Exoplanets » The Darwin Mission

The concept of the Darwin Mission was first proposed in 1993 by the European Space Agency and studies were ended or put on hold in October 2007. It was envisaged that a constellation of four 3-4 meter infrared telescopes acting together would have worked like a single large telescope, with a diameter of up to several hundred metres. The object was to search for planets the size of the Earth for signs of life which is an extremely difficult thing to do. Even for nearby stars, it is like trying to see the feeble light from a candle next to a lighthouse 1000 km away. At optical wavelengths a star outshines an Earth-like planet by a thousand million to one. Partly to overcome this difficulty, Darwin proposed to conduct observations in the mid-infrared. At these wavelengths the star-planet contrast ratio drops to a million to one, making detection a little easier. Quite apart from this, Darwin’s observations would have been carried out in the infrared since life on Earth leaves some of its marks at these wavelengths in the form of infrared spectra.

On Earth, biological activity produces gases that mingle with our atmosphere. For example, plants give out oxygen and animals expel carbon dioxide and methane. These gases and other substances, such as water vapour, leave their fingerprints by absorbing certain wavelengths of infrared light. Darwin would have split the light from an extrasolar planet into its constituent colours, using an instrument called a spectrometer. This would show the drop in light caused by specific gases being in the atmosphere, allowing them to be identified. If they turned out to be the same as those produced by life on Earth, rather than by non-biological processes, Darwin would have found evidence for life on another world. To meet its objective to find and investigate Earth-like planets, Darwin would have used a technique called 'nulling interferometry'. The light reaching some of the telescopes would have been delayed slightly before being combined again. This would have caused light from the central star to be 'cancelled out' in the resultant data. Light from planets, however, is already delayed between one telescope and the other since the planet is to one side of where the telescopes are pointed. By delaying the light a second time, the light from the planet would be combined constructively, showing the planet.

If not for this 'nulling', the starlight would overwhelm the planet's feeble glow for Darwin to work, the telescopes and the hub must have stayed in formation with millimetre precision. ESA was planning to achieve this aim using a variation of the highly successful Global Positioning System (GPS) that provides so much of the satellite-based navigation on Earth. But this was not enough, as the light collected by the telescopes was supposed to be recombined at very high precision. A deviation of more than just 100 thousandths of a millimetre could have ruined the observation. Although this sounds like an impossible feat of accuracy, ESA together with European industry had started some of the pre-developments for the necessary metrology and optical equipment that would allow such precision. The illustrations below are taken from the European Space Agency's library on the internet and due credit is extended to ESA in reproducing them below.

Ray Goodwin

Somewhere there are mountains
Glistening in the snow
Somewhere there are mountains
That we shall never know

Somewhere there are rivers
Flowing fast and free
Somewhere there are rivers
That we can never see

Somewhere there are oceans
And sun drenched island sands
Forests full of creatures
In vastly distant lands

Somewhere there’s a planet
Beneath an alien star
The people watch our tiny sun
And wonder where we are

One day perhaps we’ll find them
Across the void of space
Perhaps through ways as yet unknown
We’ll meet them face to face

The author of this web site Ray Goodwin holds B.Sc. Degrees from London University in Chemistry, Geology and Physiology and an M.Sc. in Biochemistry. He has spent most of his professional life teaching in Colleges of Technology. On his retirement he has entered the fields of astronomy, astrochemistry, astrobiology and space sciences. He has spent a great deal of his retirement in visiting amateur astronomy societies and in attending European Space Agency Symposia in ESTEC in the Netherlands and other scientific conferences in England and Sweden. He regularly attends the yearly European Astrofest in South Kensington London and other meetings in the UK. He has written scientific articles and given a number of lectures on diverse scientific subjects.

Readers of this web site are invited to e-mail the author ( ray@lifeinthecosmos.com) and discuss their opinions of the topics dealt with and suggest any changes which they think may be helpful.

Life in the Cosmos Website
Version 01.00 - April 20, 2015.