[meteorite-list] Hawaii Astronomers Keep Tabs on Asteroid Apophis

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 10 Mar 2011 14:43:30 -0800 (PST)
Message-ID: <201103102243.p2AMhUQf019747_at_zagami.jpl.nasa.gov>

March 9, 2011

Media Contact:
Ms. Louise Good
+1 808-956-9403
good at ifa.hawaii.edu

Science Contact:
Dr. David Tholen
+1 808-956-6930
tholen at ifa.hawaii.edu

Text & Image:
http://www.ifa.hawaii.edu/info/press-releases/Apophis2011Jan/

HAWAII ASTRONOMERS KEEP TABS ON ASTEROID APOPHIS

On January 31 University of Hawaii at Manoa astronomers used the UH
2.2-meter telescope on Mauna Kea to take the first new images in over
three years of the potentially dangerous near-Earth asteroid Apophis
as it emerged from behind the Sun.

The object became famous in late 2004, when it appeared to have a 1 in
37 chance of colliding with Earth in 2029, but additional data
eventually ruled out that possibility.

However, on April 13, 2029, the asteroid, which has a 900-foot (270-m)
diameter, will come closer to Earth than the geosynchronous
communications satellites that orbit Earth at an altitude of about
22,000 miles (36,000 km). Apophis will then be briefly visible to the
naked eye as a fast-moving starlike object.

This close encounter with Earth will significantly change Apophis's
orbit, which could lead to a collision with Earth later this century.
For that reason, astronomers have been eager to obtain new data to
further refine the details of the 2029 encounter.

Astronomer David Tholen, one of the co-discoverers of Apophis, and
graduate students Marco Micheli and Garrett Elliott obtained the new
images when the asteroid was less than 44 degrees from the Sun and
about a million times fainter than the faintest star that the average
human eye can see without optical aid.

"The superb observing conditions that are possible on Mauna Kea made
the observations relatively easy," said Tholen.

Astronomers measure the position of an asteroid by comparing with the
known positions of stars that appear in the same image as the
asteroid. As a result, any tiny error in the catalog of star
positions, due for example to the very slow motions of the stars
around the center of our Milky Way galaxy, can affect the measurement
of the position of the asteroid.

"We will need to repeat the observation on several different nights
using different stars to average out this source of imprecision before
we will be able to significantly improve the orbit of Apophis and
therefore the details of the 2029 close approach and future impact
possibilities," noted Tholen.

Apophis's elliptical orbit around the Sun will take it back into the
Sun's glare this summer, inhibiting the acquisition of additional
positions. However, in 2012, Apophis will again become observable for
approximately nine months. In 2013, the asteroid will pass close
enough to Earth for ultraprecise radar signals to be bounced off its
surface.

Figure caption:
Apophis (circled) in a composite of five exposures taken on January 31
with the University of Hawaii 2.2-meter telescope on Mauna Kea. The
doughnut in the upper left corner is an artifact caused by a dust
speck on the camera, and the faint vertical trail was caused by a
satellite passing through the field. Image by D. Tholen, M. Micheli,
G. Elliott, UH Institute for Astronomy.

                           # # #

Founded in 1967, the Institute for Astronomy at the University of
Hawaii at Manoa conducts research into galaxies, cosmology, stars,
planets, and the Sun. Its faculty and staff are also involved in
astronomy education, deep space missions, and in the development and
management of the observatories on Haleakala and Mauna Kea.

Established in 1907 and fully accredited by the Western Association of
Schools and Colleges, the University of Hawaii is the state's sole
public system of higher education. The UH System provides an array of
undergraduate, graduate, and professional degrees and community
programs on 10 campuses and through educational, training, and
research centers across the state. UH enrolls more than 50,000
students from Hawaii, the U.S. mainland, and around the world.
Received on Thu 10 Mar 2011 05:43:30 PM PST