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Earth has the van Allen radiation belts. Which other planets have one? Can it be determined if distant planets in other solar systems have one?

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Mars does not have a magnetic field of any strength and so does not have a van Allen belt (and this is a serious problem for potential human exploration of the planet). Similarly, neither Venus nor Mercury (nor the Moon, which is arguably part of a two-planet system with the Earth) have a van Allen belt.

The gaseous giants do, however, have radiation belts which are analogous to Earth's van Allen belt.

Spotting aurorae on distant exoplanets would be an indication of a strong magnetic field and thus of the likelihood of a radiation belt. I am not aware that such aurorae have been detected but distant aurorae have been seen around a brown dwarf - a substellar object somewhat bigger than a planet (see http://www.theguardian.com/science/2015/jul/29/astronomers-find-aurora-a-million-times-brighter-than-the-northern-lights).

Alternatively, the radio emissions from high energy electrons trapped in planetary radiation belts might be detectable - this was how Jupiter's radiation belt was discovered around 60 years ago. Work seems to be underway to detect such radiation: https://skaoffice.atlassian.net/wiki/download/attachments/22183971/PoS-exopla-AASKA14.pdf?version=1&modificationDate=1403003959989&api=v2

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  • $\begingroup$ The question was clearly about "distant planets in other solar systems" $\endgroup$ – adrianmcmenamin Aug 9 '15 at 19:36
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    $\begingroup$ OK, I see. I misread the OP. The aurora you refer to was found on a brown dwarf, not a star (or a planet). But there is every reason to expect gas giant planets to have magnetospheres. $\endgroup$ – Rob Jeffries Aug 9 '15 at 19:44
  • $\begingroup$ Auroras have been detected on Jupiter, Saturn and Uranus (big, pretty ones), and according to the article, even a small one on mars. Source: messagetoeagle.com/auroraalienworlds.php $\endgroup$ – userLTK Aug 10 '15 at 15:39
  • $\begingroup$ The question - and thus my answer - is about planets in other solar systems! How many times do I have to say this :) $\endgroup$ – adrianmcmenamin Aug 10 '15 at 20:36
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Yes, according to this recent news an aurora has been found on the brown dwarf LSR J1835+3259 which is 18½ light years from here. I suppose that an aurora which is a million times more powerful than those on Earth comes together with some kind of van Allen Belts, but real astronomers maybe have more imagination. An M class brown dwarf is maybe not the typical "planet", but it's more like Jupiter than the Sun. (All planets certainly don't have it, the headline is confusing).

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