#In the near future, Brand (played by Anne Hathaway) and Cooper (played by Matthew McConaughey), members of a National Aeronautics and Space Administration (NASA) expedition, sit dazed inside their small spacecraft after arriving at the extraterrestrial body ‘Miller Planet’ beyond the galaxy. The shocking situation that struck just moments earlier has left them reeling.

Searching for a world to which humanity can be relocated from an environmentally devastated Earth, Brand and Cooper wade into the shallow sea on Miller Planet, only knee-deep. But as they step out of the spacecraft and briefly continue their survey, a super-giant wave hundreds of ｍ high suddenly appears before their eyes.

The two barely save their lives by retreating into the spacecraft. However, water floods the engine, making normal operation difficult, and one teammate is swept away by the wave. This is a scene from the American science-fiction (SF) film <Interstellar>.

Scientists have now suggested that a world where a ‘hell of waves’ unfolds may not be imaginary but could be realized in reality. Surprisingly, that world lies within the solar system, not beyond the galaxy as in <Interstellar>. It is Saturn moon ‘Titan’.

What kind of world is Titan? To begin with, Titan is notably large. Its diameter is 5150㎞, one and a half times that of the Moon (3470㎞). After the Jovian moon Ganymede (5260㎞), it is the second-largest satellite in the solar system.

What truly draws attention to Titan, however, is not its size but its seas. Among celestial bodies in the solar system, it is the only one besides Earth with seas on the surface. The largest sea on Titan is ‘Kraken Mare’, with an area of about 400,000㎢. That is four times the size of South Korea and larger than the Caspian Sea (about 370,000㎢), the most expansive inland sea on Earth. Other seas such as Ligeia Mare (126,000㎢) and Punga Mare (60,000㎢) are found in various places.

An intriguing point is that the seas on Titan are not water. They consist of liquid methane and ethane. The surface temperature on Titan is minus 179 degrees Celsius, and these two substances remain liquid even at such ultralow temperatures.

Last month, researchers at the Massachusetts Institute of Technology (MIT) published in the international journal Geophysical Research Journal results that resolved a certain question about the seas of Titan. Their question concerned the height of its waves. Given Titan’s thick atmosphere, the space science community had expected winds to exist there and, therefore, wind-driven ripplesin other words, waves.

No ocean probe has yet been sent by humanity to Titan. Therefore, the researchers fed meteorological, oceanic, and planetary-science characteristics of Titancollected by spacecraft and telescopesinto a computer simulation to predict wave heights.

They calculated wave height using the concept of significant wave height, which is the average of the highest one-third of waves among all waves during a set period. This is the standard method used in science to quantify wave height.

The wave heights on Titan derived from the simulations were striking. Under a mere 4ｍ windthe kind that would make a flag flutter lightly on Earththe seas on Titan were found to produce waves as high as 3.3ｍ. They are, literally, house-sized waves. In seas around Korea, such waves would immediately trigger a rough-sea advisory (wave height 3ｍ or higher).

By contrast, when the team ran a simulation assuming the same 4ｍ wind actually blowing over the oceans on Earth, the situation was very different: wave height was only 0.2ｍ, and the surface remained calm. In short, at the same wind speed, waves on Titan are 16.5 times higher than on the oceans of Earth.

Why are the waves on Titan so exceptionally high? Above all, because the liquid methane and ethane that fill its seas have very different properties from the water that composes the oceans on Earth.

Liquid methane and ethane have low density. Compared with water, methane is only 42% as dense and ethane 54%. This means they ae easily driven by forces such as wind. In addition, the gravity on Titan is only 14% of that on Earth, so the force pulling a wave that has risen skyward back down to the surface is very weak.

As a result, the low density of liquid methane and ethane combined with Titan’s weak gravity creates ideal conditions for rough waves even in light winds. In official MIT materials, the researchers explained, “If someone were standing on a Titan shoreline, they would see massive waves rolling in even with a gentle breeze.”

The National Aeronautics and Space Administration (NASA) plans in 2034 to fly an unmanned rotorcraft the size of a compact car, called ‘Dragonfly’, in the skies over Titan. If meaningful findings emerge, there is a high possibility that additional unmanned boat-type equipment for surveying marine ecosystems will be deployed. Because Titan contains abundant organic compounds, the source of life, microorganisms may exist in its seas.

Attempting to put an unmanned vessel onto Titan’s seas without meticulous preparation could result in a capsizing accident due to high waves. The researchers said, “These results will be used to build probes that can overcome the power of waves on Titan.”