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Science Spotlight from this week's observations

Proposal ID = 12537
Principle Investigator =  David Ehrenreich  -  Universite de Grenoble I
Title = "Venus observed as an extrasolar planet"
Time = Jun 5, 2012 15:28:10 - Jun 6, 11:34:00
Targets = MOON-HIPPARCHUS-C
Instrument =  ACS/WFC, STIS/CCD, WFC3/UVIS

Background:

Do planets around stars outside our own solar system (i.e., extrasolar planets) have atmospheres that could support life? Astronomers are beginning to address this question using transits (eclipses) of extrasolar planets. As a planet passes in front of a star, a small fraction of the light passes through the thin atmosphere of the planet, embedding a very faint signature of its chemical composition. By very carefully comparing the spectrum of a star before and during a transit, it is now becoming possible to study the atmospheres of extrasolar planets. The recent transit of Venus across the face of the sun provided a rare opportunity to test this technique in a case where we already have a good idea of what the chemical composition should be. The problem is that the sun is much too bright for Hubble to observe directly. However, enterprising astronomers circumvented this problem by using the moon as a mirror to reflect the light of the sun. Using this technique, several Hubble instruments where used to observe the region around the craters Hipparchus and Dollond during the recent transit of Venus.

Paraphrasing from the abstract:

In the 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 40m, 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.


You can find most of this information and more from the following webpage: http://www.stsci.edu/hst/ by entering "12537" in the Prop. ID box.