The Venus Twilight Experiment: Probing The Mesosphere In 2004 And 2012

International audienceDuring the Venus transit in 2004 several observers collected data useful to the characterization of the mesosphere of the planet, by observing the solar light refracted at the corresponding altitude range. The "aureole" thus formed, is observable during the ingress and egress phases of the transit, when Venus is crossing the solar limb. For the 2012 opportunity we prepared a set of coronagraphs to obtain multi-wavelength, space- and time-resolved photometry of the aureole, in collaboration with other space- and ground-based campaigns. The coronagraphs were distributed in the visibility area around the Pacific, over eight sites where local logistic support and scientific expertise were present. Several sites obtained useful data at frame rates of several images/sec. We will give an account of the campaign presenting first results obtained at 450, 535, 607 and 760 nm (FWHM 10 nm). A comparison with data collected at the 2004 transit shows that variations in the aspects of the aureole are present. These can be linked to variations in the vertical distribution of the absorbers (aerosols and cloud-top level). A common feature in both the recent transits is the presence of a brightness peak at high latitude, which was imaged several minutes before and after first and last contact, respectively. The historical record of the aureole contains hints of varying features and a constant polar-spot presence, which can now be interpreted in the light of the measurements obtained in 2004 and 2012