DW: Is there a planet, somewhere out in the universe, that has water on it but no hurricanes? Is that possible?
Ralf Jaumann: So far, there is no planet that we know of that has liquid water on the surface, besides Earth. And Earth has hurricanes. Liquid water on the surface is a heat buffer and in any case it will produce an atmosphere and solar radiation will make turbulences. So, if you really have a planet with liquid water on the surface, you will have at least thunderstorms.
If there was water, but the planet would not turn – what would the missing rotation of the planet mean for the emergence of hurricanes?
For a hurricane you need a rotation and temperature differences. Horizontally and also vertically you need movement: The warm air going to the top and the cold air coming down. And you need to have some rotation. The planet probably has to spin at least a little bit – but that is not completely clear.
We have a planet like Venus, which doesn't spin very fast. But we see clouds and some sort of weather phenomena on Venus, too. That means there are two things: One is the rotation of the planet, which makes air masses move horizontally, and the other is the temperature difference, which is responsible for the vertical movement. In the atmosphere there you can find a lot of turbulences that are similar to a hurricane.
Jupiter has a massive hurricane. Why does that hurricane never stop spinning? What's inside it?
Jupiter's rotation axis is vertical to the ecliptic. That means that the solar radiation always has the same conditions. There are no seasons. Jupiter is also rotating very fast: A day takes only ten hours. And it has a lot of vertical wind systems: Hot air masses are coming from the interior, cool down and drop back to the interior. One of the big storms is mostly driven by these vertical wind systems.
What would have to change here on Earth to have permanent hurricanes?
Earth is a little smaller than Jupiter, it does not turn as fast and we have seasons. That provides for a much more active exchange of air masses between the poles and the equator than what we see on Jupiter. On Jupiter, the air dynamics are taking place in zones: From east to west and from west to east. On Earth it is going from south to north and from north to south.
Does that mean in turn, that if earth had an axis directly in line with the orbit, we might have more stable hurricanes?
It might happen, yes.
We always tend to see hurricanes carrying a lot of water. But there are other celestial objects like the Saturn moon Titan, which has liquid methane pooled into lakes...
There is a lot of methane rain on Titan. What we see with water on Earth - evaporating, cooling down, condensation, raining, running over the surface - we see with methane on Titan. At least Titan's atmosphere is acting in the same way as Earth's is doing. We know, that there are clouds and there are a number of theoretical [indications that suggest] there are very heavy thunderstorms. We see on the surface and in the river systems that a lot of [liquid] has to get to the surface to build the Methane river systems. Titan is acting quite similar to Earth in terms of atmospheric circulation of methane and also in terms of the liquid erosion of the surface.
So could Titan have methane hurricanes?
Yes, a hurricane is nothing but a very big thunderstorm. And Titan has thunderstorms for sure, we even see the lightning. And it could have hurricanes – there is no reason why not.
Titan is a very cold moon. But would it be possible for a very hot planet that has melted metal on it's surface to have a liquid metal hurricane?
In theory yes, but you have to consider that you would need to have a lot of heat on the surface to make metals liquid. The heat, which is coming from a sun or stars, would probably not be enough. On Venus there are temperatures between 300 and 400 degrees Celsius, which is close to the melting point of led. But you really have to evaporate the metal to make a thunderstorm. And that would require much more heat than we might expect from a planetary body. But in principle, if you have enough heat and evaporate the metals, you could theoretically do the same with liquid that you can do with water.
Professor Ralf Jaumann is head of the department for Planetary Geology at the Institute of Planetary Research of the German Aerospace Center (DLR) in Berlin.
The interview was conducted by Conor Dillon.