UH Astronomers Observe Spectacular Split Comet (57P/du Toit-Neujmin-Delporte)

New observations from Mauna Kea with the University of Hawaii's 2.2-meter telescope by Institute for Astronomy astronomers Yanga R. Fernandez, Scott S. Sheppard and David C. Jewitt have revealed a zoo of tiny mini-comets strung out in a line trailing behind the comet 57P/du Toit-Neujmin-Delporte. This comet has apparently suffered a significant catastrophe, violent enough to break off many pieces of its nucleus. The event was probably triggered by thermal stresses within the nucleus due to it being warmed by sunlight. While it is not uncommon for one or two companions to be seen near a comet that has fragmented, our observations reveal at least 19 companions, a rare finding. Monitoring of these fragments over the coming weeks and months should reveal much about the constitution and fragility of cometary material.

Motivated by an earlier report of a previously-unknown companion associated with Comet 57P/du Toit-Neujmin-Delporte, we obtained deep imaging to search for any population of fragments that might exist near the comet. We used the University of Hawaii 2.2-m telescope on Mauna Kea and a charge-coupled device (CCD) to make a digital map of the sky around the comet. The observations were performed on the nights of July 17/18 and July 18/19, 2002 (Hawaii Standard Time).

We found a zoo of fragments strung out in a line extending almost 30 minutes of arc away from the comet itself (for comparison, the diameter of the full Moon also covers 30 minutes of arc). So far we have confirmed the existence of 19 fragments, and the discovery has been announced by the Central Bureau for Astronomical Telegrams, the internationally-recognized official clearinghouse for reporting cometary discoveries. We identified the fragments by taking successive images of a field and detecting their motion against the background stars. A mosaic of the relevant mapped region is shown at http://www.ifa.hawaii.edu/~yan/57p.html with the location of the fragments circled. At the distance of the comet, the mosaic spreads over about 1,000,000 kilometers (about 620,000 miles).

We cannot be sure of the sizes of the fragments but the brightest ones are probably less than a few hundred meters (few hundred yards) across. The smallest fragments are probably no more than a few tens of meters across, roughly the size of a house. A gallery of our 18 new objects is shown on the above WWW site.

FREQUENTLY ASKED QUESTIONS

* What are comets?

Comets are conglomerates of water ice and rocky material formed in the early days of the solar system. When a comet is within roughly 400,000,000 kilometers (250,000,000 miles) of the Sun, the sunlight is strong enough to start evaporating the ice in large quantities. (For comparison, Earth is 150,000,000 km (93,000,000 miles) from the Sun.) Since the ice and rock are intimately mixed, the warming and evaporating ice produces great thermal and physical stresses on the body of the nucleus. Under normal circumstances, only vapor and tiny dust grains are all that fly off the surface of the nucleus — and here on Earth we see a comet with a long tail, for example as widely seen in the late 1990s with comets Hyakutake and Hale-Bopp.

* Why do comets split?

Occasionally thermal stresses become great enough that entire chunks of the nucleus are ejected. Now while the basic idea is thought to be understood, the details are still uncertain, basically because we do not know many fundamental structural properties of cometary nuclei. In the case of this comet we cannot yet determine even when the fragmentation took place; further observations are necessary. With sufficient data fragmenting comets can provide a laboratory for us to witness major evolutionary events and can help us understand a comet's basic constitution.

* What will happen to the fragments?

We expect that most will fade to the point of invisibility, but we don't know how long that will take. A few might last for years.

* Why that name?

Comet 57P/du Toit-Neujmin-Delporte is named for the 3 people who discovered it in 1941.

* Why 57P?

The "57P" means it is the 57th comet in the list of comets that have been seen on two of their passages around the Sun. (The first comet in this list, "1P", is the famous Halley's Comet.)

* Why didn't somebody see the 19 companions before?

Nobody looked hard enough.

* Can I see this comet by eye?

No, it is 15th magnitude and much too faint to see, even with binoculars.

WEB SITE

http://www.ifa.hawaii.edu/ifa/site.htm

The Institute for Astronomy at the University of Hawaii conducts research into galaxies, cosmology, stars, planets, and the Sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea. Refer to http://www.ifa.hawaii.edu for more information about the Institute.

For more information, visit: http://www.ifa.hawaii.edu