Kavli Affiliate: Andrew Vanderburg
| First 5 Authors: Ryan Cloutier, Michael Greklek-McKeon, Serena Wurmser, Collin Cherubim, Erik Gillis
| Summary:
Is the population of close-in planets orbiting M dwarfs sculpted by thermally
driven escape or is it a direct outcome of the planet formation process? A
number of recent empirical results strongly suggest the latter. However, the
unique architecture of the TOI-1266 planetary system presents a challenge to
models of planet formation and atmospheric escape given its seemingly
"inverted" architecture of a large sub-Neptune ($P_b=10.9$ days,
$R_{p,b}=2.62pm 0.11, mathrm{R}_{oplus}$) whose orbit is interior to that
of the system’s smaller planet ($P_c=18.8$ days, $R_{p,c}=2.13pm 0.12,
mathrm{R}_{oplus}$). Here we present revised planetary radii based on new
TESS and diffuser-assisted ground-based transit observations and characterize
both planetary masses using a set of 145 radial velocity (RV) measurements from
HARPS-N ($M_{p,b}=4.23pm 0.69, mathrm{M}_{oplus}, M_{p,c}=2.88pm 0.80,
mathrm{M}_{oplus}$). Our RV analysis also reveals a third planet candidate
($P_d=32.3$ days, $M_{p,d}sin{i} = 4.59^{+0.96}_{-0.94},
mathrm{M}_{oplus}$), which if real, would form a chain of 5:3 period ratios,
although we show that the system is likely not in a mean motion resonance. Our
results indicate that TOI-1266 b and c are the lowest density sub-Neptunes
known around M dwarfs and may exhibit distinct bulk compositions of a
gas-enveloped terrestrial ($X_{mathrm{env},b}=5.5pm 0.7$%) and a water-rich
world (WMF$_c=59pm 14$%), which is supported by hydrodynamic escape models. If
distinct bulk compositions for the transiting planets are confirmed by
atmospheric characterization, the system’s unique architecture would represent
an interesting test case for sub-Neptune formation models such as inside-out
planet formation at pebble traps.
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