New Horizons Closest Approach to Pluto

[I decided to go live with this ahead of schedule. The following text is based upon it being published at the usual 9:05 am. See the “Afterword — Live Blog” section below.]

Pluto - 13 July 2015As this is published, New Horizons will have made its closest approach to Pluto. It’s closest approach will be at 4:49 am local (Pacific!) time. Even Google is celebrating it with an unfortunately fairly boring Doodle to mark the occasion. But it’s the thought that counts. We already know so much more than we did before about the planet, dwarf planet, or space debris — depending upon how you see it. I tend to be in the “space debris” camp, but I think it is wonderful space debris. This is a great moment. We can’t manage to feed all our children. We can’t manage to stop fighting wars. We can’t even manage the European economy, but at least we can fly out to Pluto and take some measurements.

Speaking of which, the big news as I write this is, How Big Is Pluto? New Horizons Settles Decades-Long Debate. It turns out it is even bigger than we thought: almost 1,500 miles across. But just to be clear: that’s still a hell of a lot smaller than our Moon. Interestingly, Pluto’s biggest moon, Charon, turns out to be just about what we thought from ground based observations. And the reason for that is really interesting!

The problem with Pluto is that it has an atmosphere. True: not much of an atmosphere. Pluto’s atmosphere makes Mars’ atmosphere seem thick. Nonetheless, it is thick enough to cause all kinds of light disturbances. As a result, when we were observing it from the earth, we had to assume a certain level of atmospheric distortion. But it turns out that Pluto is less dense — likely containing more ice. And its atmosphere is even thinner than we had assumed before.

Meanwhile, New Horizons has been able to get better estimates of Pluto’s next two biggest moons. Hydra is about 30 miles across and Nix is about 20 miles across. We are still waiting to get better images of the two smallest moons: Kerberos and Styx. And I assume we are going to discover other small moons as well. We will see.

Afterword — Live Blog

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