Two Mauna Kea observatories confirmed this week the discovery of the first potentially habitable Earth-sized planet found outside our own solar system.
“What makes this finding particularly compelling is that this Earth-sized planet, one of five orbiting this star, which is cooler than the sun, resides in a temperate region where water could exist in liquid form,” said Elisa Quintana of the SETI Institute and NASA Ames Research Center, who led a paper on the discovery published in the current issue of the journal Science.
The Hawaii Island-based W.M. Keck and Gemini observatories participated in collecting and analyzing data to confirm the initial discovery, made using the Kepler Space Telescope, according to Keck’s communications officer, Steve Jefferson.
“Kepler was launched by NASA for the purpose of discovering how many planets are existing around stars like the sun within 300 light-years of us. Since then, it’s been doing this crazy busy survey, hitting on potential candidates constantly,” he said.
To date, however, this is the first Earth-sized exoplanet verified to be within a potentially habitable region of another star, making for a momentous step in the ongoing search for life elsewhere in the universe.
“The Keck and Gemini data are two key pieces of this puzzle. Without these complementary observations we wouldn’t have been able to confirm this Earth-sized planet,” Quintana said via a press release.
Kepler Project Scientist Steve Howell, who co-authored the paper, explained that neither the Kepler nor any other telescope is currently able to directly spot an exoplanet of this size and proximity to its host star.
“However, what we can do is eliminate essentially all other possibilities so that the validity of these planets is really the only viable option,” he said.
To ensure that Kepler’s initial findings weren’t the result of something else mimicking a planet, the team obtained “extremely high spatial resolution observations” from the 8-meter Gemini North telescope using a technique called “speckle imaging,” as well as adaptive optics observations from the 10-meter Keck II telescope, Gemini’s neighbor atop Mauna Kea.
Together, the observations from both land-based telescopes — which are much larger and capable of collecting more light than the space-based Kepler, with a mirror diameter of less than a meter — were able to rule out sources close enough to the star’s line of sight to confound the Kepler evidence and conclude that Kepler’s detected signal had to be from a small planet moving in front of its host star.
“In general, when you’re talking about space-based telescopes, the amount of data they can gather is nothing compared to what you can gather from the ground. … It’s about gathering photons (light) and sending them to instruments. We’re working with the two biggest mirrors on Earth,” Jefferson said. “Keck’s is 10 meters, which is the biggest. … That’s a big light bucket.”
Keck Observing Support Manager Bob Goodrich, who has worked with the observatory for 18 years, said Wednesday that employees there were thrilled to help make such an important discovery.
“Being part of something like that, it’s what motivates a lot of the support astronomers here. They’re sacrificing their own research time to help many astronomers in their research. In some sense, it feels like we’re having a multiplier effect. We’re helping a whole bunch of people doing a whole lot of exciting things,” Goodrich said. “At the end of the day, we know we’ve contributed to them getting the best quality data they can, and the most quantity data. It’s what keeps us coming into work every day, or night, as the case may be.”
The host star, Kepler-186, is a red dwarf star found in the Cygnus constellation, and is relatively close to our solar system, at about 500 light-years. The star is exceedingly dim, more than half a million times fainter than the faintest stars humans can make out with the naked eye.
The newly discovered planet has been dubbed Kepler-186f. The evidence for its existence was based on measurements of its transits across the face of its star — essentially a series of “tiny eclipses” of the host star as seen from Earth, according to the release. When such planets block part of the star’s light, its total brightness is diminished, and that is the telltale sign that Kepler was built to detect. So far, more than 2,500 possible planets have been detected using that technique.
“These Earth-sized planets are extremely hard to detect and confirm, and now that we’ve found one, we want to search for more,” Quintana said. “Gemini and Keck will no doubt play a large role in these endeavors.”
Added paper co-author and Kepler scientist Thomas Barclay: “The observations from Keck and Gemini, combined with other data and numerical calculations, allowed us to be 99.98 percent confident that Kepler-186f is real. Kepler started this story, and Gemini and Keck helped close it.”
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