[meteorite-list] A Poetic Asteroid Moon
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:48:56 2004
A Poetic Asteroid Moon
September 4, 2001
Astronomers have discovered a satellite orbiting asteroid Kalliope.
by Vanessa Thomas It seems there is a poetry lover among the rocky members
of our solar system. Last week, two teams of astronomers independently
discovered a small body orbiting orbiting (22) Kalliope, a main-belt
asteroid named after the Greek muse of epic poetry.
Jean-Luc Margot and Michael Brown of the California Institute of Technology
first spotted the asteroid moon on August 29 while observing Kalliope with
the 10-meter Keck II telescope atop Mauna Kea in Hawaii. A second team led
by William Merline of the Southwest Research Institute noticed Kalliope's
satellite just a few days later while using the 3.6-meter
Canada-France-Hawaii Telescope (CFHT), also at Mauna Kea. Both teams
reported the discovery to the International Astronomical Union's Central
Bureau for Astronomical Telegrams (CBAT) on Monday, September 3.
When Merline and his team saw what appeared to be a companion to Kalliope on
September 2, they kept watch for over an hour to make sure that the
unidentified body was not a background star. Because asteroids appear to
move across the sky at different speeds than background stars, stars appear
as streaks on images taken with telescopes that are tracking asteroids.
"Both the asteroid and the satellite were not streaked in the images, while
the stars were," Merline reports. So the object obviously was not a
background star, but moving at the same speed as Kalliope.
The astronomers also had to make sure that the object was not another
asteroid that happened to be in the same field of view. "It is theoretically
possible that another asteroid in the background may be very close and thus
moving at almost the same speed, appearing like it was with the asteroid,"
Merline explains. However, "we found that no known objects were in this
direction in the sky," he said.
>From the satellite's brightness, Margot and Brown estimate that it is about
one-fifth the size of the 181-kilometer-wide (112-mile-wide) Kalliope,
although Merline's team disagrees with the calculation. Margot and Brown
also predict that the moon orbits about 1,000 kilometers (620 miles) away
from its larger companion. Both teams have previously discovered satellites
of main-belt asteroids before. Merline says his team was aware of Margot and
Brown's observing run at the Keck Observatory, but Margot claims that he and
Brown did not know about the others' plans to observe Kalliope at Mauna Kea
According to Dan Green, who received the reports for the CBAT, both teams
should be credited for the discovery of Kalliope's moon. Temporarily
designated S/2001 (22) 1, the new moonlet joins a growing group of asteroid
satellites discovered since the Galileo spacecraft discovered the first -
asteroid (243) Ida's moon, Dactyl - in 1993.
In fact, Merline adds that other discoveries may be on the way. "Many other
potentially interesting objects in our data sit waiting for additional
chances to look at the objects; they are not sufficiently convincing in and
of themselves to announce without more data." This was not the case with
Kalliope's moon, however. "The moon ... was so obvious that we were certain
of it within only the first set of data," Merline writes. Margot agrees,
saying, "There was absolutely no question in our mind that this was a
Received on Thu 06 Sep 2001 02:14:05 PM PDT