A Million Comet Pieces
(poster version)
This infrared image from NASA's Spitzer Space Telescope shows the broken Comet 73P/Schwassman-Wachmann 3 skimming along a trail of debris left during its multiple trips around the sun. The flame-like objects are the comet's fragments and their tails, while the dusty comet trail is the line bridging the fragments.
Comet 73P /Schwassman-Wachmann 3 began to splinter apart in 1995 during one of its voyages around the sweltering sun. Since then, the comet has continued to disintegrate into dozens of fragments, at least 36 of which can be seen here. Astronomers believe the icy comet cracked due the thermal stress from the sun.
The Spitzer image provides the best look yet at the trail of debris left in the comet's wake after its 1995 breakup. The observatory's infrared eyes were able to see the dusty comet bits and pieces, which are warmed by sunlight and glow at infrared wavelengths. This comet debris ranges in size from pebbles to large boulders. When Earth passes near this rocky trail every year, the comet rubble burns up in our atmosphere, lighting up the sky in meteor showers. In 2022, Earth is expected to cross close to the comet's trail, producing a noticeable meteor shower.
Astronomers are studying the Spitzer image for clues to the comet's composition and how it fell apart. Like NASA's Deep Impact experiment, in which a probe smashed into comet Tempel 1, the cracked Comet 73P/Schwassman-Wachmann 3 provides a perfect laboratory for studying the pristine interior of a comet.
This image was taken from May 4 to May 6 by Spitzer's multi-band imaging photometer, using its 24-micron wavelength channel.
This image from NASA's Spitzer Space Telescope shows three of the many fragments making up Comet 73P /Schwassman-Wachmann 3. The infrared picture also provides the best look yet at the crumbling comet's trail of debris, seen here as a bridge connecting the larger fragments.
The comet circles around our sun every 5.4 years. In 1995, it splintered apart into four pieces, labeled A through D, with C being the biggest. Since then, the comet has continued to fracture into dozens of additional pieces. This image is centered about midway between fragments C and B; fragment G can be seen in the upper right corner.
The comet's trail is made of dust, pebbles and rocks left in the comet's wake during its numerous journeys around the sun. Such debris can become the stuff of spectacular meteor showers on Earth.
This image was taken on April 1, 2006, by Spitzer's multi-band imaging photometer using the 24-micron wavelength channel.
Figure 1: Band of Light Comparison
This artist's concept illustrates what the night sky might look like from a hypothetical alien planet in a star system with an asteroid belt 25 times as massive as the one in our own solar system (alien system above, ours below; see Figure 1).
NASA's Spitzer Space Telescope found evidence for such a belt around the nearby star called HD 69830, when its infrared eyes spotted dust, presumably from asteroids banging together. The telescope did not find any evidence for a planet in the system, but astronomers speculate one or more may be present.
The movie begins at dusk on the imaginary world, when HD 69830, like our Sun, has begun to set over the horizon. Time is sped up to show the onset of night and the appearance of a brilliant band of light. This light comes from dust in a massive asteroid belt, which scatters sunlight.
In our solar system, anybody observing the skies on a moonless night far from city lights can see the sunlight that is scattered by dust in our asteroid belt. Called zodiacal light and sometimes the "false dawn," this light appears as a dim band stretching up from the horizon when the Sun is about to rise or set. The light is faint enough that the disk of our Milky Way galaxy remains the most prominent feature in the sky. (The Milky Way disk is shown perpendicular to the zodiacal light in both pictures.)
In contrast, the zodiacal light in the HD 69830 system would be 1,000 times brighter than our own, outshining even the Milky Way.
The two "spots" in this image are a composite of two images of asteroid 2002 JF56 taken on June 11 and June 12, 2006, with the Multispectral Visible Imaging Camera (MVIC) component of the New Horizons Ralph imager. In the bottom image, taken when the asteroid was about 3.36 million kilometers (2.1 million miles) away from the spacecraft, 2002 JF56 appears like a dim star. At top, taken at a distance of about 1.34 million kilometers (833,000 miles), the object is more than a factor of six brighter. The best current, estimated diameter of the asteroid is approximately 2.5 kilometers.
The asteroid observation was a chance for the New Horizons team to test the spacecraft's ability to track a rapidly moving object. On June 13 New Horizons came to within about 102,000 kilometers of the small asteroid, when the spacecraft was nearly 368 million kilometers (228 million miles) from the Sun and about 273 million kilometers (170 million miles) from Earth.
Voir l'image PIA09230: New Horizons Tracks an Asteroid sur le site de la NASA.
A series of wide angle and narrow angle images, through a variety of spectral and polarizing filters, was taken of the asteroid between 7 and 5.5 hours before closest approach, from a distance of 1.6 million km, in the hopes of determining the body's size, reflectivity, asteroid type and possibly its rotation period. The face of Masursky seen by the Cassini Imaging Science Subsystem (ISS) at a Sun-asteroid-spacecraft angle of 90 degrees has been measured to be roughly 15 - 20 km in diameter, assuming a spherical shape. Preliminary determination of its reflectivity indicates that it may not, in fact, be an S-type asteroid like Gaspra, Ida and Eros, a puzzling result given its dynamical association with the Eunomia family of S-type asteroids. Examination and analysis of the remaining images may settle this matter as well as place limits on the body's rotation period.
The asteroid is named for renowned planetary geologist Harold Masursky (1923-1990), a major participant in the historic Mercury and Apollo planetary programs, the Viking mission to Mars and the Voyager mission to outer solar system.
The image above is the first wide angle (WA) image taken of Masursky on January 23,2000 at 3:01 UTC (full resolution version). In this 32 second exposure, the cameras were continuously pointed to Masursky which was traveling roughly right to left at 0.2 WA pixels/sec (about 12 microradians/sec) across the constellation of Aquila. The stars in this 3.5 degree field of view are streaked due to this target-motion compensation. Some of the streaks and point-like sources in this frame are in fact the images left by cosmic rays which hit the CCD of the camera during the exposure.
This narrow angle 1.2 second exposure was shuttered simultaneously with the wide angle image above, and is a factor of ten higher in resolution (full resolution version) . It is from images like this that the size of Masursky was determined. Some of the streaks and point-like sources in this 0.35 degree frame are infect the images left by cosmic rays which hit the camera's CCD. The imaging data were processed and released by the Cassini Imaging Central Laboratory for Operations (CICLOPS) at the University of Arizona's Lunar and Planetary Laboratory, Tucson, AZ.
Photo Credit: NASA/JPL/University of Arizona
Cassini, launched in 1997, is a joint mission of NASA, the European Space Agency and Italian Space Agency. The mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Space Science, Washington DC. JPL is a division of the California Institute of Technology, Pasadena, CA.
Voir l'image PIA02449: Masursky sur le site de la NASA.
