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  • The Comet With a Broken Heart

    European Southern Observatory
    ESO. Astronomy made in Europe


    ESO 15/06 - Press Photo

    25 April 2006
    For immediate release
    The Comet With a Broken Heart
    VLT Takes Images of Disintegrating Comet P73/Schwassmann-Wachmann 3

    On the night of April 23 to 24, ESO's Very Large Telescope observed fragment B of the comet Schwassmann-Wachmann 3 that had split a few days earlier. To their great surprise, the ESO astronomers discovered that the piece just ejected by fragment B was splitting again! Five other mini-comets are also visible on the image. The comet seems thus doomed to disintegrate but the question remains in how much time.

    Comet P73/Schwassmann-Wachmann 3 (SW 3) is a body with a very tormented past. This comet revolves around the Sun in about 5.4 years, in a very elongated orbit that brings it from inwards of the Earth's orbit to the neighbourhood of giant planet Jupiter. In 1995, when it was coming 'close' to the Earth, it underwent a dramatic and completely unexpected, thousand-fold brightening. Observations in 1996, with ESO's New Technology Telescope and 3.6-m telescope, at La Silla, showed that this was due to the fact that the comet had split into three distinct pieces. Later, in December 1996, two more fragments were discovered. At the last comeback, in 2001, of these five fragments only three were still seen, the fragments C (the largest one), B and E. No new fragmentations happened during this approach, apparently.

    ESO PR Photo 15a/06
    ESO PR Photo 15a/06

    Fragment B of Comet SW-3

    Things were different this time, when the comet moved again towards its closest approach to the Sun - and to the Earth. Early in March, seven fragments were observed, the brightest (fragment C) being of magnitude 12, i.e. 250 fainter than what the unaided can see, while fragment B was 10 times fainter still. In the course of March, 6 new fragments were seen.

    Early in April, fragment B went into outburst, brightening by a factor 10 and on 7 April, six new fragments were discovered, confirming the high degree of fragmentation of the comet. On 12 April, fragment B was as bright as the main fragment C, with a magnitude around 9 (16 times fainter than what a keen observer can see with unaided eyes). Fragment B seems to have fragmented again, bringing the total of fragments close to 40, some being most probably very small, boulder-sized objects with irregular and short-lived activity.

    The new observations reveal that this new small fragment has split again! The image clearly reveals that below the main B fragment, there is a small fragment that is divided into two and a careful analysis reveals five more tiny fragments almost aligned. Thus, this image alone shows at least 7 fragments. The comet has thus produced a whole set of mini-comets!

    ESO PR Photo 15b/06
    ESO PR Photo 15b/06

    Broken Fragments of Comet SW-3

    Will the process continue? Will more and more fragments form and will the comet finally disintegrate? How bright will the fragments be when the comet will be the closest to the Earth, on 11 to 14 May, and how many new fragments will have appeared before the comet reaches its closest approach to the Sun, around 7 June?

    Fragment C of the comet should be the closest to Earth on 11 May, when it will be about 12 million km away, while fragment B will come as 'close' as 10 million km from Earth on 14 May. Although this is the closest a comet ever approached Earth in more than twenty years - even Comet Hyakutake's smallest distance was 15 million km - this is still 26 times the distance between the Earth and the Moon and therefore does not pose any threat to our planet.

    ESO PR Photo 15/06
    ESO PR Photo 15c/06

    Mini-Comets coming off Comet SW-3

    If nothing else happens, at the time of closest approach, fragment B will be just visible with unaided eye by experienced observers. It should be an easy target however to observe with binoculars. If we are lucky, however, fragment B presents another outburst, becoming a magnificent sight in the night sky. On the other hand, it could just as well fade away into oblivion. But then, the main fragment C should still be visible, even possibly with the unaided eye.

