Scientists say they've been able to determine the strength of the magnetic field around a distant exoplanet by looking at the solar winds of its star as they slam into the planet.
This first effort could help scientists estimate the power of any exoplanet's magnetic field, which could yield important clues about the planet's characteristics since its formation and evolution can be significantly influenced by its magnetic field.
"It works as a shield against stellar wind particles, which erode the atmosphere, so it is important to know if this field is big or small," says study lead author and planetary scientist Kristina Kislyakova, of the Austrian Academy of Sciences in Graz.
Observing a Jupiter-sized exoplanet known as HD 20945b, they saw an asymmetrical pattern of highly charged atoms of hydrogen moving rapidly away from the planet.
The atmosphere is blowing away from the planet because of its close proximity to its parent star, just one-twentieth the distance from our sun to Earth, the scientists say.
The scientists applied a 3D computer model containing all known types of interactions between stellar winds and planetary atmospheres, including gravitational effects, ionization, pressure, radiation acceleration and changes in spectral lines.
That allowed the researchers to determine that the planet's magnetic field is about 10 percent as powerful as that of Jupiter.
That's in line with previous studies that suggested "hot Jupiter" planets such HD 20945b -- which is about a third larger than Jupiter but lighter -- would be expected to have magnetic fields relatively weaker than those of their cooler gas giant brethren.
"The implication of these findings is improvement of our understanding of the worlds outside the solar system -- some new light shed on bodies many light-years away from us," Kislyakova says.
The technique for using solar winds' interactions with a planet's atmosphere -- especially if it contains large amounts of hydrogen atoms that can become highly charged by such winds -- to estimate its magnetic field could have widespread utility, researchers said.
The extent of the envelope of atomic hydrogen is determined by interactions between the gas flowing out from the exoplanet and the protons of the incoming stellar wind, and the size of the envelope can be used to estimate the size of the planet's magnetosphere.
"This method can be used for every planet, including Earth-like planets, if there exist an extended high energetic hydrogen envelope around them," says researcher Maxim Khodachenko at the Skobeltsyn Institute of Nuclear Physics of the Lomonosov Moscow State University.
