Life in Space

Space. The final frontier. These are the voyages of Ravit Helled as she searches for planets beyond our solar system – planets that might harbor life. As enticing as the introduction to Star Trek adapted to suit the University of Zurich may sound, the idea of actually discovering alien life somewhere in space really is awe-inspiring. “Whether we’re alone in the universe is one of the fundamental questions of humankind,” says Ravit Helled, astrophysicist and planetary researcher at UZH. “How unique is the Earth? How do planets form and what conditions are needed to allow life to develop on them? We’re trying to answer these questions.”

In actual fact, science will probably soon be able to characterize exoplanets, which are planets beyond our solar system, with greater precision. This will be possible thanks to a space mission appropriately named LIFE, an abbreviation for Large Interferometer For Exoplanets, which is being spearheaded by group leader Sascha Quanz from ETH Zurich. The aim of the mission is to position multiple satellites in space so that they combine to create a giant telescope. This collective interferometer is designed to measure light in the medium infrared range, providing information about the surface and the atmosphere on the planets that are studied. This should make it clearer whether the conditions on each of the planets are capable of supporting life – at least that’s the hope.

Research conducted by Ravit Helled recently provided a key indication that it might work. Together with the researchers from ETH Zurich, her team examined the Earth as a test object and demonstrated that LIFE would in fact make the Earth recognizable as an inhabitable planet.

“Our view of planetary systems has long been limited to what we can see in our own solar system,” says Helled. So we focus on Earth-like terrestrial planets such as Mars or Venus, ice giants such as Uranus and Neptune, and gas giants such as Jupiter. But when the first exoplanet orbiting around the Sun-like star 51 Pegasi was discovered in 1995, there was astonishment at how this giant planet was much closer to its star than was considered theoretically possible. “Planets and their emergence are incredibly diverse. Examining this diversity will help us to estimate how prevalent planets like Earth are.”

Ravit Helled’s enthusiasm for what she does is palpable. She speaks with gusto and her office also reflects her lively demeanor, with a desk covered in books and paper, a round table for meetings, a sofa, textbooks on the shelves of course, but there’s also art – sculptures and pictures – and in the window there are a number of large plants that almost make the office feel a little like a jungle. It’s comfortably chaotic. “I spend a great deal of my time here, and it feels like a second home to me,” says Helled. The astrophysicist also feels very much at home with foreign planets. Her favorite is Jupiter, the largest planet and probably the only true gas giant in our solar system.

Beyond our solar system, astrophysicists have now discovered more than 5,000 different planets, but very little is known about them. “These celestial bodies are simply too far away to allow us to study them,” says Helled. The nearest exoplanet is Proxima Centauri b, and it’s 4.2 light years from Earth, which is around 40 trillion kilometers. By comparison, the Voyager 2 space probe launched into space in 1977, left our solar system 41 years later and, unless something happens to it, will pass by the star Sirius, which is 4.3 light years away, around 300,000 years from now. “So we’re talking about distances that we simply can’t cover within a timeframe that we humans can fathom.”

Yet this LIFE mission is designed to enable us for the very first time to at least analyze the exoplanets closest to our planet. The planned combination of different satellites will make it possible to distinguish the light spectrum of the planets from that of their stars. “The measured spectra will then be averages in space and time for what we would consider to be an incredibly tiny dot in space, and the question will be whether this data provides any indications of conditions that could support life,” explains Helled. Examples of such indications would be signs of water or gas molecules in the atmosphere that extend beyond the simplest molecules like hydrogen (H2) or helium (He) – including oxygen (O2), carbon dioxide (CO2), ozone (O3) or methane (CH4).

These were the sort of signatures the team was looking for when it tested the future LIFE mission using Earth as an example. To do this, the researchers essentially transformed the Earth into an exoplanet by studying our planet from a simulated distance of 30 light years away. They used data from a device for measuring the Earth’s atmosphere on the research satellite Aqua to generate the Earth’s emission spectra that would be captured from that distance. The team tested three different directions of observation – the two views of the North Pole and South Pole and an equatorial view – and points in time in two different seasons in the Earth year, once in January and once in July.

The result was that the team was able to detect CO2, ozone, water and methane in the simulated infrared spectra of the Earth’s atmosphere. Ozone and methane in particular are crucial because these gases are produced by the creatures that live on Earth. In addition, the data can be used to identify surface conditions that indicate the presence of water, as well as signs of a mild climate. And the researchers were able to record this signature indicating possible life in all the Earth’s orientations that they tested. “This is important because with exoplanets we won’t know the orientation in which the data is recorded,” explains Helled. What she and her colleagues have shown is that LIFE essentially makes it possible to identify exoplanets that are inhabitable or in fact inhabited.

Even the seasonal variation between January and July was discernible in the data. This is relevant because researchers believe that seasonal variations in the composition of the atmosphere are also strong biosignatures, providing signs of possible life, as Helled explains. The results also showed that the gas signatures indicating life were identifiable regardless of the seasonal variations. “Measured from afar, this means the Earth would be identified as being inhabitable not just in any orientation, but also in any season.”

However, the astrophysicist says it is also possible that entirely different types of planets may produce life. “We know that even here on Earth organisms can develop under extreme conditions, for example in very hot temperatures or under high pressure in the ocean.” What’s more, two years ago in a collaboration with the University of Bern, Helled’s research group demonstrated that under certain conditions, water could exist even on planets with a dense hydrogen and helium atmosphere. This is quite apart from the fact that it’s also possible to imagine life that is not based on carbon, as it is on Earth. “When we conduct a search, we simply start off quite pragmatically by looking for what we know best,” says Helled. “Identifying Earth-like exoplanets is the first obvious step.”

For Ravit Helled, looking to distant planets is also a way of looking at our own Earth: “We should be grateful for our planet with the ideal conditions it offers to support us and all its other living creatures,” she says. “And we should look after it properly.”

This article is part of the  UZH Magazin «Kostbare Vielfalt»