What worlds are out there? A field guide to exoplanets
A wondrous variety abounds, from hot Jupiters to mega-Earths
An Earth-like planet has been found orbiting the nearest neighbouring star to the sun, scientists announced yesterday.
It's one of thousands of exoplanets that have been discovered in recent decades, but among just a handful that are similar to our own home planet.
Here's a sample of the wondrous variety of planets that have been found outside our solar system.
Super-Earths are planets that are larger than the Earth but smaller than Neptune. While there aren't any in our own solar system, they're thought to be the most common type of planet in our galaxy. Smaller super-Earths may be rocky and able to support life if they have a temperature that allows liquid water to exist.
55 Cancri e is a super-Earth that orbits closer to its star than any other known super-Earth. The same side always faces the star, and that side is thought to be "a constantly boiling cauldron of magma-filled rivers and lakes," while the night side is a cooler 1,100 C.
GJ1214b, is a super-Earth that closely orbits a red dwarf star 40 light-years from Earth. When it was discovered in 2012, it was named a new type of planet called a "waterworld," with a steamy atmosphere that's at least 50 per cent water. Its surface may be covered in exotic materials like "hot ice" and "superfluid water."
While the gas giants in our solar system are far from the sun, many Jupiter-sized exoplanets have been found in very tight orbits around their stars. Such "hot Jupiters" may have "puffed up" atmospheres because of the heat. Their large size and short orbital period or "year" make them some of the easiest planets to detect.
WASP-12b, located about 1,200 light-years away in the constellation Auriga, was the first carbon-rich planet ever observed, with more carbon than oxygen, unlike Earth. That may mean it contains a diamond core.
Kepler 10c, discovered in 2014, was named a new type of rocky planet called a mega-Earth — it's an extremely dense, rocky planet that weights more than 17 times as much as Earth while having just twice the diameter.
Uranus and Neptune in our own solar system are ice giants. Planets that appear to have a similar size and temperature, like Kepler 421b, have also been found orbiting other stars.
Jupiter may be the largest planet in our solar system, but there are other planets in the universe that make Jupiter look puny. One such super-Jupiter (below) is four times the mass of Jupiter. Another, Gu PSc b, was found to be 10 times bigger than Jupiter and orbits its star at a record distance equivalent to 50 times the distance between Pluto and the sun.
Of course, the planets that cause the most excitement aren't the exotic ones but the rare Earth-sized rocky planets that are the right temperature for liquid water to exist on their surfaces, such as Kepler 186f. Such planets might be able to support life as we know it.