June 5, 1998 In a rare celestial spectacle near Earth's own star, two comets were seen plunging into the Sun's atmosphere in close succession on June 1 and 2. The demise of the comets was followed the same day by a dramatic ejection of hot gas and magnetic energy known as a coronal mass ejection. The observations were made by the Large-Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO). The comets belong to a family known as the "Kreutz Sun-grazers," a class of comets that pass through the solar atmosphere, or corona, at distances as close as 50,000 km (30,000 miles) from the surface. In the images taken on June 1 and 2, the comets brighten rapidly as they approach the Sun and disappear as they are evaporated by solar radiation. Solar physicists have never seen a comet actually hit the Sun's surface, as comets which appear bright against the night sky are quickly lost in the glare of the Sun.
The twin comets are named SOHO-54 and SOHO-55 as they are the 54th and 55th comets discovered since the spacecraft was launched in 1995, according to Dr. Donald Michels, solar physicist from the U.S. Naval Research Laboratory and member of the LASCO science team. Prior to the launch of SOHO, only 25 Sun-grazers had ever been discovered.
Sungrazing comets are believed to have been observed as far back as 372 B.C., according to Dr. Brian Marsden of the Harvard Center for Astrophysics. Marsden has speculated that a great comet seen by Aristotle and Ephorus may have been a Kreutz sungrazer. The Kreutz Sun-grazers are believed to be fragments of a single comet that broke up (much like Comet Shoemaker Levy 9) several thousand years ago. They are named for Heinrich Kreutz, who made the first extensive studies of sungrazing comets in the 1880s and 1890s.
In a spectacular coincidence, a coronal mass ejection (CME) accompanied by an erupting prominence occurred on the southwest limb of the Sun within hours after the destruction of the comets. The CME and prominence were probably unrelated to the comets, being instead the product of weeks of intense magnetic activity in that region of the Sun. The eruption of solar gas was directed away from Earth and does not pose a hazard to our planet or to orbiting astronauts.
SOHO is a project of international cooperation between the European Space Agency and NASA, and the spacecraft is part of the International Solar-Terrestrial Physics program, a global effort to study the interaction of Sun and Earth. The LASCO instrument was developed at the U.S. Naval Research Laboratory, with collaborators in the United Kingdom, France, and Germany. Selected images, movies, and an image sequence of the new observations can be found on the World Wide Web at:
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The above story is reprinted from materials provided by NASA Goddard Space Flight Center.
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