Science News - May 5, 2012

Bye-bye giant after finding that a gravitational interaction with Jupiter could cause a young earth to crash into Venus, researchers decided to offer Jupiter a separate partner. models suggest the ejection of an extra ice giant (gray) could help the earth survive. the extra giant also helps explain Jupiter’s and saturn’s current orbits.

carry a detectable signature. In his study, published in Astrophysical Journal Letters in January, Batygin found that the fifth giant wasn’t as necessary to save Earth as Nesvorny reports. “I’d say 50-50,” Batygin says, of the likelihood of a fifth giant being required to save Earth in his model.

Various differences in the scientists’
starting conditions — such as the amount
of material the planets are swimming
through — might produce the different
outcomes. Even if the outcast isn’t neces-
sary to solve the Earth problem, Batygin
thinks an extra giant would answer some
important questions. “Without a close
encounter, Jupiter’s and Saturn’s orbits
very rarely end up being what they are
today,” Batygin says. “The reason for this
fifth planet is to feed the big guys so they
can toss it out and be happy.”
As for that lost planet, Batygin doesn’t
know where it is today: “I’d like to say in
a galaxy far, far away.”
scientists’ other ideas will need to work
for even Earth’s most distant neighbors.
Any story that seeks to explain how
the planets are made should explain
the ranges of sizes and compositions
observed here and elsewhere. It is “dan-
gerous to compare all these models with
the solar system only,” Nesvorny says.

Explore more

s for more on the outer solar system: http://1.usa.gov/outer_solar

Exo-observations

Scientists observing faraway planetary systems around other stars are turning up data that may fill in the picture of how giant planets are made. “The extrasolar planetary systems are telling us that the basic idea of core accretion is consistent with our understanding,” Laughlin says. Uranus- and Neptune-sized bodies are also turning out to be common, suggesting that they must be easy to make and providing an important clue about how outer planets grow.