2 More Planets Found Near Stars Similar to the Sun
Adding to a growing collection of objects found orbiting distant stars, astronomers have discovered two more planets, one of which appears to be the right temperature to hold liquid water. Flowing water and organic molecules are the necessary ingredients for the creation of life.
The two newly found planets, orbiting separate stars about 35 light-years away, are the second and third planets discovered around stars similar to our sun. Swiss astronomers found the first one three months ago. Planets also have been spotted orbiting neutron stars, the charred remnants of exploded stars, but those hold little promise of containing the stuff of life.
“Planets aren’t rare after all,” said Geoffrey Marcy, an astronomer at San Francisco State University and visiting scholar at UC Berkeley. Marcy, together with Paul Butler, a postdoctoral researcher at Berkeley and San Francisco State, announced their findings Wednesday at a meeting of the American Astronomical Society in San Antonio.
What makes the discovery particularly significant is that the new planets more closely fit common notions of how planets should look and act. “This is the closest thing we’ve seen to anything like our own solar system,” Butler said of the planet he and Marcy found around 47 Ursae Majoris, a star in the Big Dipper constellation.
That planet, at least 2 1/2 times the mass of Jupiter, orbits the star in a period of just over three years. Based on the distance from the star to the planet--about twice the distance between the Earth and our sun--Marcy and Butler calculate its surface temperature to be about minus 110 degrees Fahrenheit.
The other planet, which orbits 70 Virginis in the Virgo constellation, weighs in at a minimum of 6 1/2 times Jupiter’s mass and swings around the star in an elliptical 116-day orbit. With its distance from 70 Virginis averaging half that between the sun and Earth, the planet’s surface should be a balmy, but not boiling, 185 degrees Fahrenheit, Marcy said.
“That’s cool enough to permit complex molecules to exist, ranging from carbon dioxide to complicated organic molecules,” Marcy said. “It’s like a hot, humid day on the East Coast ratcheted up a little higher. There will be zones where the water is in liquid form, maybe even lakes or oceans.”
Those organic molecules would lay the foundation for chemical reactions that could give rise to living organisms, although chances are probably “not a whole lot” that life actually sprouted, said Bruce Murray, a professor of planetary science at Caltech.
The massiveness of the newly found planets indicates that they would be of the “gas giant” variety similar to Jupiter or Saturn, where crushing pressures and the lack of a solid surface would be formidable barriers to the genesis of life. Jupiter, which also holds liquid water in its atmosphere, shows no signs of life.
More promising for life, perhaps, are potential moons around the 70 Virginis planet that would be heated to similar temperatures, Marcy said.
Over the past eight years, Marcy and Butler have looked for planets around 120 stars between 10 and 100 light-years away. (One light-year is the distance light travels in one year, about 5.88 trillion miles.) Now able to detect objects Jupiter-size and larger, they suspect that more planets will pop into view as astronomers refine their techniques.
“It’s probable that most stars harbor planets, since our technique is sensitive only to the most massive planets,” Marcy said.
“Most of us working in the field expect that planets are common,” said Murray. Though he cautioned that other researchers must confirm what Marcy and Butler claim, “I am encouraged by the findings.”
Both 47 Ursae Majoris and 70 Virginis are visible to the naked eye, but the planets are too small and dim to be seen directly, even with the largest telescopes. As with earlier discoveries, astronomers found the planets by detecting a slight wobble in the stars’ motion--the telltale sign of gravitational tugging by an unseen object.
Astronomers, using the equations first derived by Johannes Kepler nearly four centuries ago, can calculate the distance between the star and the planet based on the star’s mass and the time it takes to complete one wobble. That period is the time it takes for the planet to complete one orbit.
Until recently, decades of planet searches had come up frustratingly empty. A few promising leads--announced with much fanfare--vanished under closer scrutiny.
Ironically, astronomers’ efforts started paying off when they began looking for planets where they didn’t expect any. In April 1994, astronomers found a pair of planets orbiting a neutron star.
Last October, Michel Mayor and Didier Queloz of the Geneva Observatory in Switzerland found the first planet around a sun-like star. The planet, orbiting the star 51 Pegasus 40 light years away, is an oddity. Half the mass of Jupiter, it skims so close to the star that its surface is seared to 1,800 degrees Fahrenheit.
