Categories: Extrasolar Planets

Rocky Planets May Form Around Most Sun-like Stars

Astronomers have found numerous Jupiter-like planets orbiting other stars. But because of the limits of our current technology, they haven’t yet found any other terrestrial Earth-like planets out in the universe. But new findings from the Spitzer Space Telescope suggest that terrestrial planets might form around many, if not most, of the nearby sun-like stars in our galaxy. So perhaps, other worlds with the potential for life might be more common than we thought.

A group of astronomers led by Michael Meyer of the University of Tucson, Arizona used Spitzer to survey six sets of stars with masses comparable to our sun, and grouped them by age.

“We wanted to study the evolution of the gas and dust around stars similar to the sun and compare the results with what we think the solar system looked like at earlier stages during its evolution,” Meyer said. Our sun is about 4.6 billion years old.

They found that at least 20 percent, and possibly as many as 60 percent, of stars similar to the sun are candidates for forming rocky planets.

The Spitzer telescope does not detect planets directly. Instead, using its infrared capability, it detects dust — the rubble left over from collisions as planets form — at a range of infrared wavelengths. Because dust closer to the star is hotter than dust farther from the star, the “warm” dust indicates material orbiting the star at distances comparable to the distance between Earth and Jupiter.

Meyer said that about 10 to 20 percent of the stars in the four youngest age groups shows ‘warm’ dust, but not in stars older than 300 million years. That is comparable to the theoretical models of our own solar system, which suggests that Earth formed over a span of 10 to 50 million years from collisions between smaller bodies.

But the numbers are vague on how many stars are actually forming planets because there’s more than one way to interpret the Spitzer data. “An optimistic scenario would suggest that the biggest, most massive disks would undergo the runaway collision process first and assemble their planets quickly. That’s what we could be seeing in the youngest stars. Their disks live hard and die young, shining brightly early on, then fading,” Meyer said.

“However, smaller, less massive disks will light up later. Planet formation in this case is delayed because there are fewer particles to collide with each other.”

If this is correct and the most massive disks form their planets first and then the smaller disks take 10 to 100 times longer, then up to 62 percent of the surveyed stars have formed, or may be forming, planets. “The correct answer probably lies somewhere between the pessimistic case of less than 20 percent and optimistic case of more than 60 percent,” Meyer said.

In October 2007, another group of astronomers used similar Spitzer data to observe the formation of a star system 424 light-years away, with another possible Earth-like planet being created.

More definitive data on formation of rocky planets will come with the launch the Kepler mission in 2009, which will search to find if terrestrial planets like Earth could be common around stars like the sun.

Original News Source: JPL Press Release

Nancy Atkinson

Nancy has been with Universe Today since 2004, and has published over 6,000 articles on space exploration, astronomy, science and technology. She is the author of two books: "Eight Years to the Moon: the History of the Apollo Missions," (2019) which shares the stories of 60 engineers and scientists who worked behind the scenes to make landing on the Moon possible; and "Incredible Stories from Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos" (2016) tells the stories of those who work on NASA's robotic missions to explore the Solar System and beyond. Follow Nancy on Twitter at https://twitter.com/Nancy_A and and Instagram at and https://www.instagram.com/nancyatkinson_ut/

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