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April 19, 2011
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Radio glow could reveal elusive planets, study finds
April 19, 2011
Courtesy of the Royal Astronomical Society
and World Science staff
Radio wave emissions
similar to Earth’s Northern Lights could reveal the presence of otherwise hard-to-find planets outside our solar system, a study suggests. An image mapping ultraviolet
light emissions from an aurora on Saturn. (Courtesy NASA)
Although techniques have improved for detecting such distant worlds, called
exoplanets, it remains a challenge to find those that orbit their suns at large distances. Now, a scientist has calculated that emissions from planets like Jupiter should be detectable by radio telescopes such as the Netherlands-based Low Frequency Array, to be completed later this year.
The idea is that giant gas planets would reveal themselves through
radio emissions that are part of a phenomenon called auroras, also known to occur on Jupiter and Saturn.
Such planets are of interest to astronomers, including those searching
for extraterrestrial life. Although gas giants probably can’t support life themselves, some
scientists believe they may often serve as good signposts to life because nearby planets, or their own moons, could be habitable.
Jonathan Nichols of the University of Leicester, U.K., presented the new research at the U.K. Royal Astronomical Society’s national meeting in Llandudno, Wales, on April 18.
“This is the first study to predict the radio emissions by exoplanetary systems,” he said. At Jupiter and Saturn, “we see radio waves associated with auroras generated by interactions with ionized [electrically charged] gas escaping from the volcanic moons, Io and Enceladus. Our study shows that we could detect emissions from radio auroras from Jupiter-like systems orbiting at distances as far out as Pluto.”
Auroras are light displays in the skies caused by charged particles streaming along the magnetic field lines of a planet into its atmosphere. On Earth, Particles from the Sun bring about auroras, also called Northern Lights or Southern Lights owing to their appearance near the poles. On Jupiter and Saturn, particles from their own moons are also implicated in auroral displays,
which may include radio waves as these are simply a low-energy form
of light.
The connection with exoplanet detection arises because most
known exoplanets have been found by the so-called transit method, which detects a dimming in light as a planet moves in front of a star, or by looking for a wobble as a star is tugged by the gravity of an orbiting planet. With both techniques, it’s easiest to detect planets close in to the star and moving quickly. Of the hundreds of exoplanets found so far, less than a tenth orbit their stars at distances like those of the planets in our system to the Sun, Nichols said.
“Jupiter and Saturn take 12 and 30 years respectively to orbit the Sun, so you would have to be incredibly lucky or look for a very long time to spot them by a transit or a wobble,” Nichols explained.
Radio auroras could give away these planets to a distant observer, he argued.
He examined how the radio emissions for Jupiter-like exoplanets would be affected by the planet’s spin rate, the rate of ionized gas outflow from a moon, the orbital distance of the planet and the brightness of the parent star in ultraviolet light. He found that, in many scenarios,
exoplanets orbiting ultraviolet-bright stars at between one and 50 times the Earth-Sun distance would generate enough radio power to be detectable from Earth. For the brightest stars and fastest spinning planets, the emissions would be detectable from systems 150 light years away, Nichols maintains. A light year is the distance light travels in a year.
“In our Solar System, we have a stable system with outer gas giants and inner terrestrial planets, like Earth, where life has been able to evolve,” he said. “Being able to detect Jupiter-like planets may help us find planetary systems like our own, with other planets that are capable of supporting life.”
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Radio wave emissions of a type related to Earth’s Northern Lights could reveal the presence of otherwise hard-to-find planets outside our solar system, a study suggests. Although techniques have improved for detecting such distant worlds, called exoplanets, it remains a challenge to find those that orbit their suns at large distances. Now, a scientist has calculated that emissions from planets like Jupiter should be detectable by radio telescopes such as the Netherlands-based Low Frequency Array, to be completed later this year. The idea is that giant gas planets would reveal themselves through a phenomenon called radio auroras, also known to occur on Jupiter and Saturn. Although gas giants probably can’t support life themselves, some astronomers believe they may often serve as good signposts to extraterrestrial life because nearby planets, or their own moons, could be habitable. Jonathan Nichols of the University of Leicester, U.K., presented the new research at the U.K. Royal Astronomical Society’s national meeting in Llandudno, Wales, on April 18. "This is the first study to predict the radio emissions by exoplanetary systems,” he said. At Jupiter and Saturn, “we see radio waves associated with auroras generated by interactions with ionized [electrically charged] gas escaping from the volcanic moons, Io and Enceladus. Our study shows that we could detect emissions from radio auroras from Jupiter-like systems orbiting at distances as far out as Pluto.” Generally speaking, auroras are light displays in the skies caused by charged particles streaming along the magnetic field lines of a planet into its atmosphere. On Earth, Particles from the Sun bring about auroras, also called Northern Lights or Southern Lights owing to their appearance near the poles. On Jupiter and Saturn, particles from their own moons are also implicated in auroral displays. That’s where the subject of exoplanets comes in. Most exoplanets have been detected by the so-called transit method, which detects a dimming in light as a planet moves in front of a star, or by looking for a wobble as a star is tugged by the gravity of an orbiting planet. With both techniques, it’s easiest to detect planets close in to the star and moving quickly. Of the hundreds of exoplanets found so far, less than a tenth orbit their stars at distances like those of the planets in our system to the Sun, Nichols said. “Jupiter and Saturn take 12 and 30 years respectively to orbit the Sun, so you would have to be incredibly lucky or look for a very long time to spot them by a transit or a wobble,” Nichols explained. Radio auroras could give away these planets to a distant observer, he argued. He examined how the radio emissions for Jupiter-like exoplanets would be affected by the planet’s spin rate, the rate of ionized gas outflow from a moon, the orbital distance of the planet and the brightness of the parent star in ultraviolet light. He found that, in many scenarios, exoplanets orbiting ultraviolet-bright stars at between one and 50 times the Earth-Sun distance would generate enough radio power to be detectable from Earth. For the brightest stars and fastest spinning planets, the emissions would be detectable from systems 150 light years away, Nichols maintains. A light year is the distance light travels in a year. "In our Solar System, we have a stable system with outer gas giants and inner terrestrial planets, like Earth, where life has been able to evolve,” he said. “Being able to detect Jupiter-like planets may help us find planetary systems like our own, with other planets that are capable of supporting life.” n