We have news I didn’t think I’d see for… Well, I figured it would require the launch of a certain massive infrared telescope that is greatly delayed or about ten years in ground-based advances.

As we’ve said before, however, when scientists want to figure something out, they will do amazing things to find a way. In this case, researchers using the Planet Imager & Characterizer Instrument on Keck Observatory in Hawai’i figured out how to measure the rotation speed of planets orbiting alien stars.

The system, HR 8799, is located about 129 light-years away and has four super Jupiters. These planets are big enough and bright enough that using this new instrument, nicknamed KPIC, they can see how spectral lines are broadened by the worlds’ rotations. Or at least they could make it out for two of the four worlds. 

Essentially, if the thing emitting light is moving toward you, the light is shifted to the blue, and if it’s moving away, it’s shifted to the red, and with a rotating globe – a planet – you get redshifting from one side and blue shifting from the other, and the light from specific spectral lines is spread out over more colors. For the two worlds they could measure, they clocked rotations at 10.1 and 15.1km/s. For comparison, Jupiter rotates at 12.7 km/s. Without knowing exactly how big the planets are, we can’t know the exact day lengths, but we’ll get there and this is awesome. This work will appear in The Astronomical Journal and was led by Jason Wang.

More Information

Keck Observatory press release

“Detection and Bulk Properties of the HR 8799 Planets with High Resolution Spectroscopy,” Jason J. Wang et al., to be published in The Astronomical Journal (preprint on arxiv.org)