The fast spin-rotation of a young extrasolar planet

TL;DR

This study measures the rapid spin of the young exoplanet Beta Pictoris b using high-resolution spectroscopy, revealing it spins faster than any solar system planet, supporting the trend of increasing spin velocity with planet mass.

Contribution

First direct measurement of the spin velocity of a young extrasolar planet, providing insights into planet formation and angular momentum acquisition.

Findings

Beta Pictoris b has a rotational velocity of 25 km/sec.

The planet's spin is faster than any solar system planet.

Results support the trend of increasing spin velocity with planet mass.

Abstract

The spin-rotation of a planet arises from the accretion of angular momentum during its formation, but the details of this process are still unclear. In the solar system, the equatorial rotation velocities and spin angular momentum of the planets show a clear trend with mass, except for Mercury and Venus which have significantly spun down since their formation due to tidal interactions. Here we report on near-infrared spectroscopic observations at R=100,000 of the young extra-solar gas giant beta Pictoris b. The absorption signal from carbon monoxide in the planet's thermal spectrum is found to be blueshifted with respect to the velocity of the parent star by (-15+-1.7) km/sec, consistent with a circular orbit. The combined line profile exhibits a rotational broadening of 25+-3 km/sec, meaning that Beta Pictoris b spins significantly faster than any planet in the solar system, in line with the extrapolation of the known trend in spin velocity with planet mass.