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