The science of CONTOUR: A closer look at comet diversity
JHU-JPL PRESS KIT
Posted: June 28, 2002
CONTOUR will visit and study at least two comets - assessing their diversity, detailing their properties, and tackling some of the many questions about how comets evolve.
The 'heart' of a comet
Comas and tails are big enough to study with Earth-based telescopes, but the nucleus is so tiny that we can study it only by getting close. So far, we've gotten close enough to see the nucleus of a comet only twice: the European Space Agency's Giotto spacecraft took color photos of comet 1P/ Halley's nucleus in 1986, and NASA's Deep Space 1 collected detailed images and data on comet 19P/Borrelly in 2001.
Comets are the most numerous sizeable bodies in the solar system; current estimates place their number at a million million. Most comets remain where they formed - in the vast region of deep space that stretches beyond Neptune and Pluto - but some are bumped from their orbits and approach the Sun. Jupiter's gravity can further alter a comet's path, capturing it into an orbit that never extends far beyond the giant planet.
CONTOUR's planned targets - 2P/Encke and 73P/Schwassmann-Wachmann 3 - belong to Jupiter's "family" of comets. Encke and SW3 are among the short-period comets, meaning they take less than 200 years to orbit the Sun. CONTOUR will fly past each at the peak of its activity, taking images and spectral maps of the nucleus while measuring and analyzing the surrounding gas and dust.
CONTOUR's key measurements
First spotted in 1786, 2P/Encke has been observed at more apparitions (approaches to the Sun) than any other comet. It has the shortest orbital period of any known comet, circling the Sun every 3.2 years. Encke might be the most famous comet after Halley - American astronomer and CONTOUR scientist Fred Whipple devised the "dirty snowball" model of a comet nucleus after studying Encke more than 50 years ago.
Encke is thought to be about 8 kilometers (5 miles) long, with an average radius of 2.5 kilometers. Encke is an "old" comet that gives off relatively little gas and dust, but it remains more active than scientists expect for a comet that has made thousands of close passes around the Sun.
73P/Schwassmann-Wachmann 3 was discovered in 1930 and considered predictable by most astronomers - until it passed close to the Sun in the mid-1990s and split into several pieces. One fragment has already disappeared; the largest of the remaining sections may be no more than 2 kilometers across. A relatively young and active comet - especially when compared to Encke - SW3 takes about 5.5 years to orbit the Sun. When CONTOUR reaches SW3 in June 2006, mission scientists hope to get a great look at the comet's fresh, unaltered surfaces and evidence of the material inside the nucleus.
The 'new' comet
Near their encounter times, Encke and SW3 will be close enough to Earth for astronomers worldwide to observe them from the ground. CONTOUR's high-resolution, near-nucleus observations can be linked with pictures, spectroscopic and thermal data obtained at broader scales by ground-based and Earth-orbiting telescopes.
True to any mission selected through the competitive NASA Discovery Program, the planetary science community played a key role in approving CONTOUR and its science goals. The team will further enhance the involvement of the science community with the early release of all data to NASA's Planetary Data System.
Flight Data File
Vehicle: Delta 2 (7425-9.5)
Launch date: July 1, 2002
Launch time: 2:56:14 a.m. EDT (0656:14 GMT)
Launch site: SLC-17A, Cape Canaveral, Florida
Satellite broadcast: GE-2, Transponder 9, C-band
Launch timeline - Chart with times and descriptions of events to occur during the launch.
Launch windows - See the daily launch opportunities for CONTOUR.
Orbit trace - Maps showing the ground track for the launch.
CONTOUR - Technical look at the spacecraft and its systems.
Delta 2 rocket - Overview of the Delta 2 7425-model rocket used in this launch.
SLC-17 - The launch complex where Delta rockets fly from Cape Canaveral.
Delta manufacturing - Map of where the parts for Delta 2 rockets are made.
Hardware flow - Illustration of how Delta 2s come together at the Cape.
Delta directory - See our coverage of preview Delta rocket flights.
MISSION STATUS CENTER