Exoplanet hunter snares ‘extreme’ superhot world

Launched into Earth orbit in December, the CHEOPS space-based telescope spotted the gas giant circling close to one of the hottest known stars with a planetary system, according to a study published last week.

WASP-189b discovery

3 200 degrees Celsius

“We estimate the temperature of WASP-189b to be 3 200 degrees Celsius,” said lead author Monika Lendl, a scientist at the University of Geneva.

“This object is one of the most extreme planets we know so far,” she added, describing it as “very exotic”.

Some 322 light years away in the constellation Libra, WASP-189b is so close to its host star that it orbits in less than three days. It is too far away from Earth to see directly, but can be detected in other ways.

When a planet passes between its star and an observer – whether an astronomer on land or a telescope in space – it dims the star’s light by a tiny but measurable amount. 

This “transit” method has detected the vast majority of exoplanets discovered so far. NASA’s Kepler spacecraft used it to find thousands of candidates from 2009 to 2013.

Burning blue hot

Exoplanets – any planet outside our solar system – were first confirmed to exist in 1995 by two Swiss astronomers, Michel Mayor and Didier Queloz, an exploit that earned them a physics Nobel last year. 

Queloz is among the more than 100 co-authors of the new study, published last week in the journal Astronomy & Astrophysics.

There are 4 284 confirmed exoplanets as of 29 September 2020, according to the NASA Exoplanet Archive, and at least as many likely candidates.

The vast majority are bigger than those of our solar system: 1 339 so-called ice giants, 1 457 Neptune-like gas giants, and 1 320 “super-Earths” with masses many times greater than the rock we call home.

There are relatively few (162) terrestrial planets with Earth-like mass, and of those only, a handful are in a “temperate” zone that would support liquid water, a key ingredient for life as we know it.

Bigger than the Sun

WASP-189b is unusual in that it does not reflect a lot of star light.

“Instead, most of the starlight gets absorbed by the planet, heating it up and making it shine,” said Lendl.

WASP-189b’s star is bigger than the Sun, and about 2 000 degrees Celsius hotter, the researchers reported. Because it is so hot, the star appears blue and not yellow-white like the Sun.

Several studies estimate there could be a trillion exoplanets in our galaxy alone. Indeed, there may be as many or more exoplanets in the universe as there are stars.

CHEOPS – an acronym for CHaracterising ExOPlanet Satellite – is in orbit 700 kilometres from Earth.

Marlowe HOOD © Agence France-Presse