Breakin’ up is easy to do

The entire universe in blog form
April 27 2006 9:21 PM

Breakin’ up is easy to do

'

Remember a few days ago when I wrote about a comet that was not going to hit the Earth? Well, it turns out that even minus an impact, this is a pretty interesting object.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Advertisement

The comet's full name (take a deep breath) is 73P/Schwassmann-Wachmann. It was discovered in 1930, lost for a while, then recovered in 1979. In 1995, it broke apart into several pieces.

Why?

The exact cause is a mystery, though there are plenty of reason why a comet would fall apart. Comets are made of rock and ice. When they get near the Sun, the ice sublimates-- turns directly into a gas -- and flows into space, which is why comets look fuzzy in pictures. The actual nucleus, the solid part, is very small, but the coma, the fuzzy part, can be thousands of miles across.

It makes sense that after repeated passes of the Sun, enough ice is lost to venting that the structure of the comet can be fragile, since the ice in a way is holding the comet nucleus together. Once enough ice is gone, a breakup could occur if the sublimating ice builds up enough pressure to disrupt the structure. But that is just one explanation. The famous comet Shoemaker-Levy 9 broke apart because of the immense tidal forces of Jupiter's gravity. Most comets don't break apart; look at comet Halley, which has been circling the Sun for a long, long time (it was seen in ancient times). It goes to show that some comets are very fragile, and some are not.

73p is a fragile one. It broke apart 11 years ago, and now it's really disintegrating. The picture above is from Hubble, taken just last week, showing some of the small fragments peeling away from a bigger one, Fragment B. The whole thing busted into at least 40 pieces, and certainly there will be more. Here's another Hubble image, of Fragment G:

(Clicking on the images will bring you to the Hubble page where you can get much larger versions.)

In my other blog entry, I talked about why we won't get hit by this comet. It's simply too far away to get any pieces of any real size to hit us. The nearest they'll get, in mid-May, is about 9 million kilometers (5.5 million miles). I got an email from a reader who asked me why, then, does the JPL page which tracks Near Earth Objects give a miss distance of only about 1.5 million km (1 million miles) for fragment 3-AL? Well, conspiracy aside, that's still a fairly comfortable margin -- though I'd be happier with a bigger number! However, I am happier, because that is a statistical lower bound to the minimum distance. The far more likely miss distance is 9.4 million kilometers (about 6 million miles). We're pretty safe.

Some of the comet fragments are visible in binoculars, and I intend of trying for them tonight. If you live in the northern hemisphere, the comet is in the constellation of Corona Borealis. Ian Musgrave, an amateur astronomer in Australia, has a blog with details on where to look. Unfortunately I can't take any pictures, but I'm pretty sure I'll be able to see it. I might even haul out my 'scope to take a peek too. This is a rare opportunity.'

TODAY IN SLATE

Doublex

Crying Rape

False rape accusations exist, and they are a serious problem.

Scotland Is Just the Beginning. Expect More Political Earthquakes in Europe.

Why Men Can Never Remember Anything

The XX Factor
Sept. 19 2014 1:11 PM Why Men Can Never Remember Anything

The Music Industry Is Ignoring Some of the Best Black Women Singing R&B

How Will You Carry Around Your Huge New iPhone? Apple Pants!

Medical Examiner

The Most Terrifying Thing About Ebola 

The disease threatens humanity by preying on humanity.

Television

The Other Huxtable Effect

Thirty years ago, The Cosby Show gave us one of TV’s great feminists.

There’s a Way to Keep Ex-Cons Out of Prison That Pays for Itself. Why Don’t More States Use It?

No, New York Times, Shonda Rhimes Is Not an “Angry Black Woman” 

Brow Beat
Sept. 19 2014 1:39 PM Shonda Rhimes Is Not an “Angry Black Woman,” New York Times. Neither Are Her Characters.
Behold
Sept. 19 2014 11:33 AM An Up-Close Look at the U.S.–Mexico Border
  News & Politics
Foreigners
Sept. 19 2014 1:56 PM Scotland’s Attack on the Status Quo Expect more political earthquakes across Europe.
  Business
Moneybox
Sept. 19 2014 12:09 PM How Accelerators Have Changed Startup Funding
  Life
Inside Higher Ed
Sept. 19 2014 1:34 PM Empty Seats, Fewer Donors? College football isn’t attracting the audience it used to.
  Double X
The XX Factor
Sept. 19 2014 1:11 PM Why Men Never Remember Anything
  Slate Plus
Slate Picks
Sept. 19 2014 12:00 PM What Happened at Slate This Week? The Slatest editor tells us to read well-informed skepticism, media criticism, and more.
  Arts
Brow Beat
Sept. 19 2014 2:44 PM Where Do I Start With Mystery Science Theater 3000?
  Technology
Future Tense
Sept. 19 2014 12:38 PM Forward, March! Nine leading climate scientists urge you to attend the People’s Climate March.
  Health & Science
Medical Examiner
Sept. 19 2014 12:13 PM The Most Terrifying Thing About Ebola  The disease threatens humanity by preying on humanity.
  Sports
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.