(Credit: NASA; European Space Agency; Jian-Yang Li (Planetary Science Institute); Hubble Comet ISON Imaging Science Team)
NASA's Hubble has snapped some the first pictures in visible light of Comet ISON, which may become one of the brightest we've ever seen from Earth.
Comet ISON, discovered in September of last year by Russian Vitali Nevski, is headed in our direction. And although the sungrazing comet is still over 634 million kilometres (394 million miles) away (a little closer than Jupiter's current orbit), NASA's Hubble telescope managed to capture an amazing photograph on 10 April.
NASA believes that, when ISON is at its closest point to the sun on 28 November this year, it will briefly become brighter than the moon in the sky — making it a serious contender for "comet of the century".
Currently, the comet is headed towards the sun at a speed of around 75,000 kilometres per hour (47,000 miles per hour), has a dusty head of around 5000 kilometres (3100 miles) wide (about 1.2 times the width of Australia) and its tail trails more than 92,000 kilometres (57,000 miles) behind. And yet, the core of the comet's head is tiny — no more than around 4.8 to 6.5 kilometres (three to four miles) across.
This, according to researchers, is surprisingly small considering the comet's level of activity. Already the comet is reacting to the heat of the sun at its current distance, sublimating ice and creating a dust jet of sublimated ice and frozen gases that extends 3700 kilometres (2300 miles) in front of the comet.
When ISON reaches its perihelion, or closest point to the sun, of just over 1.1 million kilometres distance (700,000 miles), it is expected that its icy nucleus, intensely heated by the sun's rays, will sublimate not just ice and gas, but also silicates and even metals, burning brighter than the moon.
"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," said Planetary Science Institute Research Scientist Jian-Yang Li, who led a team that imaged the comet. "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."