Saturday science subject: Bigger than the sun

— 1:21 PM on November 17, 2007

With its 1.39 million kilometer (864,949 mile) diameter, which is a whopping 109 times that of the earth and 19 times that of Jupiter, the Sun is easily the largest object in the solar system. Or at least it was, until comet 17P/Holmes exploded on October 24. According to the University of Hawaii's Institute for Astronomy, the comet has continued to expand since its explosion, and on November 9 it reached a diameter of 1.4 million kilometers (869,920 miles), making it the largest object in the solar system.

Scale picture of the comet (left) and the Sun (right), with Saturn (bottom right) for comparison. Source: University of Hawaii.

The size of the comet's dust cloud is especially impressive considering it was ejected from the comet's nucleus, which is a ball of ice and rock just 3.6 km (2.2 miles) in diameter. Since the explosion on October 24, the comet's brightness has increased by a factor of half a million, and its dust cloud has expanded at a phenomenal 0.5 km/s, or 1,100 mph.

The comet is thought to originate from the Kuiper Belt that lies beyond Neptune, and it currently resides between the orbits of Mars and Jupiter. According to the University of Hawaii, the comet is likely to "either . . . hit the Sun or a planet, be ejected from the Solar system, or simply die by running out of gas" in a few thousand years.

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