[meteorite-list] Mystery Asteroid, Hermes, May Have a Partner

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:33 2004
Message-ID: <200310211503.IAA09403_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/hermes_binary_031021.html

Mystery Asteroid, Hermes, May Have a Partner
By Robert Roy Britt
space.com
21 October 2003

Astronomers have apparently discovered an interesting twist to one of the
greatest asteroid mysteries of all time. Hermes, a space rock lost to
science for 66 years and recently rediscovered, could actually be a pair of
orbiting asteroids, new radar observations suggest.

Hermes had not been seen since its 1937 discovery until found anew in a
collaborative effort last week. Once Hermes was recovered, astronomers
around the world began observing it to take advantage of its relative
proximity.

The latest look at Hermes, also named 1937 UB, comes from the Arecibo
Observatory in Puerto Rico. The radar observations were made Oct. 18 and 20
and show, according to a preliminary assessment, a "strongly bifurcated"
appearance. The images have not yet been released to the public.

"Our images show two separate components of roughly equal sizes, consistent
with an orbiting binary pair," a team of astronomers wrote to the Central
Bureau for Astronomical Telegrams.

The astronomers estimate that each asteroid is about 980 to 1,480 feet
(300-450 meters) in diameter, or possibly just over a quarter-mile. But,
they caution, additional data are needed to verify whether the object is
really a pair.

Holy Grail

When Hermes was recovered last week and thought to be a single object,
astronomers estimated its diameter at 0.62 to 1.24 miles (1-2 kilometers).

Though he didn't know it at the time, Brian Skiff of the Lowell Observatory
Near-Earth Object Search program (LONEOS) in Arizona was responsible for the
rediscovery of Hermes. Skiff said Hermes had been the "number one" unsolved
mystery for asteroid scientists.

"It was the last of the 'lost' Holy Grail asteroids," Skiff told SPACE.com.

Asteroid hunters around the world have been on a quest over the past decade
to find 90 percent of the estimated 1,000 or so large asteroids -- 0.62
miles or 1 kilometer -- thought to roam the general space through which
Earth orbits. These large near-Earth asteroids have the potential to one day
devastate a region of Earth and affect the global climate. Well more than
half have been found and none are known to be on a collision course.

Asteroid experts won't be too surprised to learn now that Hermes may have a
partner.

Dancing asteroids, known as binaries, are not uncommon. A study last year
estimated that 16 percent of near-Earth asteroids are actually double
trouble. Hermes -- be it a loner or a pair -- is now on NASA's list of
potentially hazardous asteroids. It will not hit the planet in the next 100
years, astronomers have determined, but its course thereafter is not known
with certainty.

For years, scientists have pondered the added difficulty of dealing with a
binary asteroid that might one day take aim on Earth. No one has come up
with a proven plan for deflecting a lone space rock, however, let alone a
pair.

More to come

Hermes was discovered in 1937 by German astronomer Karl Reinmuth. A few days
later it was out of sight, and astronomers didn't have enough information
about its path to find it for more than six decades, even though, they know
now, it made repeated passes relatively close to the planet.

The new Arecibo observations were made by a team from the University of
California, Los Angeles, the National Astronomy and Ionosphere Center and
NASA's Jet Propulsion Laboratory.

Later this year, Hermes will pass within about nine times the distance from
Earth to the Moon. It travels on an elliptical orbit that takes it across
Venus' orbit and then well out into the solar system.

More observations from Arecibo and other telescopes are expected. Even
astronomers with large backyard telescopes -- perhaps 8 inches or bigger --
will be able to spot Hermes later this month.
Received on Tue 21 Oct 2003 11:03:22 AM PDT