Question

Why did "hot Jupiters" dominate early planet discoveries, even though they are rare?

Answer 1

The discovery of the first hot Jupiters not only sparked a revolution in planet formation theory but kick-started the field of exoplanet discovery and characterization. If the Solar System paradigm for gas giants was the rule throughout the Galaxy, the progress of the field of exoplanetary science would have been glacially slow. Radial velocity surveys require the observation of at least one and ideally multiple orbits, which would take multiple decades for a Jupiter analog. In contrast, early planet hunters could observe multiple hot Jupiter orbits within a single week.

The reasons that the "hot Jupiters" dominated early planet discoveries, though being rare could be the following -

• Hot Jupiters cause a larger reflex motion of the star than a Jupiter analog, allowing observers to characterize the planets with fewer measurements necessary to beat down the noise. Rapid discovery and confirmation of hot Jupiters led to the build-up of a large sample of planets over a decade.
• Hot Jupiters cause a Doppler shift that is larger and easier to detect than that from other planets.
• Hot Jupiters are the easiest to find with the radial velocity (Doppler) technique and the transit method.
• The Doppler planet surveys focus on a population of stars that are in general more metal-rich, with a higher fraction of main sequence stars and a lower fraction of multiple star systems. These stellar properties determine that the occurrence rate of hot Jupiters is higher compared the population of stars for the transit surveys.