[meteorite-list] Small Asteroid Passes Between Satellites and Earth (2004 YD5)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Dec 22 13:31:48 2004
Message-ID: <200412221831.KAA17016_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/asteroid_close_041222.html

Small Asteroid Passes Between Satellites and Earth
By Robert Roy Britt
space.com
22 December 2004

Astronomers spotted an asteroid this week after it had flown past Earth
on a course that took it so close to the planet it was below the orbits
of some satellites.

The space rock was relatively small, however, and would not have posed
any danger had it plunged into the atmosphere.

The object, named 2004 YD5, was about 16 feet (5 meters) wide, though
that's a rough estimate based on its distance and assumed reflectivity.
Had it entered the atmosphere, it would have exploded high up, experts
figure.

Satellite territory

The asteroid passed just under the orbits of geostationary satellites,
which at 22,300 miles (36,000 kilometers) altitude are the highest
manmade objects circling Earth. Most other satellites, along with the
International Space Station, circle the planet at just a few hundred
miles up.

2004 YD5 is the second closest pass of an asteroid ever observed by
telescope, according to the Asteroid/Comet Connection, a web site that
monitors space rock discoveries. The closest involved a rock that flew
by last March and was not announced until August.

2004 YD5 was discovered Tuesday, Dec. 21 by Stan Pope, who volunteers
his time to examine images provided by the FMO (Fast Moving Object)
project, an online program run by the University of Arizona's Spacewatch
Project. After the initial detection, other observers noted the object's
position during the day and its path was then calculated back. Closest
approach occurred on Dec. 19.

The rock approached Earth from near the Sun and so would have been
nearly impossible to detect prior to close passage. It soared over
Antarctica -- underneath the planet, Washington State University
researcher Pasquale Tricarico told the Asteroid/Comet Connection.

Astronomers are aware of this significant blind spot
for asteroids that approach Earth while in the glare of the Sun. Only a
space telescope could detect such objects before they arrive.

Similar events

Asteroids orbit the Sun, mostly in a belt between Mars and Jupiter. Some
are redirected closer to the Sun, often by gravitational nudges provided
by the planets. Earth has been hit by devastatingly large asteroids many
times in the distant past. Astronomers say sooner or later the planet
will be struck again, but the odds of a large impact occurring in any
given century are extremely small.

This has been an interesting year for asteroid encounters.

On March 18, a giant boulder about 100 feet (30 meters) wide passed just
above the orbits of geostationary satellites. Its path was bent about
15 degrees by Earth's gravity. The asteroid, 2004 FH, was discovered a
mere three days prior.

On Sept. 29, the largest asteroid ever known to pass near Earth, named
Toutatis, roamed by at about four times the distance to the Moon.
Astronomers had known for years the flyby would occur, since Toutatis
is 2.9 miles (4.6 kilometers) long and had been in Earth's vicinity before.

But many near misses by small asteroids likely go unnoticed, astronomers
say, because the entire sky is not continuously monitored. Such small
asteroids have been detected only in recent years as more sophisticated
telescopes have been hooked up with digital cameras.

And some asteroids come even closer, entering the atmosphere. Most never
reach the ground because they break apart under the stress of entry. One
study of data collected by U.S. military satellites logged 300 in-air
asteroid explosions.

2004 YD5 was announced Tuesday evening by the Minor Planet Center in
Cambridge, Mass, where comet and asteroid observations from around the
globe are digested.
Received on Wed 22 Dec 2004 01:31:42 PM PST