Cassini radar reveals Titan’s largest seas mirror-smooth, roughness under 3.3mm

August 6, 2026 at 05:50 AM2 min

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A reanalysis of Cassini spacecraft radio data has found that the surfaces of Titan’s three largest seas — Kraken Mare, Ligeia Mare and Punga Mare — are mirror-smooth, with roughness measuring no more than 3.3 millimetres. The findings, drawn from bistatic radar experiments during four flybys in 2014 and 2016, also suggest methane-rich rivers entering ethane-rich seas near estuaries.

The Measurement

Across the open bodies of Kraken Mare, Ligeia Mare and Punga Mare, Cassini’s radio signals reflected with an intensity suggesting root-mean-square surface roughness of no more than 3.3 millimetres. Near estuaries and the straits connecting the seas, the surface was somewhat rougher, with changes in radar reflectivity consistent with methane-rich liquid meeting more ethane-rich seas — a cryogenic analogue to freshwater entering Earth’s oceans.

The Method

The work, published in Nature Communications and led by Valerio Poggiali, reanalysed data from Cassini’s bistatic radar experiments, where the spacecraft aimed its high-gain antenna at specular points on Titan’s surface while NASA’s Deep Space Network at the Canberra complex recorded the reflected signals on Earth. The team used X-band data from four egress portions of flybys T101 (17 May 2014), T102 (18 June 2014), T106 (24 October 2014) and T124 (14 November 2016), whose reflection points crossed at least one of the three northern seas.

The Interpretation

The 3.3-millimetre figure is a statistical measure of height variation at the radio wavelength scale, not a direct image of wave crests, and the river interpretation is one possible explanation for the rougher estuary signals. Cassini did not film methane rivers; rather, radar reflectivity changes hinted at compositional mixing. The study offers a snapshot of specific tracks at specific times, and the authors caution it does not represent settled consensus for all conditions in Titan’s seas.