Comets are known for their tails. In the old days that’s how you distinguished a comet from an asteroid, though with our modern understanding the line between comet and asteroid as blurred a bit.  Still, one of the big areas of comet research has been on just how comet tails and coma form.

The traditional view has been that water and other volatiles are ejected from the comet through sunlight. The ejected molecules are then broken up through a process of photoionization, where ultraviolet light strikes the molecules, causing them to break apart. It is these ionized molecules that we observe as the coma and tail of a comet.

But we now know that reactions in space can be much more complex and subtle. In this case, we now know that free electrons play a role in the breakup of ejected molecules. The work was recently published in Astronomy & Astrophysics, and details the role of electrons in the chemistry of cometary atmospheres. The data for this research came from the Rosetta probe orbiting Comet 67P/Churyumov-Gerasimenko. Using ultraviolet spectroscopy, the team found that rather than ionizing various molecules directly, the ultraviolet light liberates electrons from water molecules in the coma. These electrons then interact with other molecules to break them apart.

It’s a rather surprising result, but it’s also a great example of how better data allows us to refine a simple model into a more subtle and accurate one.

Paper: P.D. Feldman, et al. Measurements of the near-nucleus coma of comet 67P/Churyumov-Gerasimenko with the Alice far-ultraviolet spectrograph on Rosetta. A&A DOI: 10.1051/0004-6361/201525925 (2015)

The post Electric Avenue appeared first on One Universe at a Time.

[av_video src=’http://youtu.be/tMthy0RrORY’ format=’16-9′ width=’16’ height=’9′]

Yesterday Philae landed on a comet. It was the first successful soft landing on a comet, though it likely won’t be the last. This is something everyone should be excited about. With all the things to complain about in the world, here is a chance to celebrate a huge achievement of human ingenuity. We have a robotic probe on the surface of a comet.

Rosetta ground control at the moment Philae landed. Credit: ESA

There’s been a lot in the news about how this is the culmination of a 10 year mission, but that’s only the time since Rosetta’s launch. The idea for a comet lander dates at least as far back as the 1980s, when the Giotto spacecraft made a flyby of Halley’s comet. This led to plans for a mission to land on a comet and return with cometary material, but that was later scaled back to just a lander for budgetary reasons.

The Rosetta spacecraft under construction. Philae is circled. Credit: Cumbrian Sky

Design and construction of the Rosetta and Philae spacecraft date back to the 1990s, with major construction beginning around the turn of the century. It was originally scheduled to land on a comet known as 46P/Wirtanen, but delays led to the change to 67P/Churyumov–Gerasimenko.

The reason comets are such an important target is because they contain the most primal materials of the solar system. Unlike most of the bodies in the inner solar system, which have been mixed and bombarded over the ages, comets have an origin in the outer edges of the solar system known as the Oort cloud.

Philae has a planned mission of about 6 weeks, so there is going to be a lot of data gathered, and over time results will start being published. But we’ve already learned a few surprising things. One is that the comet itself sings. Not in the traditional way we think of, but rather in electromagnetic waves. The comet’s weak magnetic field interacts with the coma and solar wind to create a warbling effect. You can hear the sound in the video above, where it’s been sped up from its actual millihertz range.

So we’ve sent a spacecraft into space, put it in orbit near a comet, landed on it with a smaller probe, and listened to the comet’s song. What an amazingly human thing to do.

The post Song for a Comet appeared first on One Universe at a Time.

The Rosetta spacecraft has successfully moved into orbit around 67P/Churyumov-Gerasimenko. We’ve been getting images of the comet as Rosetta approached, but now that it’s in orbit we are getting high resolution images such as the one above. You’ll notice the comet really looks like an asteroid, with what seems to be a rocky/dusty surface. That’s because comets and asteroids aren’t as different as often portrayed.

Comets are so-named because they exhibit tails of gas and dust when passing through the inner solar system. These tails are due to volatiles such as methane and water ice on the surface of the comet. We have also seen asteroids exhibit similar tails of dust, though it isn’t as common.

The nucleus of Comet Halley. Credit: NASA

This is the first time we’ve been able to place a satellite in orbit around a comet. We’ve had several flyby missions for comets, including the famous flyby of Comet Halley by the Giotto spacecraft. One huge advantage of having an orbiter is that we can make a long-term study of the comet. Rosetta has arrived at 67P/C-G just before it begins its journey through the inner solar system, so the mission will provide a first hand look at how comets are warmed by the Sun and begin to form a tail.

One of Rosetta’s first missions, however, will be to find a good landing spot for its companion spacecraft Philae. That landing should occur sometime in mid-November.

The post Night of the Comet appeared first on One Universe at a Time.

The Rosetta spacecraft is on its way to an asteroid known as 67P/Churyumov–Gerasimenko. In August it will go into orbit around the asteroid, and then in November it will put a lander known as Philae on the rock.  The surface gravity of this asteroid is less than 1/20 that of Earth, so Philae will actually have harpoons to keep it attached to the asteroid.  It’s an ambitious mission, since unlike many landings we have no idea what the surface of the asteroid will be like. In fact until recently, we weren’t entirely sure what the shape of 67P/Churyumov–Gerasimenko actually is.

Credit: ESA/Rosetta/MPS

But as Rosetta approaches the asteroid we are starting to get an idea of its shape. What we’re finding is rather interesting. It turns out 67P/Churyumov–Gerasimenko is what’s known as a contact binary. These are thought to form when two asteroid or comet bodies come into contact at speeds low enough to remain in contact. Contact binaries are not particularly rare, but they are unusual, and we’re lucky to have the opportunity to study them close up. It will, however, make orbiting and landing on the asteroid a bit more of a challenge.

As we get higher resolution images, the necessary changes to Rosetta’s orbit can be made. Then it will just be 3 2 1 contact.

The post 3 2 1 Contact appeared first on One Universe at a Time.