The Comet Lemmon is currently visible together with the Comet PANSTARRS in the southern hemisphere. The Comet PANSTARRS will come into view also in Japan from March 10. A photo capturing the two comets together arrived from the ALMA Operations Support Facility (OSF). You can see the Comet PANSTARRS (right) and the Comet Lemmon (left) with a North American 12-m antenna (lower left). [Photographed by Tsuyoshi Sawada]
The Comet Lemmon is a new comet discovered by the Mount Lemmon Observatory on March 23, 2012. The comet becomes brighter from February to April and easily observable in the southern hemisphere. The comet will come closest to the Sun on March 24, and from that day it will be getting less bright. The observation condition is not ideal in Japan, but it may be possible to see the comet growing dim from around May.
As comets are called “dirty snowballs”, they are mainly made of ice and dust. When a comet comes close to the Sun, the melted surface of the comet generates a “tail” from its nucleus. A comet tail is classified into two types according to the chemical composition and appearance. One is the “ion tail” or plasma tail, which is made of gas (ion) from the comet, drifted by the solar wind and extended toward the direction opposite to the Sun. The photographed Comet Lemmon (left) shows its long ion tail extending toward upper left. Another is the “dust tail” which is made of dust from the comet, drifted by the pressure of the sunlight and extended toward the direction opposite to the Sun. Due to the difference of the extent of the pressure applied to each dust particle, the dust tail becomes wide unlike the ion tail. The photographed Comet PANSTARRS (right) shows mainly its dust tail.
To identify the ingredients of the comet’s tail, it is necessary to observe radio waves emitted from the molecules contained in the tail. In past observations, radio waves from organic molecules have been found in a comet tail. Comets will be a key to further understanding of the history of the chemical reactions within the solar system.
