WASP-86b and WASP-102b: super-dense versus bloated planets

Faedi, F.; Gómez Maqueo Chew, Y.; Pollacco, D.; Brown, D. J. A.; Hébrard, G.; Smalley, B.; Lam, K. W. F.; Veras, D.; Anderson, D.; Doyle, A. P.; Gillon, M.; Goad, M. R.; Lendl, M.; Mancini, L.; McCormac, J.; Plauchu-Frayn, I.; Prieto-Arranz, J.; Scholz, A.; Street, R.; Triaud, A. H. M.; West, R.; Wheatley, P. J.; Armstrong, D. J.; Barros, S. C. C.; Boisse, I.; Bouchy, F.; Boumis, P.; Collier Cameron, A.; Haswell, C. A.; Hay, K. L.; Hellier, C.; Kolb, U.; Maxted, P. F. L.; Norton, A. J.; Osborn, H. P.; Palle, E.; Pepe, F.; Queloz, D.; Ségransan, D.; Udry, S. and Wilson, P. A. (2016). WASP-86b and WASP-102b: super-dense versus bloated planets. ArXiv e-prints (In Press).

Abstract

We report the discovery of two transiting planetary systems: a super dense, sub-Jupiter mass planet WASP-86b (Mpl = 0.82 ± 0.06 MJ; Rpl = 0.63 ± 0.01 RJ), and a bloated, Saturn-like planet WASP-102b (Mpl = 0.62 ± 0.04 MJ; Rpl = 1.27 ± 0.03 RJ). They orbit their host star every ∼5.03, and ∼2.71 days, respectively. The planet hosting WASP-86 is a F7 star (Teff = 6330±110 K, [Fe/H] = +0.23 ± 0.14 dex, and age ∼0.8–1 Gyr); WASP-102 is a G0 star (Teff = 5940±140 K, [Fe/H] = −0.09± 0.19 dex, and age ∼1 Gyr). These two systems highlight the diversity of planetary radii over similar masses for giant planets with masses between Saturn and Jupiter. WASP-102b shows a larger than model-predicted radius, indicating that the planet is receiving a strong incident flux which contributes to the inflation of its radius. On the other hand, with a density of ρpl = 3.24± 0.3 ρJ, WASP-86b is the densest gas giant planet among planets with masses in the range 0.05 < Mpl < 2.0 MJ. With a stellar mass of 1.34 M and [Fe/H]= +0.23 dex, WASP-86 could host additional massive and dense planets given that its protoplanetary disc is expected to also have been enriched with heavy elements. In order to match WASP-86b’s density, an extrapolation of theoretical models predicts a planet composition of more than 80% in heavy elements (whether confined in a core or mixed in the envelope). This fraction corresponds to a core mass of approximately 210M for WASP-86b’s mass of Mpl∼260 M. Only planets with masses larger than about 2 MJ have larger densities than that of WASP-86b, making it exceptional in its mass range.

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