CoRoT-27b: A Massive and Dense Planet

Parviainen H. et al. (2014) report the discovery of a massive high-density planet on a close-in 3.58 day orbit around a 4.2 billion year old Sun-like star. The planet is identified as CoRoT-27b. Like Jupiter, CoRoT-27b is a gas-giant planet. Its presence was detected by the CoRoT space telescope as the planet periodically transits its parent star and blocks a small fraction of the star’s light. CoRoT-27b weighs in at 10.39 ± 0.55 Jupiter-masses and has 1.01 ± 0.04 times the radius of Jupiter. This gives CoRoT-27b a mean density of 12.6 times the density of water, which is more than twice the mean density of Earth and almost 10 times the mean density of Jupiter.

Figure 1: Artist’s impression of a gas-giant planet.

Like Jupiter, CoRoT-27b is a gaseous planet comprised primarily of hydrogen and helium. The structure and composition of CoRoT-27b can be inferred from two models. For the first model, the planet is assumed to be made of a central rocky core surrounded by an extensive hydrogen-helium envelop. The 1st model is consistant with a heavy element mass fraction of 0.11, representing a core mass of 366 Earth-masses. For the second model, a central rocky core is absent and the heavy elements are present throughout the hydrogen-helium envelop. The 2nd model is consistant with a heavy element mass fraction of 0.07, representing a heavy element mass of 219 Earth-masses.

CoRoT-27b falls within a sparsely populated overlapping mass regime between the most massive planets and brown dwarfs. Given its high mass, gravity on the “surface” of CoRoT-27b is 27 times the surface gravity on Earth. Technically, CoRoT-27b does not have a surface since it is gaseous through, right down to a central rocky core, if one is present. Being so near to its parent star, the equilibrium temperature on CoRoT-27b is estimated to be 1500 ± 130 K. The discovery of CoRoT-27b is an important addition to a scarcely populated class of massive close-in planets.

Figure 2: Radial velocity curve showing how much CoRoT-27b gravitationally tugs at its parent star. This information allows the planet’s mass to be estimated. Parviainen H. et al. (2014).

Figure 3: Transit light curve showing the amount of dimming of the parent star when CoRoT-27b passes in front of it. This information allows the size of the planet to be measured. Parviainen H. et al. (2014).

Figure 4: CoRoT-27b mass, period and density compared with the population of confirmed transiting exoplanets. Parviainen H. et al. (2014).

Reference:

Parviainen H. et al. (2014), “Transiting exoplanets from the CoRoT space mission XXVII. CoRoT-27b: a massive and dense planet on a short-period orbit”, arXiv:1401.1122 [astro-ph.EP]