Distant solar system is similar to Earth's

THE BALTIMORE SUN

Another planet has been added to the list of 100 or so worlds that astronomers have discovered around distant stars - but unlike all those other planets, this one is in a solar system that might be capable of supporting another Earth.

The discovery, to be announced today at a conference in Paris and published in a future issue of the Astrophysical Journal, marks the first time that the search for extrasolar worlds has produced a planet orbiting in a system so strikingly similar to our own.

"This planet and its orbit are quite reminiscent of Jupiter," said Brad Carter, an astronomer at the University of Southern Queensland and lead author of the planned article.

The planet, a gas giant about twice the size of Jupiter, travels around a star very much like our sun in a nearly circular orbit. Located 90 light-years from Earth in the southern sky constellation Puppis, this planet circles its sun, known as HD70642, every six years.

What is most interesting about this system, though, is what astronomers didn't find.

Unlike other systems with Jupiter-like planets orbiting at Jupiter-like distances, this system does not have any other gas giants closer to its sun in the region where liquid water could exist - the so-called habitable zone. The finding suggests that this void could be filled by smaller rocky planets.

"If we see a big empty gap," said astronomer Debra A. Fischer, co-author of the Astrophysical Journal article, "we have to wonder if it's really empty."

Our own solar system is "filled up with planets," Fischer said. "If you dropped another planet in, all the other orbits would become chaotic." Because the Jupiter-like planet is in a stable circular orbit it's a good indication that smaller, more Earth-like planets could also be in stable orbits.

The vast majority of the 100 or so extrasolar planets that astronomers have discovered to date are in somewhat chaotic orbits, making it unlikely that a tiny rocky planet could remain in the habitable zone long enough for advanced life forms to evolve. The larger gas giants would most likely kick them out.

The technique that astronomers used to discover this planet, along with the majority of the other planets found over the past decade, will not reveal any "Earths," which would be too small to detect. But it will help astronomers refine their search so, as Carnegie Institution of Washington astronomer Paul Butler said, "perhaps in the next 20 years - within our lifetimes - Earth-like planets might be found."

The method, which Butler pioneered with University of California, Berkeley, astronomer Geoff Marcy, is known as the Doppler Wobble technique. True to its name, this technique detects the slight "wobble" that stars exhibit when their large planets tug on them. The larger the planet, the more the stars wobble, making it much easier to detect huge gas giants than tiny rocky worlds.

Allison M. Heinrichs is a reporter for the Los Angeles Times, a Tribune Publishing newspaper.

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