In Coming Apart, Comet LINEAR Exposes its Deepest Secrets

Donald Savage/Dolores Beasley
Headquarters, Washington, DC
(Phone: 202/358-1547)

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5017)

Donna Weaver
Space Telescope Science Institute, Baltimore, MD
(Phone: 410/338-4493)

RELEASE: 01-94

Breaking up is hard to do, even for a comet. When such a cosmic break-up occurred last year, scientists watched it happen and came away with new insights and new questions.

Teams of scientists, using telescopes ranging from the W. M. Keck Observatory and NASA's Infrared Telescope Facility, both on Mauna Kea, HI, to the European Southern Observatory's (ESO) Very Large Telescope in Chile, the NASA/European Space Agency (ESA) SOHO satellite and NASA's Hubble Space Telescope, have been studying Comet LINEAR (C/1999 S4). This spectacular comet last year broke apart as it circled the Sun. The researchers' results will appear tomorrow in a special issue of the journal Science dedicated to studies of the comet.

One team, led by Dr. Michael Mumma of NASA's Goddard Space Flight Center, Greenbelt, MD, used the NASA/ESA Solar and Heliospheric Observatory (SOHO) to examine LINEAR. These scientists found the first evidence ever seen that supports the theory that comet impacts may have played a significant role in the formation of life on Earth by providing most of the water in Earth's oceans, as well as organic material. LINEAR is the first comet observed to have a composition that would allow it to carry the same type of water found in oceans on Earth.

"The idea that comets seeded life on Earth with water and essential molecular building blocks is dramatic, and for the first time, we have seen a comet with the right composition to do the job," Mumma said.

A separate announcement, also to appear in Science, is a unique observation that reveals just how much water comets of this type can carry. LINEAR, with a nucleus estimated at 2,500 to 3,300 feet (about 750 to 1,000 meters) in diameter, carried about 3.6 million tons (3.3 billion kilograms) of water within its bulk, according to astronomers who used the Solar Wind Anisotropies instrument on the SOHO spacecraft to observe water vapor released as the comet fragmented.

Pictures and more information about these findings can be found on the Internet at:

http://www.gsfc.nasa.gov/GSFC/SpaceSci/origins/linearwater/linearwater.htm

A second team, led by Dr. Hal Weaver, an astronomer at the Johns Hopkins University in Baltimore, MD, studied the broken fragments of LINEAR with the Hubble Space Telescope, the Very Large Telescope (VLT) and other ground-based telescopes. The researchers found there is not as much material in the fragments as there was in LINEAR before it broke apart. The leftover material just wouldn't add up to a comet as large as LINEAR.

Information about the Hubble and VLT observations are available on the Web at:

http://oposite.stsci.edu/pubinfo/pr/2001/14

There are no new Hubble pictures, but previously released Hubble Space Telescope images of Comet LINEAR's breakup are available at:

http://oposite.stsci.edu/pubinfo/pr/2000/26.html
http://oposite.stsci.edu/pubinfo/pr/2000/27.html

Comet LINEAR completely disintegrated late last July as it made its closest approach to the Sun, at a cozy 71 million miles. Hubble tracked the comet, finding at least 16 fragments that resembled "mini-comets" with tails. Now LINEAR is little more than a trail of debris orbiting the Sun. The comet is believed to have wandered into the inner solar system from its home in the Oort Cloud, a reservoir of space debris on the outskirts of the solar system. It took comet LINEAR about 60,000 years to travel once around the Sun.

Comet LINEAR was named for the program that first spotted it, the Lincoln Near Earth Asteroid Research (LINEAR), headquartered at the Massachusetts Institute of Technology's Lincoln Labs, Lexington, MA. LINEAR is a highly successful NASA-funded program to search for near-Earth objects, which has also become a premier discoverer of comets.