The mystery of Titan’s craters

Titan, the largest moon of the planet Saturn, is the only star other than Earth that is known to have an atmosphere as well as liquids in the form of rivers, lakes and seas on its surface. Due to its extremely cold temperature, Titan’s liquids are made up of hydrocarbons such as methane and ethane, and the surface is largely made up of water ice.

Analysis of observations of Titan made by NASA space probes that traveled to the Saturn system have revealed the existence of a great mystery: the impact craters on Titan are hundreds of meters shallower than expected and only 90 have been identified. craters on this moon, an insignificant amount compared to the number of craters on other comparable stars.

In a recent study, researchers have analyzed the enigma and found a possible explanation.

The study is the work of a team led by Lauren R. Schurmeier, from the Institute of Geophysics and Planetology at the University of Hawaii in the American city of Manoa.

The scarcity of craters and how shallow they are left scientists baffled. Based on the characteristics and abundance of craters on other moons of Saturn, it was expected to see many more impact craters on Titan’s surface and at much greater depths than the few craters observed on that satellite. “We realized that something unique to Titan must be causing them to become shallower and disappear relatively quickly,” Schurmeier explains.

To investigate what could be behind this mystery, Schurmeier and his colleagues tested in a digital model how Titan’s topography might react after an impact if the ice crust were provided with a layer rich in methane clathrate, a kind of layer of water ice with methane trapped within the crystalline structure.

Methane clathrate is stronger and more insulating than regular water ice. This means that any internal heat that Titan may have, coming from the deep subsurface, is retained much better in the subsurface than if the crust were exclusively made of normal water ice.

Since the initial shape of Titan’s craters is unknown, the researchers modeled and compared two plausible initial depths, based on cool-looking, similarly sized craters on a similarly sized icy moon, Ganymede.

Using this modeling method, they were able to narrow the thickness of the methane clathrate crust to between five and ten kilometers, as simulations performed at that thickness produced crater depths that better fit the observed craters.

Titan seen using VIMS, a visible-light and infrared-mapping spectrograph aboard NASA’s Cassini space probe. An impact crater can be seen near the center. The dark zones near the equator are dunes of organic-rich sand, and the dark zones in the north polar region are lakes of liquid methane and ethane. White clouds are also seen in the northern hemisphere. (Photo: NASA/Cassini VIMS)

The methane clathrate crust keeps Titan’s interior hot and ductile and causes surprisingly rapid topographic relaxation, resulting in a decrease in crater depth at a rate similar to that of Earth’s fast-moving glaciers.

All this and the existence of convection generate a more favorable scenario for the detection of life, if there is any on that star. Specifically, this scenario would make it easier to transport biomarkers to the surface or not far below it, where they would be much more accessible for extraction by robotic systems from spacecraft that land there.

With NASA’s Dragonfly mission to Titan, scheduled to launch in July 2028 and arrive in 2034, there will be a good opportunity to get a closer look at this moon and further investigate its icy surface, including a crater called Selk.

The study is titled “Rapid Impact Crater Relaxation Caused by an Insulating Methane Clathrate Crust on Titan.” And it has been published in the academic journal The Planetary Science Journal. (Fountain: NCYT by Amazings)