The Earth’s coolest exoplanet has an overheated, polluted surface, study says

Two groups have published discoveries from the Hubble Space Telescope, both finding evidence of planets with warm surface temperatures extending beyond the first atmosphere.

The most detailed of these discoveries, a study by a group from the University of California, Los Angeles and Harvard University, adds the best evidence yet for the existence of exoplanets beyond the gas giants of the big TRAPPIST-1 system. The study published May 19 in the journal Nature has led to both speculation and admiration for what the discovery means for extraterrestrial life.

The TRAPPIST-1 system is a joint effort between the European Southern Observatory and the University of Melbourne. Two Earth-sized worlds are also orbiting a third planet, the TrES-1 system, but results from the larger systems has been more difficult to interpret because TRAPPIST-1 already has a host of optical and infrared imagery, the researchers said.

“This system really blows me away,” Shannon Parker, the former chair of the Department of Astrophysics at Stanford University, said in a statement. “I had the pleasure of working on the formation and evolution of exoplanets using the Kepler Space Telescope. The Kepler data is fantastic, but we knew there was more to Kepler. The TRAPPIST-1 system turns out to be a clean set of data with which to test whether we can detect planets that form outside the system.”

The research shows that the habitable exoplanet PDS 70, located 70 light-years away, is the most scorching, with surface temperatures reaching a maximum of 5,000 degrees Fahrenheit. PDS 70 is twice as large as Earth and is currently orbited by a single planet.

PDS 70 also orbits in the direction of the star, which the researchers said helps explain the heavy radiation there.

Meanwhile, new observations from another team show that TRAPPIST-1 can glow dimmer than scientists thought. Because its average star mass is about 50 percent less than that of the sun, it contains less hydrogen and helium than our solar system does. In order to match the sun’s luminosity, TRAPPIST-1 needs to be smaller than the Sun, said Andrew Vanderburg, an astronomer at the University of California, San Diego.

The effect is that its surface temperature drops as it draws closer to the star. TRAPPIST-1 is now known to be 85 percent dimmer than average. That low luminosity is likely caused by powerful winds blasting the sunward side of the TRAPPIST-1 system, Vanderburg said.

Based on the size of the TRAPPIST-1 system, and its low luminosity, Vanderburg suspects that some of the planets have tiny orbits — just a fraction of a day — that could take anywhere from months to years to orbit the stars.

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