Astronomers and solar physicists are thrilled by the spectacular passage of a bright comet close to the sun last week. A solar satellite took detailed images as the visitor, called Comet NEAT, swept past and spewed wide trails of dust and gas. The images may include the first recorded interactions between a comet and violent eruptions of magnetized gas from the sun.
Formally known as C/2002 V1, Comet NEAT was spotted in November 2002 by NASA's Near- Earth Asteroid Tracking system in Hawaii. It grew bright enough in early February 2003 for viewers in the Northern Hemisphere to see after sunset with binoculars. On 18 February, the comet dived within 14.8 million kilometers of the sun, just 1/10th the distance of Earth's orbit. That put Comet NEAT within viewing range of a camera on the Solar and Heliospheric Observatory (SOHO), a joint NASA-European Space Agency satellite that watches the sun.
As its icy surface roasted at about 1000 kelvin, the comet disgorged a surprisingly broad dust tail and a fainter but pronounced tail of ionized gas. Indeed, NEAT became the brightest of more than 600 comets seen by SOHO's Large Angle and Spectrometric Coronagraph (LASCO), which studies the sun's blazing outer atmosphere, or corona, and its steady wind of charged particles.
Photos revealed the solar wind in unprecedented detail as it bombarded the comet, says LASCO operations scientist Gareth Lawrence of NASA's Goddard Space Flight Center in Greenbelt, Maryland. In particular, the sun unleashed two giant eruptions of gas and tangled magnetic fields, called coronal mass ejections, as the comet whipped past at 100 kilometers per second. Early analysis suggests that one of the ejections split the ion tail and perhaps even disrupted part of the dust tail, a disturbance that astronomers have never witnessed.
"This is a fantastic laboratory for studying the interaction between the sun and a violently active comet," says planetary scientist Casey Lisse of the University of Maryland, College Park. Lisse plans to scrutinize the dust-tail images for clues about the sizes of particles that boiled off Comet NEAT's nucleus at its closest approach. "It's a fantastically structured and highly spread-out tail, the best I've seen since Comet West in 1975," he notes.