page_title: Exoplanetology
section_title: Rotation and axial tilt
hierarchical_section_title: Exoplanetology / Rotation and axial tilt
caption_attribution_description: English: This graphic shows the rotation speeds of several of the planets in the Solar System along with the recently measured spin rate of the planet Beta Pictoris b. Français&#160;: Ce graphe montre les vitesses de rotation de plusieurs des planètes de notre Système Solaire ainsi que celle de la planète Bêta Pictoris b dont la détermination est toute récente.
context_page_description: Exoplanetology, or exoplanetary science, is an integrated field of astronomical science dedicated to the search for and study of exoplanets. It employs an interdisciplinary approach which includes astrobiology, astrophysics, astronomy, astrochemistry, astrogeology, geochemistry, and planetary science.
context_section_description: In April 2014, the first measurement of a planet's rotation period was announced: the length of day for the super-Jupiter gas giant Beta Pictoris b is 8 hours (based on the assumption that the axial tilt of the planet is small.) With an equatorial rotational velocity of 25 km per second, this is faster than for the giant planets of the Solar System, in line with the expectation that the more massive a giant planet, the faster it spins. Beta Pictoris b's distance from its star is 9 AU. At such distances the rotation of Jovian planets is not slowed by tidal effects. Beta Pictoris b is still warm and young and over the next hundreds of millions of years, it will cool down and shrink to about the size of Jupiter, and if its angular momentum is preserved, then as it shrinks, the length of its day will decrease to about 3 hours and its equatorial rotation velocity will speed up to about 40 km/s. The images of Beta Pictoris b do not have high enough resolution to directly see details but doppler spectroscopy techniques were used to show that different parts of the planet were moving at different speeds and in opposite directions from which it was inferred that the planet is rotating. With the next generation of large ground-based telescopes it will be possible to use doppler imaging techniques to make a global map of the planet, like the mapping of the brown dwarf Luhman 16B in 2014.
  A 2017 study of the rotation of several gas giants found no correlation between rotation rate and mass of the planet.
caption: Plot of equatorial spin velocity vs. mass for planets comparing Beta Pictoris b to the Solar System planets.
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