Discovered by: Kailash Sahu et al.
Distance from Earth: ~27,7000 light-years
Mass: <3.8 Jupiter masses
Radius: ~0.8 Jupiter radii
Surface climate: Distantly warm
Habitability for humans: Doubtful
Orbiting a yellow-white star near the Milky Way’s center is a hot Jupiter.
There’s quite a bit more to tell here. Nearly 28,000 light-years away from Earth, SWEEPS-04 is one of the most distant confirmed exoplanets to date. The SWEEPS-04 we’re seeing now is actually how it was when prehistoric Europeans were coloring the first cave paintings.
There are a few candidates that could top it; there’s evidence pointing to at least one planet in the Andromeda Galaxy, some 2.5 million light-years away, and astronomers have claimed to find indirect evidence for planets even further than that. But for now, SWEEPS-04 and its ilk are the furthest.
I say “SWEEPS-04 and its ilk,” and by this point, you might be wondering what SWEEPS is at all. It wasn’t just some strangely-named initiative to sweep drugs out of American schools; it was actually a sky survey called the Sagittarius Window Eclipsing Extrasolar Planet Search.
See, the constellation Sagittarius is especially important for certain astronomers — it pinpoints the direction of the Milky Way’s center and the dense bright mass of stars that lie there. That is why the Milky Way’s central supermassive black hole is called Sagittarius A*. But it’s normally difficult for us to peer into that galactic center, because there’s too much dust in the way, muddying our vision.
The Sagittarius Window, on the other hand, is a patch of sky with comparatively little dust. SWEEPS sought to peer through and find any traces of exoplanets that it could.
How do you find exoplanets that far away? The answer: very similarly to finding exoplanets that are nearer. SWEEPS found exoplanets through the transit method, looking for drops in light caused by planets passing in front of their host stars. (Hence the “Eclipsing” in its name.)
In fact, SWEEPS found several dozen planets, but only two orbited stars that were distinct enough in the sky for follow-up observations to confirm their mass. The larger of the two was SWEEPS-11, a colossal hot gas giant that is almost ten times the mass of Jupiter.
The other planet is SWEEPS-04. It too is a hot Jupiter, orbiting at one-sixth the distance of Mercury and taking less than five Earth days to complete an orbit, but it’s almost more interesting for being smaller. At most, it’s “only” around four times Jupiter mass; it’s likely even lighter than that.
SWEEPS-04 and its ilk are reminders that there are planets like them all over the universe — not just in Earth’s local area.