Online Astronomy eText: Asteroids, Comets, and Interplanetary Debris
The 2006 Breakup of Periodic Comet P73/Schwassman-Wachmann 3
 In 2006, Comet P73/Schwassmann-Wachmann 3 broke into several dozen pieces (for reasons unknown, since it was hundreds of millions of miles away from any object of substantial mass). This was not the first time that the comet has fallen apart. It split into several large pieces during its perihelion passage in 1995. Some comets may simply become piles of sooty rubble as they lose mass, unable to generate a head or tail due to their lack of ice; but many, if not most, are such fragile conglomerates of ice, soot and dust that they simply fall to pieces. As it happens, the pieces of Schwassmann-Wachmann passed only a few million miles from the Earth in May 2006, but since they are so small, they were impossible to see in bright skies, and difficult to see even in dark skies without the aid binoculars or telescopes. In the image above, taken in late April 2006, Fragment B of the comet is shown on the left, as it passed the 5th magnitude star χ (Chi) Böotis; and much fainter fragment G is barely visible at far top right. (Mike Holloway,

 Comet P73/Schwassmann-Wachmann 3 continued to disintegrate, as shown in these images of fragment B and G as viewed by the Hubble Space Telescope, each of which was fragmenting into numerous 'mini-comets'. (H. Weaver (JHU/APL), M. Jäger, G. Rhemann, ESA, NASA)

 A larger view of the HST image of fragment B of Comet P73/Schwassmann-Wachmann 3, taken on April 18, 2006, when the comet was 32 million miles from Earth, shows a multitude of fragments scattered over a two thousand mile span. The comet passed closest to Earth on May 13, at a distance of about 7 million miles. (NASA, ESA, H. Weaver (JHU / APL), M. Mutchler and Z. Levay (STScI), apod060504)

 An infrared mosaic of forty-five of the sixty-plus fragments of Comet P73/Schwassmann-Wachmann 3, spanning about six degrees. Fragment C is the bright fragment at upper right, while fragment B is the bright fragment below and left of center. Although the comet has broken into many pieces, they continue to follow the original orbit of the comet, which is clearly delineated by them and the debris left by their deterioration. When the Earth passes closes to the orbit of the comet, portions of the debris lost in past passages around the Sun may run into our atmosphere, creating a meteor shower. (William Reach (SSC/Caltech), et al., JPL, Caltech, NASA, apod060513)

 Fragment B "passes" globular cluster M13 on May 3, 2006. Despite their apparent nearness, the comet was only 10 million miles from the Earth, or about fifteen billion times closer than the 25,000 light year distant globular cluster. (Aletti Aletti and Buzzi Luca,

 Above: Fragment C of Comet P73/Schwassmann-Wachmann 3 passes the Ring Nebula (M57) on May 8, 2006. As in the case of fragment B passing M13 on the 3rd, it was more a case of "passing in front of" than actually passing, as the fragment was only a few million miles away, while planetary nebula M57 is 2,000 light years away. Still further, at a distance of 200 million light years, is the spiral galaxy (IC 1296) faintly between the comet's head, and the nebula. (Note: Because the comet was so close to the Earth, it moved noticeably relative to the stars during the time required to properly expose this image. To sharply image both stars and comet, two images were taken -- one following the comet, and one following the stars -- and superimposed to produce this montage. To see how rapidly the comet was moving, compare this image with the one below, taken only half an hour later.) (Stefan Seip and Steffen Bruckner, apod060511)
 Below: A second image of the previous scene shows the position of fragment C half an hour later. Usually, comets don't seem to move this much relative to the background stars in only half an hour; but since the comet fragments were less than ten million miles from the Earth, they appeared to move much faster than they would if they had been at larger distances. (Sheldon Faworski and Sean Walker (MASIL Astro-Imaging Team) apod060512)

 The motion of Comet P73/Schwassmann-Wachmann 3 over a period of sixty-seven minutes on May 16, 2006 (or more accurately, of fragment B of that comet, after the comet's breakup into dozens of pieces, earlier that year). Usually, comets are so far away that they seem to move very slowly against the background of stars; but at the time that the eighty-three images which comprise this animation were taken, the cometary fragment was only a little over six million miles from the Earth, one of the closest passages of a comet in historic times, and its motion could easily be observed to move against the starry background even with binoculars (presuming, of course, a location where the sky was dark enough for binoculars to reveal such a faint object). It should be noted, in light of the many hoaxes about collisions of fragments of this comet with the Earth, that even at its closest distance, it was 25 times further from the Earth than the orbit of the Moon. Debris lost by the comet over previous centuries has gradually drifted away from its orbit, and microscopic and pebble-sized pieces of the comet may produce a meteor shower around mid-May, but none of those small pieces have any chance of penetrating our atmosphere, and will all be vaporized more than fifty miles above the surface of the Earth. (Thad V'Soske (, apod060523)