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Comet ISON pictured on its way to the inner solar system

Charles Black, Founder and CEO of Sen
May 1, 2013, 7:00 UTC

Sen—Comet ISON, which is making its way to the inner Solar System for the first time, has been imaged by the Hubble Space Telescope.

The Comet, C/2012 S1 ISON, which will pass within 1.2 million km (730,000 miles) of the Sun on November 28 this year, was pictured by Hubble's Wide Field Camera 3 on April 10 when the comet was 621 million km (386 million miles) from the Sun and 634 million km (394 million miles) from Earth. The comet is now slightly closer than Jupiter.

The comet originated in the Oort cloud, a band of icy bodies beyond the orbit of Neptune in the outer Solar System. Astronomers believe that this is ISON's first trip to the inner Solar System and are excited to have the opportunity to study the change in the comet as it heads toward the Sun. The comet's flyby of the Sun is close enough for ISON to be labelled as 'sungrazer'. 

As Comet ISON approaches the Sun it is expected to become an extremely bright object in the night sky as its icy nucleus begins to melt creating a tail of gas and dust - a process known as sublimation. The jets powered by sublimating ice also release dust which reflects sunlight and makes the comet brighter.

Jian-Yang Li of the Planetary Science Institute who led a team that imaged the comet, said: "As a first-time visitor to the inner solar system, Comet C/ISON provides astronomers a rare opportunity to study a fresh comet preserved since the formation of the solar system. The expected high brightness of the comet as it nears the Sun allows for many important measurements that are impossible for most other fresh comets."

Measurements from Hubble and from NASA's Swift space telescope calculate the comet's icy nucleus at about 5 km (3 miles) across. However, the head of the comet, or 'dusty coma', is about 5,000 km (3,100 miles) across. Comet ISON's tail already extends about 92,000 km (57,000 miles). From the sunward-facing side of the comet's nucleus is a jet extending out about 3,700 km (2,300 miles). 

Comet ISON

Computerised view of Comet ISON. In this computer-processed view, the Hubble image has been divided by a computer model coma that decreases in brightness proportionally to the distance from the nucleus. Credit: NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team

On October 1 the comet will pass within 10.8 million km (6.7 million miles) of Mars. Data may be captured by spacecraft operated by NASA and the European Space Agency as it makes its way past the Red Planet. 

After Mars it will head towards its close encounter with the sun, passing within 1.2 million km (730,000 miles) of the the sun on November 28. 

It will make its closest approach to Earth on December 26, coming within 64 million km (40 million miles).

The comet was discovered on September 21, 2012 by Russian astronomers Vitali Nevski and Artyom Novichonok using the International Scientific Optical Network (ISON) telescope. Its progress was recently studied by NASA's Swift space telescope.