Press Release

More Fragments Discovered in Comet Schwassmann-Wachmann 3 Nucleus

April 24, 2007

Fragment B at the upper left corner and small split fragments.

Precise analysis of a high-resolution image of Comet 73P/Schwassmann-Wachmann 3 (SW3) taken in May 2006 by the Subaru Telescope, reveals that one chunk called Fragment B is split into at least 50 fragments. This is well more than the 13 estimated when the image was first released in 2006.

The comet, which orbits the Sun every 5.36 years, first began splitting into pieces in 1995, and further fragmented in 2000. By the time the comet came around again in 2006, there were dozens of fragments. During its 2006 approach, a research team led by Dr. Tetsuharu Fuse (of the National Observatory of Japan), focused on a larger chunk called Fragment B of SW3's nucleus as it came within 16.5 million kilometers (just over 10 million miles) of Earth. The team used the Prime Focus Camera (Suprime-Cam) attached to the Subaru Telescope to capture an image, that showed 13 pieces that had split from Fragment B. They announced their finding in a press release on May 11, 2006.


Since that time, the team has made further study of the images and found many more pieces of the comet's rapidly fragmenting nucleus. Their result is being published in the April 25, 2007 issue of Publications of the Astronomical Society of Japan.

Due to the short data-processing time between the original observation and the press release, the science team did a brief analysis of the image. In the extended data processing, which included removing the influence of Fragment B from the image, scientists were able to find fainter fragments in the image. The team searched the Fragment B's southwest area, whose size is approximately 5,500 km by 7,700 km (approximately 1.6 arcminutes x 1.1 arcminutes), and found 54 fragments, including the 13 previously announced.

The process of discovering the fragments in the busy environment of a cometary nucleus was painstaking and exciting. "After processing the data, I could hardly sleep, especially when the split fragments gradually started showing up in the data. This result displays the Subaru's great high-resolution ability," said Mr. Naotaka Yamamoto, a team member from the National Institute of Advanced Industrial Science and Technology.

The Subaru Prime Focus Camera (Suprime-Cam) has a field of view that encompasses about the same size as the full moon as seen from Earth. This gives it an advantage over other telescopes in capturing wide areas of the sky. Even with this large field of view, however, the comet fragments had spread so far apart that they couldn't all be seen in the same image. The large Fragments C and E, which split from the main nucleus before 2006 along with Fragment B, are now too far from Fragment B (10.9 degrees and 16.1 degrees respectively) to be seen in one field of view.

However, there is still a possibility that unknown small fragments exist between the Fragments C and B, or B and E. The team searched the one-shot image from Suprime-Cam, which was centered on Fragment B and whose size corresponds to an area on the sky of 130,000 km x 170,000 km, but found no pieces of nucleus between Fragment C and B, or B and E. Due to the limiting magnitude of 24.3 for this observation, scientists could detect fragments with diameters larger than several meters.

If the current collection of fragments of the comet remains stable (that is, if the comet pieces do not further break apart or evaporate), the team is planning to track them during future observations. This will allow them to understand the evolution of comet fragments and the gases and ices they contain.

Cometary nuclei, which are often referred to as "dirty snowballs," contain dust and ice that existed when our solar system was first forming. According to Dr. Fuse, they are an important key to understanding the conditions that existed some 4.6 billion years ago. "Researching comets and understanding the nature of their nuclei is gradually helping us get more information about the birth of the solar system," he said.

* arcminute: an angle of 1 in 60 degrees. 1 degree = 60 arcminutes.

Reference: Fuse, T., Yamamoto, N., Kinoshita, D., Furusawa, H., and Watanabe, J. 2007, Publ. Astron. Soc. Japan 59, 381-386

Object: Comet 73P/Schwassmann-Wachmann 3 Fragment B
Telescope and Focus: Subaru Telescope Prime Focus
Instrument: Suprime-Cam
Filter: R-band (0.65 micrometers)
Observation Time: May 3, 2006, UT
Exposure Time: 8 minutes
Field of View: Approximately 1.6 arcminutes x 1.1 arcminutes
Orientation: North is up. East is left.
Explanation: Fragment B at the upper left corner and small split fragments. Since the telescope was tracking the motion of the comet, stars seems to be streaks.


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