Comet ISON, C/2012 S1 (ISON): Maybe Smaller Than Expected, 3 Miles Across, Currently Shedding 112,000 Pounds Dust Per Minute!
. by Anura Guruge
A lot of incisive insights in this NASA update. The latest estimate is that the nucleus of C/2012 S1 (ISON) is about 3 miles across. That is 1/2 the size that had been initially postulated.
Not that a 3 mile diameter comet is a ‘midget’. That is actually quite a respectable size for a comet — NASA even saying that such a size is typical.
The irregular shaped, Halley’s, 1P/Halley, still the most famous comet of them all, has dimensions of 9.3 x 5 x 5 miles. So, ISON is thought to be smaller than that, and Halley’s is not a big comet.
Hale-Bopp, C/1995 O1 (Hale-Bopp), the ‘Great Comet of 1997‘, the last great comet that most of us in the northern hemisphere got to enjoy, and do so for over a month, was around 37 miles across. So, ISON is less than 1/10th the size of Hale-Bopp. That alone should not be a problem.
Comet Lovejoy, C/2011 W3 (Lovejoy), the ‘Great Comet of 2011‘ (though it was primarily a southern hemisphere spectacle), is thought to have had a nucleus just 1,600’ across [i.e., 1/3rd of a mile] across. So, ISON is 9 times larger than Lovejoy — and Lovejoy did regale.
NASA also states, based on UV observations by Swift towards the end of January 2013: “ISON was shedding about 112,000 pounds (51,000 kg) of dust, or about two-thirds the mass of an unfueled space shuttle, every minute. By contrast, the comet was producing only about 130 pounds (60 kg) of water every minute“.
In January ISON was still quite aways from the Sun.
This is bit a heads up. Just remember: comets love to tease, they love to be unpredictable. I remember Kohoutek, C/1973 E1 (Kohoutek) — though ‘remember’ is not really the right word since it was quite unmemorable. And that was said to be THE ‘comet of the century‘.