Probing the viscosity of Venus mantle from dynamic topography at Baltis Vallis

The Baltis Vallis channel on Venus preserves a record of long-wavelength
deformation generated by a convecting mantle, providing a unique window
into the planet's geodynamics. Notably, the observed topography along
the channel is not downhill, suggesting complex interactions between
surface processes and mantle dynamics. We statistically compare the
observed dynamic topography of Baltis Vallis with dynamic topographies
generated by a suite of stagnant-lid mantle convection models to constrain
Venus' interior dynamics. Baltis Vallis's relatively young age
(likely less than 250 Myr) and low root-mean-square relief of 217 m
indicate vigorous convection in Venus's mantle, with a Rayleigh
number greater than 4x108, implying a mantle viscosity 1-2 orders of
magnitude lower than Earth's. This difference may result from either
a water-rich, less-degassed interior or a higher-temperature mantle
beneath an insulating lid. Additionally, our simulations suggest that melt
advection may dominate heat transport on Venus, potentially leading to
non-linear temperature profiles in the crust. Upcoming missions such as
VERITAS and EnVision will deliver higher-resolution gravity and
topographic data, providing further constraints on Venus's
present-day internal dynamics and the origin of Baltis Vallis.