    ESO telescopes will observe the comet in the greatest detail at the end of May, when it is best observed from Chile and is brighter. These observations will obtain invaluable information, especially as the fragmentation process is revealing all the pristine material buried below the crust of the comet. As such, these observations will prove an ideal complement to the most comprehensive observation campaign made with ESO telescopes of Comet Tempel 1 when it was being bombarded by the Deep Impact spacecraft, on 4 July 2005.

    High resolution images and their captions are available on this page.

    Notes

    About 30 comets have been observed to split in historical times and this process is almost always accompanied by a significant brightening. For instance, the nucleus of comet Shoemaker-Levy 9 broke up into at least 21 individual pieces when it passed very close to Jupiter on July 8, 1992; this was the reason that it became bright enough to be detected some eight months later. In the case of SW-3, the opening of rifts and the subsequent splitting took place far from any planet and must in some way have been caused by increased solar heating. It is possible that major cracks and rifts opened in the irregularly shaped icy nucleus already before perihelion as the surface temperature began to increase. Completely "fresh" cometary material was thereby exposed to the solar light and the evaporation rate increased quickly, releasing more gas and dust into space. In the course of this process, the rifts gradually widened until the definitive breakage occurred somewhat later.

    Comet Schwassmann-Wachmann 3 was discovered on May 2, 1930, on a photographic plate obtained at the Hamburg Observatory (Germany) by two astronomers at this institution, Arnold Schwassmann and Arthur Arno Wachmann. The subsequent observations showed that the comet moved in an elliptical orbit with a revolution period of somewhat more than 5 years. Great efforts were expended to observe the comet during the next returns, but it was not recovered until nearly 50 years and eight revolutions later, when its faint image was found of a plate obtained in August 1979 with a telescope at the Perth Observatory in Western Australia. It was missed in 1984, but was sighted again in 1989 and since then, it is observed at each close approach. Thus this comet has only been observed during six out of fifteen approaches since 1930. While this may be partly due to a less advantageous location in the sky at some returns, it is also a strong indication that the comet behaves unpredictably and must have a quite variable brightness. Orbital calculations have shown that it was inserted into the present, short-period orbit by the strong gravitational pull of Jupiter during several, relatively close encounters with this giant planet. For instance, it passed Jupiter at a distance of about 30 million kilometres in 1882 and 1894, and again at 40 million kilometres in 1965. SW-3 belongs to the so-called "Jupiter family" of comets.

    The observations were done with the FORS1 multi-mode instrument on Kueyen, the second 8.2-m Unit Telescope of the Very Large Telescope located at Cerro Paranal (Chile). The fragment was observed in four bands (B, V, R, and I) for a total of 30 minutes by Emmanuel Jehin, Olivier Hainaut, Michelle Doherty, and Christian Herrera, all from ESO. The astronomers had the telescope track the comet, which explains why the stars appear as trails of coloured dots, each colour corresponding to the order in which the observations were done in the various filters. At the time of the observations, the comet was 26.6 million km away from the Earth, in the constellation Corona Borealis. The seeing was 1.5" as the comet was observed when it was rather low on the horizon as seen from Paranal. The final processing of the image was done by Haennes Heyer and Olivia Blanchemain (ESO).

    More observations of the comet are foreseen from 20 till 30 May with ESO telescopes on the three sites of La Silla (NTT, 3.6m), Paranal (VLT) and Chajnantor (APEX). These observations will study aspects as diverse as the presence of organics in the dust, the composition of this dust, the structure of the coma, and the presence of deuterated water.

  • #2
    Re: The Comet With a Broken Heart

    News And Photo Releases
    News - heic0605: Hubble provides spectacular view of ongoing comet breakup

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    27-Apr-2006: The NASA/ESA Hubble Space Telescope is providing astronomers with extraordinary views of comet 73P/Schwassmann-Wachmann 3 as it disintegrates before our eyes. Recent Hubble images have uncovered many more fragments than have been reported by ground-based observers. These observations provide an unprecedented opportunity to study the demise of a comet nucleus.

