JPL Finds Signs of Planets Circling Seven Other Stars : Astronomy: Existence of such bodies has been widely theorized but never proven. Two scientists use new techniques to analyze 9-year-old data.
Jet Propulsion Laboratory scientists reported Thursday that they have found evidence of planets circling as many as seven other stars in our galaxy, including one body that orbits its sun at 93 million miles, the distance between Earth and the sun.
Although several other astronomers have previously reported the existence of planets outside our solar system, none of the claims has been proven.
The discovery, reported at a meeting of the American Astronomical Society in Columbus, Ohio, by JPL astrophysicists Kenneth Marsh and Michael J. Mahoney, is thought to be the strongest evidence yet of the existence of such objects.
The key to the discovery, they said, lies in a new way of analyzing 9-year-old data from an orbiting observatory.
Marsh and Mahoney’s technique represents a “whole new way of looking for planets,†according to astronomer Steve Maran of NASA’s Goddard Space Flight Center, and opens the door for the discovery of many other planets.
Most astronomers believe that planets occur routinely throughout the universe, but proving it has been very difficult. The problem is not simply that planets are much smaller than stars, but that they also are much dimmer. It has so far been impossible to capture their image, even with the most powerful telescopes.
Thus researchers have had to use more indirect techniques to infer the existence of planets. Most often, this has involved looking for a slight “wobble†in the motion of stars.
Contrary to popular belief, planets do not revolve around stars. Rather, planet and star both revolve around a common center of mass. Because the star is so much larger, its orbit is small and difficult to detect. Nonetheless, researchers in recent years have identified several stars--including two exceptionally energetic stars called pulsars--that have such wobbles, leading them to suspect the presence of planets that are not visible from Earth.
Marsh and Mahoney chose instead to focus on the large, thin disks of dust and debris that surround young stars. Astronomical theory holds that planets form when the debris in such disks clumps together, continuing to grow as their gravitational fields sweep up more and more dust. The planets in our solar system are believed to have been formed in this manner about 4.5 billion years ago.
The JPL researchers relied on the fact that the dust in the disks emits infrared radiation as a result of the heat it receives from the star. As the distance of the dust from the sun increases, the dust becomes cooler and the infrared wavelength changes. If the disk is continuous, then astronomers should observe a smooth infrared spectrum emanating from it.
Using data from the Infrared Astronomy Satellite, Marsh and Mahoney looked at dozens of stars with disks in the Taurus-Auriga region of the Milky Way, about 450 light years from Earth. They found eight stars with gaps in the infrared spectrum.
When a gap in the radiation is detected, Mahoney said in a telephone interview, it means the dust “is either blown away, which is unlikely . . . or it’s forming planets, brown dwarfs or stars. “ (More than 70% of stars have a companion star orbiting them.)
A brown dwarf is a small star that didn’t have enough mass to ignite and, therefore, cannot be observed directly.
One of the eight stars, called DF Tauri, definitely has a visible star in the gap, Mahoney said. For six of the stars, it could not be determined whether the gap contained a star, a planet or a brown dwarf.
But for one star, called GK Tauri, the scientists were able to obtain data when the object in the gap passed between the star and Earth. The data indicated that the object is definitely not a star, so it must be either one or more planets or a brown dwarf, Mahoney said.
The orbit of that object (or objects) is about one astronomical unit (93 million miles) from GK Tauri, the same distance as Earth from the sun. Mahoney speculated that it could be an early model of our own solar system. “It’s very likely, but we just don’t know at this time,†he said.
The scientists’ confidence that they were observing planets was bolstered by their discovery that the dust temperature at the outer boundary of the gap was minus 56 degrees Fahrenheit--the temperature at which gaseous water condenses into ice under interstellar conditions. Theory holds that this is the approximate temperature at which planets form, Mahoney said.
Although other scientists were encouraged by the novelty of the JPL technique, most urged caution until the results can be verified. As astronomer David Black, director of the Lunar and Planetary Institute in Houston, noted, “The landscape of previous efforts to detect planets is littered with the corpses of claims that haven’t been substantiated.â€
Times science writer Judy Pasternak contributed to this story.
Evidence of a Planet?
Observations from an orbiting observatory suggest that the disk of dust and debris around the star GK Tauri has a broad gap in it. This indicates that a planet--or a very dim star called a brown dwarf--may have condensed from the dust. GK Tauri is about the same size as our own sun, but is much younger.
Source: Jet Propulsion Laboratory
