Category Archives: comet dust

comet, Comet 67P/Churyumov-Gerasimenko, comet dust, rosetta, rosetta spacecraft

Snake Eyes on a Comet

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Weird-looking Jets from Comet 67P Tell Tales of Interior Activity

This image of Rosetta’s comet taken on April 25, 2015 from a distance of approximately 93 kilometers (57 miles) shows clearly distinguishable dust jets persisting after nightfall. (Click image for a larger view.) ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The Rosetta Mission’s OSIRIS camera team released an image of jets blasting out from beneath the dusty surface of Comet 67P/Churyumov-Gerasimenko. The instant I saw the image, the jets reminded me of fangs on an alien snake or laser-like eyes on some strange sci-fi monster (how’s that for some Monday-morning pareidolia?). Actually, the truth is far more interesting than fiction.

What we’re looking at here is what happens when the Sun warms a comet. It’s a view of two jets on the side of the comet that will shortly be in darkness. And therein lies an interesting suggestion about jet activity on 67P. All along, since Rosetta arrived at the comet, we’ve been getting treated to increasing amounts of jet activity as 67P gets closer to the Sun and gets heated up. But, until recently, the jets were only active on the daylight side of the comet. Now, they’re persisting after sunset, and showing up prior to sunrise. So, what has changed?

The answer is pretty simple: as the comet gets closer to the Sun, its activity is increasing. The OSIRIS team suggests that the comet can store heat beneath the dusty crust, and the deeper layers remain warm quite a while after sunset and after the surface cools. This isn’t a new idea, since other comets have shown similar post-sunset activity, but this is the first time that astronomers have been able to get a good, high-resolution look at post-sunset jets on a comet. It’s the kind of detail that will help comet scientists understand their targets better.

Comet 67P has its closest approach to the Sun on August 13, 2015, and the Rosetta spacecraft will be tracking right along with it through this incredibly busy (and somewhat dangerous) time. For some comets, perihelion passage can break them apart. Comet 67P may not face as much danger as sun-grazing comets that come too close to the Sun. That’s because the closest it will come to the Sun is 186 million kilometers (115 million miles). Earth is 150 million kilometers (93 million miles) away, so that puts the comet’s perihelion distance at outside the orbit of Earth. Still, the comet should show quite a bit more activity, which the spacecraft will be documenting along the way. Stay tuned!

comet, comet dust, panSTARRS

A Comet Over Time

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Pan-STARRS Pans Out

 

Comet Pan-STARRS has been tantalizing viewers for weeks now, and we finally got our chance to see it this week. Of course, it clouded up and snowed for the first night, but for the past couple of nights we’ve been able to step out and watch it in the twilight about 40 minutes or so after sunset.  It’s not huge, it’s certainly not Hale-Bopp or Hyakutake, but it’s there and even folks who have never taken a pic of a celestial object before are getting some decent snaps of it. We set up our camera and tripod and took these timelapses of it last night, which was really the first time I could make it out naked-eye.

Comets are pretty cool — in both literal and figurative senses. They are made up of ice (mostly), and as they get close to the Sun they develop a dust tail, as well as (often enough) a plasma tail. The plasma tail is simply a long “tube” of gases that are energized by interactions with the solar wind. That interaction causes the gases to glow and that forms that second tail we often see in comet images. So, they LOOK cool, too!

If you get a chance to step outside over the next week, look west about 40 minutes after sunset and see if you can spot Pan-STARRS.  There are some gorgeous finder charts at Fred Espenak’s Astropixels site: they’ll help you locate the comet. And, don’t forget to bring along binoculars!