More planets!

A team of astronomers led by scientists at the California Institute of Technology have found 18 planets orbiting stars more massive than our Sun.  Finding planets is becoming more and more routine with the Kepler telescope, but these planetary discoveries help to answer questions about planetary formation–and raise other questions about planetary orbits.

The scientists focused on stars more than 1.5 times more massive than our Sun.  To look for planets, they used the “wobble” method, which looks for shifts in the apparent wavelengths coming from the star.  The 18 planets that they found are all larger than Jupiter.

According to John Johnson, assistant professor of astronomy at Caltech, these discoveries support a theory of planet formation. There are two competing explanations for how planets form: a) tiny particles clump together to make a planet and b) large amounts of gas and dust spontaneously collapse into big dense clumps that become planets.

The discovery of these planets supports the first explanation.

If this is the true sequence of events, the characteristics of the resulting planetary system — such as the number and size of the planets, or their orbital shapes — will depend on the mass of the star. For instance, a more massive star would mean a bigger disk, which in turn would mean more material to produce a greater number of giant planets.

So far, as the number of discovered planets has grown, astronomers are finding that stellar mass does seem to be important in determining the prevalence of giant planets. The newly discovered planets further support this pattern — and are therefore consistent with the first theory, the one stating that planets are born from seed particles.

The larger the star, the larger the planets that orbit it.

“It’s nice to see all these converging lines of evidence pointing toward one class of formation mechanisms,” Johnson says.

But there’s another mystery that’s come out of this discovery.  The orbits of these 18 newly-discovered large planets are mainly circular.  Planets around other Sun-like stars have circular and elliptical orbits.  Is there something about the larger stars that make it more likely  that planets will have a circular orbit?  Or is it just a phenomenon noticed because of the small sample size? Johnson says he’s now trying to find an explanation.

Stay tuned–not only may we find a planet that could harbor life, we could also learn something about the origin of our own solar system!

Learn more about finding planets and the search for extraterrestrial life in the High-Adventure Science investigation, Is there life in space?

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