    Amateur and professional astronomers around the world have been tracking the spectacular disintegration of 73P/Schwassmann-Wachmann 3 for years. As it plummets towards a close encounter with the Sun, swinging round the Sun on 7 June and heading away to begin another loop round the Solar System, the comet will pass the Earth on 12 May, at a distance of 11.7 million kilometres, or 30 times the distance between Earth and the Moon.

    The comet currently comprises a chain of over 33 separate fragments, named alphabetically, and stretching across several degrees on the sky (the Sun and Moon each have an apparent diameter of about 1/2 a degree). Ground-based observers have noted dramatic brightening events associated with some of the fragments indicating that they are continuing to break up and that some may disappear altogether.

    Hubble caught two of the fragments, B and G, shortly after major outbursts in activity. The resulting images reveal that an amazing process of hierarchical destruction is taking place, in which the larger fragments are continuing to break up into smaller chunks. Several dozen "mini-fragments" are to be found trailing behind each main fragment, probably associated with the ejection of house-sized chunks of surface material that can only be detected in these very high-resolution Hubble images.

    Sequential Hubble images of the B fragment, taken a few days apart, suggest that the chunks are pushed down the tail by outgassing from the icy, sunward-facing surfaces of the chunks, much like space-walking astronauts are propelled by their jetpacks. The smaller chunks have the lowest mass, and so are accelerated away from the parent nucleus faster than the larger chunks. Some of the chunks seem to dissipate completely over the course of several days.

    One of the European team members, Philippe Lamy from Laboratoire d?Astrophysique de Marseille, France, says ?When we observed the comet in late 2001 we concluded that many small, by then invisible, fragments had to be created by fragmentation to account for the missing mass. The new Hubble observations beautifully confirm and illustrate our past findings.?

    Cometary nuclei are deep-frozen relics of the early Solar System, consisting of porous and fragile mixes of dust and ices. They can be broken up by many different mechanisms: be ripped apart by gravitational tidal forces when they pass near large bodies (for example, Comet Shoemaker-Levy 9 was torn to pieces when it skirted near Jupiter in 1992, before plunging into Jupiter?s atmosphere two years later), fly apart as the nucleus rotates rapidly, crumble under thermal stresses as they pass near the Sun, or pop apart explosively like corks from champagne bottles as trapped volatile gases burst out.

    "Catastrophic breakups may be the ultimate fate of most comets," says planetary astronomer Hal Weaver of the Johns Hopkins University Applied Physics Laboratory, who led the international team that made the recent Hubble observations and who used Hubble previously to study the fragmentations of comets Shoemaker-Levy 9 in 1993-1994, Hyakutake in 1996, and 1999 S4 (LINEAR) in 2000. Analysis of the new Hubble data, and data taken by other observatories as the comet approaches the Earth and Sun, may reveal which of these breakup mechanisms are contributing to the disintegration of 73P/Schwassmann-Wachmann 3.

    German astronomers Arnold Schwassmann and Arno Arthur Wachmann discovered this comet during a photographic search for asteroids in 1930, when the comet passed within 9.3 million kilometres of the Earth (only 24 times the Earth-Moon distance). The comet orbits the Sun every 5.4 years, but it was not seen again until 1979. The comet was missed again in 1985 but has been observed at every return since then.

    During the autumn of 1995, the comet had a huge outburst in activity and shortly afterwards four separate nuclei were identified and labelled "A", "B", "C", and "D", with "C" being the largest and the presumed principal remnant of the original nucleus. Only the C and B fragments were definitively observed during the next return, possibly because of the poor geometry of the 2000-2001 apparition. The much better observing circumstances during this year?s return may be partly responsible for the detection of so many new fragments, but it is also likely that the disintegration of the comet is now accelerating. Whether any of the many fragments will survive the trip around the Sun remains to be seen.

