Three Earths Around a Red Sun

TRAPPIST-1 is what astronomers call an "ultracool dwarf" — a red star roughly the size of Jupiter, burning so faint that if you swapped it for our sun, Earth would freeze in days. The three planets announced this week in Nature orbit so close to it that their years last roughly one to two Earth weeks. Close enough that liquid water might pool on their surfaces. Close enough that from their surface, TRAPPIST-1 would hang vast and red in the sky — not quite the sun you'd imagine when someone says another sun.

This is the part where I'm supposed to tell you scientists are excited about the possibility of life.

I am telling you that. Scientists are very excited.

But the honest thing is harder to sit with: forty light-years is 235 trillion miles. The fastest spacecraft humans have ever built would take 37,000 years to arrive. If intelligent life exists on one of those planets right now — and the word if is doing a lot of heavy lifting — they are so completely unreachable that the gap between us and them makes our most ambitious space dreams look like trying to cross the Pacific on a pool floaty.

And yet the universe arranged for three Earth-sized rocks to orbit a dim star at exactly the right distance for liquid water, around a star that will burn for another 10 trillion years — roughly 700 times longer than the universe has existed so far — and placed this configuration 40 light-years from us. Which is, cosmically speaking, next door.

The astronomers found them by watching TRAPPIST-1 dim slightly as each planet crossed its face. They used a telescope in Chile. They did math. They wrote a paper. The universe, which had been arranging these particular rocks around this particular star for longer than complex life has existed on Earth, did not seem to notice.

That's what doesn't fit cleanly into a headline: the discovery is ours. The planets are not. They have their own history, their own relationship with their star, their own physics — and maybe their own chemistry, their own weather, their own something. We found out about them this week. They were happening either way.

Three worlds around a red sun that barely qualifies as a sun, 40 light-years from here. The scale of this should produce a kind of pleasant nausea — the recognition that the universe is much larger and stranger than anything our nervous systems evolved to process. We are a species that recently learned how to look for neighbors and found some. We cannot visit. We cannot call. We can only watch a star dim for a few minutes and know, from that dimming, that something is there.

That something might be nothing. Rocks and radiation and no one to notice either.

Or it might be something. Either answer is cosmically deranging.

Welcome to the neighborhood.

i · sources

• Three Temperate Planets Orbit Nearby Ultracool Dwarf Star — Nature, 2016-05-02
• TRAPPIST-1 — NASA Science Exoplanet Exploration