Comet ISON is a comet from the edge of our Solar System, a region called the Oort Cloud. Discovered in September 2012 at a distance farther from the Sun than Jupiter, it's orbit is taking the comet to closer than 900,000 miles from the Sun's surface. The Earth is 93 million miles away from the Sun, and Mercury, the closest planet, only gets as close as 29 million miles. We call this type of comet a sungrazer. The comet seems to be large enough, that in November it may be bright enough to see in the daytime. But, comets are difficult to predict, especially those that were recently discovered. Observations of the comet are continuously pouring in and improving our knowledge of the comet's activity and orbit, and I give an update below. I also contacted a meteoroid stream expert, Jeremie Vaubaillon, about the possibility of an ISON produced meteor shower in January 2014.

The Activity of ISON

Comet ISON's activity is what makes it so exciting. If its present brightness and increase in activity is sustained throughout this year, we will have a big bright comet on our hands. But anything can happen, so astronomers, amateur and professionals alike, are closely watching the comet, and constantly refining their predictions. NASA's Swift satellite observed ISON's activity in January, and a report on those observations are posted at NASA's website. There you can also find diagrams of Comet ISON's orbit to help you visualize the comet's journey toward the Sun.

ISON Meteors?

Comet ISON and Earth

A close approach between Earth and Comet ISON's orbit. Will this encounter produce a meteor shower? Probably not. The green orbit is Comet ISON's orbit and has been split into two parts: the solid line is the path before grazing the Sun, and the dotted line is after.

In January 2014, the Earth will swing past a part of space that Comet ISON already traveled through, at a small distance of only 0.03 AU. This encounter brings up the possibility of a meteor shower on Earth. Meteor showers can be used to study the size, composition, and shape of dust grains, but only if they can be predicted in advance. In addition, meteor showers from Oort Cloud comets are rare events. So will ISON's dust hit the Earth next January? I posed the question to Jeremie Vaubaillon, meteoroid stream expert at the Institut de Mecanique Celeste et de Calcul des Ephemerides in Paris, France. Assuming that Comet ISON has been in the Solar System before (more on this below) then his preliminary simulations suggest that the meteoroid stream will not cross the orbit of the Earth. Jeremie writes, "I don't really foresee any meteor shower from the comet, unfortunately." Oh well, it was an interesting possibility!

The Orbit of Comet ISON

Comet ISON is clearly from our Oort Cloud. The Oort Cloud is a huge region of space surrounding our Solar System. It is so large, in fact, that it may extend one-third of the way to alpha Centauri, the closest star system to our Sun! The Oort Cloud was formed in early in our Solar System's history, about 4 billion years ago. Comets from the Oort Cloud fall into two orbital categories. They can be: 1) on their first trip back into the Solar System; or, 2) on a subsequent returning trip. Comet Hale-Bopp and Hyakutake, the two great comets from the 1990's, are both in this later group. They have been to the inner-Solar System several times, and will be back again, Hale-Bopp in a few thousand years, and Hyakutake in several tens of thousands of years.

In my previous post, I wrote about the similarity of the orbits of Comet ISON and the Great Comet of 1680, and the possibility that these comets are two pieces of a larger object that split sometime in the distant past. However, the latest orbit solution from the International Astronomical Union's Minor Planet Center, based on all the best observations of the comet to date, shows that Comet ISON is probably on it's first passage into the Solar System [1], making a genetic link to the Great Comet of 1680 very unlikely. Another busted prediction!

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  1. International Astronomical Union, Minor Planet Center Comet C/2012 S1 (ISON)


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