First Posted: Jul 02, 2013 09:11 AM EDT
Astronomers have uncovered a little bit more about an exoplanet that hovers just 70 light-years from Earth--practically next door by astronomical standards. Researchers have learned the planet's true size and mass, opening up the path to future studies on other alien planets. This image shows the relative size of the Earth and Sun next to those of HD 97658 (the star) and HD 97658b (the super-Earth exoplanet). (Photo : Jason Eastman and Diana Dragomir)
Astronomers have uncovered a little bit more about an exoplanet that hovers just 70 light-years from Earth--practically next door by astronomical standards. Researchers have learned the planet's true size and mass, opening up the path to future studies on other alien planets.
The planet itself, known as a super-Earth, is named HD 97658b. It was first discovered in 2011 by a team of astronomers using the Keck Observatory and a technique that's sometimes called Doppler wobble. This method examines the gravitational pull of a planet on its parent star, which causes it to "wobble" slightly. While the researchers were able to determine the lower limit on the planet's mass, though, they were not able to determine its exact size.
So what did they find? It turns out that the average density of HD 97658b is about four grams per cubic centimeter--that's a third of the density of lead, but denser than most rocks. In fact, it's about 70 percent of the average density of Earth, which means that it could potentially hold onto a thick atmosphere. Despite these positive conditions, though, it's unlikely that alien life is located on the planet. Since it orbits its star once every 9.5 days, the planet is far too close to be in the habitable zone.Now, scientists have been able to learn a little bit more about this planet. They used HD 97658b's transit as a means to discover its exact size. Transits occur when a planet's orbit carries it in front of its parent star and reduces the amount of light we see from the star ever so slightly. These dips in brightness happen during every orbit--assuming the orbit is aligned with our line of sight from Earth.
"Measuring an exoplanet's size and mass leads to a determination of its density, which in turn allows astronomers to say something about its composition," said Diana Dragomir, a postdoctoral astronomer with UC Santa Barbara's Las Cumbres Observatory Global Telescope, in a press release. "Measuring the properties of super-Earths in particular tells us whether they are mainly rocky, water-rich, mini gas giants, or something entirely different."
The findings still have implications for further research, though. Astronomers are continuing to refine their techniques not only for detecting these exoplanets, but also for understanding the conditions on their surfaces. This could allow them to eventually discover a planet that's habitable which, in turn, could lead to the finding of life.
"This discovery adds to the still small sample of transiting super-Earths around bright stars," said Dragomir in a news release. "In addition, it has a longer period than many known transiting exoplanets around bright stars, including 55 Cnc e, the only other super-Earth in this category. The longer period means it is cooler than many closer-in exoplanets, so studying HD 97658b's properties is part of the progression toward understanding what exoplanets in the habitable zone might be like."
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