What question are ELTE researchers trying to answer with the help of the Hungarian astronaut?

What are atmospheric flow conditions like on the various planets and moons of our Solar System? Spacecraft and telescope observations are already well supplemented by computer fluid dynamics simulations and even laboratory experiments—but these processes have never been studied in microgravity in space until now.

The DiRoS (Differential Rotation on a Sphere) fluid dynamics experiment was developed jointly by the Kármán Environmental Flow Laboratory at ELTE’s Institute of Physics and Astronomy (led by Associate Professor Miklós Vincze of the Department of Materials Physics) and an engineering team from SGF Ltd. (led by Pál Gábor Vizi).

The Kármán Lab’s research profile focuses on experimental modeling of planetary-scale atmospheric and oceanic flows. The DiRoS experiment also falls within this scope, the main goal is to understand better the atmospheric dynamics of the giant gas planets.

For example, researchers have long known that Saturn—like the other gas giants (and even the Sun)—rotates differentially around its axis. Its equatorial regions complete a rotation faster than the polar regions. When gases or fluids circulate at different speeds along a boundary, shear arises, and under suitable conditions, regular wave patterns can form—this is why we see a perfectly regular, 30,000 km-wide hexagonal cyclone at Saturn’s north pole. A similar phenomenon is demonstrated in the following video from the Kármán Lab:

In the simple experiment shown above, pink-colored water was poured into a special “bucket”, the bottom of this bucket was rotated while the vertical side walls remained stationary. The shear arises here because the fluid in the center tries to move with the rotating bottom, while fluid elements near the stationary wall are slowed down by contact. The combined effect produces a regular triangular vortex, which becomes clearly visible on the water’s surface.

However, unlike the “bucket,” Saturn is nearly spherical—so to study this configuration, you need a spherically shaped, differentially rotating free water surface—a giant droplet. Such an experiment can’t be done on Earth, but it can in microgravity! In space, it’s possible to create a free spherical water surface, because expelled water naturally forms a sphere thanks to surface tension.

The experimental platform developed under the DiRoS program allows the astronaut to set the attached water droplet rotating differentially, while tracking particles mixed into it can be recorded on video. These recordings can contribute to better understanding the atmospheric circulation of giant planets—and, to some extent, flow instabilities in Earth’s own atmosphere.

Cover Photo: Tibor Kapu getting familiar with the Columbus module at the European Space Agency / HUNOR – Hungarian Astronaut Program