There’s life on Earth!

Indeed. We knew that. However, in the search for life in other parts of the universe, it is important to know what planets look like from a distance when there is life on them. The recent lunar eclipse helped astrophysicists gain insight into this – Earth has now been seen from ‘outside’.

2015.10.22 | Rasmus Rørbæk Christensen

This illustration shows how our planet’s atmosphere is illuminated by the Sun, making it possible to see bioindicators. This light could be detected on the surface of the Moon during the autumn eclipse. (Illustration: Stellar Astrophysics Centre, Aarhus University)

The red glow of the Moon concealed valuable data for the physicists, who were able to find information from our atmosphere. In a way, the Earth was virtually a slide that could be seen on the surface of the Moon during the eclipse. (Photo: Tina Temkiv)

While science and space exploration have made great advances since 1995 – when the first exoplanet was discovered in orbit around a star – there is still a long way to go to gain a complete understanding of conditions for life in the universe. One step in this direction is knowing how life leaves its mark on a planet’s atmosphere by means of bioindicators.

Researchers would like to observe the atmosphere around an exoplanet – one of the many Earth-like planets they helped to discover in recent years, including researchers at the Stellar Astrophysics Centre, Aarhus University. However, this is not possible with the instruments currently available to science.

So what should be done?
They are practising by observing the Earth’s atmosphere to see whether it is possible to find traces of life there. If this could be done, it would be much easier to know what life ‘looks like’ through an atmosphere and thereby find out which bioindicators to look for when the right instruments are available for looking further out into the universe.

The method used by physicists at Aarhus University is somewhat intricate. It involves looking at light from the Sun that has passed through the Earth’s atmosphere. This makes it possible to see whether the light has been affected by life processes on the way through the atmosphere.

During a total lunar eclipse, Earth is between the Sun and the Moon. The Moon is thereby illuminated by sunlight that slips past through the Earth’s atmosphere. In this way, it is possible to look for signs of life in our atmosphere. This is precisely what Mads Fredslund Andersen and his colleague Frank Grundal at the Stellar Astrophysics Centre managed to do. They measured the red-coloured Moon during the lunar eclipse on 28 September 2015 using the SONG telescope on the island of Tenerife.

“The Moon itself is a neutral grey colour, so it doesn’t affect the measurements of the filtered red sunlight. We know the actual composition of the sunlight very well, so if we subtract the sunlight’s ‘fingerprint’ from the light we measured by looking at the Moon during the eclipse, we’re left with the impact of the Earth’s atmosphere – and it worked,” says Mads Fredslund Andersen.

Within the narrow wavelength range covered by the SONG telescope, there were very clear signs of oxygen, which in itself is one of the obvious signs of life.

So the researchers have now demonstrated that there is life on Earth – should anyone be in doubt. And the fact that we can do it in this crafty way can possibly prove not only that life on Earth is quite intelligent, but also that we can eventually hope to find traces of life using the same methods when studying the thousands of exoplanets we already know about.

For more information, please contact

Research Assistant Mads Fredslund Andersen
Stellar Astrophysics Centre
Mobile: +45 2152 7146

Original article written by Ole J. Knudsen

Science and Technology, Public / media