Bad Astronomy: Sharpest image of Pluto ever taken

Astronomers using the monster twin Keck 10 meter telescopes have produced the sharpest image of the Pluto system ever taken! Now, mind you, these are the largest optical/IR telescopes on the planet, capable of incredibly high-resolution images. If you ever were wondering just how small and far away Pluto is, then keep that in mind when you look at this picture:

Pluto is small, and far away.

Pluto is the larger of the circular blurs, and its big moon Charon is the somewhat smaller blur (the sizes of the dots are not because of the sizes of the objects, but rather their brightnesses: brighter objects appear bigger). You can also see the dinkier moons Nyx and Hydra above and to the right.

These images are a little frightening, since they really bring home — literally — the scale of the solar system. Pluto is 2300 km across (smaller than the Earth’s Moon) and was about 4.8 billion kilometers away when that image was taken.

More images will be taken so that the astronomers can track the moons as they orbit Pluto. Better observations means the orbits can be measured more precisely, which in turn will yield better measurements of Pluto’s mass (the mass of the planet asteroid dwarf iceball thingy determines its gravity, which in turn drives the orbits of the moons, so by studying the moons you get Pluto’s mass).

Getting the mass of Pluto precisely is a little bit difficult since it’s so hard to observe — it’s really far away. When it was first discovered and its distance determined, it was thought to be a giant planet because it was so bright for that distance. More observations showed that it was actually small, but very reflective (its surface is very white), so it fooled astronomers into thinking it was bigger. Over time, the mass/size measurements got smaller and smaller, until Charon was discovered and Pluto’s size and mass were found with some accuracy. There was a joke that if we kept observing Pluto, it would disappear entirely.

It may not be considered a full planet anymore, but it’s still a pretty interesting place. It’ll be years before the New Horizons probe gets there, so until then we’ll have to be satisfied with it being a blurry dot.