    Notes for editors:

    The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

    Besides Weaver, the other members of the Hubble observing team are: Carey Lisse (JHU/APL), Philippe Lamy (Laboratoire d'Astronomie Spatiale, France), Imre Toth (Hungarian Academy of Sciences), William Reach (IPAC/Caltech) and Max Mutchler (STScI).

    Image credit: NASA, ESA, H. Weaver (JHU/APL), M. Mutchler and Z. Levay (STScI)

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    • #3
      Re: The Comet With a Broken Heart

      http://www.space.com/scienceastronom..._noimpact.html
      NASA Says Comet Fragments Won't Hit Earth
      By Tariq Malik
      Staff Writer
      posted: 27 April 2006
      3:00 p.m. ET

      Chunks of a comet currently splitting into pieces in the night sky will not strike the Earth next month, nor will it spawn killer tsunamis and mass extinctions, NASA officials said Thursday.
      The announcement, NASA hopes, will squash rumors that a fragment of the crumbling Comet 73P/Schwassmann-Wachmann 3 (SW 3) will slam into Earth just before Memorial Day.
      ?There are some Internet stories going around that there?s going to be an impact on May 25,? NASA spokesperson Grey Hautaluoma, told SPACE.com. ?We just want to get the facts out.?
      Astronomers have been observing 73P/Schwassmann-Wachmann 3, a comet that circles the Sun every 5.4 years, for more than 75 years and are confident that any of the icy object?s fragments will remain at least a distant 5.5 million miles (8.8 million kilometers) from Earth ? more than 20 times the distance to the Moon ? at closest approach between May 12 and May 28.
      "We are very well acquainted with the trajectory of Comet 73P Schwassmann-Wachmann 3," said Donald Yeomans, manager of NASA's Near-Earth Object Program Office, in a written statement. "There is absolutely no danger to people on the ground or the inhabitants of the International Space Station, as the main body of the object and any pieces from the breakup will pass many millions of miles beyond the Earth."
      The main SW 3 fragment, dubbed Fragment C, will make its closest pass by Earth on May 12 at a safe distance of 7.3 million miles (11.7 million kilometers), NASA said, adding that skywatchers will be able to use small telescopes to spot the comet chunks by scanning the constellation Vulpelca during the early-morning hours. [Click here for a map of SW 3?s path across the sky.]
      NASA?s Hubble Space Telescope and other instruments have been watching SW 3?s disintegration. The comet?s numerous fragments stretch across several degrees of the night sky. For comparison, the Moon?s diameter covers about one-half a degree in the sky.
      "Catastrophic breakups may be the ultimate fate of most comets," explained Hal Weaver, a planetary astronomer of the Johns Hopkins University Applied Physics Laboratory, in a statement.
      Weaver led a team of researchers during the Hubble observations of SW 3, and used the space telescope to study the break up of comets Shoemaker-Levy 9 ? which was ripped apart by Jupiter?s gravity and hit the giant planet between 1993 and 1994 ? Hyakutake in 1996, and 1999 S4 (LINEAR) in 2000, NASA said.
      Hubble?s new SW 3 observations suggest that chunks of the comet are pushed behind its tail by the outgassing of Sun-facing pieces. Smaller pieces appear to be ejected from their nucleus faster than their larger brethren, while other fragments seem to simply fade away.
      When set alongside studies by other observatories, Hubble?s images may help astronomers determine what is causing the comet?s disintegration as it nears the Earth and Sun, the space agency added.
      German astronomers Arnold Schwassmann and Arno Arthur Wachmann first discovered the SW 3 comet in 1930 while hunting for asteroids. Despite its relatively short orbital period, the icy object was not seen again until 1979, and then was missed during a 1985 pass.
      Since then, however, astronomers have kept a close eye on SW 3 and in 1995 observed its initial break up.
      Aside from a great sky show, the comet poses no danger to Earth and its inhabitants, NASA officials said.

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