Look for Comet Linear
28 July 2000It may not be as spectacular as Comets Hyakutake or Hale-Bopp in 1996-97,butComet Linear is currently the best show in town for European observers.But dont waste any time. The icy intruder, which is making its first visitto the innerSolar System and has just passed within 114 million km (71 million miles) ofthe Sun,seems to have broken up in the last few days and may rapidly fade fromview.
For anyone hoping to see the newcomer, binoculars or small telescopes are essential. However, if the skies are clear, it should be possible to find the fuzzy comet to the south west of the bowl of the Big Dipper.
Linear will remain well above the northern horizon for the next few days as it passes through the constellation of Ursa Major (the Great Bear) and travels south through Leo (the Lion).
Unfortunately, after heading into the galaxy-rich constellation of Virgo (the Virgin), in the first week of August, it will dip below the horizon and disappear from sight for viewers in the Northern Hemisphere.
Although its brightness has not been as great as hoped, Comet Linear has occasionally burst into life. One of these brief, violent outbursts occurred in early July, when a chunk of the comet broke away and spewed a great deal of dust into space. The Hubble Space Telescopes Imaging Spectrograph observed a sudden, but relatively short-lived, rise in brightness of about 50 percent in less than four hours.
Then, on 25 July, ground observers noticed that the central condensation was seen to be strongly elongated. Its brightness faded and its length increased on the following nights. It seems that the comet completely blew apart.
The gas tail, which virtually disappeared between July 23rd and 24th, has reformed as an extension of the central condensation. Observations with the Jacobus Kapteyn Telescope on La Palma suggest that the comet is dying very quickly and may disappear completely within a few days.
Comet C/1999 S4 Linear was first found 10 months ago by the Lincoln Laboratory Near-Earth Asteroid Research project, which uses a robotic one metre telescope to search for asteroids and comets whose orbits pass close to the Earth. The comet is formally known as Comet 1999 S4, to distinguish it from several other faint comets discovered by the project.
S4 Linear originated in the distant Oort Cloud of comets in the outer reaches of the Solar System, far beyond the outer planet, Pluto. Its brightness has been hard to predict with any accuracy because it is making its first close flyby of the Sun, and more than one short period of heating is usually needed to liberate enough dust particles and water vapour to create a spectacular coma and tail.