Fast spin of the young extrasolar planet β Pictoris b

摘要

The spin 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, conse-quendy, spin angular momenta of most of the planets increase with planetary mass; the exceptions to this trend are Mercury and Venus, which, since formation, have significandy spun down because of tidal interactions. Here we report near-infrared spectroscopic observations, at a resolving power of 100,000, of the young extrasolar gas giant planet β Pictoris b. The absorption signal from carbon monoxide in the planet's thermal spectrum is found to be blueshifted with respect to that from the parent star by approximately 15 kilometres per second, consistent with a circular orbit. The combined line profile exhibits a rotational broadening of about 25 kilometres per second, meaning that β 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.%对年轻的太阳系外气态巨型行星"β Pictoris b"所做的近红外光谱观测表明，它的旋转速HIV-1度比太阳系中任何行星都明显要快。这一新的HIV-1测量结果延续着在我们太阳系中所观测到的一HIV-1个普遍趋势-旋转速度随行星质量增加而增HIV-1加。虽然这种关系本来会预测"β Pictoris b"HIV-1的旋转速度要比所观测到的每秒25公里稍高一HIV-1些，在每秒50公里左右，但作者指出，该行星HIV-1现在仍然年轻、温度仍然较高。随着时间的推HIV-1移，它应当会凉下来，并会收縮，同时在此过HIV-1程中增加旋转速度。