As a possible method of detecting an extrasolar planet, astrometric spectroscopic, and photometric methods are considered. Interest has been focused on the search for a planet whose physical conditions appear to favor biological evolution that could lead to the development of life as advanced as that on the Earth. In order to avoid speculative arguments, the set of assumptions introduced consists of only those that are acceptable at the present stage of our scientific knowledge. These basic assumptions are: (1) The speed of biological evolution is about the same as on the Earth; (2) a planet of our interest has to be within a certain distance from the parent star, so that the planetary temperature can be kept on a range where life can exist; and (3) atmospheric conditions, and the chemical composition of the air, are similar to those on the Earth and such conditions depend only on the ratio of mean thermal to escape velocities. Theoretically computed planetary models are used in determining mass-radius relations. It has been found that the photometric method is far superior to the other two. In fact, it is the only means of detecting a planet of the proposed kind, and as a consequence, the conclusions do not strongly depend on the basic assumptions. Since the probability of success in the search appears to be quite high and various by-products are anticipated, the author proposes that an extensive photometric survey of late type stars be planned before much effort is expended on any radio astronomical search.
Proceedings of the Iowa Academy of Science
©1964 Iowa Academy of Science, Inc.
"Astronomical Limitations on Detecting Habitable Planets Beyond the Solar System,"
Proceedings of the Iowa Academy of Science, 71(1), 401-412.
Available at: https://scholarworks.uni.edu/pias/vol71/iss1/59