Darwin (spacecraft)

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Darwin
Mission type
observatory
OperatorESA
Websitewww.esa.int/science/darwin
Orbital parameters
Reference system
Sun–Earth L2
RegimeHalo orbit
Epochplanned
 

Darwin was a suggested

interferometer array, and which would have also acted as a communications hub. There was also an earlier design, called the "Robin Laurance configuration," which included six 1.5 metre telescopes, a beam combiner spacecraft, and a separate power and communications spacecraft.[3]

The study of this proposed mission ended in 2007 with no further activities planned.[1] To produce an image, the telescopes would have had to operate in formation with distances between the telescopes controlled to within a few micrometres, and the distance between the telescopes and receiver controlled to within about one nanometre.[4] Several more detailed studies would have been needed to determine whether technology capable of such precision is actually feasible.[2]

Concept

The space telescopes were to observe in the

milliarcsecond
) infrared images, allowing detailed study of a variety of astrophysical processes.

The infrared region was chosen because in the visible spectrum an Earth-like planet is outshone by its star by a factor of a

billion.[3] However, in the infrared, the difference is less by a few orders of magnitude. According to a 2000 ESA bulletin, all spacecraft components in the optical path would have to be passively cooled to 40 kelvins to allow infrared observations to take place.[3]

The planet search would have used a

nulling interferometer
configuration. In this system, phase shifts would be introduced into the three beams, so that light from the central star would suffer destructive interference and cancel itself out. However, light from any orbiting planets would not cancel out, as the planets are offset slightly from the star's position. This would allow planets to be detected, despite the much brighter signal from the star.

For planet detection, the telescopes would operate in an imaging mode. The detection of an Earth-like planet would require about 10 hours of observation in total, spread out over several months.[citation needed] A 2002 design which would have used 1.5 metre mirrors was expected to take about 100 hours to get a spectrum of a possibly Earth-like planet.[5]

Were the Darwin spacecraft to detect a suitable planet, a more detailed study of its atmosphere would have been made by taking an infrared spectrum of the planet. By analyzing this spectrum, the chemistry of the atmosphere could be determined, and this could provide evidence for life on the planet. The presence of oxygen and water vapour in the atmosphere could be evidence for life. Oxygen is very reactive so if large amounts of oxygen exist in a planet's atmosphere some process such as photosynthesis must be continuously producing it.

The presence of oxygen alone, however, is not conclusive evidence for life. Jupiter's moon

photolysis of carbon dioxide. Photolysis of water vapor and carbon dioxide produces hydroxyl ions and atomic oxygen, respectively, and these in turn produce oxygen in small concentrations, with hydrogen escaping into space. When O2 is produced by H2O photolysis at high altitude, hydrogenous compounds like H+, OH and H2O are produced which attack very efficiently O3 and prevent its accumulation. The only known way to have a significant amount of O3 in the atmosphere is that O2 be produced at low altitude, e.g. by biological photosynthesis, and that little H2O gets to high altitudes where UV is present. For terrestrial planets, the simultaneous presence of O3, H2O and CO2 in the atmosphere appears to be a reliable biosignature, and the Darwin spacecraft would have been capable of detecting these atmospheric components.[5]

Candidate planets

Planet

Gliese 581 d, discovered in 2007, was considered a good candidate for the Darwin project.[6] It orbits within the theoretical habitable zone of its star,[7]
and scientists surmise that conditions on the planet might be conducive to supporting life.

Similar initiatives

The interferometric version of

Hypertelescope
project would be much more expensive and complex than the Darwin and TPF missions, involving many large free-flying spacecraft.

References

  1. ^ a b "Darwin factsheet: Finding Earth-like planets". European Space Agency. 2009-10-23. Archived from the original on 2008-05-13. Retrieved 2009-10-27.
  2. ^ a b c "Darwin: study ended, no further activities planned". European Space Agency. 2009-10-23. Retrieved 2009-10-27.
  3. ^ a b c Fridlund, CVM (August 2000). "ESA Bulletin 103: Darwin: The Infrared Space Interferometry Mission" (PDF). ESA. Retrieved 2016-11-07.
  4. ^ Penny, Alan J (1999-07-27). "A concept for the 'Free-Flyer' version". Rutherford Appleton Laboratory. Archived from the original on 2005-10-28. Retrieved 2009-10-30.
  5. ^ a b Karlsson, Anders; Malcolm Fridlund (April 2002). "Darwin: The Infrared Space Interferometer". Alcatel. Archived from the original (GIF) on 2005-10-28. Retrieved 2009-10-30.
  6. S2CID 14475537
    .
  7. ^ Science Daily: Extrasolar planet may indeed be habitable
  8. Planetary Society. 2006-02-06. Archived from the original
    on 2006-06-16. Retrieved 2006-07-17.
  9. ^ "NASA President's FY 2007 Budget Request" (PDF). Archived from the original (PDF) on 2021-02-28. Retrieved 2008-11-14.

External links