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Title: What empties the hot Neptune desert?
Plain: Planets the size and mass of Neptune are rare on orbits shorter than a few days, even though both smaller and larger planets are found there. Starlight stripping their gas, and the way giant planets arrive in such close orbits, are proposed causes.
Precise: Neptune-mass and Neptune-radius planets are depleted at $P$ below $\sim 2-4\,\mathrm{d}$, with the upper desert boundary following mass decreasing with period and a differently shaped lower boundary (Mazeh, Holczer and Faigler 2016, A&A 589, A75). Determine whether photoevaporation of irradiated sub-Neptunes sets the lower boundary and the tidal-disruption limit of high-eccentricity migration sets the upper one (Owen and Lai 2018, arXiv:1807.00012), or whether formation-location or tidal decay effects dominate. The answer is a mechanism reproducing both boundaries versus stellar type and age.
Settled by: Masses, radii, ages and measured escape rates (helium $10830\,\mathrm{Angstrom}$ and Lyman-alpha transits) for planets in and near the desert from TESS follow-up, compared with each boundary's predicted dependence on host properties.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)