This post has been updated.
I went to the 30th Space Symposium this week in Colorado Springs, which was quite the shindig, with lots of military brass and much talk of “disaggregation” and “resilience” and “hosted payloads” and so on — terms I’ll need to explain in future stories. One highlight was Alan Stern’s talk on New Horizons, the NASA probe going to Pluto. It’ll fly by the planet* on July 14, 2015.
Stern is a former associate administrator at NASA for science, and he’s a great salesman for New Horizons, for which serves as principal investigator. Basically this is a better, smarter, faster version of Voyager, only it costs two dimes on the dollar in comparison, and there’s just the one probe instead of Voyager’s two. The modest price of New Horizons is important, because NASA is facing a future of constrained budgets, and you’re not going to be seeing many Cassinis anymore (Stern boasts that the entire New Horizons
spacecraft suite of instruments weighs less than Cassini’s camera).
The target is a planet that we’ve barely glimpsed. No one knows what it looks like up close. I know this may come as a shock to anyone who has Googled “Pluto” and seen all the high resolution images there. Sorry, those are illustrations (and in most cases not clearly labeled as such). The Hubble’s images of Pluto show a pixelated blob. New Horizons will begin achieving better-than-Hubble imagery of Pluto next April.
I learned from Stern a bunch of Pluto facts:
It has five moons — at least. They’ve found a couple of new ones just recently while keeping an eye out for hazards that may face New Horizons when it flies through the Pluto system.
It has an atmosphere and is 70 percent rock, with an ice crust.
Its eccentric orbit — which is at an angle to the orbital plane of the rest of the planets and brings Pluto at times within the orbit of Neptune — is normal for objects that far from the sun.
We don’t know much about Pluto: “What we know about Pluto is what we knew about Mars before Mariner 4,” Stern said, referring to an early robotic fly-by of Mars in July 1965, precisely 50 years before the New Horizons encounter with Pluto.
*Now to touch on the eternal question about Pluto: Is it a planet or a “dwarf planet”? The A-blog is on record grousing about Pluto’s demotion from “planet” status in 2006. See also this contemporaneous report.
Stern calls Pluto a planet. He doesn’t like the reclassification of Pluto as a dwarf planet or minor planet or “plutoid” or whatever the term is. Pluto is fairly small but it’s big enough that gravity has given it a spherical shape. Stern points out that to drive around Pluto at the Equator would be akin to driving from Manhattan to Moscow. By his standards, Ceres in the asteroid belt is also a planet. You could argue that our moon is a planet — that the Earth and moon are a double-planet system.
When I asked Stern if Pluto is “a Kuiper Belt Object” he said that’s merely a description of location.
You could also call it a “trans-Neptunian object,” though to my ear that sounds like a pejorative.
[Update: The International Astronomical Union created three criteria for a planet: 1) Must orbit the sun; 2) Must be spherical; 3) Must have cleared other material out of its orbit around the sun. Now, in the boodle (in reply to bc’s 10:49 a.m. comment), Alan Stern himself has weighed in on this definition: “The whole zone clearing idea is poorly conceived. After all, Pluto’s zone is larger than the entire region from Neptune inward! Zone clearing gets harder and harder as you move outward in the solar system because the zone sizes grow. You could put the Earth in the Kuiper Belt and it would not clear the zone. Would we then say the Earth is not a planet? Nuts.” Thank you Dr. Stern for the comment!
See also alice13’s 11:36 a..m. comment in the boodle: “Just back from the AAS Division on Dynamical Astronomy meeting (Philly), where I learned something new about Pluto. Check it out: Pluto and Charon orbit around their mutual center of mass. But all those other moons? They orbit around Pluto and Charon! So P+C really ARE a binary planet with a swarm of little moons orbiting them both. So maybe we can stop fretting about whether Pluto is a planet or not. In fact, it’s something far more interesting!”]