Volcanism on Venus and Titan : Constraints from Present and Future Radar Observations

English Abstract:

 

One of the most pressing questions about our sister planet is the degree of present-day volcanism. Estimates range from around 0.01 km^3/yr to roughly that of the Earth, 10 km^3/yr, some three orders of magnitude. I consider how well a future radar mapper, with a resolution equal to or better than Magellan (~120m), might constrain this rate. Were such a mission to fly in the 2020s, three decades of volcanic change on the surface will have accumulated. I use observed lava volume/area relationships from terrestrial volcanoes to estimate the area change that may have occurred, and consider the issue of detection of new flows against old. In essence, a volcano may choose a new flow from a 'palette' of radar colors, and only if a new flow is the same (to within measurement accuracy) of the one(s) on which it is superposed. Again, terrestrial data offers some insights into how random the color selection may be. It is of note in this context that part of Venus' surface was imaged twice by Magellan, albeit with a relatively modest separation in time : the lack of any identifiable temporal change places a (probabilistic) constraint on the eruption rate. (Similar considerations confront Titan, but there the repeat coverage is rather small).

 Microwave radiometry is another approach that might indicate present-day or recent volcanism; unlike near-infrared observations which only sense the upper surface and therefore only active lavas, microwave thermal emission may probe deeper, older flows. Again, terrestrial examples, and the search for volcanism on Titan with the Cassini radar radiometer, inform the application of this technique to Venus.