KOI 408.05 is a Warm Neptune in the Habitable Zone
Kunimoto et al. (2016) present the discovery of a warm Neptune in the habitable zone around a Sun-like star. This planet is identified as KOI 408.05. It orbits a host star with ~0.963 times the mass and ~0.931 times the radius of the Sun, and the effective temperature of the host star is ~5862 K. The planet's orbital period is 637 days and it is 1.472 times further from its host star than Earth is from the Sun, in a Mars-like orbit. KOI 408.05 is estimated to receive ~60 percent the amount of flux Earth gets from the Sun and its equilibrium temperature is predicted to be 252 K. For comparison, Earth's equilibrium temperature is 255 K.
The transit of KOI 408.05 in front of its host star has 1555 ppm (parts-per-million) transit depth and transit duration of about 16.7 hours. From the transit depth, the size of KOI 408.05 is estimated to be ~4.92 times the radius of Earth. With these properties, KOI 408.05 is a warm Neptune-sized planet in the habitable zone of its host star. Although KOI 408.05 is expected to be like Neptune with a think hydrogen-helium envelope, a large moon in orbit around it can potentially be habitable.
NASA's Kepler space telescope has so far detected ~5000 planets and planet candidates. However, only 20 or so have orbital periods longer than the orbital period of KOI 408.05. In addition to KOI 408.05, Kunimoto et al. (2016) also presented the detection of three other planets around three different host stars. KOI 205.02 is a Mercury-sized planet with ~0.449 times the radius of Earth in a 4.813 day orbit around its host star at 0.052 AU. Its equilibrium temperature is predicted to be 902 K and it receives ~100 times the amount of flux Earth gets from the Sun.
KOI 290.02 is a scorchingly hot Earth-sized planet with ~1.29 times the radius of Earth in a 6.828 day orbit around a relatively luminous host star at 0.078 AU. Its equilibrium temperature is predicted to be 1654 K and it receives ~1015 times the amount of flux Earth gets from the Sun. KOI 488.02 is also an Earth-sized planet with ~1.14 times the radius of Earth in a 17.39 day orbit around its host star at 0.119 AU. Its equilibrium temperature is predicted to be 736 K and it receives ~43 times the amount of flux Earth gets from the Sun.
Reference:
Kunimoto et al. (2016), “Lifting Transit Signals from the Kepler Noise Floor: I. Discovery of a Warm Neptune”
