It's coming right at us! But don't worry, it shouldn't hurt too much when it hits.
On Christmas Day, the sun decided to get into the festive mood by laying on some decorations. Lacking the tinsel and tacky glow-in-the-dark reindeer on its front lawn, our nearest star decided to create a humongous coronal mass ejection (CME) in the shape of an interplanetary bauble, firing it right at us.
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One of NASA's twin Solar-Terrestrial Relations Observatory (STEREO) spacecraft managed to get a side-on view of the CME racing toward Earth and Mars on Dec. 26. Also, the veteran NASA/ESA Solar and Heliospheric Observatory (SOHO) nabbed a picture of the CME at around the same time (pictured above).
All predictions suggested the CME would likely hit us on Dec. 28 (Wednesday) and it appears that is going to happen.
Depending on the orientation of the magnetic field wrapped around the CME bubble of highly charged solar particles when it hits the Earth's geomagnetic field, there will be a chance of some auroral activity.
"There is a 20-40% chance of geomagnetic storms! If you live at a high latitude, look out for #auroras today," tweeted NASA's Solar Dynamics Observatory team on Wednesday.
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Although being hit by a CME is a very well-known phenomenon for Earth, a CME impact on Mars will have a very different effect.
"Different world, different space weather," writes NASA's Tony Phillips of Spaceweather.com.
When a CME hits Earth, our planet's global geomagnetic field deflects the energy, interacts with the CME's magnetic field and funnels the solar energetic particles toward high latitude regions. The more fierce the geomagnetic storm, the deeper the particles penetrate.
As these particles rain down on high-latitude regions -- typically forming an "oval" around the polar caps when viewed from space -- interactions between the solar particles and molecules in our atmosphere generate light. The light is known as aurorae.
On Mars, it's a different story.
The Red Planet does not have a global magnetic field. Whereas Earth's magnetic field and thick atmosphere protects us from the worst ionizing effects of the sun's high-energy particles, Mars' thin atmosphere and insignificant magnetic field allow these CME particles to hit the surface.
Mars is therefore often bathed in the sun's high-energy particles -- a factor that could seriously hamper future human colonization efforts.
However, Mars does have pockets of magnetic "umbrellas." They are the ancient remnants of a once global magnetic field. It is thought that early in Martian history a huge asteroid smashed deep into the planet, interrupting the inner "dynamo" that generated its global magnetic field.
This effectively "switched off" Mars' geomagnetic field, leaving its atmosphere open to the ravages of the solar wind. That may be one of the reasons why the Martian atmosphere is 100 times thinner than Earth's -- it has quite literally been "blown away."
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So if you are lucky enough to witness the beautiful, dynamic aurora that may occur tonight or tomorrow, spare a thought for Mars where the majority of that radiation will rain down onto its surface.
Image: The sun as seen through SOHO's LASCO C3 instrument. The glare of the sun is obscured by an artificial "occulting disk" so that faint CME features can be seen in interplanetary space. The Earth-directed CME can be seen emerging from the left of the disk. Credit: NASA/ESA
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As a science geek, once of the coolest gifts I ever received was a copy of The Physics of Christmas, given to me by my grandmother only a few years before her death. ?In addition to some discussion of the thermodynamics of cooking turkey and the possible scientific explanation of the Christmas star, there's a great historical analysis of how Christmas has change over the years. One of the most fun parts for me was the chapter which discussed Santa. How could he travel the whole world in one night? Well, physics offers some ideas.