About one-fifth of them are home to a gas giant like Jupiter or a still more massive planet.
The majority of these planets are gas giants, a bit like Jupiter or Saturn in our own Solar System.
We're talking here in particular about big things like Jupiter, like Saturn.
In their paper, the co-authors argue that gravitational tidal heating caused by the gravitational friction of an earth-like exo-moon on an eccentric orbit around a Jupiter-like planet lying at a Jupiter-like distance from its parent star, could, in fact, create habitable conditions.
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Most are gas giants like our Jupiter, and many orbit so close to their parent stars that any microbes would have to survive roasting temperatures.
If the question is life - and that's one of the most profound questions we can ask, he says - the answer is almost certainly not Mars or an asteroid, but rather the icy moons orbiting distant planets like Saturn and Jupiter.
Others look like enormous balls of gas, much bigger than Jupiter, or like huge spheres of ice, similar to Neptune.
Their simulations included the effects of eclipses and tidal heating on climate for an earth-twin in orbit around a Jupiter-like gaseous giant planet.
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This is easily enough to detect Jupiter-like planets around distant stars, and it should also be enough to detect smaller, Uranus-like planets around stars within the sun's stellar neighbourhood.
Lying only 10 light years away in the equatorial constellation of Eridanus, it was already known to harbor at least one extra-solar Jupiter-like planet, which orbits the star roughly every 7 years.
On September 26th the group announced, in a paper posted to arXiv, an online database, that its participants had discovered two probable exoplanets, one a Jupiter-like gas giant, and the other, possibly, a smaller, rocky world about twice the diameter of Earth.
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It seems there are now going to be two kinds of planets: the real thing, like Earth and Mars and Jupiter, and then something called plutons, which are funny things that are kind of planets and kind of not planets.
The first two are plentiful in outer space, and mounting evidence, like recent photographs of Mars and Jupiter's moon Europa, suggests that water is plentiful as well.
Galilei discovered the moons of Jupiter in, mebbe 1608, 1610, something like that.
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