THE EXOTIC EXOPLANETS THAT DEFY THE LAWS OF PHYSICS

We’re discovering and uncovering details about new exoplanets all the time, with some really weird worlds existing beyond the Solar System

Written by Ian Evenden

Ever since humans started discovering exoplanets – planets that orbit around stars other than the Sun – in 1992, scientists have been hunting for one that’s similar to Earth. Exoplanets exist everywhere we look, and around many different types of stars. Yet none of them are Earth-like. They’re too big, too hot or too bathed in radiation from their star to ever support life as we know it. The search goes on, and as new data comes in from planet-hunting missions such as the Transiting Exoplanet Survey Satellite (TESS) and ground-based telescopes such as the Very Large Telescope (VLT), there’s one thing that we can be sure of: many of the exoplanets we find will be extreme.

THE BIGGEST EXOPLANET YET

Discovering the precise size of an exoplanet is a tricky thing to do. You’re inferring characteristics about an object many light years away, and there’s also a bit of a grey area between whether a massive object is a large planet or a small brown dwarf. HD 100546 is a star 316.4 light years from Earth that’s orbited by a planet approximately 20 times the mass of Jupiter. The boundary for becoming a brown dwarf is around 19 times Jupiter’s mass, putting this object well into the grey area. There are at least three other stars that are orbited by known brown dwarfs – substellar objects large enough to begin hydrogen fusion but not to sustain it. They gradually cool and darken over time, but while hot they can see a rain of molten iron on their surfaces thanks to atmospheric convection.

“HD 100546 is orbited by a planet approximately 20 times the mass of Jupiter”

TOASTY TEMPERATURES

WASP-76 b was first discovered in 2013, but an examination by the VLT in 2020 discovered that it’s tidally locked. This means that, just like our Moon, one side of it constantly faces the body it orbits, in this case WASP-76, a yellow-white star in the constellation of Pisces. The planet, which is slightly less massive than Jupiter but almost twice as large, is very close to its star and orbits once every 1.8 days. Being tidally locked means one side of the planet receives an extreme amount of solar radiation, with a daytime temperature of more than 2,000 degrees Celsius (3,632 degrees Fahrenheit). Meanwhile, the nighttime side is a relatively balmy 1,000 degrees Celsius (1,832 degrees Fahrenheit). This difference in temperature means metals, vaporised by the high temperatures on the dayside, could be carried across to the night side and turn into dense clouds of aluminium, iron or magnesium.