What other species are there in space

Technical progress in astronomy In 20 years we will know if there is extraterrestrial life

One of the greatest unsolved questions of mankind could soon be answered: Are there other living beings in the universe or are we alone? A new generation of extremely large telescopes should provide the crucial information, says astronomer Markus Kissler-Patig from the European Southern Observatory (ESO). It could be in the next ten to twenty years at the latest.

Kissler-Patig, astronomer at the scientific headquarters of the Southern Observatory in Garching near Munich, has worked on the construction of the "Extremely large Telescope" (ELT) on the summit of the Cerro Armazones in Chile. The ESO project should be completed by 2024 and will then be the largest telescope in the world with a mirror diameter of almost 40 meters. Among other things, it is intended to provide more information on the atmospheres of planets outside the solar system that have already been discovered and thus provide answers about whether there is life there.

SETI made very daring assumptions about aliens

Mankind has been searching for clues to extraterrestrials for over 30 years with some scientific effort, but so far without success. The US SETI Institute has been listening for radio signals from space that are supposed to give clues to extraterrestrial technology since 1984.

This restricted the search to intelligent forms of life that use a technology similar to that of humans, "and maybe spark something for us," says Kissler-Patig. In the 1960s and 70s, this approach was very inspiring. "It resulted in astrobiology programs being developed and NASA making the search for life its business," he says.

However, it was very daring to assume that there is a human-like civilization that communicates with us precisely when we can listen to it. "Nevertheless, it was an important first step and, until the 1990s, our only chance to find life beyond the solar system."

Optical telescopes bring about a breakthrough

In the meantime, the focus has shifted because optical telescopes have once again become the most important instruments in research. With their help, scientists have discovered more than 3,000 exoplanets over the past twenty years. For around ten years now, researchers have been able to determine how big the planets are, whether they are made of gas or - like Earth - are rocky planets.

Astronomers now also know about 50 of these celestial bodies that they are in the so-called inhabited zone. This means that their distance to the star of the respective system is exactly so great that the temperatures on the surface allow water in the liquid state. So there could be living beings that, like us, use water for their metabolism.

Oxygen is the most important indicator for life

So far, however, astronomers have mostly been blinded too much by the light from the stars. The upcoming, much larger telescopes such as the ELT should enable more distinctions between stars and planets flying by and thus bring new knowledge, for example about the atmosphere of the distant earths. The central questions are: Is there really water there and which gases are present in the atmosphere.

The gases in particular could provide the strongest evidence of extraterrestrial life, explains Kissler-Patig. "At the moment, oxygen and the ozone that goes with it is our best candidate. It can only be found in abundance in the atmosphere if there are biological processes such as photosynthesis," he says.

The reason for this is the reactivity of oxygen, for example with iron. "Every bicycle chain rusts when it is left in the air, and so does every rock." The gas has to be refilled by plants practically all the time so that the concentrations currently measured on earth can occur at all.

Many types of life are possible

However, completely different types of life are also conceivable, for example based on silicon instead of carbon. And the traces of life on earth have also changed completely, 4.5 billion years ago they were completely different from today. This is why astronomers generally search for chemical imbalances in the atmospheres of exoplanets that cannot be explained by geological processes alone.

There are enough potential candidates for life among the already known exoplanets. If the scientists cannot find any clues even with the new instruments, this is also an important finding, says Markus Kissler-Patig. "Then we know that we have to take even better care of our planet."

Correction note: In an earlier version of this article, the planned mirror diameter was given as over 20 meters. This is wrong. The main mirror of the ELT will have a diameter of 39 meters.