Planet: Wolf 503b
Discovered by: Merrin Peterson, et al.
Date: June 2018
Key Facts: A newly discovered planet twice as big around as Earth is about 145 light years away -- close enough to offer a prime target for follow-up investigations. The planet orbits a type of star known as an "orange dwarf," and is so close to the star that it completes an entire orbit -- a "year" on Wolf 503b -- in only six Earth days.
What's new: Astronomers who study exoplanets -- planets around other stars -- have found thousands so far in our galaxy. They've also noticed an odd gap, called the Fulton gap, of planet sizes that seem to be very rare. This gap occurs between about 1.5 and 2 times the size of Earth. One possibility is that planets on the lower side of this size range are rocky, while those twice Earth size or bigger are gaseous, like Neptune.
Wolf 503b's star is relatively close to Earth, making it appear brighter than more distant stars (though it is far too dim to see with the naked eye). This means the planet, discovered using the Kepler space telescope, will be easier to investigate with other instruments. Telescopes that can track the star's "wobble" -- how much it is tugged back and forth by the gravity of the orbiting planet -- will reveal the planet's "weight," or mass. Combining that with the planet's diameter will tell us whether Wolf 503b is very dense, like a rocky planet, or less dense, like a planet with a puffy, gaseous atmosphere. That, in turn, could tell us more about the nature of planets close to the Fulton gap.
Its star's brightness also makes Wolf 503b a likely candidate for closer inspection by the James Webb Space Telescope, scheduled for launch in 2021. The Webb telescope will be equipped to probe the chemistry and composition of the planet's atmosphere -- perhaps like Earth's, or Neptune's, or like nothing we've ever seen before.
See details and check the official NASA planet count at the NASA Exoplanet Archive