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First results from Cheops reveal extreme alien world

on 29 September 2020

ESA’s new exoplanet mission, Cheops, has found a nearby planetary system to contain one of the hottest and most extreme extra-solar planets known to date: WASP-189 b. The finding, the very first from the mission, demonstrates Cheops’ unique ability to shed light on the Universe around us by revealing the secrets of these alien worlds.

Launched in December 2019, Cheops (the Characterising Exoplanet Satellite) is designed to observe nearby stars known to host planets. By ultra-precisely measuring changes in the levels of light coming from these systems as the planets orbit their stars, Cheops can initially characterise these planets — and, in turn, increase our understanding of how they form and evolve.

The new finding concerns a so-called ‘ultra-hot Jupiter’ named WASP-189 b. Hot Jupiters, as the name suggests, are giant gas planets a bit like Jupiter in our own Solar System; however, they orbit far, far closer to their host star, and so are heated to extreme temperatures.

WASP-189 b sits around 20 times closer to its star than Earth does to the Sun, and completes a full orbit in just 2.7 days. Its host star is larger and more than 2000 degrees hotter than the Sun, and so appears to glow blue. “Only a handful of planets are known to exist around stars this hot, and this system is by far the brightest,” says Monika Lendl of the University of Geneva, Switzerland, lead author of the new study. “WASP-189b is also the brightest hot Jupiter that we can observe as it passes in front of or behind its star, making the whole system really intriguing.”

First, Monika and colleagues used Cheops to observe WASP-189 b as it passed behind its host star – an occultation. “As the planet is so bright, there is actually a noticeable dip in the light we see coming from the system as it briefly slips out of view,” explains Monika. “We used this to measure the planet’s brightness and constrain its temperature to a scorching 3200 degrees C.”

This makes WASP-189 b one of the hottest and most extreme planets, and entirely unlike any of the planets of the Solar System. At such temperatures, even metals such as iron melt and turn to gas, making the planet a clearly uninhabitable one.

In the next few years, Cheops will follow up on hundreds of known planets orbiting bright stars, building on and extending what has been done here for WASP-189b. The mission is the first in a series of three ESA science missions focusing on exoplanet detection and characterisation: it has significant discovery potential also – from identifying prime targets for future missions that will probe exoplanetary atmospheres to searching for new planets and exomoons.

More information about this discovery can be found at this link.

Image credit: ESA