This is pretty nifty: astronomers have discovered a fourth moon orbiting Pluto!
The tiny chunk of ice was found in Hubble images taken just a few weeks ago, and was clearly seen among the three previously known satellites:
It doesn’t have a name yet — it’s designated S/2011 P1 (or just P4 informally) — and it’s only about 13 – 34 km (8 to 21 miles) across. The size is estimated by measuring its brightness and assuming it’s icy like Pluto itself — a more reflective (white or icy) object would appear brighter than a darker object if they are the same size. Since its actual reflectivity isn’t known, the size has a wide range. But it’s still pretty dinky. For comparison, Pluto itself is 2300 km across, and its biggest moon Charon is well over 1000 km in size. I’ll note our own Moon is 3470 km across, so even Pluto is pretty small.
The thing is, in that single image above you can’t be sure if the object is a moon or a coincidentally placed background star. The solution: take a second image! That was done, clinching the ...
