Dazzling Comet Approaching Sun

NASA's Swift satellite has captured images of comet C/2012 S1 (ISON), which may be one of the brightest comets to round the sun in the last 50 years. Using images acquired over the past two months, astronomers from the University of Maryland at College Park (UMCP) and Lowell Observatory have made estimates of the comet's water and dust production and used them to conclude the size of its icy nucleus.

Image of comet ISON captured by NASA's Hubble Space Telescope. Image via nasa.gov.

Like all comets, ISON is made of frozen gases mixed with dust. In January, when it was 375 million miles from Earth and 460 million miles from the sun, observations revealed that ISON was shedding about 112,000 pounds of dust every minute, and producing about 130 pounds of water at the same rate. According to astronomer Dennis Bodewits from UMPC, the mismatch between the amount of dust and water produced means that ISON's water sublimation is not yet powering its jets, as it's too far from the sun. Once the comet nears the sun, its icy materials will transform to a solid gas, feeding it more fuel. Materials such as carbon dioxide or carbon monoxide ice evaporate at greater distances and are currently fueling ISON's activity.

From now through October, ISON will be traveling through the constellations Gemini, Cancer and Leo, toward the sun. Image via nasa.gov.

Though the water and dust production rates aren't exactly accurate because of the comet's faintness, they're used to estimate the size of ISON's body. Scientists believe the nucleus is about three miles across, a typical size for a comet.

Lined up to soar through the inner solar system, ISON remains unusually active for its distance from the sun. If it continues this way, it will rank as one of the brightest comets in decades by the time it approaches the sun in late November. Once it departs the sun and moves toward Earth, it will appear in evening twilight through December, at a safe 39.9 million miles away.

Story via nasa.gov.