Spatially variable crater morphology on the dwarf planet Haumea

Abstract: Haumea, thought to be the Kuiper Belt's 3rd most massive object, has a fast 3.92 hr rotational period, resulting in its shape as a triaxial ellipsoid. Here, we make the first detailed predictions of Haumea's surface morphology, considering in particular effects stemming from its unique shape. Given observations have indicated Haumea's surface to be predominantly inert water ice, we predict crater characteristics, with craters likely to be the predominant surface feature on Haumea. In calculating Haumea's surface gravity, we find that g varies by almost two orders of magnitude, from a minimum of 0.0126 m/s^2 at the location of the equatorial major axis, to 1.076 m/s^2 at the pole. We also find a non-monotonic decrease in g with latitude. The simple to complex crater transition diameter varies from 36.2 km at Haumea's location of minimum surface gravity to 6.1 km at the poles. Equatorial craters are expected to skew to larger volumes, have depths greater by a factor of > 2, and have thicker ejecta when compared with craters at high latitudes. Considering implications for escape of crater ejecta, we calculate that Haumea's escape velocity varies by 62% from equator to pole. Despite higher escape velocities at the poles, impacts there are expected to have a higher mass fraction of ejecta escape from Haumea's gravitational well. Haumea may be unique among planet-sized objects in the solar system in possessing dramatic variations in crater morphology across its surface, stemming solely from changes in the magnitude of its surface gravity.