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rfmcdonaldMany cool things have come from Kepler's success. Among the coolest is the planetary system of Kepler-11, a yellow dwarf like Sol in the direction of the constellation Cygnus some two thousand light years away from us that has six close-orbiting planets within the orbital distance of Venus. Centauri Dreams does a good summary.
What's exciting about this? Apart from the remarkable configuration of the system, such a tight packing of planets--in our solar system, the six Kepler-11 worlds would fit easiyl between the orbits of Earth and Mars--says exciting things about the potential for extraterrestrial life. Imagine a planetary system where six rocky Earth-like worlds would exist in the habitable zone of a star. This is a planetary system that's potentially full of life; this is a planetary system that makes the planets of the quaternary system in the canonical Battlestar Galactica map looks sparse, this could inspire Firefly.
Made. Of. Win.
I want to focus on the unusual case of Kepler-11, a system that contains no fewer than six planets orbiting a Sun-like star. Ponder this: Before the new discovery, we had determined both the size and mass for only three exoplanets smaller than Neptune. Now, in a single planetary system, we have added five more, all in tightly packed orbits around the primary. There is a sixth planet as well, though its mass remains undetermined.
The five inner planets in this system range from 2.3 to 13.5 times the mass of Earth. All have orbital periods of less than fifty days, meaning they would fit inside the orbit of Mercury within our own Solar System. The sixth planet has an orbital period of 118 days and, as noted above, we have no data on its mass. All six of these worlds have densities lower than the Earth’s. Jonathan Fortney (UC-Santa Cruz) led the work on the structure and composition of the planets:
“It looks like the inner two could be mostly water, with possibly a thin skin of hydrogen-helium gas on top, like mini-Neptunes,” Fortney said. “The ones farther out have densities less than water, which seems to indicate significant hydrogen-helium atmospheres. … These planets are pretty hot because of their close orbits, and the hotter it is the more gravity you need to keep the atmosphere. My students and I are still working on this, but our thoughts are that all these planets probably started with more massive hydrogen-helium atmospheres, and we see the remnants of those atmospheres on the ones farther out. The ones closer in have probably lost most of it.”
Finding six planets around the same star allows us to make advances in the burgeoning study of comparative planetology, and Kepler-11 seems to hold clues to planetary formation. Because stellar disks should lose their hydrogen and helium gas within about five million years, the assumption here is that the numerous small planets with hydrogen/helium atmospheres must have formed quickly. Moreover, their crowded location near the parent star suggests planetary migration, with at least some of the planets forming further out and spiraling inward over time.
What's exciting about this? Apart from the remarkable configuration of the system, such a tight packing of planets--in our solar system, the six Kepler-11 worlds would fit easiyl between the orbits of Earth and Mars--says exciting things about the potential for extraterrestrial life. Imagine a planetary system where six rocky Earth-like worlds would exist in the habitable zone of a star. This is a planetary system that's potentially full of life; this is a planetary system that makes the planets of the quaternary system in the canonical Battlestar Galactica map looks sparse, this could inspire Firefly.
Made. Of. Win.
