Crunch time for ISON, 10 days from perihelion

The clock is ticking on Comet ISON, which is now less than 10 days from its perihelion date with the sun on November 28th. The comet began its long (very, very long) journey through the solar system when it was kicked out of the Oort cloud, a mass of ice and rock in the far reaches of the solar system. ISON is taking a not-so-well-traveled path through the inner solar system, not along the typical belt or path which comets have taken. This means a few things. First of all, ISON is unpredictable. We’ve never seen a sungrazing comet quite like it before. But second and more importantly, ISON is a great tool of study for scientists. How ISON behaves exactly will be very important to scientists and astronomers. So it is safe to say that all eyes will be on the now famous comet over the next 10 days.

What is perihelion exactly? Without getting too technical, it is the point when ISON will come closest to, or “graze” the sun. Comet ISON will feel the intense gravitational pull, incredible temperatures, and full force of solar wind from the sun. In fact, the comet is already experiencing the increasing impacts of all three as it dives towards the sun. The comet recently experienced an “outburst”, with a dramatic increase in brightness by almost 2 magnitudes — and began spewing gas and other volatiles from its surface into space. As it did so, it developed a dramatic tail (which at one point was 16 million kilometers long) and became a naked-eye object in the pre-dawn sky.

Comet ISON, imaged after its outburst on November 16th 2013.

Comet ISON, imaged after its outburst on November 16th 2013.

How can I see ISON now? You can catch a view of ISON in the pre-dawn skies, but there are a few catches, and it is getting harder to see it each day. ISON is diving towards the sun, which means that it will become increasingly dim in the suns glow over the next few days. Additionally, you’ll need to travel away from the city light and have a good view of the eastern horizon. It will be impossible to see ISON with the naked eye within 30 miles of New York City’s urban light. If you can find a suburban location with a good view, you may want to bring binoculars along just in case. ISON is located near the bright star Spica. But as we mentioned, it is diving towards the sun at a fast pace now — and will be nearly impossible to see by the end of this week. Given the uncertainty, which will discuss below, you may not get another chance to see it at all.

View of constellations and Comet ISON to the east on November 18th 2013.

View of constellations and Comet ISON to the east on November 18th 2013.

 

What will happen to Comet ISON next? Quite simply, we don’t know. There are many theories beginning to surface regarding the recent outburst of brightness and the developing long tail of ISON. What we do know, is that the outburst occurred as a result of increasing solar wind and heat as ISON dives closer to the sun. It is impossible to know right now, however, if the nucelus of Comet ISON has fragmented from this outburst, or if it remains intact. The forces from the sun are very powerful, so ISON will have to put up quite a fight to survive. The nucelus of the comet is quite small for a sungrazer as well.

But the latest imagery and analysis seems to show that not only is the nucelus in one piece, but it looks to be quite a healthy comet with a sustained sunward facing jet. The volatiles which are burning off ISON are creating quite a spectacle with the long tail and plentiful colors as seen on the images above.

Astronomers processing of Comet ISON imagery showing potential jet structure.

Astronomers processing of Comet ISON imagery showing potential jet structure.

On November 28th, ISON will reach perihelion and will be monitored by several spacecraft and imaged like no comet has been before. At that point, it will become apparent whether ISON has survived its encounter with the sun or not. Comet ISON will then slingshot out from the sun, and if it survives in one piece, should put on quite a show for Earth in the few weeks thereafter. ISON could also break up near perihelion, with the volatiles and tail swinging around the sun and becoming visible from Earth. The third, and most disappointing, potential result would be if Comet ISON broke up prior to perihelion, which would almost ensure that the comet would dive close to the sun in several fragments, and never be seen from earth.

One thing we can say with certainty is that over the next few weeks, the eyes of scientists and astronomers alike will be peeled to the behavior of Comet ISON, hoping that it will eventually put on an astronomical show later this month into December.

 

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