[meteorite-list] Closing in on Near Earth Objects (Comet C/1976 D1 Bradfield)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:31 2004
Message-ID: <200302271725.JAA13773_at_zagami.jpl.nasa.gov>

http://space.com/searchforlife/seti_neo_030227.html

Closing in on Near Earth Objects
By Peter Jenniskens
Principal Investigator, SETI Institute
27 February 2003

While many astrobiologists follow the water, some are following the dirt.
SETI Institute astronomer Peter Jenniskens is hot on the trail of an elusive
comet whose last visit was in 1976, and whose lingering debris may help
scientists warn us about the imminent return of a mysterious class of Near
Earth Objects (NEOs).

We believe that prediction models tested on the Leonid showers can also be
used to predict when these dust trails are steered in the Earth's path by
the gravitational influence of planets, and we are about to travel to South
Africa to observe a new meteor shower thus predicted.

When Comet C/1976 D1 Bradfield passed uncomfortably close to Earth's orbit
on its sweep through the inner solar system, it was a faint +8 magnitude
binocular object in the Southern hemisphere. Its passing was poorly
communicated by observers who lacked today's connectivity. The best
determination astronomers can make of the comet orbit places a return visit
about 1,000 years into the future.

Before we all heave a sigh of relief, thousands of such comets remain
undetected. A similarly sized comet in such a fast moving orbit in another
solar system may long ago have wiped out a civilization before it could be
detected in our SETI searches.

The key to finding the approaching comets is to recognize the new meteor
shower when Earth hits its dust trail.

In a paper soon to be published in the journal Icarus, Finnish colleague
Esko Lyytinen and I predict a number of such showers, first on the list is
the trail of C/1976 D1.

Joining members of the Astronomical Society of South Africa - Meteor section
just outside of Cape Town in South Africa, we hope to witness the meteor
outburst, which peaks at 21:54 GMT (give or take 20 minutes) on March 1 and
will last for approximately half an hour (14 minutes, full-width at
half-maximum). The shower's radiant will be in the southern constellation
Tucana, the Toucan, and will become known as the "Beta Tucanids."

The dust trails stretch far in front of and behind the comet, but that only
when the planets cooperate can we observe a meteor shower. Jupiter and the
other large outer planets in our solar system tug upon the path of comet
dust particles. The tugging perturbs the orbits of the dust trails such that
they are moved into Earth's path about once or twice every sixty years,
through the combined effects of Jupiter and Saturn planets with 12 and
30-year rotation periods.

A successful observation will help read other such showers for useful
information regarding their parent comet. These encounters offer a chance to
study the comet's debris and infer properties such as comet size, surface
composition, and orbit. Repeated observations can in principal reveal
whether a long period comet is approaching us, or returning back to the dark
frontier of the solar system far beyond the outer planets.

The viewing location is not ideal-unfortunately, the best seats in the house
are found in hard to get to locations in Antarctica. Are we disappointed
that we may never see this elusive comet again? Not at all. What's left
behind after the comet has departed can provide as important information and
we're learning to read the playbill.
Received on Thu 27 Feb 2003 12:25:30 PM PST