NEWS | Jan. 19, 2012

Karl Battams Co-authors Paper in Science

By Donna McKinney

Karl Battams, a researcher in the Naval Research Laboratory's Space Science Division, has a paper published in the 20 January 2012 issue of Science. The paper, Destruction of Sun-grazing comet C/2011 N3 (SOHO) within the low solar corona, reports the observation of a Kreutz-group comet within the solar atmosphere.

Observations of comets in Sun-grazing orbits that survive solar insolation long enough to penetrate into the Sun's inner corona provide constraints on the solar atmosphere and magnetic field as well as on the make up of the comet. On 6 July 2011, the Solar Dynamics Observatory (SDO) observed the demise of comet C/2011 N3 (SOHO) within the low solar corona in five wavelength bands in the extreme ultraviolet (EUV). The comet penetrated to within 0.146 solar radii (≈ 100,000 km) of the solar surface before its EUV signal disappeared. Before that, material released into the coma - at first seen in absorption - formed a variable EUV-bright tail. The deceleration of the tail due to the interaction with the surrounding coronal material yields an estimate for the total mass lost in the 10 minutes during which it was observed by AIA of ≈ (0.06 &mdash 6) 1010 g (corresponding to an effective nucleus diameter of ≈ 10 — 50 m); the EUV absorption by the comet and the brightness of the tail suggest that the mass was at the high end of this range. These observations provide evidence that the nucleus had broken up into a family of fragments, resulting in accelerated sublimation in the Sun's intense radiation field.

Sun-grazing comets have been observed for many hundreds of years. In the late 1880's and early 1890's, Heinrich Kreutz studied the possible sun-grazing comets, which had been observed until then, and determined that some were sun-grazers and some were not. He also found that those which were indeed sun-grazers all followed the same orbit. That is, they were all fragments of a single comet, which had broken up. It is probable that the original comet, and its fragments, have broken up repeatedly as they orbit the sun with a period of about 800 years. In honor of his work, this group of comets is named the Kreutz sun-grazers.