The search for extraterrestrial life — and can we broaden our ideas about it?

In the search for extraterrestrial life, we generally look at planets that are more or less similar to Earth. This week, 19–23 January 2026, astronomers from all over the world are coming to Groningen to talk about this type of rocky planets at the Rocky Worlds 4 conference. ‘But it is possible that some of these rocky planets and their atmospheres are very different from Earth,’ say Inga Kamp and Floris van der Tak, astrophysicists at the University of Groningen. For example, Kamp discovered that the gas and dust rings in which planets form near small stars — which are the most numerous in the Milky Way — are composed of entirely different molecules.

FSE Science Newsroom | Text Charlotte Vlek |Visual editing Leoni von Ristok

Mars has empty riverbeds, Enceladus (one of Saturn’s moons) has liquid water below a layer of ice, and Titan (another of Saturn’s moons) has an atmosphere and liquid hydrocarbons. These are conditions that may enable or have enabled life. It is only when you see something unusual happening in the atmosphere that you genuinely have an indication of potential life, according to Van der Tak: ‘You see, the Earth’s atmosphere contains both oxygen and methane. These gases should not be able to exist alongside each other because they would immediately react with each other. Nevertheless, these gases are present because the methane gas is continually supplemented by the cycle of life.’

Van der Tak is hoping to see something like that with the upcoming international LIFE mission, something he is currently working on for SRON, the Space Research Organisation Netherlands. A new space telescope is going to observe directly a few hundred planets outside our Solar System. Such exoplanets are at present mainly observed indirectly, as a shadow in the light of a star behind them. By eliminating that light using smart techniques, the LIFE mission will make it possible to take direct measurements, for example of the temperature of the exoplanet.

By the way, this mission is not aimed at taking photographs of extraterrestrial beings. ‘I am searching for something like bacterial life,’ says Van der Tak. ‘Or actually, only for something unusual in the atmosphere that may be an indication of life. ‘What that something unusual is, you never really know beforehand.’

Can we extend the boundaries of the habitable zone?

‘We are currently drawing up lists of likely candidate planets where life might be possible,’ says Van der Tak. ‘Planets where life is possible must, at least, meet three conditions: (1) there must be liquid water; (2) there must be an atmosphere; and (3) there must be some kind of solid surface.’ Okay, that water could also be a different liquid, for example Titan’s liquid hydrocarbons.

But let us assume for the moment it is water: in that case, a planet must be at a certain distance from its star for the water to be liquid. That distance is referred to as the habitable zone, within which the temperature is just right. ‘However, this relies on all kinds of assumptions,’ explains Kamp. ‘A planet’s temperature is also determined by the gases in its atmosphere; think of the greenhouse effect that we are familiar with here on Earth. So maybe liquid water is possible outside that habitable zone, depending on the planet’s composition.’

The stuff that's baked into a planet

To investigate what planets and their atmospheres could be made up of, Kamp is looking at the phase in which planets first form, in the protoplanetary discs — thin discs made up of gas and dust particles around a young star. ‘Look, you can study existing planets, but you often don’t know much more than their mass and their size. We are looking at the early formation of planets and assume that the material that orbited such young stars in the early phase will become part of those planets.’

‘We are seeing many different compositions,’ reports Kamp, who often compares hundreds of protoplanetary discs. ‘For example, we are seeing stars that contain much more sulfur than the Sun, which could then potentially be present in their protoplanetary discs.’ Colleagues in the lab showed that that has consequences for a planet’s core and mantle. On Earth we have an iron core, but you would expect iron and sulfur to react with each other in such a sulfur-rich planet. ‘And this, in turn, has consequences for, for example, the magnetic field, the CO₂ cycle, and plate tectonics; all of that can be very different on such a planet.’

Furthermore, Kamp and colleagues discovered that the composition of a planet is possibly different in smaller stars compared to stars with a size similar to that of the Sun. And exactly those smaller stars are widespread in the Milky Way and are often on the list of likely candidates for life. Their mass is approximately one tenth of that of our Sun, and the planets near such stars could possibly contain much more hydrocarbons than planets near Sun-like stars. Kamp now wants to find out whether that is indeed the case in a new project for which she recently received a grant. ‘We would like to broaden the ideas about what a rocky planet could be made up of. That will help us better understand where to search for life.’

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