Tuesday, May 25, 2010

Upsilon Andromedae, Tilted Orbits, and Habitable Worlds

"Weird Orbits of Alien Planets Could Affect Chances for Life"
Space.com (May 24, 2010)

"The ability of life to thrive on alien worlds may be impacted by the wild and weird orbits of giant neighboring planets, new studies suggest.

"The heftier worlds in other planetary systems could exert large forces on smaller worlds, pushing and pulling them into changing orbits. In some cases, these weird orbits could cause some extrasolar planets to fluctuate between being habitable and being inhospitable to life.

"These changing conditions of habitability could impact the search for life on other worlds and astronomers' theories on the formation of planetary systems like our own.

" 'There is this crazy zoo of planets out there that probably are habitable,' research team member Rory Barnes of the University of Washington said, 'but their properties are very different from Earth and they're different from Earth because of their eccentric neighbors.'..."

(from NASA, ESA, and B. McArthur (The Univ. of Texas at Austin, McDonald Observ.), via Space.com, used w/o permission)
"An artist's illustration that compares the solar system with the Upsilon Andromedae system. Astronomers have recently discovered that not all planets orbit the bright yellow-white star Upsilon Andromedae in the same plane, as the major planets in our solar system orbit the Sun. The orbits of two of the planets, c and d, are inclined by 30 degrees with respect to each other. Credit: NASA, ESA, and A. Feild (STScI) Science: NASA, ESA, and B. McArthur (The Univ. of Texas at Austin, McDonald Observ.)"

Until very recently, the only planetary system we could observe - or knew existed - was our Solar system: the planets, asteroids, and assorted things orbiting our sun, Sol. The planets, from Mercury out to Neptune, and the asteroids, all orbit in almost exactly the same plane. Even Pluto isn't that far out of the ecliptic, the plane of Earth's orbit.

Then, a decade or so back, astronomers developed ways to detect planets circling other stars. The number of known exoplanets, planets circling other stars, is over 400 and is still growing.

Three of them orbit Upsilon Andromedae. Upsilon Andromedae is quite a bit like our sun: It's about the same temperature, but younger and somewhat more massive. When the three planets were detected, a reasonable assumption was that they all orbited in the same plane.

They don't.

"...But, new findings from computer modeling indicate that the habitability of some exoplanets could vary, based on the orbits of giant planetary neighbors.

"The discovery of these so-called weird orbits will have important implications for existing theories of how multi-planet systems evolve. The findings also show that some violent events can happen to disrupt planets' orbits after a planetary system forms.

" 'The findings mean that future studies of exoplanetary systems will be more complicated,' said Barbara McArthur of The University of Texas at Austin, who was the lead researcher for one of the studies. 'Astronomers can no longer assume all planets orbit their parent star in a single plane.'..."

The odds are that the Upsilon Andromedae planets formed in a single plane - but that something happened after that to tilt the orbits of the outer two. That "something" could have been a fourth massive planet that got thrown out of the system in the process, Upsilon Andromedae's binary companion (it's a double star), or - well, something else.

The tilted orbits of Upsilon Andromedae's outer planets - and the very eccentric orbits of massive planets in other systems - means that ideas like "habitable planet" and "habitable zone" are probably much more complicated than we thought.

"...'The bigger issue here is that the habitable zone is very complicated,' Barnes said. 'Earth's climate is affected slightly over tens of thousands of years by the orbits of other planets in the solar system, but it is possible that in many exoplanetary systems the layout of the planets is very important to habitability.'..."

As often happens in the sciences, the more we know, the more we discover that we don't know. That certainly keeps things from getting boring.
Related posts, at

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