PLEASE NOTE:
*
Date sent: Fri, 23 May 1997 09:36:42 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: NEW SCIENTIST, 24 May 1997
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
WHO IS SHOOTING AT US? LOOKING FOR THE SMOKING CANNON
Everyone in danger of being targeted by terrorists needs to know
i) who the potential culprits are, ii) when they might strike,
iii) which weapons they might use, and iv) where they are based.
Once this vital information is obtained, effective measures can
then be worked out and implemented in order to save lifes.
Exactly the same holds true for the cosmic culprits which - in
the distant (and not so distant) past - have repeatedly
devastated
our habitat and terrorised its inhabitants. Currently, most
cosmic
crime watchers are looking out for approaching bullets targeted
at
us; but where is the smoking cannon which is firing these deadly
missiles at us?
New research suggest that (just like in billiard) stars smashing
into the Oort Cloud might kick start some comets out of their
orbits and right into the inner Solar System. I have attached the
latest research findings regarding these questions below. I have
also asked Robert Matthwes, science correspondent of the Sunday
Telegraph, to comment briefly about these findings since he has
done some research on this subject in the past.
Benny J Peiser
---------------------------------------------------------------
from: NEW SCIENTIST, 24 May 1997, p. 17
DOOM STAR MAY BE HEADING OUR WAY
by Hazel Muir
A star in the constellation Ophiuchus may be on collision course
with the Oort Cloud, the region on the outskirts of the Solar
System containing thousands of millions of comets. If it hits the
cloud, possibly in about a million years, the star will send
comets
plummeting towards the Sun and so put Earth at risk.
The star is a red dwarf known as Gliese 710. It is more than
100 000 times as massive as the Earth and is moving towards us at
14 kilometres per second.
A team led by Robert Preston and Joan Garcia Sanchez of the Jet
Propulsion Laboratory in Pasadena, California, made the discovery
using data from the European Space Agency's Hipparcos satellite,
which can pinpoint stars with an accuracy of half a millionth of
a
degree. By measuring how the positions of stars changed over
time,
the team picked out around 1200 stars that moved sideways least.
If
they are moving, they must be heading towards the Earth or away
from it.
The researchers then used data from ground-based telescopes to
measure the Doppler shifts in the stars' spectral lines, which
show
how fast the star is moving towards or away from us. Along with
distance measurements for the stars, again from Hipparcos, this
told the astronomers whether the stars will one day pass our way.
At last week's Hipparcus symposium in Venice, the team announced
that eight stars look set to come within about 5 light years of
the
Sun within the next million years. In just 10,000 years, a red
dwarf called Barnard's Star in the constellation Ophiuchus will
be
closer to the Solar System that the 4.3 light years that now
separates us from Proxima Centauri, our current nearest
neighbour.
The stellar passers-by may spell trouble for the Earth, Preston
adds. Gravitational tugs from the eight stars will disturb the
Oort
Cloud, which extends far beyond the outer planets. This could
nudge
some comets out of their orbits and send them tumbling towards
the
Sun, making a comet strike on Earth - possibly causing mass
extinctions - more likely.
Gliese 710, another Ophiuchus red dwarf currently 63 light years
away, could be most dangerous of all. This star seems to be on
course for a direct hit on the Oort Cloud. "If you believe
that
data we have, it will strike the Oort Cloud in around a million
years," says Preston. "It would certainly throw lots of
comets
inward."
One factor not taken into account, adds Preston, is the
possibility
that stars in the study have a companion that is too faint to be
visible from Earth. In that case, the visible star's motion would
include a contribution from its orbital speed, and the
predictions
about its destinantion will be wrong.
"As Preston says, one must be a little careful about these
results," warns Hal Weaver, an expert on comets at John
Hopkins
University in Baltimore. But he admits they are intriguing.
"They
may provide the 'smoking gun' that allows us to quantify this
process,", he says.
Preston is also studying stars heading away from Earth, having
made
a close flyby long ago. He says it might one day be possible to
find a star that unleashed the comet that may have wiped out the
dinosaurs. "Fossils tell us of past disasters," he
says. "We hope
to identify culprits among stars now hurrying away from the
scene."
===================================================================
from: Robert Matthews
Thanks for the chance to comment on the new findings.
I guess the thing that surprises me about the story is that they
have focused in on an event that - if it occurs at all - will
take
place ~ 1 million years from now.
Some years ago, I looked at the implications of the pre-Hipparcos
proper motion/doppler motion/parallax data for nearby stars on
the
perturbation of the Oort Cloud (see QJRAS vol 35 p 1-9 1994). It
turns out that there are five stars that will all come within 1
pc
of the Solar System as "soon" as the next 44,000 years,
with the
Alpha Cen A/B system being massive enough to affect the Oort
Cloud.
Indeed, a simple back-of-the-envelope estimate based on the
inverse
square law suggests the perturbations may have already begun.
That said, it would take ~ O(10^7) years for the perturbed comets
to wend their weary way into the inner Solar System, so perhaps a
really close approach by this (or some as-yet undiscovered) red
dwarf star will give the Oort Cloud a really good stir, and fire
stuff our way a lot sooner.
I think we can leave our hard hats on the peg for a bit longer
yet,
though.
Robert Matthews
*
Date sent: Fri, 23 May 1997 08:55:56 -0400 (EDT)
From: Benny J Peiser <B.J.PEISER@livjm.ac.uk>
Subject: Re: sgf-info
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
from Duncan Steel <dis@a011.aone.net.au>
SPACEGUARD FOUNDATION INFO
================================================================
Any recipients of this message who are interested in NEOs and the
work of The Spaceguard Foundation, and would like to be put on
the
SGF email distribution list for future news summary messages such
as that recently distributed, may do so by sending a message
saying
SUBSCRIBE on the "subject" line (there is no
subscription fee!) to:
sgf-info@brera.mi.astro.it
===============================================================
Dr Duncan Steel
dis@a011.aone.net.au
Spaceguard Australia P/L
P.O. Box 3303
Rundle Mall
Adelaide, SA 5000
AUSTRALIA
Phone: +61 8 8232 6133
Fax: +61 8 8232 6103