How did Cassini unlock the watery secrets lying below the outer crust of Saturn’s largest moon?
Cassini has been trying to peek below the mysterious surface of Titan for some time now, as NASA has long suspected there was more to the moon than meets the eye.
In its most recent flyby, Cassini recorded the most compelling evidence yet to suggest there is a subsurface ocean.
As the moon orbited Saturn, researchers saw bulges appear on its surface as Titan was squeezed and stretched under the immense gravity of Saturn.
This is a phenomenon common to all satellites including Earth, as the gravity of both the Sun and the Moon doesn’t just cause the oceans to bulge by as much as 60 centimetres (23 inches), but our planet’s crust too, by up to 50 centimetres (20 inches).
These are known as ‘solid tides’ and, if Titan were solid rock, scientists calculated that it would be bulging by up to a metre (3.3 feet). Instead, Titan’s solid tides are as big as ten metres (33 feet) in height, indicating there is an ocean beneath its surface. Using data from Ave previous flybys, NASA was able to calculate Titan’s internal structure layer by layer, including a global body of water between its silicate core and its solid surface.
Why Titan’s unique
So what if there’s water on Titan, a moon that’s over 1.5 billion kilometres (932 million miles) from Earth? We’re searching for the presence of water on Mars because there it’s in contact with rock, but on Titan scientists aren’t sure whether the bottom of this ocean is rock or ice. Instead, NASA is interested in the presence of methane and the effect of a liquid water ocean on methane escaping to the surface. According to the Cassini team, the abundance of methane on Titan is what makes everything that is unique about this moon.
Yet we don’t fully understand how the methane gets to the surface in sufficient quantities, because once there it dissipates in a relatively short time. A subsurface ocean of liquid water would act as a reservoir for methane and would also free gas from the ice.