Letter

Nature 459, 814-816 (11 June 2009) | doi:10.1038/nature08050; Received 30 December 2008; Accepted 8 April 2009

Earth's transmission spectrum from lunar eclipse observations

Enric Pallé1, María Rosa Zapatero Osorio1, Rafael Barrena1, Pilar Montañés-Rodríguez1 & Eduardo L. Martín1,2

  1. Instituto de Astrofísica de Canarias, Vía Láctea s/n, E38205 La Laguna, Tenerife, Spain
  2. Physics Department, University of Central Florida, PO Box 162385, Orlando, Florida 32816, USA

Correspondence to: Enric Pallé1 Correspondence and requests for materials should be addressed to E.P. (Email: epalle@iac.es).

Of the 342 planets so far discovered1 orbiting other stars, 58 'transit' the stellar disk, meaning that they can be detected through a periodic decrease in the flux of starlight2. The light from the star passes through the atmosphere of the planet, and in a few cases the basic atmospheric composition of the planet can be estimated3, 4, 5. As we get closer to finding analogues of Earth6, 7, 8, an important consideration for the characterization of extrasolar planetary atmospheres is what the transmission spectrum of our planet looks like. Here we report the optical and near-infrared transmission spectrum of the Earth, obtained during a lunar eclipse. Some biologically relevant atmospheric features that are weak in the reflection spectrum9 (such as ozone, molecular oxygen, water, carbon dioxide and methane) are much stronger in the transmission spectrum, and indeed stronger than predicted by modelling10, 11. We also find the 'fingerprints' of the Earth's ionosphere and of the major atmospheric constituent, molecular nitrogen (N2), which are missing in the reflection spectrum.

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