This is it. New Horizons makes its closest approach to Pluto today. The last unvisited planet is finally getting its close-up, and …
What? Yes, I called Pluto a planet. Not Dwarf Planet or Kuiper Belt Object, but planet. P-l-a-n-e-t. It has enough gravity to pull itself into a nice, spherical, shape, and has five moons, to boot. It’s really the only double-planet in our solar system, with the barycenter of Pluto and Charon outside both bodies. Yes, I know the International Astronomer’s Union demoted it on the grounds “it has not cleared its orbit,” but, if you look at the asteroids that cross the Earth’s, neither has ours. Very arbitrary, and I’m quite sure its discovery by an American astronomer had absolutely nothing to do with it.
New Horizons is already turning up interesting details about Pluto. For one, planetary scientists now know Pluto’s diameter, which is larger than estimated. Eris was previously thought to be larger than Pluto, but now it’s in second place. But this means Pluto is even less dense than previously thought.
Until now, Pluto, Charon, and Pluto’s moons all were just blobs of light. They are so far away not even Hubble could resolve surface features. That’s all changed. Pluto has ice caps, a heart-shaped feature, and is relatively smooth, which, with the lower density, might mean it’s mostly ices like water and methane.
The fly-by will happen this morning about 7:49:58 EDT, but even if New Horizons sends Earth a “Howdy” at that point, Mission Operations wouldn’t know about it until about 12:15 EDT, because it will be about 4.771×109 km (that’s about 2.964×109 miles) from Earth, and it takes light over four hours, 25 minutes, to travel that far. It would actually take longer to process the signal, since the data rate is real slow because the signal is so faint. So New Horizons is storing all this information and will be sending it to Earth long after it’s left Pluto far behind and (maybe) heading for a Kuiper Belt Object.
Even though New Horizons is the fast spacecraft ever launched. New Horizons’ principle investigator Alan Stern, on the July 10th, edition of NPR’s Science Friday, pointed out that it took three days for Apollo astronauts to get to the moon, and it only took New Horizons nine hours. Even so, it’s not the fastest human made object. In response to the question of when would New Horizons “catch up” to the Voyager craft, Stern pointed out it never will, since the Voyager craft got a bigger gravitational boost than New Horizons, so they ended up moving faster.
Stern also hit on a strong point. This is the last new planetary fly-by. In my lifetime man has all the known planets except for Pluto. This is almost like exploring the last unknown territory, or climbing the last unclimbed mountain. When New Horizons leaves Pluto, it will close a major chapter in human exploration: when mankind sent the first probes to the planets.
Here’s hoping it won’t be the last.