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Why worry about the transit of Venus?

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The sight of the planet Venus crossing the disk of the sun may be an interesting spectacle, worth the many pictures and articles which the press carries, but are scientists interested in it? Wikipedia describes how it was used to measure the size of the solar system, starting during the transit in 1639. Now, when this is not a hot topic any more, a transit of Venus is really a tool for calibration. Astronomers want to use this to find what to expect when an extra-solar planet transits its sun. Here is a proposal from Alfred Vidal-Madjar of the Paris institute of astronomy for using the Hubble Space Telescope to do exactly that tomorrow morning:

In a relatively near future, numerous transiting extrasolar planets will be discovered {gaseous giant planets, Earth-size planets and temperate Uranus in the form of “Ocean-planets”}. Space telescopes operating in the UV-optical-IR will allow the study of their atmospheres. We have to show if and how these observations will give access to the detection of atmospheric species, particularly when telluric planets will be observed, to demonstrate that life may be possible on one of them. For that purpose, we propose to use the unique event of the century, the Venus transit in 2012 {next Venus transits are in 2117 and 2125!}, to demonstrate the feasibility of these observations and show precisely what a Venus-like planet will look-like. To observe the Venus transit with similar conditions as extrasolar planets {no spatial resolution}, we propose to observe the solar light reflected on the Moon during the Venus transit on June 5-6 2012, lasting about 7h 40mn, i.e. about 4 HST orbits. A total of 5 HST orbits will allow us to obtain high S/N transit spectra and reference spectra to reveal the detectable atmospheric species with current space instrumentations. Similarly, in a companion proposal, we propose to observe the Earth transit on the Moon through the reflected light during a total Moon eclipse to directly compare the observed atmospheric signatures of Earth-like and Venus-like extrasolar planets.

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Written by Arhopala Bazaloides

June 5, 2012 at 9:57 am

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