Even in our cosmic backyard, the solar system, many questions remain open. On Venus there are formations similar to volcanoes, but it is not known if they are active. The surface of Mars suggests that there was once a vast ocean, but how it disappeared remains unclear. On the other hand, recent detections of chemical compounds that may indicate the presence of biological activity on Mars and Venus, so-called biosignatures, keep the search for life outside Earth alive. The answers may lie in the analysis of the light that reaches us from these planets, through the "fingerprints" that the molecules leave in the spectrum of that light.
