Total Solar Irradiance at the 2006 Transit of Mercury and Application to Transiting-Exoplanet Observations

Following our earlier work on the Total Solar Irradiance (TSI) at the 2004 transit of Venus, in which an 0.4 percent drop in TSI was readily detectable with the ACRIM3 instrument on NASA's ACRIMsat, we report on ACRIM3 observations of the 29 November 2006 transit of Mercury. We also observed the transit from Haleakala and from Sacramento Peak. Mercury's cross-sectional angular area is only 1/30th that of Venus's, so the expected drop in TSI was only 0.01 percent. As expected, this tiny drop was not detected, though detailed statistical analysis continues. Our Venus and Mercury transit observations provide closeup views of phenomena increasingly observed for exoplanets and provide examples by which one can assess the limits at which exoplanet discoveries can be made with the transit method.

Acknowledgments: JMP's planetary occultation work and the POETS instrument (Portable Occultation, Eclipse, and Transit System) were funded in part by NASA Planetary Astronomy grants NNG04GE48G, NNG04GF25G, NNH04ZSS001N, and NNG05GG75G to M.I.T. and Williams College, and continues under NNX08AO50G. Our transit work was funded in part by the Committee for Research and Exploration of the National Geographic Society. ACRIMsat is supported by a grant from NASA to Columbia University.