08 October 2009

Meteor/Meteorite News- NASA Refines Asteroid Apophis' Path Toward Earth 7OCT09

NASA Refines Asteroid Apophis' Path Toward Earth

PASADENA, Calif. -- Using updated information, NASA scientists have
recalculated the path of a large asteroid. The refined path indicates
a significantly reduced likelihood of a hazardous encounter with
Earth in 2036.

The Apophis asteroid is approximately the size of two-and-a-half
football fields. The new data were documented by near-Earth object
scientists Steve Chesley and Paul Chodas at NASA's Jet Propulsion
Laboratory in Pasadena, Calif. They will present their updated
findings at a meeting of the American Astronomical Society's Division
for Planetary Sciences in Puerto Rico on Oct. 8.

"Apophis has been one of those celestial bodies that has captured the
public's interest since it was discovered in 2004," said Chesley.
"Updated computational techniques and newly available data indicate
the probability of an Earth encounter on April 13, 2036, for Apophis
has dropped from one-in-45,000 to about four-in-a million."

A majority of the data that enabled the updated orbit of Apophis came
from observations Dave Tholen and collaborators at the University of
Hawaii's Institute for Astronomy in Manoa made. Tholen pored over
hundreds of previously unreleased images of the night sky made with
the University of Hawaii's 88-inch telescope, located near the summit
of Mauna Kea.

Tholen made improved measurements of the asteroid's position in the
images, enabling him to provide Chesley and Chodas with new data sets
more precise than previous measures for Apophis. Measurements from
the Steward Observatory's 90-inch Bok telescope on Kitt Peak in
Arizona and the Arecibo Observatory on the island of Puerto Rico also
were used in Chesley's calculations.

The information provided a more accurate glimpse of Apophis' orbit
well into the latter part of this century. Among the findings is
another close encounter by the asteroid with Earth in 2068 with
chance of impact currently at approximately three-in-a-million. As
with earlier orbital estimates where Earth impacts in 2029 and 2036
could not initially be ruled out due to the need for additional data,
it is expected that the 2068 encounter will diminish in probability
as more information about Apophis is acquired.

Initially, Apophis was thought to have a 2.7 percent chance of
impacting Earth in 2029. Additional observations of the asteroid
ruled out any possibility of an impact in 2029. However, the asteroid
is expected to make a record-setting -- but harmless -- close
approach to Earth on Friday, April 13, 2029, when it comes no closer
than 18,300 miles above Earth's surface.

"The refined orbital determination further reinforces that Apophis is
an asteroid we can look to as an opportunity for exciting science and
not something that should be feared," said Don Yeomans, manager of
the Near-Earth Object Program Office at JPL. "The public can follow
along as we continue to study Apophis and other near-Earth objects by
visiting us on our AsteroidWatch Web site and by following us on the
@AsteroidWatch Twitter feed."

The science of predicting asteroid orbits is based on a physical model
of the solar system which includes the gravitational influence of the
sun, moon, other planets and the three largest asteroids.

NASA detects and tracks asteroids and comets passing close to Earth
using both ground and space-based telescopes. The Near Earth-Object
Observations Program, commonly called "Spaceguard," discovers these
objects, characterizes a subset of them and plots their orbits to
determine if any could be potentially hazardous to our planet.

JPL manages the Near-Earth Object Program Office for NASA's Science
Mission Directorate in Washington. Cornell University operates the
Arecibo Observatory under a cooperative agreement with the National
Science Foundation in Arlington, Va.

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