The Cassini spacecraft has spotted MeV (million electron volt) electrons coming from the shock wave around Saturn's magnetic field. These aren't the "ultra-high-energies" the story claims (those probably come from supernova shock fronts), but they are higher energy than the theory predicts.
This observation is of electrons accelerated where the magnetic field points more or less in the same direction as the shock front. (The case where the shock and the field are perpendicular is already known to accelerate electrons, and there are some models for how--but how well they describe Saturn's environment I don't know.) The shock front in question is from the solar wind hitting Saturn's magnetic field. For scale, the solar wind is mostly protons at about 1MeV kinetic energy and electrons with correspondingly smaller (1/2000) energy. This acceleration is able to bounce sling electrons back with energies as much as 2000 times what the incoming electrons have. (Usually smaller energies, though)
Together with the Fermi LAT spotting supernova remnant gamma rays we're starting to converge on some solid data we can use to test models with. Maybe we'll start to understand cosmic rays soon.
This reminds me to ask you whether you know anything about the current thinking on cosmic rays and their impact on cloud formation and, therefore, global warming/cooling? Was that a fluky fad of a notion, or real stuff?
ReplyDeleteI find it hard to say. The paper http://www.ann-geophys.net/30/9/2012/angeo-30-9-2012.pdf has points of interest and several things that leave me scratching my head. Figure 9, for instance, does not define what ΔT is; section 2 (page 10) seems to blur solar activity and cosmic ray intensity (the latter we can guestimate from induced radioactivity, but how does one determine the former?), and so on.
ReplyDeleteThat cosmic ray showers can provide seeds for lightning seems plausible--some cosmic ray showers have a startlingly tight core: a few meters wide.
That the more diffuse showers could provide seeds for droplet growth is also plausible, but I don't have a good intuition for how droplets form at different altitudes. The CLOUD results from 2009 were suggestive but fell short of proof.
So: real effect, but I'm not sure how big.
I'd expect the magnetic pole areas to have somewhat more clouds at high altitudes, because of solar wind particles streaming in and ionizing the air high up (they don't reach very far down in the atmosphere). But that is complicated by the lack of open water nearby. Phooey. http://www-das.uwyo.edu/~geerts/cwx/notes/chap08/cloud_lat.html
I appreciate your looking into it. Sounds iffy, but perhaps something that we're not in a position to rule out at the moment.
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