Most detailed exoplanet weather map ever developed

Written by Press Trust of India | Washington | Updated: Oct 11 2014, 00:27am hrs
Using the Hubble Space Telescope, scientists, including one of Indian-origin, have created the most detailed map ever of the temperature of an exoplanet's atmosphere and traced the amount of water it contains.

WASP-43b is a planet the size of Jupiter but with double the mass and an orbit much closer to its parent star than any planet in the Solar System.

It has one of the shortest years ever measured for an exoplanet of its size - lasting just 19 hours.

A team of astronomers working on two companion studies created detailed weather maps of WASP-43b. One study mapped the temperature at different layers in the planet's atmosphere, and the other traced the amount and distribution of water vapour within it.

"Our observations are the first of their kind in terms of providing a two-dimensional map of the planet's thermal structure," said Kevin Stevenson from the University of Chicago, lead author of the thermal map study.

"These maps can be used to constrain circulation models that predict how heat is transported from an exoplanet's hot day side to its cool night side," he said.

The planet has different sides for day and night because it is tidally locked, meaning that it keeps one hemisphere facing the star, just as the Moon keeps one face toward Earth.

The Hubble observations showed that the exoplanet has winds that howl at the speed of sound from a day side that is hot enough to melt iron - soaring above 1500 degrees Celsius - to the pitch-black night side that sees temperatures plunge to a comparatively cool 500 degrees Celsius.

To study the atmosphere of WASP-43b the team combined two previous methods of analysing exoplanets for the first time.

By looking at how the parent star's light filtered through the planet's atmosphere - a technique called transmission spectroscopy - they determined the water abundance of the atmosphere on the boundary between the day and night hemispheres.

In order to make the map more detailed the team also measured the water abundances and temperatures at different longitudes.

To do this they took advantage of the precision and stability of Hubble's instruments to subtract more than 99.95 per cent of the light from the parent star, allowing them to study the light coming from the planet itself - a technique called emission spectroscopy.

By doing this at different points of the planet's orbit around the parent star they could map the atmosphere across its longitude.

Nikku Madhusudhan of Cambridge University, UK, was the co-author of both studies.

The results are presented in two papers, one on the thermal mapping of the planet's atmosphere - published in Science Express - and the other on mapping the water content of the atmosphere - published in The Astrophysical Journal Letters.