Archive for the ‘Pluto’ Tag

Explore space with probes and telescopes, not people

The Economist has an interesting short article criticizing manned space exploration and praising the Obama administration for appearing ready to reprioritize America’s goals in space.

Mr Obama’s transition team had already been asking difficult questions of NASA, in particular about the cost of scrapping parts of the successor to the ageing and obsolete space shuttles that now form America’s manned space programme. That successor system is also designed to return humans to the moon by 2020, as a stepping stone to visiting Mars. Meanwhile, Mr Obama’s administration is wondering about spending more money on lots of new satellites designed to look down at the Earth, rather than outward into space.

These are sensible priorities. In space travel, as in politics, domestic policy should usually trump grandiose foreign adventures. Moreover, cash is short and space travel costly.

The article recommends using space probes and robots, like New Horizons (going to Pluto), Cassini (already at Saturn), and Mars Pathfinder to explore our Solar System.

While it'd be neat to have people on the Moon, this is a bad idea

While it'd be neat to have people on the Moon, the idea is not cost-effective at all

While nothing is as cool as people in space, I wholeheartedly support investing our scarce space dollars in robotic and remote exploration instead of for crewed (“manned” is a bit androcentric) missions.  For instance, NASA’s Moon Base proposal, despite being very modest, will still cost hundreds of billions of dollars. And it is unlikely that the knowledge and experience that we gain from such a base will justify the expense.  The last Apollo missions were canceled and we haven’t been back to the Moon since the early 70s precisely because the place isn’t all that interesting.  (For a good critique of NASA’s moon base idea, see “Moon Baseless“, an article by Gregg Easterbrook, who has been following the space program for decades.)

By contrast, excellent science is being done by our newest space probes and robots—and for far less money.  New Horizons will have a total mission cost (from planning through the end of operations) of just $650 million; the total cost of the Cassini-Huygens mission is about $3.26 billion (including $1.4 billion for pre-launch development, $704 million for mission operations, $54 million for tracking and $422 million for the launch vehicle).  Telescopes are also very cost effective.  The Sptizer Space Telescope itself cost just $800 million and the planned James Webb Space Telescope will have a total cost (including planning, launch, and operation) of about $4.5 billion.

In short, for the cost of a Moon base we can explore the entire Solar System with probes and robots and explore the depths of space across all portions of the spectrum via orbiting and ground-based telescopes.  If funding were unlimited things would be different; but it’s not and they aren’t.  We have limited money for science, so we should spend it wisely.


Tweaking definition of planet

Well, the Solar System reforms of 2006, which I strongly supported, have not been as successful as I’d hoped. As many of you probably know, the International Astronomical Union then came up with the first formal definition of planet. The definition stated that a celestial object is a planet if and only if it:

  1. is in orbit around the Sun,
  2. has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and
  3. has “cleared the neighbourhood” around its orbit.

Furthermore, objects that met the first two criteria were termed “Dwarf Planets.” Pluto, Ceres (the largest inhabitant of the asteroid belt), and Eris were immediately classified as dwarf planets, and many other objects were candidates for the designation, once more was known about their sizes.

This resulted in there being eight planets in our Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; Pluto was “demoted.” It was this last item, Pluto no longer being a planet, that has caused most of the popular discontentment and news stories over the reforms. Personally, this doesn’t bother me any and I find the use of school children, who are told to write letters to astronomers and museums complaining about “Pluto being taken away” to be totally shameless.

However, I do now recognize legitimate problems with the 2006 definition, as much progress as it represented. It is somewhat confusing that “dwarf planets” are not planets, though it sounds like they should be a subset thereof. Beside the other technical ambiguities, the whole debate is also something of a distraction, and draws attention away from the important things.

For these reasons, I am glad that the Great Planet Debate is resuming, according to, my previous support for the present definition notwithstanding. I now support redefining as a planet any object that:

  1. is in orbit around a star and
  2. has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape.

That would give us twelve planets. But, I would furthermore subdivide planets into major planets and minor planets, the former being those that have “cleared the neighbourhood” around its orbit and the later being those that haven’t. This would give us eight major planets–the current ones, or the old nine less Pluto–and several minor planets, including Ceres, Pluto, Makemake, and Eris–with more minor planets to come as we learn more about the thousands of objects in the Kuiper Belt.

I think this definition would be clear, for both astronomers and laymen, and would be very useful, which, after all, is the sine qua non of a good definition. The only problem is that the term “minor planet” is already in use; it is virtually synonymous with asteroid. Those objects, which will not be planets or minor planets under my suggested definition, will need to be called planetoids, asteroids, or any of many other suitable terms.

Finally, the definition will need to be tweaked to exclude brown dwarfs and to address the issue of so-called rogue planets–round objects that have been ejected from any stellar system–and binary planets, which would include systems like Pluto-Charon where the barycenter (gravitational center) of the system lies above the surface of both objects. This would make Charon and Pluto binary (minor) planets.

I think these reforms could greatly aid discussions about the fascinating Solar System in which we find ourselves situated. Eight (major planets) is great and more (minor planets) are good too!