Kepler 78-b is very similar to Earth. It features a similar mass and composition, with lots of rock and iron in the surface. It’s only 1.2 times wider than the Earth, and orbits a star that gives it sufficient energy like the Earth. The difference? As researcher Andrew Howard states:
“From an Earth-centric perspective, we’d like to have liquid water on the surface [and] this planet is obviously way too hot.”
That’s what kills it for us. Kepler-78b is 100 times closer to its star than Earth, so its orbit is only 8.5 hours and a surface temperature of — wait for it — 3700 to 5100ºF. Asinine levels of UV radiation coupled with that and lots of lava, and you have a planet that could never realistically support an Earth-like atmosphere; forget about your terraforming project, kiddies.
Meanwhile, scientists are still interested in researching the planet, one reason being of which: why didn’t it fall into the star at some point?