Abnormal Reflections from Titan may be from Paleolakes

Image credit: Hofgartner et al., 2020

On the surface of Titan—Saturn’s largest moon and the solar system’s second-largest natural satellite—volatiles are actively cycled in a way much like the hydrological cycle on Earth. Apart from Earth, Titan is the only body that we know of that has liquid present on its surface; however, unlike the lakes and seas that are filled with water on Earth, Titan’s are filled with methane and ethane. Radar observations from Arecibo Observatory and the Green Bank Telescope found anomalously specular radar reflections from the equatorial regions of Titan that were initially interpreted as evidence for liquid on the surface. Subsequent data from the Cassini spacecraft has shown that Titan has an abundance of lakes and seas near its poles, but not in the equatorial regions as suggested by the ground-based radar observations. Revisiting the radar data from Arecibo Observatory and the Green Bank Telescope and Cassini radar altimetry data, research led by Jason Hofgartner at NASA’s Jet Propulsion Laboratory found that paleolakes/paleoseas (dry lakes and sea beds) in Titan’s equatorial regions could produce the anomalously specular radar reflections without the need for liquid on the surface. These radar-bright regions are spectrally distinct from their surroundings, are topographic lows, and have morphologies similar to other possible paleolakes nearer to Titan’s poles. This new research shows that care must be taken in interpreting specular reflections as evidence of liquid on the surface of a body and suggests that the coherence of the reflection, not just the specular nature of the reflection, must be considered. These observations and interpretations provide a cautionary tale and have the potential to aid in robust searches for surface liquids on other planets, exoplanets, or satellites. READ MORE