SUMMARY

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.

DETAILS

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.