Home Whats New Location Equipment Software Methods Results Gallery Links Ephemerides Moon
(C) Copyright
2003 - 2006 Great Shefford Observatory
|
|
|
For Immediate
Release October 3, 2003
Contact: Asteroid Whizzes Very Close By Earth
FLAGSTAFF, AZ—A small asteroid, perhaps 3 to 6 meters in diameter—the size of
a room or house—came within 88,000 km of Earth late on Friday, September 27.
Less than a quarter of the distance to the Moon, this is the closest
well-documented Earth encounter of an asteroid that has not struck our
atmosphere.
“In a good month, we find five to 10 near-Earth asteroids, but usually, the
ones we discover are as big as mountains, or at least football stadiums, so this
one was unique for us,” said Edward Bowell, Director of Lowell Observatory’s
Near-Earth-Object Search (LONEOS).
Known as 2003 SQ222, the asteroid was imaged a few hours after close approach
by Michael Van Ness, a graduate student at Northern Arizona University,
Flagstaff.
LONEOS
is one of five teams funded by NASA’s Near Earth Objects Observations program to
look for asteroids and comets that could come close to or strike our planet.
LONEOS is the third leading discoverer of asteroids.
The first images of SQ222 were made on a series of CCD-camera frames
(charge-coupled device) taken for Minor Planet Research, an
organization collaborating with LONEOS on a project with an aim of having high
school students make asteroid discoveries at the Challenger Learning Center in
Peoria, Arizona. Robert Cash, of MPR, used automatic moving-object detection
software to find three trailed images of an object moving at 20 degrees per day,
almost twice as fast as the Moon, across the sky. Cash relayed his discovery
back to Lowell Observatory and to the international clearinghouse for asteroid
and comet observations, the Minor Planet Center, in
Cambridge Massachusetts.
Predicted positions were posted on the MPC’s Near-Earth Object Confirmation
Page so observers worldwide could follow the object.
Meanwhile, Bowell noticed that it was possible to compute a fairly reliable
orbit. “The orbit showed clearly that SQ222 had passed within a quarter of the
Moon’s distance to the Earth, some 11 hours before being discovered,” said
Bowell. “So, I e-mailed our results to the Minor Planet Mailing List, to which hundreds
of amateur and professional astronomers subscribe, with a request for further
observations.”
Brian Skiff, LONEOS’ chief observer, acquired fresh CCD frames on September
29, but the LONEOS team was unable to locate the asteroid’s images. Once again,
Bob Cash found the by then very faint images of the asteroid after visually
searching the frames for more than three hours in the wee hours of September
30th. You can view two sequences of
LONEOS images of SQ222.
Independently, British amateur astronomer Peter Birtwhistle, using a 30-cm
telescope west of London, was able to image the asteroid. “It is remarkable that
Birtwhistle was able to detect the asteroid using such a small telescope,” said
Bowell. “He did so by tracking the motion of the asteroid and by aligning and
co-adding (or stacking) the frames to bring out the faint asteroid images.”
“The essential rapid teamwork between Lowell Observatory and keen amateur
astronomers made it possible to confirm and image this fast-moving, small
asteroid as it shot past us,” said Bowell.
SQ222’s known brightness and distance allow calculation of its size. Most
asteroids have either coal-black surfaces or are about four times more
reflective. Bowell estimates the asteroid to be just 3 to 6 meters in diameter,
most likely making it the smallest asteroid for which we have a reliable orbit.
(Smaller and closer asteroids have been seen in space, especially by the Spacewatch team at the University of
Arizona, but it has not been possible to follow them long enough to secure
good orbits.)
Perhaps the final detection of SQ222 was made by British astronomer Alan
Fitzsimmons (Queen’s University Belfast) on October 2. Fitzsimmons, working
through thin cloud, managed to detect the asteroid using the 2.5-m Isaac Newton
Telescope at La Palma in the Canary Islands. By then, SQ222, receding rapidly
from Earth, was about 100 times fainter than at discovery.
After Fitzsimmons’ observations, the orbit of SQ222 was good enough to
compute a reliable value of what astronomers call the minimum orbital
intersection distance, (MOID).
This is the minimum distance between the orbit of the asteroid and that of
the Earth. Bowell calculated the MOID to be a little over 4 Earth radii (about
27,000 km).
“This distance is, roughly speaking, the very closest the asteroid could have
come to the center of the Earth during its fly-by,” said Bowell. “Therefore,
SQ222 could not possibly have struck the Earth.” Even if it could have, it would
have exploded harmlessly in the upper atmosphere, with an energy comparable to
that of a small atomic bomb, as friction with the air vaporized its surface,
added Bowell.
“Objects the size of SQ222 actually do burn up in Earth’s atmosphere every
year or so, producing a spectacular light show,” said Bowell.
In what is most likely a coincidence, an intense shower of meteorites was
reported in India about 10 hours before SQ222’s closest approach to Earth. Could
the asteroid and the meteorites be fragments of a larger asteroid that was
broken apart by a collision with another asteroid or by tidal disruption during
a previous very close Earth approach? It seems very unlikely, but work is
ongoing to test the plausibility of the idea.
Will SQ222 make another close pass by Earth? It is hard to say, as the orbit
is not accurate enough to make reliable predictions for more than a few years
into the future. Certainly, there seems no possibility of it returning within
the next decade. Also, SQ222 will be too faint to see in the foreseeable future,
even using the most powerful telescopes.
—END—
Founded in 1894, the mission of Lowell Observatory is to pursue the study of
astronomy, especially the study of our Solar System and its evolution; to
conduct pure research in astronomical phenomena; and to maintain quality public
education and outreach programs to bring the results of astronomical research to
the general public. Visit Lowell Observatory on
the web.
For more information:
The MPR detection software used to find SQ222, called PinPoint, was developed
by Robert Denny, and is commercially available
You can view
Peter Birtwhistle’s images of SQ222.
At discovery, the asteroid was about 18th magnitude in the R band.
It is estimated that there are about 500 million near-Earth asteroids of
SQ222’s size or larger. Alan W. Harris, of the Space Science Institute,
calculates that about 3,000 such objects per year come closer than the Moon, and
about 100 of them come closer than SQ222 each year. Moving at an average speed
of 17 km/s, any one of them stays within the Moon’s orbit for 8 hours or less.
Thus, it is likely that there are a couple of asteroids like SQ222 within the
Moon’s distance right now, and two more will come close to us tomorrow. Why
don’t we see more of them? Usually, they are moving too fast for our CCD cameras
to register. Harris points out that “these things are completely harmless. They
are no more than interplanetary tourist attractions.”
2003 SQ222 was moving across the sky at more than 30 degrees per hour at its
closest approach. It would not have been observable from the U.S. as it was in
the daylight sky. It could have been seen, with difficulty, from Europe. The
closest approach is about twice the distance of geosynchronous communications
satellites. Aside from the occasional fireball, an asteroid that explodes in the
upper atmosphere, only 10 asteroids are known to have approached the Earth
closer than the Moon’s distance.
For documentation of SQ222’s discovery, visit: http://groups.yahoo.com/group/mpml/message/10707
and
|
|
Home Whats New Location Equipment Software Methods Results Gallery Links Ephemerides Moon
|