Wasp-127B: Scientists discover giant planet with super fast winds
bbc.co.uk
bbc.co.uk
> To calculate the wind speed on WASP-127b, the team tracked how fast molecules in the planet's atmosphere moved using the 'Very Large Telescope' (VLT) located in the south American country of Chile.
Could you provide anymore insight into how this was achieved? Any interesting challenges associated with the measurement? What are the practical limitations of this methodology? How did you pick the planet as a target to measure?
None of these questions are necessary, I'm just genuinely curious if you could provide any insight
> Could you provide anymore insight into how this was achieved? The observations we have consist of spectra - light from the star is split into wavelengths with a fine resolution (we can distinguish very small differences in wavelength/frequency). When the planet passes between the star and us, its atmosphere absorbs a tiny fraction of the stellar light and we can see that : Fingerprints in the spectrum that are associated to molecules we have characterized in the lab (here we see carbon monoxide and water). The way we can isolate the signature from the planet - compared to the signature from the star or say the water in the earth atmosphere - is that the planet is moving and its velocity with regards to us is varying ! The Doppler effect (think ambulance coming towards you making the sound higher pitch) means that the signature from the planet also get shifted in frequency.
> Any interesting challenges associated with the measurement? Yeah, one of the big challenge is that the Earth atmosphere is not so transparent in the near-infrared so it absorbs a lot of light and pollutes a lot our data. Getting rid of the atmospheric spectrum with high enough accuracy is challenging, but we manage - either doing some physics and modelling it -- and/or using some data analysis tool (PCA for instance).
> What are the practical limitations of this methodology? The main one is the amount of light we need, that's why this instrument sits at the Very Large Telescope (the primary mirror is 8m in diameter) one of the largest European telescope. We need to have very good signal, as we are splitting the light into many wavelengths. And we cannot just take very long exposures, because the transits of the planets in front of the star is done in a limited time (few hours)
> How did you pick the planet as a target to measure? Normally we start with a big spreadsheet of all planets, and we work out which ones are observable from a given telescope, which stars are bright enough, which planet could have observable signal. WASP-127 was studied in the past and other teams already detected some molecules, but we did not expect to measure this kind of winds.