Researchers from the University of Washington found that planets orbiting cooler stars are more likely to be ice free and warmer than planets orbiting hotter stars like the Earth.
Stars emit different types of light and heat waves depending on how hot or cool they are and it is only logical to assume that planets orbiting hotter stars are warmer than planets orbiting cooler stars. However, in a new study, researchers from the University of Washington revealed a startling discovery that is quite contrary to this popular assumption. They found that planets orbiting cooler stars are more likely to be ice free and warmer than planets orbiting hotter stars like the Earth.
Hotter stars emit high-energy visible and ultraviolet light that has shorter wavelengths while cooler stars emit infrared and near-infrared light that has longer wavelengths and much lower energy.
Researchers state that planets orbiting cooler stars are warmer because the ice on such planets absorbs more longer wavelength, near-infrared light emitted by cooler stars while the ice of planets like the earth reflects the short wavelength, ultraviolet light emitted by hotter stars. Also, the greenhouse gases in atmospheres of planets orbiting cooler stars help in absorbing light emitted by the star, thus, enhancing the warming effect.
When planets orbiting cooler stars are given same amounts of light as planets orbiting hotter stars, the former are less likely to be covered in ice from pole to equator, known as "snowball state." However, in the latter, since most of the light from the star is reflect by the ice, the planet is more likely to experience snowball states.
Researchers note that even Earth has experienced many snowball states during the course of its 4.6 billion year history.
"The last snowball episode on Earth has been linked to the explosion of multicellular life on our planet," Aomawa Shields, a doctoral student in the University of Washington astronomy department, said in a press release. "If someone observed our Earth then, they might not have thought there was life here - but there certainly was."
"So though we'd look for the non-snowball planets first, we shouldn't entirely write off planets that may be ice-covered, or headed for total ice cover. There could be life there too, though it may be much harder to detect."
