planetary rivers

Rivers on Mars and Titan

Titan, Saturn’s largest moon, is the only other solar system world we know of with active rivers and coasts. But Titan differs from Earth in some important and surprising ways: it has one-seventh the gravity, it’s incredibly cold, the landscapes are made of ice and organic compounds, and it has a methane cycle (natural gas) instead of a water cycle. If we apply what we know about Earth’s rivers to Mars and Titan, what can it teach us about planetary climate, tectonics, and habitability?

We use images and other data from the Cassini-Huygens mission to study Titan’s landscapes, with the main goal of understanding its present and past climate. For example, we used the river networks near the Huygens probe landing site to estimate the methane rainfall rate, and found that the rate was similar to storms on Earth. Ben Black and Yodit Tewelde, in collaboration with Devon Burr (U. Tennessee), mapped river networks and used landscape evolution models to estimate the extent to which erosion by rivers has shaped Titan’s surface.

• Tewelde, Y., J.T. Perron, P.G. Ford, S.R. Miller and B.A. Black (2013), Estimates of fluvial erosion on Titan from sinuosity of lake shorelines. J. Geophys. Res., 118, 2198–2212, http://doi.org/10.1002/jgre.20153.
• Black, B.A., J.T. Perron, D.M. Burr and S.L. Drummond (2012), Estimating erosional exhumation on Titan from drainage network morphology. J. Geophys. Res., 117, E08006, http://doi.org/10.1029/2012JE004085.
• Burr, D.M., J.T. Perron, M.P. Lamb, R.P. Irwin, G.C. Collins, A.D. Howard, L.S. Sklar, J.M. Moore, M. Adamkovics, V.R. Baker, S.A. Drummond and B.A. Black (2013), Fluvial features on Titan: Insights from morphology and modeling. GSA Bulletin, 125, 299-321, http://doi.org/10.1130/B30612.1.
• Perron, J.T., M.P. Lamb, C.D. Koven, I.Y. Fung, E. Yager and M. Adamkovics (2006), Valley forma­tion and methane precipitation rates on Titan. J. Geophys. Res., 111, E11001, http://doi.org/10.1029/2005JE002602.
• Perron, J.T., and I. de Pater (2004), Dynamics of an ice continent on Titan. Geophys. Res. Lett., 31, L17S04, http://doi.org/10.1029/2004GL019802.

Sam Birch is working with Jason Soderblom, Andrew Ashton (WHOI), Juan Lora (Yale) and Alex Hayes (Cornell) to estimate rates of flow and sediment transport in major rivers on Titan and Mars. His results will allow us to place bounds on how long it took to form features like the possible river delta in Ontario Lacus on Titan and the delta in Jezero Crater that the Mars 2020 rover is exploring.

Paul Corlies is working with Jason Soderblom to explore the thermodynamic evolution of a hydrocarbon river on Titan, which may be quite different than rivers on Earth!

With rivers visible on Earth, Mars, and Titan, it is natural to ask what differences they reveal between the three worlds. Ben Black and Elizabeth Bailey worked with Doug Hemingway (Berkeley), Francis Nimmo (UC Santa Cruz), and Howard Zebker (Stanford) to ask a simple question: how well do river flow directions align with a planet’s topography at various scales? They found that rivers on Mars and Titan generally align well with large-scale topography, unlike Earth, where plate tectonics builds mountain ranges that can interrupt the flow of rivers from continental interiors to the ocean. This is useful because we don’t know much about the mechanisms that formed Titan’s topography; Ben’s and Elizabeth’s results suggest that those mechanisms produced mainly long-wavelength relief.

• Black, B.A., J.T. Perron, D. Hemingway, E. Bailey, F. Nimmo and H. Zebker (2017). Global drainage patterns and the origins of topographic relief on Earth, Mars, and Titan. Science, 356, 727–731, http://doi.org/10.1126/science.aag0171.