There are many planets that scientists are currently studying to see if they could possibly support life. Of all of the exoplanets (planets outside of our solar system) currently being studied, Kepler-438b has the highest Earth Similarity Index. It is similar in size and temperature to Earth, but is much closer to its Red Dwarf parent star than we are to the Sun.
Despite the similarities, recent research indicates that the planet's atmosphere has been stripped away by its parent star, and that the planet is likely uninhabitable. According to ScienceDaily.com, the Red Dwarf produces superflares every few hundred days that are about ten times stronger than any that have been recorded by our sun. It is not likely that the flares are the direct cause of the atmosphere being stripped away. More likely it is a phenomenon known as Coronal Mass Ejection (CME) that has stripped away the planet's atmosphere and left it uninhabitable.
Lead researcher, Dr. David Armstrong of the University of Warwick's Astrophysics Group had this to say:
If the planet, Kepler-438b, has a magnetic field like the Earth, it may be shielded from some of the effects. However, if it does not, or the flares are strong enough, it could have lost its atmosphere, be irradiated by extra dangerous radiation and be a much harsher place for life to exist.
Chloe Pugh of the University of Warwick's Centre for Fusion, Space and Astrophysics adds:
Coronal mass ejections are where a huge amount of plasma is hurled outwards from the Sun, and there is no reason why they should not occur on other active stars as well. The likelihood of a coronal mass ejection occurring increases with the occurrence of powerful flares, and large coronal mass ejections have the potential to strip away any atmosphere that a close-in planet like Kepler-438b might have, rendering it uninhabitable. With little atmosphere, the planet would also be subject to harsh UV and X-ray radiation from the superflares, along with charged particle radiation, all of which are damaging to life.
Bottom line: Of all of the exoplanets discovered to date, the planet most similar in size and temperature to Earth appears to be uninhabitable.