Friday, September 24, 2010

Southern Saturnian Aurora

Image credit: NASA/JPL/University of Arizona/University of Leicester
I am absolutely fascinated by the planets. In fact, if I had to choose another field of science to go into it might just be planetary science. As such, when I see new data, particularly images, of planets I just jump on the story. I mean, just look at the above picture...its pretty incredible. What you are looking at is a picture of the planet Saturn (in case the rings didn't give it away). Its what's called a false-color composite image. These types of images show colors that differ from what you would see in a true color image, which are how an object appears to the human eye. Usually they either turn up a color aspect, change one color to another to make a feature more visible, or assign colors to particular aspects or features. When NASA's Cassini space craft took some 65 pictures with its visual and infrared mapping spectrometer (VIMS) one of these features to stand out were the glow of auroras in the south polar region. These auroras were seen streaking out about 600 miles from the cloud tops and were clearly visible in the near-infrared wavelengths of light.

In the false-color images scientists usually designate blue to indicate sunlight reflected at a wavelength of 2 microns, green to indicate sunlight reflected at 3 microns, and red to indicate thermal emission at 5 microns. Since the auroral emission appears to be green, this suggests emissions from hydrogen ions of light between 3 and 4 microns in wavelength. You can clearly see the contrast with the rings which appear blue and have a wavelength of 2 microns. The red, 5 micron, wavelengths you see in the southern hemisphere are due to the heat emission from the interior of Saturn.

Image credit: NASA/JPL/University of Arizona/University of Leicester
The auroras were seen to vary over the course of the Saturnian day. This gas giant rotates extremely fast and so a day only lasts 10 hours and 47 minutes. On what is the Saturn's day equivalent to noon and midnight the aurora can be seen to brighten significantly for several hours. This brightening is likely due to the planets angle to the Sun. The auroras are thought to occur in processes similar to those on Earth, where particles from the solar wind are channeled by the magnetic field toward the planet poles. On Saturn you also add in the effects of the electromagnetic waves generated by the moons moving through Saturn's plasma-filled magnetosphere.

And ok, these are not the first pictures of Saturn's aurora. Cassini has returned a number of detailed snapshots in the past. These images are more data scientists can use to understand this phenomena. Not to mention they look pretty bitchin'.

First, I highly recommend watching this short video by NASA/JPL:
http://saturn.jpl.nasa.gov/multimedia/videos/movies/aurora20091123-480.mov

And here are some story links:
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4142
http://www.jpl.nasa.gov/news/news.cfm?release=2010-313
http://www1.nasa.gov/mission_pages/cassini/whycassini/cassini20100923.html
http://www2.le.ac.uk/ebulletin/news/press-releases/2010-2019/2010/09/nparticle.2010-09-24.0238525751
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