How are exoplanets named?

07 March 2017

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Question

How are exoplanets named?

Answer

Chris put this question to David Rothery from the Open University...

Chris -  There were 7 ones that were discovered recently, you were talking about them earlier, they’re called TRAPPIST-1a-f, which we thought were a little boring, so we asked you for your suggested names on twitter and Facebook…

Some of my favourites:
Planety Mcplanetface from Stephen on Facebook
Colours of the rainbow - Odysseus on FB
Seven dwarves from Marius on FB
Jeremy wants to name them after types of alcohol

But actually, how do scientists do this? How do you come up with names for these exoplanets?

David - The scientific designation for exoplanets are that the follow the name of the star or the catalogue number of the star. The first exoplanet that you find of a star you never use the letter ‘a’. You could started with ‘b’...

Chris - David Bowie - that would be a good star, wouldn’t it?  Tina Turner… Rod Stewart...

David - Only for terrestrial planets because they need to be “rock stars!”

The Trappist planets are Trappist- b. Trappist-1, that’s a star. It was discovered and this star wasn’t even catalogued. It didn’t have a designation until it was studied. It was studied with a telescope called the transiting planets infrared survey telescope or something like that. So from that you can get Trappist, and the first star that they studied Trappist-1, the first star that the found to have planets going around it. They then found seven planets in total which are: Trappist-1b, c, d, e - all the way to h, or however many seven letters goes. Those are the scientific names, scientific designations.

A few years ago (2014 I think) the International and Astronomical Union, the same body responsible for trying to define what planet it is in this solar system said “OK. Let’s see about giving some names to some of these planets.” Now if any of you are offered to buy the name of a planet for a loved one as a birthday present - don’t, it’s a con! Nobody else will recognise this. The IAU said “let’s try out some names.” It puts out a call for names and I’m sure there’ll be a call for the Trappist planet names because it is a very close star.

It wasn’t open to the public, it was open to astronomical societies and the like. The Astronomical Society of Lucerne in Switzerland - the 51 Pegasi, the first sunlight star to have a known Earth like planet, suggest the name Helvetios, which is to do with Switzerland. And they suggested the name Dimidium for its planet. And 51 Pegasi-b is now Helvetios and 51 Pegasi-b the planet is known as Dimidium. Now I couldn’t remember how dimidium goes with helvetios - I had to look it up. But I know that 51 Pegasi-b is a planet going around 51 Pegasi.

So I’m not sure of these names. We’re not meant to give scientific planet designations, they’re meant to be used in parallel. I don’t know that they will catch on. I think it’s a bit gimmicky. But there are now ways to give names to the stars and their planets and we’ll see what comes of it.

Chris - Anna?

Anna - Well it worked with the chemical elements.. We don’t just call them 1, 2, 3, 4, 5, 6, 7, and so on.

David - Yeah. But there are only 92 naturally occurring elements. We’ve got 3,000 stars with known planets and 4,000 known exoplanets - it’s something like that. And the numbers are just going to keep on growing, and growing, and growing.

Chris - Michael?

Michael - I just like the fact that one of your listeners suggested they should be named after types of alcohol because Trappist beer is a thing. And I believe that’s where the acronym was meant to homage. The Trappist order of monks are known for brewing their own beers.

David - Well, I dare say they had that in mind. I’ve seen some really contorted acronyms. This one isn’t bad - transiting planets infrared survey telescope. You can get Trappist out of that fairly simply. But maybe we start with really powerful, hot, short drinks close to the star and have nice cool drinks further away.

Chris - There’s one made with liquid nitrogen perhaps like in a nightclub. Those test tubey ones for the distant ones, far away from the star. I like that idea. I think I might propose it.

David - Feel free.

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