My new paper, published in ApJ this month, tackles a question I always assumed the answer was “no” to in exoplanet dynamics: if a giant planet becomes a close-in hot/warm Jupiter via high-eccentricity tidal migration, can any short-period inner planets survive the chaos? What about ultra-short period companions?
Using a mix of analytic estimates and N-body simulations that include equilibrium tides and general relativistic precession, in this new paper I map where survival is even possible. The main result is a clear stability boundary: inner planets typically survive only if the migrating giant’s closest approach stays more than ~14 mutual Hill radii away. Cross that line, and secular eccentricity pumping, orbit crossing, and tidal evolution tend to eliminate the inner planet. Applying the framework to known multi-planet systems with a close-in giant and an inner companion, the conclusion is stark: none of the observed systems are consistent with having formed through high-eccentricity tidal migration of the giant. If a system has a hot Jupiter and a nearby inner planet today, the hot Jupiter likely didn’t arrive via the disruptive “high-e” tidal pathway. This is what I think most people expected already, so it’s not a huge surprise.
But there’s an important nuance: my simulations show a narrow region where warm Jupiters or possibly the coldest hot Jupiters can migrate tidally without wiping out inner planets. If the giant’s periastron is roughly 0.05–0.08 au (corresponding to final semimajor axes around 0.10–0.16 au), inner planets can sometimes remain intact, and the giant can still circularize on less than Gyr timescales. That makes warm Jupiters a potential “sweet spot” where tidal migration and inner companion survival can coexist. In the future, the ~14 mutual hill radii boundary can be used as a first check to assess whether new discoveries of multi-planet systems including a Jupiter-mass planet are plausible under the tidal migration hypothesis.