Kepler’s Bonanza of Earth-Like Planet Candidates

Coughlin et al. (2015) present the seventh Kepler planet candidate catalogue. It contains data collected by NASA’s Kepler space telescope over 48 months. This catalogue brings the total number of planet candidates to 4696. It also contains several new planet candidates that are likely to be rocky and in the habitable zone of their host stars. A few noteworthy planet candidates are further discussed in this article.

Figure 1: Artist’s impression of a habitable planet.

Figure 2: A plot of planet radius versus insolation flux for all planet candidates known in this catalogue. (Note that some planet candidates, particularly those with large radii, lie outside the chosen axis limits for the plot, and thus are not shown.) The temperature of the host star is indicated via the colour of each point, and the signal-to-noise of the detection is indicated via the size of each point. The two vertical dashed lines indicate the insolation flux values of Mars and Venus as a broad guide to a potential habitable zone. The horizontal dotted line is set at 1.6 times the Earth’s radius as a suggested guide to where roughly half of the planets with this size are expected to be rocky. Coughlin et al. (2015)

KOI 1681.04 is a sub-Earth-sized planet candidate in a 21.9 day orbit around a red dwarf star with 0.35 times the Sun’s radius and effective temperature 3669 K. The planet receives an insolation flux 1.63 times what Earth gets from the Sun and the estimated equilibrium temperature on the planet is 288 K, or 15°C. The radius of KOI 1681.04 is 0.77 Rᴇ and it resides in a planetary system with three other planet candidates whose radii are 0.69, 0.71 and 0.99 Rᴇ, and whose orbital periods are 1.99, 3.53 and 6.94 days, respectively. The fact that KOI 1681.04 is in a multi-planet system gives it a high confidence that it is a real planet.

Figure 3: Artist’s impression of a potentially habitable planet.

Figure 4: Artist’s impression of a potentially habitable planet.

KOI 7179.01 is an Earth-sized planet candidate measuring 1.18 Rᴇ in radius. It orbits a Sun-like star with 1.2 times the Sun’s radius and effective temperature 5845 K. The planet’s orbital period is 407.1 days and it receives an insolation flux 1.29 times what Earth gets from the Sun. The equilibrium temperature on KOI 7179.01 is estimated to be 272 K, or -1°C. KOI 7179.01 appears to be a good Earth-like planet candidate given its Earth-like size and Earth-like insolation flux, and that it also orbits a Sun-like host star.

Measuring 1.53 Rᴇ in radius, KOI 7223.01 is somewhat larger than Earth. It orbits a star with 0.73 times the Sun’s radius and effective temperature 5370 K. The orbital period of KOI 7223.01 is 317.1 days and the planet receives an insolation flux 0.57 times what Earth gets from the Sun. The equilibrium temperature on KOI 7179.01 is estimated to be 221 K, or -52°C. KOI 7223.01 has a high probability of being a true rocky planet in orbit around a somewhat Sun-like star.

Reference:
Coughlin et al. (2015), “Planetary Candidates Observed by Kepler. VII. The First Fully Uniform Catalog Based on The Entire 48 Month Dataset (Q1-Q17 DR24)”, arXiv:1512.06149 [astro-ph.EP]