MAN had been searching for a companion since decades.. i mean a companion from outer world.. from the blank dark space..
there had been various incidents when people complained that they had sighted an UFO....
in simple terms vehicle of aliens..(life from other planet).. did those people really see UFO's...
who knows..??
but i can say one thing few became popular n rich...
Directors cashed upon people belief n became rich...
movies like ET,Independence day,Star wars n many more.. r based on the same concept..
k lets come to the point..
about extra terrestrial life..
Few people believe n few dont .....
but man has his own fears so we have many missions to space..
one of them is.....
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One of Darwin's telescopes |
Darwin will be a flotilla of four or five free-flying spacecraft that will search for Earth-like planets around other stars and analyse their atmospheres for the chemical signature of life.
In addition the flotilla will be able to carry out high-resolution imaging using aperture synthesis, to provide pictures of celestial objects with unprecedented detail.
Looking for extrasolar planets, that is, planets orbiting around stars, is very hard. Even for nearby stars, it is like trying to see the difference between the feeble light from a candle next to a lighthouse from a point 1000 kilometres away.
At optical wavelengths, a star outshines an Earth-like planet by a thousand million to one. Partly to overcome this difficulty, Darwin will observe in the mid-infrared. At these wavelengths, the star-planet contrast drops to a million to one, making detection a little easier.The science objectives of DARWIN are:
- to detect and analyse Earth-like worlds
- to detect atmospheres on these planets and to search for gases that can indicate life
- to solve the technological challenges of far infrared interferometric imaging in space
 | Darwin is an infrared (6 - 30 microns wavelength) nulling interferometer. It will reduce the intensity of the host star, so the faint reflected light from planets can be detected. DARWIN will detect gases in the atmospheres terrestrial exoplanets. The earth's spectrumis shown opposite has easily identifiable lines of water, carbon dioxide, oxygen and ozone |
Looking for life
Another key reason for observing in the infrared is because life on Earth leaves its mark at these wavelengths. 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 others, such as water, leave their fingerprints by absorbing certain wavelengths of infrared light. Darwin will split the light from an extrasolar planet into its constituent wavelengths, using a device called a spectrometer. This will show the drop in light caused by the presence of certain gases in the atmosphere, allowing them to be identified. If they are the same as those produced by life on Earth, rather than by non-biological processes, Darwin will have found evidence for life on another world.
Why does the mission have to be in space?
The mission has to be in space for two reasons. Firstly, on Earth, the atmosphere blocks the mid-infrared wavelengths of light that Darwin is designed to observe.
At room temperature, the telescopes would themselves emit infrared radiation, swamping their own observations. It would be like using a conventional telescope to perform optical astronomy with a bank of floodlights pointing into the telescope.
However, in space it is so cold that the telescope can be designed to be just 40 K (-233 °C) whilst the actual detector can be reduced in temperature further to just 8 K (-265 °C). This all but stops the telescope radiating its own infrared signal and allows it to search for the faint light of distant planets.
How will Darwin find planets?
There are two overwhelming challenges when trying to take images of planets around other stars. Firstly, the planet will appear to be very close to its parent star. Secondly, the star will outshine the planet by a factor of a million or even a billion.
The first condition requires that Darwin possess superb resolving power. This is the technical term for a telescope's ability to discern closely spaced celestial objects. The larger the telescope, the better its resolving power.
To see planets around nearby stars would require a telescope of roughly 30 metres in size and this is way beyond the current limits of technology. The Hubble Space Telescope (HST) is just 2.3 metres and even the planned Next Generation Space Telescope (JWST) will be, at most, 6.5 metres. The largest telescopes on Earth are 10 metres in diameter.
To overcome this limitation, Darwin will use a technique known as interferometry. Pioneered during the 1950s by astronomers in Cambridge, United Kingdom, originally using radio telescopes, the technique uses a number of smaller telescopes and combines their individual signals to mimic a much larger telescope.
The technique can also be applied to optical and infrared telescopes and will be used by Darwin. Six separate space telescopes will combine their individual signals to produce the final, high-resolution image.
The second problem means that Darwin must cut out the blinding light from the central star. In 1978, Ronald Bracewell, a physicist and electrical engineer interested in telescopes, pointed out that an interferometer can do this too if the signals from some of the telescopes are delayed slightly. By precisely adjusting this delay, the central bright object is 'cancelled' out, allowing the faint, nearby planet to stand out. Working like this, the instrument is known as a nulling interferometer.
Technologies:
Darwin is a highly complex optical
system containing a range of advanced
optical, infrared, cryogenic and photonics
technologies. The next article provides an
overview of the mission science and
technical challenges
 | Nulling Interferometry adds a 180 degree phase shift in one of the light paths of the interferometer. By placing the image of the star in the moddle of the destructive fringe, or null, the faint reflected light from nearby planets to the star can be |
Launch:
Each of the four telescopes will have a diameter of around 3.5m in diameter based on the design used for the Herschel mission. The small flotila will be launched on 2 Soyuz-Fregat rockets.
Because the telescopes will be used to detect infrared light, they must be shielded from the Sun's rays. If not, sunlight would heat the telescope, causing it to emit its own infrared radiation, blinding its view of the distant planets. To prevent this, each telescope is equipped with a large sunshield.
During launch, the sunshields are wrapped around their telescopes to save space. Once Darwin is in orbit, the shields are deployed like unfurling an umbrella. Although, Darwin will face away from the Sun, it must also tilt up and down by an angle of 45 degrees, to see all of its target stars, whilst keeping the telescope's tube in the shade, requiring a large sunshield with a diameter of 7.4 metres.
A platform will sit behind the sunshield, consisting of a communications antenna, various receivers to detect the motion of the spacecraft and a small propulsion system. Below this, constantly facing the Sun, will be a solar array to generate power.
Journey
Darwin's launch date is to be defined in the context of ESA's Cosmic Vision scientific programme. For the launch, ESA will use two launches with Soyuz-Fregat rockets, probably from ESA's Spaceport at Kourou in French Guiana.
Instead of an orbit around the Earth, Darwin will be placed far away, beyond the Moon. At a distance of 1.5 million kilometres from Earth, in the opposite direction from the Sun, Darwin will operate from a special location known as Lagrangian Point L2.
History
The idea for this mission was proposed in 1993. Darwin's goals were to detect Earth-like planets circling nearby stars and to set constraints on the possibility of the existence of life as we know it on these planets.
Since then, the goals have been expanded to include the capability to provide high-resolution images, at least ten to one hundred times more detailed than the James Webb Space Telescope (JWST), a joint ESA/NASA mission due for launch around 2013.
Since the mid-1990s, ESA has been working on a feasible design. Scientists and engineers have redesigned the Darwin flotilla and have found ingenious ways to reduce the demanding technological requirements of the various spacecraft. ESA continued to investigate whether there was any way to achieve the same scientific results using just four free-flying telescopes instead of eight.
Partnerships
NASA is also considering missions similar to Darwin. They have a programme called the Terrestrial Planet Finder (TPF) and is the subject of on-going studies. TPF consists of two separate missions, consisting of a single spacecraft which could only study a few of the most nearby stars. The second mission, with a performance similar to Darwin, with a launch foreseen some years after the single spacecraft mission.
Despite some great efforts put into this article some errors might have crept in so i request the readers to kindly report them as a comment below.
Your Suggestions will be greatly entertained.
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