Near-Earth Asteroid Hermes Re-spotted: Its a Bright Binary

Flagstaff, AZ–The re-discovery of Hermes started early on October 15th by Brian
Skiff of the Lowell Observatory Near-Earth-Object Search (LONEOS). Not seen
since 1937, asteroid 1937 UB (Hermes) continues to astonish and excite astronomers
worldwide. Further observations revealed late yesterday that Hermes is actually
two objects–called a binary–circling around one another while about to pass
by Earth again.

"This re-sighting of Hermes is the Holy Grail of near-Earth asteroid discovery,"
said Edward Bowell, LONEOS Director. "Its orbit has been better calculated
and observers have confirmed its re-appearance and also shown its binary nature…
well, an asteroid’s return just does not become more profound than this."

The binary object was some 19 million miles out at the time of re-discovery
last Wednesday, nearly 66 years after it was first seen. Hermes, which poses
no threat to Earth, will make its closest approach on November 4th. By then
it will be 4 million miles away and bright enough for amateurs to see using
backyard telescopes.

The same day Skiff captured the first images of Hermes, Discovery Communications,
Inc. and Lowell Observatory announced a partnership to build the new Discovery
Channel Telescope near Flagstaff, Arizona. (http://www.lowell.edu/press_room/releases/recent_releases/dct_rls.html)
One research objective for this new $30-million, 4.3-meter telescope will be
to significantly accelerate the search for near-Earth objects, including those
smaller than Hermes.

First images of the kilometer-size asteroid were captured by a CCD camera during
early morning observation through the LONEOS 24-inch Schmidt telescope. More
than six decades ago, Hermes was discovered by Karl Reinmuth at Heidelberg,
Germany on October 25, 1937. Fast forward to a few days ago when Andrea Boattini
of Instituto di Astrofisica Spaziale, Rome, Italy, and Timothy Spahr of the
Minor Planet Center in Cambridge, Massachusetts analyzed the new positions of
Hermes and determined what it was: the long-lost asteroid.

"Since we find new near-Earth asteroids fairly regularly (I found, for
instance, two near-Earth asteroids the same night), my only reaction upon finding
it was that it was unusually bright," Skiff told BBC News Online on Friday.

Up before dawn, Spahr quickly posted Skiff’s discovery on the web, alerting
astronomers to follow the asteroid. James Young, at the Jet Propulsion Laboratory’s
Table Mountain Observatory in California, was the first to respond, just five
hours later. Spahr then located observations made on October 5 by the Near-Earth
Asteroid Tracking program (http://neat.jpl.nasa.gov),
LONEOS observations from September 28, and unpublished observations made by
the MIT Lincoln Laboratory Near Earth Asteroid Research program (http://www.ll.mit.edu/LINEAR),
extending the observational arc back to August 26 (http://cfa-www.harvard.edu/mpec/K03/K03T74.html).

At this point, the identification with Hermes was clear from the similarity
of the orbits from the 1937 and 2003 sightings, but it was not a simple matter
to compute an orbit that linked all the observations together. Steven Chesley
and Paul Chodas of the Jet Propulsion Laboratory found that Hermes’ trajectory
is very chaotic due to frequent close encounters with the Earth and Venus. Following
its flyby of the Earth in 1937 at a distance of 460,000 miles (just 1.8 times
the Moon’s distance), Hermes made an unobserved close approach to the
Earth in 1942 of just 1.6 lunar distance. Using JPL’s Sentry impact monitoring
software, Chesley and Chodas were able to find twelve distinct dynamical pathways
that produced an encounter in 1937. Picking out the true orbit was then an easy
matter , and led to the further prediction that Hermes will not approach the
Earth more closely than 8 lunar distances within the next century (http://neo.jpl.nasa.gov/news/news140.html).

On October 16, Andrew Rivkin and Richard Binzel of MIT observed a spectrum of
Hermes using the NASA Infrared Telescope Facility in Hawaii, and were able to
ascertain that the asteroid is of a type known as S class. Because the surfaces
of S-class asteroids reflect, on average, 24% of the sunlight falling on them,
Rivkin and Binzel were able to deduce that Hermes is 0.9 km (about 1,000 yards)
in diameter.

Over the next few days, the world’s most powerful radar, the 1,000-foot
dish, at Arecibo, Puerto Rico, projected radar beams on to the asteroid and
captured the faint returning echoes. Jean-Luc Margot, of the University of California,
Los Angeles, and his team saw that the asteroid is strongly bifurcated. Two
separate components, of roughly equal size and almost in contact, are revolving
about their common center of mass in up to 21 hours. It appears that the components
have tidally evolved into a situation where their spin period is equal to their
orbital period and therefore present the same face to one another all the time,
just like the Pluto-Charon system. There are now about 10 radar-observed binary
near-Earth asteroids, about 1 in 6 of NEAs larger than 200 m in diameter. "We
certainly did not expect to find a binary with roughly equal-sized components,"
said Margot. "All the binary NEAs that we have imaged so far show a secondary
that is only a fraction of the size of the primary."

Amateur and professional astronomers are collaborating to observe the way Hermes
changes in brightness as its components rotate. Eventually, they should be able
to determine the components’ orbital plane, an accurate period of revolution,
and, perhaps, the shapes of the individual bodies. See http://www.asu.cas.cz/~asteroid/binneas.htm
for a list of binary NEAs.

The only near-Earth object not also identified by number, Hermes shares a name
in Greek mythology with the son of Zeus, messenger of the gods, god of science,
commerce, eloquence, and arts of life. "The name ‘Hermes’ also
means hastener, and representations of him are symbolic of the messenger or
the speed and majesty in flight," according to Schmadel’s Dictionary
of Minor Planet Names.

Lowell Observatory was founded in 1894 by Percival Lowell with a mission 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 results of astronomical
research to the general public. Visit http://www.lowell.edu;
and Friends of Lowell at http://www.lowell.edu/friends/.

LONEOS is one of five programs funded by NASA to search for asteroids and
comets that may approach our planet closely. Their current goal is to discover
90% of near-Earth asteroids larger than 1 km in diameter by 2008. There are
thought to be about 1,200 such asteroids.

For more information on the discovery and images of Hermes, visit the LONEOS
website at http://asteroid.lowell.edu/asteroid/loneos/loneos.html.