2021 Volume 70 Issue 6 Pages 309-326
Based on increased knowledge about the surface environment of the planet and other bodies in the solar system, the possible presence of life in the solar system becomes the scientific research target. The existence of liquid water on the surface of Mars 4 billion years ago has been postulated. The surface environment of Mars used to be similar to the Earth then. These similarities between ancient Mars and Earth prompt us to consider the probable emergence of life on Mars. Methane, energetic substrates, and organic compounds have been found in the present Mars surface: Life may be present on Mars now. Phosphine at about 55 km above the surface of Venus has been reported recently. Because there is no known chemical process that can explain the presence of phosphine, the presence of life in the environment has been proposed. The life-search can be done either by in situ measurement with the equipment carried on the spacecraft or by the analysis of the samples returned to the Earth. The latter method can be done with state-of-art techniques using big and sensitive machines. However, because of the limitation of the sample amount that can be brought back to Earth, in situ measurements of the signature of life is also essential. In this chapter, we have reviewed the past life-signature exploration experiments, the possible life-signature search targets, possible life-signature search methods, and future life-signature search missions.
