Earth-Like Planet Discovered 50 Light-Years Away
A European team of astronomers has discovered the lightest known planet orbiting a star other than the sun (an “exoplanet”).
The new exoplanet orbits the bright star mu Arae located in the southern constellation of the Altar. It is the second planet discovered around this star and completes a full revolution in 9.5 days.
With a mass of only 14 times the mass of the Earth, the new planet lies at the threshold of the largest possible rocky planets, making it a possible super Earth-like object. Uranus, the smallest of the giant planets of the Solar System has a similar mass. However Uranus and the new exoplanet differ so much by their distance from the host star that their formation and structure are likely to be very different.
This discovery was made possible by the HARPS spectrograph on ESO’s 3.6-m telescope at La Silla, which allows radial velocities to be measured with a precision better than 1 m/s. It is another clear demonstration of the European leadership in the field of exoplanet research.
In a discovery that has left one expert stunned, European astronomers have found one of the smallest planets known outside our solar system, a world about 14 times the mass of our own around a star much like the sun.
It could be a rocky planet with a thin atmosphere, a sort of “super Earth,” the researchers said.
But this is no typical Earth. It completes its tight orbit in less than 10 days, compared to the 365 required for our year. Its daytime face would be scorched.
The planet’s surface conditions aren’t known, said Portuguese researcher Nuno Santos, who led the discovery. “However, we can expect it to be quite hot, given the proximity to the star.”
Hot as in around 1,160 degrees Fahrenheit (900 Kelvin), Santos said.
Still, the discovery is a significant advance in technology: No planet so small has ever been detected around a normal star. And the finding reveals a solar system more similar to our own than anything found so far.
The star is like our sun and just 50 light-years away. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers). Most of the known extrasolar planets are hundreds or thousands of light-years distant.
The star, mu Arae, is visible under dark skies from the Southern Hemisphere. It harbors two other planets. One is Jupiter-sized and takes 650 days to make its annual trip around the star. The other planet, whose existence was confirmed with the help of the new observations, is farther out.
The three-planet setup, with one being rocky, is unique.
“It’s much closer to our solar system than anything we’ve found so far,” said Alan Boss, a planet-formation theorist at the Carnegie Institution in Washington.
“This really is an exciting discovery,” said Boss, who was not involved in the work. “I’m still somewhat stunned they have such good data.”
The discovery was made with a European Southern Observatory telescope at La Silla, Chile, working at the verge of what’s possible to detect.
Most of the more than 120 planets found beyond our solar system are gaseous worlds as big or larger than Jupiter, mostly in tight orbits that would not permit a rocky planet to survive.
A handful of planets smaller than Saturn have been found, but none anywhere near as small as the one announced today. And a trio of roughly Earth-sized planets was found in 2002 to orbit a dense stellar corpse known as a neutron star. They are oddballs, however, circling rapidly around a dark star that would not support life. Some planet hunters don’t consider these three to be as important as planets around normal stars.
At 14 times the mass of Earth, the newfound planet — circling a star similar in size and brightness to our sun — is about as heavy as Uranus, a world of gas and ice and the smallest giant planet in our solar system. Theorists say 14 Earth-masses is roughly the upper limit for a planet to possibly remain rocky, however.