|
Astrobiology
| |
| Astrobiology
is the study of life in space. More precisely it is the study of
the origin, evolution and distribution of life in the Universe.
As a subject it is highly speculative. We know there is life on
Earth, but is there any life anywhere else ? This quandary can be
summed up in the diagram below which describes the possibilities
for the distribution of life: |
|
|
|
The 5 possibilities
in the above figure are all valid, we simply do not know which
is correct. The idea is that there may be life on Earth and also
perhaps in space. By having the circles for each of different
sizes the relative amounts of life in each place are being expressed
(big circle = relatively a lot of life, little circle = relatively
little life). Finally, if the circles overlap, it is being suggested
that life might mix between the two locations, i.e. life might
naturally travel through space to or from the Earth.
The idea of
life naturally travelling through space may seem strange. But
it is a scientific hypothesis of long standing. It has a name
- Panspermia. Several versions exist. Pure Panspermia has life
originating in space itself and travelling to planets. Other views
hold that comets somehow carry life and that whenever our planet
passes through a comet's tail, the dust and debris that falls
into the atmosphere can carry this life. Rocky (or litho-) Panspermia
holds that life starts on one planet, is then ejected in to space
(perhaps as ejecta from the giant impact of an asteroid or comet)
and then falls on a meteorite onto a new planetary surface. Certainly
debris from space does rain down upon the Earth. Rocks of Lunar
and Martian origin have been recovered on Earth as meteorites.
Claims have indeed been made that one such Martian meteorite contained
possible fossil bacteria.
So speculation
about topics like Panspermia is not as silly as it might sound
to some. But the scientific study of an idea requires more than
just speculation.
|
| |
| Research
into Panspermia at Kent |
|
We have been
considering the steps involved in rocky Panspermia. A lump of
rock would have to contain bacteria. Not an implausible assumption
(if there is life on the planet in the first place !). A giant
object then falls at high speed (many km s-1) from space causing
a massive impact, leaving a crater on the landscape, maybe kilometres
across. This sounds dramatic, but it happens. The Moon and Mars
are peppered with impact craters. Even the Earth carries the scars
of such impacts. As part of the impact process rocks will be ejected
away from the impact site at high speed, maybe even at escape
velocity (i.e. fast enough to leave the planet and not return).
Such a rock would then travel through space and could eventually
hit another planet (again at high speed).
In Canterbury,
we have been investigating what happens to bacteria carried in
projectiles accelerated to speeds of 5 km s-1 which
then hit targets. We use a two-stage
light gas gun to accelerate the projectiles.
|
| |
| Results |
| In
our preliminary work, we failed to recover any viable bacteria from
the impact site. However, more recently we have at last been successful.
In Burchell et al. 2002 we describe how we successfully recovered
viable bacteria after an impact at 5 km s-1. |
| |
| The
Future |
| Having
achieved this success, we are now determining survival rates as
a function of impact speed, for different target types, for spores
as well as bacteria, etc. We are also improving techniques for recovery/identification
of bacteria at the impact site. |
| |
| Who
? |
| Work
at Kent is led by Prof.
Mark Burchell in the Centre for Astrophysics and Planetary Sciences,
and Dr. Alan
Bunch in the Department of BioSciences, assisted by research
students: Jo Mann is currently in the final year of her PhD on this
topic (funded by the University Alumni fund) and James Galloway
has completed an MSc on the work. |
| |
| PUBLICATIONS: |
|
Burchell,
M.J., Cole, M.J., McDonnell, J.A.M., and Zarnecki, J.C. 1999.
Hypervelocity impact studies using the 2 MV Van de Graaff accelerator
and two-stage light gas gun of the University of Kent at Canterbury.
Meas. Sci. Technol. 10, 41-50.
Burchell M.J.,
Shrine N.R.G, Bunch A.W. and Zarnecki, J.C., 2000. Exobiology:
Laboratory tests of the impact related aspects of panspermia.
In: Gilmour, I., and Koeberl, C. (eds.) Impacts and the Early
Earth pub. Springer pp 1-26.
Burchell M.J.,
et al., 2001. Laboratory Investigations of the Survivability of
Bacteria in Hypervelocity Impacts. Advances in Space Research
28,707-712.
Burchell M.J.,
Mann J., Bunch A.W. and Brandão P.F.B., 2002. Survivability of
Bacteria in Hypervelocity Impact. Icarus 154, 545 - 547.
|
|
