Space.com (January 4, 2010)
"Some astronomers say that a planet the size of Mars or Earth could be lurking on the fringes of our solar system. But even the latest space telescopes that launched in 2009 stand little chance of finding such a distant object.
"Such a world, if it exists, would probably have an orbit far beyond Pluto or similar dwarf planets in the outer solar system. It would likely resemble a frozen version of Mars or Earth at best, a most unsuitable home for life. And it would not be alone.
" 'When the solar system's story is finally written, it's much more likely that it will have closer to 900 planets rather than the nine that we grew up with,' said Alan Stern, a planetary scientist at the Southwest Research Institute (SwRI) in Boulder, Colo...."
"Finally written?" That may take a while. ("Once it Was Believed / Now We Know" Brian H. Gill (2003))
Anyway, this article is an interesting look at what we know, and don't know, about the outer reaches of the Solar system.
"...[Caltech astronomer Mike] Brown noted that any future discovery of larger objects in the outer solar system would either suggest that scientists have the wrong idea of how planets form, or might indicate that the early solar system had more material available than previously suspected.
" 'More interesting to me, though, is that it would be an entirely new class of large body,' Brown said. 'We don't have any ice rich planetary-sized bodies in the solar system, so we don't really know what they would be like and how they would work.'
"[Southwest Research Institute planetary scientist Alan] Stern has long supported the idea of many planet-sized lurkers in the outer solar system. He referred to computer models that show how medium-sized planets might have formed during the chaotic creation of gas giants such as Jupiter, when swirling smaller pieces clumped together to form larger bodies...."
Looks like it's another case of current mathematical models for how the cosmos works being pretty close matches to reality - or not. Either way, it's exciting.
The article brings up the ongoing debate about what a "planet" is - exactly. I have a notion that's going to be going on for quite a while. Me? I think if it's round, doesn't either have fusion going on inside or is a star that ran out of fuel, and isn't orbiting something else that's round and isn't a star - it's a planet. That would include 'brown dwarfs' - so there would have to be an upper mass limit, too: which would be somewhat arbitrary. Jupiter, arguably, is a brown dwarf in relatively close orbit around Sol.
Like the fellow said:
"Not only is the universe stranger than we imagine, it is stranger than we can imagine."
Sir Arthur Eddington English astronomer (1882 - 1944)
Finally, besides 'pure science' and the joy of discovery, I think there are some exciting possibilities in those possible planets.
If one is big enough, and mostly rock and metal, like the inner planets (Mercury through Mars, maybe Ceres): it could be moved in, warmed up, and terraformed. There are stable points in the inner Solar system: 60 degrees away from Earth, ahead and behind in our orbit, for starters.
Granted, right now we can't move planets around. But there's nothing in physics that says it's impossible: it just takes more energy than we can handle right now. I've gotten used to the idea that nothing - technology included - stays the same. And growing up when computers and interplanetary spaceships with robot explorers weren't a part of everyday life gives me a certain perspective.
Terraforming is taking a planet and modifying it until it's a reasonable facsimile of Earth. It's another thing we can't do - now - but probably could, after we work out technical details.
Since it seems a little more likely that what we found outside the orbits of Neptune and Pluto/Charon will be more frozen water and other volatile substances than rock and metal, moving one and terraforming it may not be practical.
Unless we figure out how to transmute elements on a planetary scale. We can change lead to gold now, on a very small scale - but it costs too much to be a commercially viable process. I'm getting off-topic.
Where was I? Frozen slushballs. Right.
If we find something, say, the size or Ceres of Mars, made mostly of water ice and frozen methane, hydrogen, and other substances that are normally gas or liquid at "normal" temperatures, that could be moved in and used as a reservoir for terraforming Mars or Venus.
Of course, comets are falling in toward the sun at a fairly steady rate: so there wouldn't really be any point.
That article in Space.com? It's a pretty good look at where we are at, studying the outer Solar system.
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- "Another Super-Earth: Probably With Water, Possibly With Strange Chemistry"
(December 17, 2009)
- "Earth May Not Be a "Class M" Planet"
(December 5, 2009)
- "Water on Mars: The Lost Ocean of Barsoom?"
(November 23, 2009)
- "Another Hot Jupiter With Organic Compounds"
(October 21, 2009)
- "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"
(May 29, 2009)
- "The Caves of Mars"
(October 26, 2009)
- "Cloud Cities of Venus"
(July 25, 2008)
More in this blog:
- "Change, American Culture, Trilobites, Humanity's History, and the Big Picture"
(Last updated December 21, 2009)
- "Mars, Mostly