Darwin Look For Alien Life
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Is Earth the lonely outpost of life? Does life really exist elsewhere in the universe? To find an answer, astrobiologists from European Space Agency have embarked on an ambitious plan to launch a spacecraft called Darwin, which will eavesdrop on alien planets for signs of life. By 2014, an Ariane-5 rocket will dispatch Darwin to a remote orbit beyond the Moon, at a distance 1.5 million kilometers from Earth. It will wander there for five years and look for Earth-like planets with subtle signs of life.
Darwin’s eyes are more powerful than human eyes. Darwin’s eyes are actually six telescopes with a master satellite and a hub. These telescopes will observe in the mid-infrared region of light, which human eyes cannot see. Why look for infrared light for signs of life? Life on Earth has been around for thousands of millions of years, but humans have used radio waves for less than a century. So, the detection of infrared light is better than trying to look for emission of radio waves, which will only locate intelligent life like us. But, by detecting infrared radiation even the presence of humble life forms like viruses or bacteria can be found. “If other planets follow Earth’s pattern, it is much more likely that they will be inhabited by dinosaurs or even bacteria than something that can count,” says Malcom Fridlund, project scientist for ESA’s Darwin mission.
Any warm objects, animate or inanimate, emit infrared radiation. On Earth, life leaves its imprint in the shape of infrared radiation. On Earth, biological activity produces various gases. For instance, plants give out oxygen and animals expel carbon dioxide and methane. These gases, and other substances, such as water absorb certain wavelengths of infrared light. With this clue, an alien eavesdropper armed with infrared light detection equipments can know that Earth is teeming with life. In similar way, Darwin will look for alien life on other planets.
In the 1970s, the British scientist James Lovelock pointed out that, just by breathing, life affects the composition of the Earth’s atmosphere. “It is better to look for similar effects as a way to search with telescopes for life on other planets,” said Lovelock. “Thus, you can study the composition of an atmosphere by splitting a planet’s light into a rainbow of colours.” The image of colours is called ‘spectrum’ which contains dark lines made by various chemicals present in the planet’s atmosphere. The spectrum is like a chemical signature of a planet, which helps scientists to guess whether a planet is humming with life.
Darwin will look for oxygen. We know that oxygen is closely associated with life. Some life forms use it and some produce it as waste. Without life, all free oxygen in a planet’s atmosphere would vanish within just four million years, as it reacts so easily with other chemicals. “The best estimates suggest that Darwin will be able to detect the build-up of oxygen caused within a few hundred million years of life’s origin,” says Fridlund.
Darwin will also be on the lookout for ‘ozone’, a form of oxygen. The ozone layer on Earth filters out the harmful ultraviolet light, which helped in the origin and evolution of life. It will also see carbon dioxide, water, and, in certain cases, methane. “The general consensus is that if we find ozone, lquid water, and carbon dioxide simultaneously, it will be a strong indicator of life’s presence,” says Fridlund.
Astrobiologists from ESA dub such signs of life as ‘biomarkers’. Such ‘biomarkers’ leave their fingerprints in the infrared light they absorb. As light of various wavelengths emanating from alien planets radiate into space, Darwin’s six telescopes become active like detective. These telescopes will catch the signs of ‘biomarkers’ recorded in the infrared light. Then they will feed the information to a central processing unit called hub. Now, a spectrometer in hub will split the infrared light into their constituent parts and the resultant information will be radioed back to Earth. From radioed back information, scientists on Earth will try to infer whether the signs will have emanated from a planet inhabited by life. The master satellite sits behind the six telescopes and look up at them like a watchdog. It also ferries commanding signals from hub to six telescopes thereby synchronizing their activities.
In space, it is very cold. But, Darwin’s telescopes are designed to work at just -233°C. The actual detector can remain active even when temperature drops to -265°C. Such a cold climate prevents the telescopes from radiating their own infrared radiation allowing them to search for the faint light of distant planets. At the wavelengths of visible light, a star outshines an Earth-like planet by a thousand million to one. It becomes difficult to locate an Earth-like planet. Darwin’s infrared vision overcomes this problem. Having infrared vision Darwin reduces the star-planet contrast to a million to one. It increases the chances of detecting an Earth-like planet.
The work will continue even after Darwin finishes its survey of the nearest several thousand star-planet systems. After finding a living planet, the quest will be on to understand the nature of its life forms. Future missions may look for chlorophyll as a biomarker. This molecule helps plants and certain bacteria to trap sunlight, which runs their various biochemical activities. “Finding next generation of biomarkers is a very active field of research at the moment,” concludes Fridlund.
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