In this artist’s conception GJ 1132b, a rocky exoplanet very similar to Earth in size and mass, circles a red dwarf star. GJ 1132b is relatively cool, about 450 degrees F, and could potentially host an atmosphere. At a distance of only 39 light-years, it will be a prime target for additional study with Hubble and future observatories like the Giant Magellan Telescope. Credit: Dana Berry
The collection of rocky planets orbiting distant stars has just grown by one, and the latest discovery is the most intriguing one to date. The newfound world, although hot as an oven, is cool enough to potentially host an atmosphere. If it does, it’s close enough (only 39 light-years away) that we could study that atmosphere in detail with the Hubble Space Telescope and future observatories like the Giant Magellan Telescope.
“Our ultimate goal is to find a twin Earth, but along the way we’ve found a twin Venus,” says astronomer David Charbonneau of the Harvard-Smithsonian Center for Astrophysics (CfA). “We suspect it will have a Venus-like atmosphere too, and if it does we can’t wait to get a whiff.”
GJ 1132b, as the planet is known, orbits a red dwarf star only 1/5 the size of our Sun. The star is also cooler and much fainter than the Sun, emitting just 1/200th as much light. GJ 1132b circles its star every 1.6 days at a distance of 1.4 million miles (much closer than the 36-million-mile orbit of Mercury in our solar system).
As a result, GJ 1132b is baked to 450F. Such temperatures would boil off any water the planet may have once held, but still allows for the presence of an atmosphere. It is also significantly cooler than any other exoplanet confirmed to be rocky. In comparison, well-known worlds like CoRoT-7b and Kepler-10b possess scorching temps of 2,000 degrees F or more.
GJ 1132b was discovered by the MEarth-South array, dedicated to the hunt for terrestrial worlds orbiting red dwarf stars. MEarth-South monitors several thousand red dwarf stars located within 100 light-years of Earth. It looks for planets that transi. When a planet transits its star, the star’s light dims by a small but detectable amount. This dimming gives an indication of the planet’s physical size.
After MEarth-South detected a transit in real time, additional observations were gathered by the array and the Magellan Clay telescope in Chile. The team also measured the host star’s gravitational wobble using the HARPS spectrograph to determine the planet’s mass. They found that GJ 1132b is 16% larger than Earth, with a diameter of about 9,200 miles. It has a mass 60% greater than Earth. The resulting density indicates that the planet has a rocky composition similar to Earth.
The planet also has an Earth-like force of gravity. A person standing on the surface of GJ 1132b would weigh only about 20% more than they do on Earth.
Since the red dwarf star is small, the relative size of the planet to the star is larger than it would be for a Sun-like star. This, combined with the star’s close distance, makes it easier to detect and study any planetary atmosphere, should one exist. The team has requested follow-up observations with the Hubble and Spitzer Space Telescopes. Future observatories like the James Webb Space Telescope also will undoubtedly take a close look at GJ 1132b.
A final intriguing possibility is that GJ 1132b has sister planets that have not yet been detected. The research team plans to examine this system closely for signs of siblings. https://www.cfa.harvard.edu/news/2015-24
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