Ice, Gas and Fire: Comet ISON's Stunning Portrait
Comet ISON has just become a naked eye object in the night sky after rapidly brightening last week. Just before the potential “Comet of the Century” erupted, a specialist telescope at the European Southern Observatory’s (ESO) La Silla Observatory zoomed in on the erupting dirty snowball to resolve stunning detail in the comet’s coma and tail.
This striking observation of ISON was made possible by using the TRAnsiting Planets and PlanetesImals Small Telescope (TRAPPIST) 60 centimeter telescope. TRAPPIST was built to detect and characterize planets orbiting other stars, but it is just as adept at imaging objects closer to home, specifically comets zooming through the solar system.
The telescope has been monitoring ISON since mid-October, allowing a broad spectrum view of the comet. Through the use of narrowband filters, however, TRAPPIST has also been able to gather valuable emission data on specific gases being vented by the comet.
As ISON gets ever closer to the sun, solar energy is heating up its nucleus, causing rapid sublimation of the ices contained within. (Sublimation occurs when an ice turns directly from a solid to gas without passing through the liquid phase — an everyday example of this would be carbon dioxide ice — also known as “dry ice” — venting gas at room temperature.) The comet, which is thought to be making its very first inner solar system appearance after originating from the Oort Cloud, will make closest approach to the sun on Nov. 28 (Thanksgiving), coming within 1.2 million kilometers from its surface.
Currently, the nucleus is retaining its structure, but that could change at any time. Should the nucleus succumb to the searing heat of the sun’s corona, it could break apart and fragment.
But will Comet ISON truly become the Comet of the Century? It will have to overcome its trial by fire and swing past the far side of the sun before we find out. In short, all bets are off.