D-24: The Hermit

The following was originally published on the Stellaris forums.

 

Yesterday was our weekly “EJ talks about something terrifying and destructive” episode. Today we go for something bleak but also hopeful. Let’s talk about the catchily named WISE 0855-0714.

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(Image courtesy sci-news.com)

It’s a gas giant between three and ten times the size of Jupiter, which means that it’s big by gas giant standards but Latham’s Planet might well still consider it a moon. (This gives you an idea of how large Latham’s Planet is.) This is not remarkable at all. There are lots of gas giants this size.

What makes WISE 0855-0714 remarkable is that it is not a planet, if by “planet” you mean “object orbiting a star.” It formed alone, out in interstellar space. WISE 0855-0714 is what some people call an orphan planet or rogue planet. There is a very slender theoretical possibility that WISE 0855-0714 might one day be captured by a star system, but space is very large and the chances of it coming close enough are slender. In all likelihood WISE 0855-0714 will remain out in the beautiful void until the end of the galaxy.

WISE 0855-0714 is about 7 light years from the Sun, making it by some counts the fourth-closest object to us.

Isn’t a ball of gas floating around on its own considered a star?

A star is a ball of gas which is undergoing fusion or at one point was undergoing fusion. WISE 0855-0714 is too small to be able to fuse hydrogen; however it has a temperature above the background temperature of space so there may be some activity going on there. (It’s a chilly -13 C to -48 C, if you’re wondering.) This energy may be coming from radioactive activity rather than from the fusion.

We think some of its mass is made of up water, intriguingly.

So why is this worth pointing out?

Planets die when their stars explode and destroy them. WISE 0855-0714 has no star. It could be very, very old indeed. We don’t know how old. It would be extremely difficult to find out how old.

It’s a gas giant. This means it could well have rocky moons. Those rocky moons could be far older than any rocky planet we’ll ever find in a star system. If you put something there, it would remain long after the stars have burned out.

Rocky orphan worlds do exist, but they’re difficult to see. WISE 0855-0714 is large enough to be visible. If we wanted to put something somewhere where it would outlive our star and could be found by others, this might be a good place for it.

Long after all the fuel in the galaxy has been burned and every star has dwindled into ash, WISE 0855-0714 may be there, cold and alone, a testament to all the civilisations that rose and fell around it.

We should go there sometime. It’s not that far. We should leave something there to remind those who come after us that we once existed, a cenotaph for humanity and a memorial that against all the odds we managed to survive, at least for a while, and travel through space.

That is, if someone else hasn’t done that already.

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