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Transit of Venus demonstrates method to be used when searching for life

When the planet Venus on June 6 moves across the solar disk we get a demonstration of the method which has the highest probability of giving evidence of alien life forms. In 2012 the search for terrestrial planets has reached a decisive phase.


During the transit: We can observe the atmosphere of Venus as a bright arc outside the solar disk. This exceptionally sharp image was made with the 1 meter Swedish Solar Telescope at La Palma. Due to its sharpness there are also hints of the atmosphere around the rest of the planet.
Photo: Swedish Solar Telescope/Institute for Solar Physics

For more than three years NASAs space observatory Kepler has been in space to search for terrestrial planets around other stars. The observatory is looking for temporary, small reductions in luminosity of stars that are fairly equal to our Sun. The luminosity reductions are sometimes caused by planets transiting the star and blocking a small fraction of the stellar light. It is necessary to observe the stars for several years to prove that the changes in luminosity are due to planets. But then many details about the planets can be calculated, including their orbits, size, mass, density and temperature. More than 100 000 stars have been surveyed by Kepler.

A terrestrial planet will typically reduce the luminosity by only 1/10 000, or 0.01 percent. The mini eclipse may last for 1 - 16 hours. In order to learn more about the conditions on the planets possible detections are followed up by studies with other telescopes in space and at ground.


Using specialized instruments the atmosphere of the planet can be studied. When the planet transits its mother star some stellar light will pass through the atmosphere of the planet. At some wavelengths (colors) the stellar light will be absorbed by the substances in the atmosphere. By measuring these “fingerprints” the chemical compositions of exoplanetary atmospheres can be measured. The method has already been applied to find the composition of atmospheres around exoplanets, even though these have never been observed directly, they have never been photographed and we will probably never be able to visit them.

Move the arrow over the illustration and the animation will start, if it has not begun automatically. (GIF loop, requires JavaScript); To view or download an MPEG-animation (270 K) click on the illustration.

When a planet transits its mother star it will eclipse some of the light. The phenomenon can be observed with modest instruments. Advanced spectrometers can reveal signs of oxygen and water in the atmopshere of the remote exoplanet.
Illustration and animation: STARE project based on work by Hans Deeg, from
'Transits of Extrasolar Planets'

An image of Venus just one day after its transit in 2004. The atmosphere can be seen as a bright ring around the night side of the planet. This is a truly unique view!
Photo: Odd Trondal

If we detect substantial amounts of oxygen or ozon we have the first solid evidences for alien forms of life. These substances react quite easily and would disappear rather soon (in geological and astronomical terms) unless something replenishes the loss. The source could be photosynthesis. If all forms of life were eradicated it would take “only” 30 – 40 million years before most of the oxygen (and ozone) had gone. The oxygen would react with other substances in the atmosphere and in the ground.

Photosynthesis means that plants or other green life forms are present, but more advanced forms of life could of course also be present. If someone had observed the Earth from outside our Solar system 200 years ago, they could have used the same method to find the presence of oxygen and ozone and they would have known that the Earth was inhabited by plants. But they would have detected humans, although they were about as intelligent as we are today. But 200 years radios were not invented and our presence was therefore not revealed.

Kepler has already found numerous planets and planetary candidates and many of these will be examined in 2012. Some of the planets are about the size of Earth and may contain liquid water. Researchers from all over the world are therefore extremely interested in the results of the ongoing studies!


On June 6 we will have a demonstration of the method. Without telescopes, only with the protection of eclipse glasses we can observe a planet with a dense atmosphere transiting its mother star – the Sun! Using eclipse shades we can see Venus as a black spot while it slowly slides acros the solar disk, in the same way as exoplanets transit their mother stars.

The atmosphere of Venus is quite dense, the planet is about the same size as the Earth and the solar light will pass through the upper atmospheric layers during the transit. This will be a unique, natural demonstration of the most promising method for searching for alien life. Of course we know there is no life on Venus, but the method will be used to examine thousands of distant planets with more promising conditions than Venus can offer.

For almost 7 hours Venus will cross the solar disk early in the day of June 6. The atmosphere should be particularly easy to spot when the planet is entering and leaving the disk. During the rest of the transit special instruments can be used to tell the chemical composition of the atmosphere around Venus.
Photo: NASA, collage: / Knut Jørgen Røed Ødegaard


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Contact: Knut Jørgen Røed Ødegaard, PO. Box 1029 Blindern, NO-0315 Oslo, NorwayPhone: (47) 992 77 172 E-mail: