A very unusual comet has been stirring up the astronomy community in the last few weeks. Called Lovejoy after its discoverer, the Australian amateur astronomer Terry Lovejoy, this is a Kreutz sungrazing comet. It was spotted in late November as a series of very faint smudges in three images of the sky. Lovejoy has discovered other comets – but this was the first one using a new set of equipment – and his first discovery in four years. Sungrazers are those comets that pass the sun within one or two solar radii, most are discovered from SOHO satellite images on their one way trip towards the Sun. Since they pass so close to the Sun, almost all are vaporized. Comet Lovejoy is doubly unusual – it is the first Kreutz comet to be discovered from the ground since 1970, and it survived perihelion!
There are several spacecraft that observe the Sun – many of these started to return images of Comet Lovejoy in December. Even though these cameras are usually set for solar observing, they were adapted by using shorter than normal exposure times and running through different filters more frequently. Given that Comet Lovejoy got as bright as Venus, it took some fancy footwork to get decent images.
The comet made its closest approach to the Sun on December 16th– only 120,000 km above the solar surface. This took it through the several million degree solar corona and few astronomers expected it to survive. But survive it did! In the past, sungrazing comets would have been lost in the Sun’s glare – often permanently, but, thanks to the number of sun-watching spacecraft, comet Lovejoy was seen re-emerging from its close solar shave. As it passed through the solar corona, Lovejoy’s extended dust tail was completely severed. As the comet reappeared from perihelion, all that remained was an intense, condensed nucleus with no tail at all. But within just three-and-a-half hours, it underwent a spectacular and unexpected resurgence and returned to its former glory! Observers from the southern hemisphere were treated to the magnificent sight of one of the brightest recent comets shining above the eastern horizon during Christmas week. One of the best images of the comet was taken by the crew of the International Space Station – from orbit they were treated to what Dan Burbank described as “”the most amazing thing I have ever seen in space.”
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From this we have an almost overwhelming catalogue of data of a comet going through the most extreme environment the solar system has to offer. The effects of the solar wind and corona on the comet’s nucleus and tail allow us to gain an understanding of the Sun, and how it drives Space Weather at Earth.
The comet is now rapidly fading as it moves away from the Sun, it will not be a naked eye comet for observers in the Northern Hemisphere. It is expected back in 565 years (plus or minus 30 years) –we might get a better view next time!
This episode of “What is the Stars?” was first broadcast January 16, 2012. Listen live, Mondays and Fridays on lyric fm.
