====== 'Hot Jupiter' planets ======

The phrase// 'Hot Jupiter'// was first suggested in 1995 and covers very large (.i.e. Jupiter-sized) planets that are very close to the star which they orbit - and with a typical orbit time of just a few days.

Their existence had been predicted in the 1950s - though at the time there was no way to reliably detect them. In the 1990s astronomers Michel Mayor and Didier Queloz won a Nobel Prize for discovering the first examples. They also came up with the name.

New space-based planet-scanning technology has already found many hundreds of such planets.

They are a cosmological puzzle, because they are so close to the host star that its intense radiated heat would presumably have 'evaporated' their structure many millions of years ago - or have prevented their formation in the first place.

There are currently three theories about their formation ;

[1] They formed far away from the parent star and then somehow their orbit progressively became smaller ([[https://www.nature.com/articles/380606a0|ref.]])

[2] They managed to form in situ without getting evaporated ([[https://iopscience.iop.org/article/10.3847/0004-637X/829/2/114|ref.]])

[3] The 'core' formed in a remote orbit and then migrated inwards - subsequently accreting more material to form a Jupiter-sized planet. (ref. as above)

To date, none of the explanations has been fully accepted.

Note that the question of how// any// planets form has still not been fully agreed - see [[content:physics:cosmology:planet_formation]]