Exoplanets: bodies that go around other stars

What are exolanets?

Planets outside the Solar System, usually orbiting another star. The TRAPPIST-1 System is a system of exoplanets.

Where are they found?

Mostly in a relatively small region of the Milky Way, up to which telescopes can currently see. Astronomers think that nearly every star in the universe could have at least one planet — that’s trillions of planets waiting to be found.

How many are there?

More than 3,400 “confirmed”; over 2,000 “candidates” are under observation. The first ones were discovered in the early 1990s, numbers have since doubled every about 27 months.

Which is the closest?

Proxima b — about 4 light-years away. 1 light-year is the distance that light, travelling at about 300,000 km per second, covers in a year — or about 9 trillion km. The star of Proxima b, Proxima Centauri, is a dim red dwarf that gives off about 600 times less light than the Sun.

Are exoplanets reachable?

Not anytime soon. Perhaps a robot, one day very far in the future. We’re still trying to find a way to get a human to Mars, which is a mere 225 million km away.

Are there any pictures of them?

Yes. NASA has many of exoplanets several light-years away, for example those orbiting the stars Fomalhaut, HR 8799, and Beta Pictoris. They look like faint spots next to blotted out regions.

Do they have life?

No — so far. A search of the galaxy for planets similar to Earth — and signs of life — continues. Water molecules have been found in the atmosphere of more than one exoplanet, but no liquid water, like oceans or lakes, has been discovered.

How are they named?

Long and complicated, but logical. First part of the name is usually the telescope or survey that found it — in HD 189733 b, for example, ‘HD’ is “Henry Draper Catalogue”, a widely-used star catalogue. ‘189733’ is the position of the star in the catalogue. ‘b’ stands for the planet, in the order in which it was found. The first planet found is always named ‘b,’ with future planets named c, d, e, f and so on. The star that the exoplanet orbits is usually the undeclared ‘A’ of the system. If the system contains multiple stars, they may be designated B, C, etc.