New Horizons...

I recently finished reading a new book by Dava Sobel called "The Planets". I picked it up after Christmas with some gift card money mainly because I have read one of Sobel's previous works (Galileo's Daughter) and had enjoyed it immensely. "The Planets" is basically just a series of interesting vignettes about each one of the planets in turn, from Mercury through Pluto.

Pluto has had a lot of attention lately. NASA just launched its New Horizons mission, scheduled to do a flyby of Pluto in about 2015 and then go on to study at least one other Kuiper Belt object. I always find these long-duration space missions fascinating, especially one this long. The Mars rovers only took a number of months to reach their destination, though the planning and behind-the-scenes wrangling took years. The Pluto mission is going to take *9 years* just to get where it is going, and it is traveling faster than any previous space probe ever launched. To give you an idea of how big the solar system is, it is going to reach Jupiter in 2007 for a gravity assist, and then take another 8 years to get to Pluto, even with that boost in speed.

Pluto is the only planet in the solar system that has yet to be visited by a probe from Earth, which New Horizons will remedy, though by that time, we might have more planets to visit. Scientists and astronomers have recently identified a Kuiper Belt object that is even larger than Pluto, once again opening the debate as to whether Pluto is even a planet, or just an anomalously large Kuiper Belt object itself. As Sobel's book points out, there are a lot of arguments both for and against calling these objects planets, but Pluto seems to be firmly ensconced as a planet if for no other reason than sentimentality.

Pluto was really discovered by accident. Herschel had discovered Uranus in the mid-1800's, but there was difficulty in accurately determining its orbit, which scientists attributed to another large body farther out that was perturbing Uranus's orbit. Through sheer force of calculation and the elegance of mathematics, the location of Neptune was calculated and then observed. An excellent account of the discovery of Neptune is given in "The Neptune File". However, even after Neptune's discovery, anomalies in the orbits remained, which sent astronomers hunting for another planet in much the same way as Neptune.

Pluto was eventually discovered in 1930, but when it was, it quickly became obvious that it was not massive enough to have caused the observed anomalies in Uranus and Neptune's orbits. It wasn't until the Voyager probes in the mid-1980's that the mystery was solved: The effect of both Uranus and Neptune's gravity on the probes allowed an accurate determination of their mass that Herschel and others had lacked. Pluto has no discernible effect on their orbits. The fact that it was being searched for at all was based on an erroneous data. But once the moniker of planet is given, inertia takes over, and ratcheting back to an 8-planet solar system seems like a step backward. It will be interesting to see what the discussion on this latest object yields - will we be adding a 10th planet to the pantheon? Time will tell...

On a personal note, the reactor in lab had first plasma last week. It only took two and a half goddamn years.