With numerous planets outside the solar system, there is a possibility that some of these alien worlds have conditions that could possibly support life. While scientists do not have precise ideas on what alien life would look life if it does exist, they may have an idea of how much these extraterrestrial beings might possibly weigh.

Fergus Simpson from the University of Barcelona has come up with a statistical argument showing that alien life forms would have weight comparable to that of full grown bears on Earth, with the cosmologist estimating that that aliens would weigh about 660 lbs.

Simpson began his calculation by considering the number of individuals that would likely live in an alien civilization. He came up with up to about 50 million individuals. Simpson thought that any individual alien has higher odds of coming from a highly populated civilization.

In his paper, the cosmologist argued that most cultures would support an average number of people, although there are few that may have very low or very high populations.

The idea is comparable to Earth's population. If somebody would have to pick a single person from our planet, that person would likely be from China rather than New Zealand. The researcher wrote that the size of a life-supporting alien planet is likely smaller compared with Earth most of the time. He assumed that about half of the diameter of Earth is at the lower limit because anything smaller than that would mean that the planet would have difficulty retaining an atmosphere or water.

Simpson argued that an individual alien would have increased odds of living on a big planet because these planets are likely able to support more people. Whole species, however, are more likely to come from a small one given that there are more small planets. He wrote that planets have a radius 1.4 times that of the Earth or less 95 percent of the time.

On Earth, the size of animals is relative to the number of individuals, and this means that the smaller the species is, the more individuals belonging to that species exist. This relation can likewise be plotted on a curve against the probability suggesting that the average weight of an alien would be about the size of a bear.

"Since population density is widely observed to decline with increasing body mass, we conclude that most intelligent species are expected to exceed 300 kg," Simpson wrote.

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