The TRAPPIST-1 red dwarf star compared to the Sun (via Wikipedia)
One of the most Earth-like exoplanets yet discovered has been identified, but it is a bit of a hike to visit at 39.6 light years from Earth.
The TRAPPIST-1 system provides an exquisite laboratory for understanding exoplanetary atmospheres and interiors. Their mutual gravitational interactions leads to transit timing variations, from which Grimm et al. (2018) recently measured the planetary masses with precisions ranging from 5% to 12%. Using these masses and the <5% radius measurements on each planet, we apply the method described in Suissa et al. (2018) to infer the minimum and maximum CRF (core radius fraction) of each planet. Further, we modify the maximum limit to account for the fact that a light volatile envelope is excluded for planets b through f. Only planet e is found to have a significant probability of having a non-zero minimum CRF, with a 0.7% false-alarm probability it has no core. Our method further allows us to measure the CRF of planet e to be greater than (49 +/- 7)% but less than (72 +/- 2)%, which is compatible with that of the Earth. TRAPPIST-1e therefore possess a large iron core similar to the Earth, in addition to being Earth-sized and located in the temperature zone.Gabrielle Suissa, David Kipping, "TRAPPIST-1e Has a Large Iron Core" (April 26, 2018).
Planet e has a surface gravity of 0.93 times that of Earth, a radius 0.91 times that of Earth, a mean surface temperature of −16.69 ± 6.30 °F, and a six day orbital period. The red dwarf star TRAPIST-1 that it orbits is much less potent than our Sun and would be somewhat more dim than our Sun. It could have water. We don't know if it has an atmosphere.
It is tidally locked, however, which means a light side always faces the star and a dark side is always pointed away from it. This would make it warmer on the light side, but colder on the dark side, potentially making the light side a quite comfortable temperature for humans (perhaps ca. 50 °F).