Hot Jupiters are large planets – about the size of Jupiter or larger - that orbit very close to their star. They comprise the upper left corner of
this plot. A year on one of these planets is only a few days, or even less. These planets are relatively easy to discover because of their large and short-period effect on their star's motion and a much higher probability of transit, so the statistics we have on extrasolar planets are skewed a bit toward this type of planet. Nevertheless, they appear to be fairly common, though are no longer in the majority of the
843 2030 exoplanets
catalogued to date.
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| Exoplanet Orbital period vs. age of host star |
Hot Jupiters were a surprise to astronomers when first discovered, although Otto Struve had
speculated on their existence in 1952, arguing that they were the only planets detectable by ground based telescopes. Hot Jupiters were not a real paradigm-buster, but were unexpected, because they can't form that close to the star - it's like trying to get steam to condense on a hot soldering iron. Hot Jupiters have to form much further out from their star, and then migrate inward. There are plausible models for how this could happen fairly quickly as a result of complex tidal interaction with a disk of dust still surrounding the star shortly after it forms. Such a natural migration may take only a few million years, but it has to happen early or there won't be enough of a disk to interact with. What astronomers would really like to do is catch one of these planets in the act of migrating, but that will require a bit of luck and probably better telescopes.
