Monthly Archives: June 2015

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

Snake Eyes on a Comet

Leave a comment

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!

New Horizons mission, Pluto

High Noon on Pluto: What’s it Like?

2 Comments

Get Ready for Pluto

Artist's conception of New Horizons at Pluto and Charon. Courtesy: JHUAPL/SwRI
Artist’s conception of New Horizons at Pluto and Charon. Courtesy: JHUAPL/SwRI

As the New Horizons spacecraft enters its final five-week dash to Pluto, the news hits just keep rolling in. Yesterday, I talked about the tumbling moons affected by the orbits of Pluto and Charon. I expect we’ll find more information about them as the spacecraft gets closer, plus some more new images to whet our appetites for all things Pluto.  Five weeks from now, it will be Pluto Partay time, for sure!

Have you ever wondered what it is like on the surface there? Of course, we already know that it’s icy and cold. The presence of nitrogen ice on the surface tells us it’s cold enough on Pluto to freeze this gas (which happens at -195.8 C). The mean surface temperature at Pluto is -229 C (44 K), and that’s mighty cold.  The atmosphere, while thin, is mostly nitrogen, with contributions from methane and carbon monoxide. As Pluto moves away from the Sun in its 248-year orbit, most of that atmosphere will “freeze out” and fall to the ground as a frost. So, it’s pretty clear things are distinctly chilly at the planet.

The Sun doesn’t do a lot to warm things up. It’s too far away to provide the kind of heat we take for granted here on Earth.  And, due to that distance, days aren’t as bright on Pluto as they are here on warm, comfy Earth. Now, New Horizons isn’t going to land on Pluto; it’s a flyby mission. And, it will be a long time before anybody has the chance to send people to Pluto. But, there is a way to experience Pluto’s lighting conditions for yourself. It’s called “Pluto Time”.   There’s a time between dawn and dusk when the lighting conditions where you are will be just like it is at noon on Pluto.  It’s easy to do; just go to the Pluto Time web page at NASA and follow the directions. In  less than a minute, you’ll know when the next “Pluto Time” at your location occurs. You can take a picture of what Pluto Time looks like wherever you are and share it with others, too. I encourage you to check the page out; you’ll be surprised at what you find out about how bright/dim it is at this distant dwarf planet.