“I believe alien life is quite common in the universe, although intelligent life is less so. Some say it has yet to appear on planet Earth”*…
If the range of habitable radii is sufficiently broad, most inhabited planets are likely to be closer in size to Mars than the Earth. Furthermore, since population density is widely observed to decline with increasing body mass, we conclude that most intelligent species are expected to exceed 300kg…
From the summary of University of Barcelona cosmologist Fergus Simpson‘s paper, “The Nature of Inhabited Planets and their Inhabitants” (which can be downloaded as a PDF here).
* Stephen Hawking
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As we phone home, we might recall that it was on this date in 1960 that the first weather satellite, TIROS I, was launched from Cape Kennedy (or Canaveral, as then it was) and sent back the first television pictures from space. The first in a long series of launches in the TIROS program (Television Infrared Observation Satellite), it was NASA’s initial step, at a time when the effectiveness of satellite observations was still unproven, in determining if satellites could be useful in the study of the Earth. In the event, TIROS I and it successors proved extremely useful in weather forecasting.
TIROS I prototype at the Smithsonian National Air and Space Museum