One reason for this change is that a tiny thing has a large surface area relative to its mass.

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And, at this point, the tiny, dry insulin particles had such a large surface area relative to their mass that, like popcorn or flour, they poured unevenly, leaving air pockets and inconsistent doses.

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To compare alien planets, Dr. Mendez at the Planetary Habitability Laboratory and his colleagues are creating an Earth Similarity Index that ranks worlds by their resemblance to our own planet, on a scale from zero to one, based on their mass, radius, density and surface temperature.

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Its mass is also miniscule, so that the gravitational pull on its surface is just 6% of that on Earth.

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Venus is a twin to the Earth in terms of size and mass, yet has evolved in a very different direction, with a surface temperature hotter than a kitchen oven and a choking mixture of noxious gases for an atmosphere.

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