Comet ISON's Size

Observations of Comet ISON


The Dimensions and Diameter of Comet ISON (C/2012 S1)

NASA's SWIFT satellite typically studies the aftermath of exploding stars in distant galaxies. However, the satellite was used in January and February of 2013 by astronomers from the University of Maryland at College Park and Lowell Observatory to study the dust and water being expelled from the comet. These studies have also led to the first estimate of the size of Comet ISON's nucleus.


The studies determined that Comet ISON is expelling roughly 130 pounds (60 kg) of water and 112,000 pounds (51,000 kg) of dust every minute. These shed materials create Comet ISON's coma, dust tail and dust trail.


Astrophysicists compared the dust amount of dust being blown from the comet to observations of other comets of known size. Using this information, they estimated the size of Comet ISON to be 3 miles (5 km) in diameter.


Size of Comet ISON


Shapes and sizes of Tempel 1, Borrelly, Wild 2, Hartley 2 and Halley's Comet.

Credits:  Images by NASA spacecraft in parenthesis

Of course, Comet ISON isn't a perfect five mile wide sphere.


Although the comet is still too far to determine the exact dimensions of its nucleus, it will be like other comet nuclei - unevenly shaped with valleys and peaks, and pockmarked with tiny craters. The image to the left shows the size of dimension of comet nuclei snapped during close fly-bys by the spacecrafts. Giotto, EPOXI, Stardust and Deep Space 1 have all increased on understanding of the dimensions and size of comets.


A U.S. probe named Deep Impact went one step further. It successfully hit Comet Tempel-1 in order to discover the chemical composition beneath the icy surface.  For once we created a crater, albeit a small one at 492 feet (150 m), on a comet rather than the other way around.


The European Space Agency will go even further, when it will attempt to attach a lander to the surface of Comet Churyumov-Gerasimenko in August of 2014.


Comet ISON is expected to lose 10% of its size / mass during this, its first-ever, orbit through the inner solar system.


Planetary Science Institute research scientist Jian-Yang Li led a team of scientists that used The Hubble Space Telescope's Wide Field Camera 3 on April 10, 2013 to determine the size of Comet ISON's coma. On April 10, 2013 Comet ISON was around 386,000,000 miles (621,000,000 km) from the Sun. This put it inside the orbit of Jupiter. Li and his team determined the coma was roughly 3,100 miles (5,000 km) in diameter. This made it almost as wide as the distance between Los Angeles and Augusta, Maine.


Li and his team observed a jet spewing dust from the Sun-facing side of the comet. The dust tail was already 2,300 miles (3,700 km) long. If Comet ISON continues to perform, as expected, it will be one of the brightest comets in history.




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