Category Archives: comet

astronomy news, comet, x-ray astronomy
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Comet Schwassmann-Wachmann 3 in a new light, Courtesy NASA/SWIFT/XRT/U.Leicester/Richard Willingdale.
Comet Schwassmann-Wachmann 3 in a new light, Courtesy NASA/SWIFT/XRT/U.Leicester/Richard Willingdale.

As Comet Schwassmann-Wachmann 3 continues what may be its final trip around the Sun(breaking up along the way), astronomers are turning everything they have toward it. While it isn’t as bright to the naked eye as Hyakutake or Hale-Bopp were a few years back, S-W3 is turning out to be dazzler in other wavelengths, most notably x-rays. In fact, it’s the brightest x-ray comet ever. The folks using the Chandra Observatory, the XMM-Newton satellite, and the Suzaku satellite (all three in orbit around Earth) are all getting ready to study the x-rays streaming off the comet.

The image above is what the comet looks like in x-ray wavelengths. It was taken using the NASA Swift satellite, which studied the comet recently. The data showed that the comet is about 20 times brighter in x-ray wavelengths of light.

How can a comet produce x-rays? It seems somewhat counterintuitive that such a cold, icy object would glow in wavelengths more commonly associated with hot, active events and objects. Astronomers are still characterizing the interactions that occur that cause cometary x-rays, but the basic story is this: as the comet plows through the solar wind, something called “charge exchange” occurs. Okay, that sounds appropriately mysterious, but what does it mean?

The solar wind is a stream of particles (electrons and protons). The comet is a lump of ices and dust. As it moves through the solar wind, those particles and gases fly away from the comet, particularly as the ices are warmed by the Sun. Those cometary bits are usually particles of molecules of water, methane, and carbon dioxide. When they the high-speed, high-energy particles from the solar wind encounter these lower-energy particles from the comet, electrons get “stolen” from the cometary chemical particles. In the process, a tiny bit of charge is exchanged and the result is a spark of energy, which results in an x-ray. So, it’s a collisional process that depends on an interaction between the comet and the solar wind. It’s not just from something the comet itself is generating.

Now, if you know enough about the x-ray energies that are given off in these collisions, you can make some deductions about the content of the solar wind and the makeup of the gases and materials being emitted by the comet. And this is one of the results of studying x-rays (and other high-energy emisssions) from such events as comets plowing through the solar wind.

astronomy news, comet, comet dust

Dust in the Wind

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Comet Schwassman-Wachmann 3
Comet Schwassman-Wachmann 3

Comet Schwassman-Wachmann 3 is really putting on quite a show as it heads into perihelion passage by late this month. Its nucleus, which broke apart into three big chunks in 1995, has now crumbled into more than 50 pieces. Everybody seems to be tracking this thing. Spitzer Space Telescope’s image is nicely reminiscent of Shoemaker-Levy 9.

Subaru Observatory (on the Big Island of Hawai’i), has released this image of just one of the pieces, called Fragment B. It’s not the brightest of the chunks of the nucleus (that would be Fragment C), but it is showing some unusual activity.

Fragment B is itself a series of little comet nucleus shards, numbering more than 13. What does this tell us about the comet? That it most likely has a pretty delicately structured nucleus. It may also be rotating very quickly, or its ices could be vaporizing rapidly. These actions, combined with its approach to the Sun (which warms the ices even more), could be applying just the stress needed to shatter this cometary nucleus once and for all.

Fragments as seen by Subaru Observatory
Fragments as seen by Subaru Observatory

Of course that won’t be the end of this comet. It has been long associated with the Tau Herculid meteor shower, but this year’s recurrence of that shower probably won’t benefit from the breakup.

All of the pieces of the comet will continue to orbit the Sun in a trail of debris that is the source of the Tau Herculids. It’s a sort of diaphanous ring of dust and ice particles that have been sloughed off the comet in the past. In time, Earth could experience some heightened meteor shower activity from this breakup, but there’s good news and bad news there. The good news is that even if the shower is stronger in the future, the particles will simply collide with our atmosphere, enter it, and most likely burn up as they plow through the air.

The bad news isn’t so bad, really, just sort of disappointing: the pumped-up amount of debris in the trail of the comet won’t encounter Earth until 2022. So, it’s possible that the meteor shower probably could become quite spectacular in the future. Or not. So stay tuned.