[meteorite-list] Astronomers Searching For Asteroids Near The Sun

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:51 2004
Message-ID: <200205231749.KAA01230_at_zagami.jpl.nasa.gov>

http://www.guardian.co.uk/science/story/0,3605,720087,00.html

Vulan Fires Up
The Guardian (United Kingdom)
May 23, 2002

Astronomers are racing to identify what may be a cloud of tiny planets near
the sun, says Duncan Steel

Over the past several weeks, you've had a chance to see all the bright
planets lined up in the north-western sky, after sunset. Venus, Jupiter,
Saturn and Mars are easy to spot.

Mercury is less straightforward because it's faint and low in the sky.
Because of its proximity to the sun, it can be difficult to find in the
twilight.

Now think of a celestial rock far smaller, fainter and closer to the sun.
Even with the best telescope you'd have difficulty detecting it, and you
can't point the Hubble space telescope that near because of the potential
damage from the intense light.

Nevertheless, astronomers think there may be a cloud of small planets (or
asteroids) close to the sun, and they're in a race to detect them first. The
theory is simple. Everywhere we look in the solar system, there are
asteroids and comets. There are relatively sparse numbers on planet-crossing
orbits, because they either hit the planet concerned, or get thrown on to
different paths by the planet's gravity. So, where might asteroids safely
roam?

One region is the well-known main belt, between Mars and Jupiter. Another is
the trans-Neptunian zone, its first inhabitant (not counting Pluto) having
been found a decade ago, joined by hundreds since. Another feasible location
is within Mercury's orbit. That planet has a low mass, producing only weak
perturbations, and so any asteroid on a near-circular orbit interior to
Mercury might be safe.

Pretty hot, but safe. This suspicion was confirmed three years ago when
numerical experiments by Wyn Evans (University of Oxford) and Serge
Tabachnik (now at Princeton University) showed that this region represents a
dynamically stable zone. They employed dozens of personal computers, working
non-stop for four months, to get their results. This near-sun region might
contain hundreds, or even thousands, of so-called vulcanoids.

The term derives from Vulcan, the Roman god of fire and metalworking, a
mythological blacksmith hammering away deep beneath a volcano, causing it to
rumble and erupt. This is not a new idea. In the 19th century, astronomers
went Vulcan crazy, due to the suggestion that at least one undiscovered
planet might exist close to the sun. The cause of their expectation was the
apparently anomalous movement of Mercury, seemingly tugged along by an
unseen mass.

It was only when Einstein's theory of relativity was published in 1915 that
physicists could show that Mercury's "anomaly" was actually because Newton's
gravitational theory was incomplete.

Another consideration is how such an asteroid population might grind itself
away to nothingness through mutual collisions. Sunward of Mercury is only a
tiny volume of space, and bodies orbiting there travel at very high speed,
only taking a few weeks to complete a lap of the sun. Impacts would
therefore be at hypervelocity, and destructive.

Vulcanoids would need to be in near-circular orbits, each avoiding the
others, if they were to have survived the billions of years since the solar
system formed. If they exist, how could they be found, perennially in the
solar glare?

Recent attempts to detect them have made use of images returned by the
coronagraph on the Solar and Heliospheric Observatory (Soho) satellite,
which produces an artificial eclipse so as to block out the photosphere and
lower corona. Comets are frequently found near the sun in Soho images,
largely by ama teur astronomers. Bare, rocky (or maybe metallic) asteroids
are much dimmer, though. The limiting sensitivity of the Soho instrument
corresponds to a vulcanoid around 60km in diameter. No such behemoth has
been found.

Alternatively, one might imagine a ground-based search for vulcanoids just
after the sun has set, or before it rises. But it seems to be an impossible
task: the vulcanoids would need to be larger than about 20km, dependent on
their reflectivities, to be detectable from a mountaintop observatory. Few
targets that large are expected. The cloud, if it exists, would comprise
mostly smaller asteroids. Spacecraft travelling into the inner solar system
are a possibility, and the European Space Agency's Bepi Colombo probe to
Mercury may carry a small asteroid camera, but that mission is almost a
decade away.

The way around this problem, at far lesser expense, involves heading just to
the fringes of space, using a high-flying aircraft. At its Dryden Flight
Research Center (near Edwards in California, where the space shuttle lands)
Nasa stations a small fleet of high-altitude jet planes. One is an F18
Hornet.

Space researchers at the Southwest Research Institute's Department of Space
Studies in Boulder, Colorado, realised that this might provide a valuable
opportunity. They had developed a small camera used for planetary and
cometary observations on several space shuttle missions in the late 1990s.
Now it has been mounted in the cockpit of Nasa's F18, and is used to chase
asteroids.

Vulcanoids, in fact. Flying at an altitude of near 15km (50,000 feet), most
of the detrimental effects of the Earth's atmosphere can be avoided. Close
to the horizon, where one needs to look, the sky is darker, and clearer.

Two preliminary observational programmes have been conducted, and another is
due in September (searches close to the times of the equinoxes are
advantageous in terms of the viewing geometry). No vulcanoids have been
detected, but that in itself is a useful result, allowing limits to be
placed on how many exist. Some believe there is a Vulcan: it's the home
planet of Mr Spock, Leonard Nimoy's character in Star Trek. His planet is a
member of a planetary system circuiting the nearby star Epsilon Eridani. Two
years ago, astronomers found at least one planet in orbit around it.
Unfortunately, it seems to be a Jupiter-sized object, presumably a gas giant
unlikely to support life, at least humanoid life like Mr Spock. We must be
content with the fact that of all the thousands of asteroids named and
numbered, there is one called "2309 Mr. Spock".

Finally, another link between asteroids and Vulcan. In 1995 I attended a
conference entitled Beginning the Spaceguard Survey, about our search for
asteroids that might impact the Earth, creating a crash to make even the
mythological Vulcan envious. The conference was held on his island, Vulcano,
off the north-east coast of Sicily, and the origin of our word for
volcanoes.

- Duncan Steel will be talking about hazardous asteroids at the Cheltenham
Science Festival on Sunday. The Cheltenham Festival of Science runs from
22-26 May. Visit or call the box office on 01242 227979
Received on Thu 23 May 2002 01:49:45 PM PDT