Laura Kreidberg from the University of Chicago explains.

To make these observations, the WASP-43 team used transmission spectrography, which filters the parent star's light through the planet's atmosphere. They measured water abundances and temperatures at different longitudes by taking advantage of the precision and stability of Hubble's instruments to subtract more than 95.5% of the light from the parent star. This allowed them to study the light coming from the planet itself, a technique called emission spectroscopy.


The team also found that WASP-43b reflects very little of its host star's light, and that it has water vapour in the atmosphere. As noted by the ESA, this is important because

Water is thought to play an important role in the formation of giant planets. Astronomers theorise that comet-like bodies bombard young planets, delivering most of the water and other molecules that we observe. However, the water abundances in the giant planets of the Solar System are poorly known because water is locked away as ice, deep in their atmospheres which makes it difficult to identify.

"Space probes have not been able to penetrate deep enough into Jupiter's atmosphere to obtain a clear measurement of its water abundance. But this giant planet is different," added Derek Homeier of the École Normale Supérieure de Lyon, France, co-author of the studies. "WASP-43b's water is in the form of a vapour that can be much more easily traced. So we could not only find it, we were able to directly measure how much there is and test for variations along the planet's longitude."

In WASP-43b the team found the same amount of water as we would expect for an object with the same chemical composition as the Sun.


Which is an important clue in understanding how the planet formed.

[ ESA ]