With over 2,000 extrasolar planets found around nearly as many stars, there’s still no place like home.
“Why aren’t we finding other planetary systems like our own?” PhysOrg asked. While the menagerie of planets discovered by the Kepler spacecraft is exotic and curious, it primarily shows that our earth escaped certain death.
Most planetary systems found by astronomers so far are quite different than our own. Many have giant planets whizzing around in a compact configuration, very close to their star. An extreme case in point is a newly found solar system that was announced on October 15, 2012 which packs five—count ‘em—five planets into a region less than one-twelve the size of Earth’s orbit!
An attending scientist at the American Astronomical Association’s Division of Planetary Sciences (DPS) meeting commented, “If we can understand this one, hopefully we can understand how these types of systems form and why most known planetary systems appear different from our own solar system.” Now, though, it is not clear. Most planets orbit very close in, but our sun’s planets are widely spaced.
The fact that almost all solar systems found so far are so different than our own has astronomers wondering if we are, in fact, the oddballs. A study from 2010 concluded that only about 10 – 15 percent of stars in the Universe host systems of planets like our own, with terrestrial planets nearer the star and several gas giant planets in the outer part of the solar system.
This might be a selection effect based on what our instruments are capable of detecting, but the discovery of so many close-in planets is sending theorists back to the drawing board.
There are several theories about the formation of the large planets in our outer solar system which involves the planets moving and migrating inward and outward during the formation process. But why didn’t the inner planets, including Earth, move in closer, too?
Fact is, “We don’t know why this didn’t happen in our solar system,” the spokesperson said. It’s going to require “a new generation of theories to explain why our solar system turned out so differently.”
Several science sites like National Geographic gawked at another oddball system that finds a planet orbiting a four stars, leading to inevitable comparisons with Tatooine of the Star Wars mythology. The real story is that the planet also “challenges conventional notions of how planets form,” an astronomer said. “The discovery of these systems is forcing us to go back to the drawing board to understand how such planets can assemble and evolve in these dynamically challenging environments.”
Update 10/17/2012: An earth-size planet has been found! –but you wouldn’t want to visit there. Space.com said that the earth-size planet orbits a member of the Alpha Centauri system closer than Mercury orbits the sun, making it a “hellish, lava world.” On Oct 18, Space.com used the opportunity of this discovery to list some of the requirements (and desirements) for a planet to be hospitable for life.
This is not what the astrobiologists, astronomers and modelers expected. Migration was brought into the nebular hypothesis in response to discoveries, not as a prediction of those discoveries. What have “conventional notions” done for you lately? The sight of experts rushing back to their drawing boards implies that planetary evolution theory is in a mess. Hot Jupiters abound, requiring them to posit rapid migration toward the star. Who knows how many fell in? On the way in, if indeed they migrated, they would have sent rocky planets with interior orbits careening out of their stellar systems.
Another problem posed by the hot Jupiters and closely-orbiting rocky planets is the realization that planets had to form much more quickly than the nebular hypothesis allowed. Instead of slow “core accretion,” theorists invented new ideas out of whole cloth, like “disk instability,” trying to get gas giants to form in decades or centuries instead of millions of years, to allow them time to clear out their orbital debris before the nebula dragged them inward. This is another example of how inept astronomers are at explaining planets despite their admirable skill at observing and describing them. Virtually every planet in our solar system surprised them: none of them fit the predictions of the nebular hypothesis and billions of years.
Meanwhile, here our earth sits, safe inside our sun’s habitable zone, as most of us pay these cosmic billiard games little mind. Instead of thanking your lucky star, you might try thanking your Creator.