[meteorite-list] Asteroid 2004 FH's Record Flyby

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:53 2004
Message-ID: <200403251810.KAA02792_at_zagami.jpl.nasa.gov>


Asteroid 2004 FH's Record Flyby
By Sean Walker
Sky & Telescope
March 24, 2004

Right on schedule, asteroid 2004 FH made its dramatic pass
about 42,700 kilometers (26,500 miles) above the Earth's surface on March
18, 2004, at 22:08 Universal Time. This is Earth's closest known encounter
with a small solar-system body if you don't count objects that have actually
entered the atmosphere. The object is believed to be about 30 meters (100
feet) across.

Just 10 hours before the flyby, Grant Christie of Auckland Observatory, New
Zealand, detected periodic brightness fluctuations (amplitude 0.9 magnitude)
in CCD images taken during a 17-minute interval. These suggest that 2004 FH
rotates about once every 90 seconds, as reported on International
Astronomical Union Circular 8310.

On Siding Spring Mountain, Australia, Robert McNaught and Gordon Garradd
observed the flyby visually, three hours before closest approach, using a
5-inch (12.5-centimeter) refractor. "It was then magnitude 11 and moving
about 10 arcseconds per second! The motion at 80x was quite obvious in real
time," McNaught told members of the Minor Planet Mailing List.

Meanwhile, due to a power failure, astronomers at the giant Arecibo radio
telescope in Puerto Rico were unable to make the radar observations they'd

Using the remote imaging capabilities of SoTIE (Southern Telescopes in
Education) at Las Campanas, Chile, Gianluca Masi and Franco Mallia of Campo
Catino Astronomical Observatory, Italy, were able to record a brief movie of
the event shortly before the closest approach. "Because of bad weather, we
were going to miss the event here in Italy," said Masi. "However, our Web
interface made the experience almost like we were right there at the
telescope, collecting the data on site."

Not only is the flyby of 2004 FH the closest known pass of a solar system
object, but the encounter was discovered with the Lincoln Near-Earth
Asteroid Research (LINEAR) robotic telescope in New Mexico shortly before
closest approach. The next three record encounters, listed below, were only
detected after closest approach.

                      Closest Recorded Asteroid Flybys

  Designation Fraction of Earth-Moon Distance (384,000 km) Date

    2004 FH 0.13 Mar. 18, 2004
   2003 SQ222 0.22 Sept. 27, 2003
    1994 XM1 0.28 Dec. 9, 1994
   2002 XV90 0.30 Dec. 11, 2002
Received on Thu 25 Mar 2004 01:10:30 PM PST

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