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rfmcdonaldIn astronomer and writer Chris Impey's 2010 Talking About Life, an anthology of his interviews with leading experts in astronomy and related fields about extraterrestrial life, there was a passage in his interview with Debra Fischer that caught my attention for its alternate history potential. Solar systems, including our own, are apparently as densely packed with planets as possible.
The WI question is obvious. What if there was a planet the mass of Venus orbiting in our solar system between Mars and Jupiter?
This planet--call it *Ceres, after the largest dwarf planet orbiting between Mars and Jupiter--would be a big one. Venus is more than 80% as massive as the Earth. Such a massive planet would be able to hold onto its volatiles--its atmosphere, its water--in a way that a nearer Mars could not. This planet might even be massive enough to be geologically active. *Ceres might provide a relatively hospitable environment, more hospitable than Venus or even Mars.
It's important to not overstate this potential habitability. Whatever the precise nature of its orbit, *Ceres would also be very cold, orbiting outside of the orbit of Mars and likely even an elastic definition of our sun's circumstellar habitable zone. A sufficiently dense heat-retaining atmosphere might change things, but would it warm *Ceres enough?
Given *Ceres' location near the frost line of the solar system, and its high gravity, it's likely to have attracted and kept quite a lot of ice. Perhaps it will be an ocean world; perhaps it will be a world with a frozen surface on top of a planet-wide ocean, a super-Europa even. As seen in the night sky from Earth, its atmosphere and icy surface may make it very bright indeed.
Thoughts?
DF: The amazing thing I learned when we discovered the Upsilon Andromedae system is that our Solar System s actually dynamically full of planets. When people who model the Solar System try to drop in an extra planet, the whole system goes into chaos--some planets are lost, some fall into the star, some are ejected, and then everything finally settles down. Each planet has its own gravitational domain and those domains are pushed up next to each other. Our Solar System resides on the verge of instability it's stable, but only just.
CI: Is this related to the numerical coincidence of their nearly geometric spacing?
DF: Bode's law? Yes. They clear out disks; many lines of evidence suggest that core accretion is the correct model. Then they begin to migrate in until they come into a zone; again, if they get any closer. they're ejected. When I noted this back in 2000, Hal Levinson raised his hand and said, "No, no, that's not true--there a place between Mars and Jupiter where a Venus-sized planet will survive." And I think, "How many simulations did you have to run to find that tiny little window? That doesn't count!" [Laughs](269-270).
The WI question is obvious. What if there was a planet the mass of Venus orbiting in our solar system between Mars and Jupiter?
This planet--call it *Ceres, after the largest dwarf planet orbiting between Mars and Jupiter--would be a big one. Venus is more than 80% as massive as the Earth. Such a massive planet would be able to hold onto its volatiles--its atmosphere, its water--in a way that a nearer Mars could not. This planet might even be massive enough to be geologically active. *Ceres might provide a relatively hospitable environment, more hospitable than Venus or even Mars.
It's important to not overstate this potential habitability. Whatever the precise nature of its orbit, *Ceres would also be very cold, orbiting outside of the orbit of Mars and likely even an elastic definition of our sun's circumstellar habitable zone. A sufficiently dense heat-retaining atmosphere might change things, but would it warm *Ceres enough?
Given *Ceres' location near the frost line of the solar system, and its high gravity, it's likely to have attracted and kept quite a lot of ice. Perhaps it will be an ocean world; perhaps it will be a world with a frozen surface on top of a planet-wide ocean, a super-Europa even. As seen in the night sky from Earth, its atmosphere and icy surface may make it very bright indeed.
Thoughts?
