Waiting for data from Jupiter’s icy moons

Hauke Hußmann - GALA
Planetenforscher Dr. Hauke Hußmann mit einem "aufgeschnittenen" 1:1-Modell der optischen Einheit des Laser-Altimeters GALA.

Since 14 April 2023, the instrument for which planetary scientist Hauke Hußmann has been responsible in recent years has been moving further and further away from him. The GAnymede Laser Altimeter (GALA) is travelling to the Jupiter system on board ESA’s  Jupiter Icy Moons Explorer (JUICE) spacecraft. It will arrive in eight years. Physicist Hußmann is the Principal Investigator for the instrument, that is, the scientific lead. What does the work consist of before such an instrument sets off on its long journey to the exploration site? And what does a researcher actually do during the time when he can neither see nor touch the instrument? In this interview, our planetary scientist tells us what is happening until GALA points its lasers at the surface of Ganymede from a distance of approximately 500 kilometres in the summer of 2031.

Where will you be in July 2031?

I hope to be at DLR in Berlin-Adlershof and see when the data from the Jupiter system arrives. However, we will already get our very first dataset on 15 May 2023 – when we will switch on GALA and do a technical check-up. This is the first time to see if everything has survived the launch. We will test the entire functionality of the instrument. But of course, this will not be scientific data.

Why are the icy moons of such a distant planet and their exploration so special for you?

The Galilean moons (from left to right) Io, Europa, Ganymede and Callisto



I am a planetary scientist and, of course, interested in the most diverse planetary bodies – not just the icy moons of Jupiter. With the four Galilean moons of Jupiter, we are dealing with four very different planetary bodies. They all have had very different developmental histories, and for the icy moons – especially Ganymede, Europa and Callisto – we know or rather suspect from previous missions that there is liquid water beneath their icy surfaces. In the case of Europa and Ganymede, this could be more water than Earth’s oceans hold. In addition, energy sources are available, so Jupiter’s moons can also be possible candidates in the search for life in the Solar System beyond Earth. The important question is – ‘Is there life beyond Earth?’

The GALA instrument will fly in a rather hostile environment at an almost unimaginable distance. What is it like to send your instrument off knowing that from now on, it is out of your reach?

It is not completely out of reach, even though we cannot repair anything on the hardware, of course. When we launched the rocket with the JUICE spacecraft, we had no control, but switching on the instrument is a different story because we will see the first data and find out how the instrument is doing. If we see malfunctions, we can change the instrument’s software as necessary.

When does the process of working on such a mission and such an instrument begin?

It really goes back a long way. ESA’s first plans to fly to the Jupiter system, which I was also involved in, date back to 2007. A mission proposal like this is in strong competition with other mission proposals in ESA’s selection process. It takes years of preparatory work, because the mission concepts have to be very elaborate, and the feasibility has to be proven. The JUICE mission was decided upon in 2012, the instruments were selected in 2013, and we started with the design, construction and testing of the GALA instrument. The launch took place in 2023, and the arrival at the Jupiter system will be in 2031.

As a planetary scientist, do you need a lot of patience and perseverance in your job?

Yes, definitely. If only to get a mission off the ground because the time spans are so long. You need patience and perseverance. And of course, the flight duration to the outer Solar System is long – it will be a while before we get the first data. So, you definitely need the patience to wait for the data from Jupiter.

What kind of education did you receive and what brought you to DLR?

I am a physicist and did my doctorate in Planetary Physics – even then, with a thesis on Jupiter’s moons Io and Europa. Then I came to DLR in 2007. DLR gave me the opportunity to get involved in missions and instruments. That is something special, that the science is so closely linked to the instruments and missions.

What is your job as Principal Investigator for GALA and the JUICE mission?

The surface of Jupiter’s moon Ganymede



The important thing is that the whole project is based on a large and international team of people with very different areas of expertise. The engineers who build the instrument have a very technical background and the scientists who are interested in the Jupiter system have a scientific background. As the scientific lead of an instrument, you have to keep the project going, you need to have funding and the necessary people in the right roles. One of my most important tasks was to define the science – what do we want to measure with the instrument, what do we want to achieve when we are at Ganymede, and what are the real scientific goals? One must work very closely with the technical team – what must the instrument be able to do, what performance must the instrument deliver? All of this is closely intertwined. We have all this expertise under one roof here at DLR.

I am also the link between the instrument team and ESA, which is responsible for the spacecraft. My tasks are varied, and you also learn a lot yourself. But it really only works as a team, and I have to keep it together. There has to be a good team spirit – even when things do not go the way we want. The team has to stay calm and look for solutions. Now we are on the road with a good instrument.

Is a mission then more or less a scientist’s life?

I am 53 and was lucky enough to be involved with Jupiter’s moons during my doctoral studies. The topic actually extends through my entire working life. And as the mission comes to an end, my retirement will start. But the work as a planetary scientist is cross-generational – I will not be the one who will primarily evaluate GALA’s data. It will be younger colleagues who are perhaps working on their doctoral theses. Such missions go on for decades.

What will you do during the eight years that the JUICE spacecraft is on its way to Jupiter?

We will conduct check outs every six months during the ‘flight phase’ to test the instrument. In September 2024, we will have a flyby of the Moon and hope to acquire data about the lunar surface. But during the ‘cruise phase’ to Jupiter, we will also point GALA at Earth and establish a laser link to a ground station on Earth to calibrate the instrument. The real excitement for us will come when we enter orbit around Jupiter and fly past the moons.

I am also involved in the laser altimeter for the BepiColombo mission to Mercury. We will arrive there in 2025 and measure Mercury’s topography. Right now, we are in the phase where we are preparing the scientific data acquisition. After arrival, we will be in Mercury orbit for several years, which will be my main project during that time. There are also new mission proposals that we are preparing. There are always several projects running in parallel for me.

In December 2034, JUICE will move from orbiting Jupiter to orbiting Ganymede – this will be the first time a spacecraft will orbit a moon that is not Earth’s. What would you like to see in the first dataset if you could wish for anything?

The JUICE mission will explore the moons of the gas giant Jupiter



When we reach orbit around Ganymede, we will measure its topography – we will create a 3D model of the surface in combination with image data from the JANUS camera. An exciting measurement is also to determine the tidal deformation of Ganymede’s surface. This will tell us whether an ocean actually exists in its interior. If there is an ocean, the surface of Ganymede is in fact deformed by tides. These have amplitudes of approximately eight metres, which we can measure with GALA. With our measurements, we can therefore detect a possible ocean and also draw conclusions about the thickness of the ice layer. So, how deep is the ocean? That would be my desired result – if what we have planned on based on model calculations works. However, we will also need the results of the other instruments on JUICE. That is what is so exciting – working with all the instrument teams to get the best science out of the data sets.