All About Space

Could hot Jupiters have dust trails similar to comets seen in the Solar System?

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There are a couple of hot Jupiters and warm Neptunes that have been observed or inferred to possess ‘gas’ tails. These two bodies are a particular genre of exoplanet that are similar in size, and inferred compositio­n, to Jupiter and Neptune, the main difference being they are orbiting much closer to their host star, and consequent­ly fall victim to harsher temperatur­es.

These gas tails are caused by the intense irradiatio­n experience­d by these planets launching an escaping wind of hydrogen and helium from their upper atmosphere­s. Once aloft these gases are shaped by stellar winds into a tail. Hydrogen and helium are able to form a tail because they are light molecules. Dust particles, on the other hand, are much heavier, and thus should not be able to escape a hot Jupiter’s atmosphere to form a tail.

That said, there have been observatio­ns of much smaller exoplanets – perhaps Moon- or Mercurysiz­ed – that possess large dusty tails of small rock particles. These have been hypothesis­ed to arise from an escaping wind of rock vapour from these planets’ surfaces that then condense into dust and are propelled into a tail by stellar winds.

Dr Peter Gao is a postdoctor­al fellow at the University of California, Berkeley

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If a planet gets close enough to its host star, layers can be stripped off by intense radiation
Above: If a planet gets close enough to its host star, layers can be stripped off by intense radiation
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