Snowball Fight in the Solar System

NASA: We have booster ignition and liftoff of Columbia, reaching new heights for women and X-ray Astronomy.

Martin Elvis: The main thing Chandra does is take these superb, sharp images.

Cady Coleman: Nothing as beautiful as Chandra trailing off on its way to work

Narrator: The Solar System is our cosmic home. The Sun, Moon, planets, comets, and asteroids are all our neighbors. Many objects in the Solar System are visible with the unaided eye, such as the Sun on a clear day, the Moon during the night, and many planets, and then the occasional comet.

But what happens when you look at the Solar System through a new set of eyes? That's what astronomers have been learning since they have been using the Chandra X-ray Observatory to study objects within our own Solar System. Chandra can see what happens when radiation from the Sun interacts with the colder objects in our Solar System like planets, comets, and even our own Earth and Moon.

Dr. Scott Wolk of the Chandra X-ray Center has been involved with Chandra observations of objects in our Solar System. In particular, Scott has been involved with many observations of comets, which have turned out to be fascinating objects to study in X-rays.

Scott: Probably the most surprising objects observed in X-rays are comets. Now X- rays are normally associated with the hottest things in the universe, black holes, the beginning of the universe... Comets were pretty well described by Fred Whipple as being "dirty snowballs". So how does a snowball make X-rays? It gets back to a strange phenomenon called charge exchange. The Sun is constantly streaming very hot particles called ions into the Solar system. This stream is called the solar wind, and the ions are so highly charged that they will actually steal electrons from cold gas if they can. A comet becomes active when it gets close to the Sun and it starts putting cold gas out into space, and as you can imagine, it is quite cold. This charge exchange takes place every time an ion gets close to a cold gas molecule, and each time this happens, an X-ray is emitted. This makes comets very bright in X-rays. Comets are so bright that some scientists think we will be able to see comets around other stars in X-rays, and this could become a very powerful way to find planet systems around stars which are not suitable for the current method.

We have looked at something like 8 comets so far, and they all look different. We are learning how much gas leaves the comet each time it passes in front of the sun, what the "snow" inside of the comet is really made of. We observed the collision of Deep Impact into the comet Temple 1 on the 4th of July, 2005 and could actually see the jet of material freed from the comet by that impact flying off into space.

Narrator: Chandra has made observations of individual comets so far, but thats not the end of the story. In fact astronomers hope that they can use X-ray observations of comets as probes into the solar wind throughout the solar system.

Scott: Not only do the comets tell us about themselves, they also tell us about the solar wind that theyre traveling through and what it is made of and how fast it is going. This is sometimes called space weather. Now, bad space weather can be a pretty bad thing. It can interrupt communications on Earth. It can actually interrupt electrical power on Earth, and it can be very dangerous to satellites and astronauts. The space station even has a special room just in case of bad space weather, and NOAA, which is responsible for hurricane forecasts on Earth, also has satellites to help predict space weather. Most satellites are very close to the Earth and don't tell us a lot about what the space weather is like in different parts of the solar system. So this is a lot like living in Boston and trying to predict the weather without knowing much about the weather in Chicago. Comets on the other hand are all over the place and give us occasional space weather reports from all over the solar system and these give us a better idea about how the space weather differs from place to place in our solar system. And this will be very important when Astronauts move further out into space.

Narrator: While many objects in our Solar System are familiar to us, we learn even more about our local neighborhood in the cosmos, including our comets, by looking through Chandra's X-ray eyes.