A lowest circular orbit to remain stable around the Earth is possible at an altitude of about 95 mi (155 km) while the lowest perigee for a stable elliptical orbit around the Earth would be around 55 mi (88.5 km). I'd like to know these values on the moons Titan and Triton.
Titan's atmosphere reaches very high, and I suppose a stable circular orbit around Titan isn't possible below 500 mi (805 km). Triton's atmosphere on the other hand is very weak but still a more essential one, and you can't orbit Triton just above the surface (like you could above Mercury and many moons) while in Orbiter2016 I approached Triton as close as 33 mi (53 km) above its surface and my spacecraft's instruments still didn't show any air pressure nor any dynamic pressure at all. On Triton's surface my spacecraft would show an air pressure of 1.45 pa.
What would be the lowest possible circular orbit and the lowest possible perigee around Titan and Triton?