astrobiology Magazine (AM): What is the importance of studying different
meteorites?

Monica Grady (MG): Looking at meteorites that come from different
asteroids, we can see that some meteorites have been altered and some
haven't. Some have been melted and differentiated, while others are
still primitive and full of carbon. Why? Because there's a spectrum of
compositions within the asteroid belt, and a spectrum of
different parent bodies that have accumulated and broken apart in the
asteroid belt.

The more meteorites we look at, the more parent bodies we think there
were. It gives you a more complete picture of the solar system and the
heterogeneity of the material that we came from. The turbulent cloud of
gas and dust that was the solar nebula managed to produce some
things that are full of carbon, and others that aren't full of carbon.

One of the projects I'm working on is Stardust, which now has primitive
dust that was collected in a comet. The dust hasn't evolved in the last
4.5 billion years. The amazing thing about the particles collected by
the Stardust mission is that some of the grains seem to be rich in
calcium and aluminum, which are refractory elements in grains that
formed close to the sun. But we expected comets to only have grains that
formed far away from the sun. So Stardust puts a different spin on our
knowledge of how the solar system formed.

I've been studying dust for a long time, looking at infrared
spectroscopy observations made by astronomers on planet formation, star
formation, and the presence of disks around stars, and linking that with
what we see on Earth -- in terms of interplanetary and interstellar dust
which coagulated to form asteroids and meteorites. I'm interested in the
process from planet formation right through to meteorites arriving on
the Earth.

Infrared spectroscopy is a way you can follow that, because you can make
measurements on Earth and with telescopes. I've also shifted wavelengths
and gone from infrared to the visible and ultraviolet regions to try and
make sense of the spectra and look at the spectral signatures of the
materials that are coming in on dust grains, meteorites, and star dust
particles to see what that can tell us about the materials. Ultraviolet
visible spectroscopy is sensitive to mineral composition and also the
presence or absence of organics.

AM:Are you looking for the organics that may have played a role in the
origin of life?

MG: Just the precursors that might be within cometary particles. But I
am looking for the conditions that we think could have led to the origin
of life on Mars. My work with martian meteorites has led to my
involvement in a project to develop a water sensor for Mars. Not just to
look for signs that water's been there in terms of channels or minerals,
but actually to look for liquid water, to see if it's there as a film on
minerals. I'm working with teams from Norway and Portugal to build a
sensor. We're hoping to persuade the European Space Agency that this
small sensor can be integrated with its other density, porosity and the
permittivity sensors, fitting them all on ExoMars.

AM: So are comets and meteorites our friends or our foes?

MG: They're both! They're friend and foe. They can be foe if they are
too big. Something on the 1 to 10 kilometer scale would be catastrophic.
But certainly they were friendly in the past, bringing water and the
organic building blocks of life. And they can be our friends today,
because as long as a meteorite doesn't kill anybody or destroy a house
when it falls, then it stimulates the public's interest in meteorites.

AM: Plus, they're our friends because of the changes they've helped to
bring about in evolution?

MG: The K-T boundary is what people always point to as being caused by
a 10 kilometer-sized meteorite. The evolutionary consequences of that
were enormous, setting in motion a whole chain of environmental
changes -- wildly swinging fluctuations in temperature of the
atmosphere, the opacity of the atmosphere, the acidity of the surface
waters, and changes which led eventually to the extinction of many
species. But it also allowed evolutionary niches to be inhabited and
expanded by other species. Change in the balance from vertebrates to
mammals occurred at the K-T boundary.

AM:How often do incoming meteorites arrive on the Earth today?

MG: Meteorites come all the time, and tiny cosmic dust arrives by the
ton every year. I think it's somewhere between 40 to 60 thousand tons,
but estimates vary. So each year we receive a huge amount of material:
several thousand tons of dust, about a thousand football-sized
meteorites, and maybe one washing machine-sized meteorite.

AM:And yet we're not seeing these things raining down on us through the
atmosphere constantly. Are they getting burned up?

MG: Well, you don't notice it because it's mostly dust. We can pick it
up in the stratosphere, we can collect it in Antarctica, or we can
dredge it up from the ocean floor.

AM: How often is that done? How many people are studying and collecting
this cosmic dust?

MG: The Antarctic Ice Program has been in place for 20 or so years now.
I don't know that they are collecting any stratospheric dust at the
moment, but NASA has made such samples available internationally.

AM:Are you referring to the Don Brownlee experiments where he
essentially waved fly paper around in the stratosphere to collect dust?

MG: Yes.

AM:What about Chandra Wickramasinghe's sterile collection from a balloon
and his interpretation of the biogenic materials as originating from
cosmic dust?

MG: I think the experiments he's been doing with the balloons are
fascinating. If he has managed to collect some cosmic dust, it would be
great. I have asked for some to analyze, but I don't know whether I'll
get some or not.

But I have no great belief that this is biological material that has
come from beyond Earth. It could well have come from beyond the
stratosphere; it could be bits and pieces from shuttle astronauts or
satellites. But I don't believe it's biological material that has
traveled from many light years away.

AM: If Panspermia -- life being delivered within or beyond our solar
system -- happened in the past, why should it not continue to happen now?

MG: Yes, but Chandra and Max Wallace are specifically talking about
bacteria. I'm not a believer that Panspermia happened in the past, in the
sense of bringing bacteria to the Earth. I'm happy with the idea that
carbon dioxide and water were brought to the Earth in the past. I
believe in Panspermia to that extent, but not the extent of bringing
actual living organisms.
Received on Thu 09 Nov 2006 12:31:48 PM PST