Hovering about 70 light-years from Earth -- that's "next door" by astronomical standards -- is a star astronomers call HD 97658, which is almost bright enough to see with the naked eye. But the real "star" is the planet HD 97658b, not much more than twice Earth's diameter and a little less than eight times its mass. HD 97658b is a super-Earth, a class of planet for which there is no example in our home solar system.
While the discovery of this particular exoplanet is not new, determining its true size and mass is, thanks to Diana Dragomir, a postdoctoral astronomer with UC Santa Barbara's Las Cumbres Observatory Global Telescope (LCOGT). As part of her research, Dragomir looked for transits of this exoplanet with Canada's Microvariability & Oscillations of Stars (MOST) space telescope. The telescope was launched in 2003 to a pole-over-pole orbit about 510 miles high. Dragomir analyzed the data using code written by LCOGT postdoctoral fellow Jason Eastman. The results were published online today in the Astrophysical Journal Letters.
A super-Earth is an exoplanet with a mass and radius between those of Earth and Neptune. Don't be fooled by the moniker though. Super-Earth refers to the planet's mass and does not imply similar temperature, composition, or environment to Earth. The brightness of HD 97658 means astronomers can study this star and planet in ways not possible for most of the exoplanet systems that have been discovered around fainter stars.
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