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.
A super-Earth is AN exoplanet with a mass and radius between those of Earth and Neptune. do not be fooled by the nickname tho’. Super-Earth refers to the planet’s mass and doesn’t imply similar temperature, composition, or setting to Earth. The brightness of HD 97658 means that astronomers will study this star and planet in ways in which impracticable for many of the exoplanet systems that are discovered around fainter stars.
HD 97658b was discovered in 2011 by a team of astronomers mistreatment the Keck Observatory and a way typically known as Christian Johann Doppler wobble. however solely a lower limit can be attack the planet’s mass, and zip was glorious regarding its size.
Transits, like those ascertained by Dragomir, occur once a planet’s orbit carries it before of its parent star and reduces the quantity of sunshine we have a tendency to see from the star ever slightly. Dips in brightness happen each orbit, if the orbit happens to be nearly precisely aligned with our line of sight from Earth. For a planet not abundant larger than our Earth around a star nearly as huge as our Sun, the dip in lightweight is little however detectable by the ultraprecise MOST house telescope.
The first report of transits within the HD 97658 system in 2011 clothed to be a warning. that may are the top of the story, however Dragomir knew that the yearbook of the world’s orbit (a timetable to predict once the planet would possibly pass before of the star) wasn’t precise. She convinced the foremost team to widen the search parameters, and through the last doable observant window for this star last year, the information showed tantalizing signs of a transit — tantalizing, however not sure positively. A year later, MOST revisited HD 97658 and located clear proof of the planet’s transits, permitting Dragomir and therefore the MOST team to estimate the planet’s true size and mass for the primary time.
“Measuring AN exoplanet’s size and mass ends up in a determination of its density, that successively permits astronomers to mention one thing regarding its composition,” Dragomir aforementioned. “Measuring the properties of super-Earths particularly tells United States of America whether or not they square measure chiefly rocky, water-rich, mini gas giants, or one thing entirely completely different.”
The average density of HD 97658b is regarding four grams per ml, a 3rd of the density of lead however denser than most rocks. Astronomers see nice significance therein worth — regarding seventy % of the typical density of Earth — since the surface gravity of HD 97658b may hold onto a thick atmosphere. however there is unlikely to be alien life respiratory those gases. the world orbits its sun each nine.5 days, at a distance a dozen times nearer than we have a tendency to square measure from our Sun, that is simply too near be within the inhabitable Zone, nicknamed The Aster linosyris Zone. The Aster linosyris nickname is apropos: If a planet is simply too near its star, it’s too hot; if it’s too remote, it’s too cold, however if it’s within the zone, it’s “just right” for liquid water oceans, one condition that was necessary for keeps here on Earth.
Over the past few years, systems with large planets at terribly little orbital radii have verified to be quite common despite being typically sudden. this range of confirmed exoplanets exceeds 600, with the overwhelming majority having been discovered by velocity surveys. These square measure severely biased toward the detection of systems with large planets (roughly the mass of Jupiter) in little orbits. Bucking that trend is HD 97658b, that orbits its star at a distance farther than several of the presently glorious exoplanets. HD 97658b is barely the second super-Earth glorious to transit a awfully bright star.
“This discovery adds to the still little sample of transiting super-Earths around bright stars,” aforementioned Dragomir. “In addition, it’s a extended amount than several glorious transiting exoplanets around bright stars, together with fifty five Cnc e, the sole alternative super-Earth during this class. The longer amount means that it’s cooler than several closer-in exoplanets, therefore finding out HD 97658b’s properties is a component of the progression toward understanding what exoplanets within the inhabitable zone could be like.”