Surface Gravity and Interstellar Settlement (version 3.0 September 2016) by Gerald D. Nordley 1238 Prescott Avenue Sunnyvale, CA 94089-2334
[email protected] Abstract. Gravity determines the scale of many physical Jupiter's inner satellites melts the ice of Europa and drives phenomena on and above a world's surface. Assuming that tool- volcanoes on Io, and that Mars in the past has had rain and using intelligences come from, and would settle, worlds with solid floods serves notice that worlds that are significantly less surfaces and gravities equal or less than that of their origin, we massive than Earth and have significantly less surface gravity note that such worlds in the Solar System have surface gravities can still have the deep atmospheres and liquid water significantly lower than that of Earth. The distribution of these temperatures needed to sustain life. surface gravities clumps around factors of about 2.5 and favors worlds with about one-sixth Earth gravity, conventionally 2. Surface Gravity Basics considered too small to retain atmospheres. Titan, however, Mass is, roughly, a measure of the amount of substance. shows that low surface gravity does not, in itself, preclude the Weight is the force by which that substance is attracted to presence a substantial atmosphere. Where small worlds have another mass. This force is directly proportional to the product of low exobase temperatures,and protection from stellar winds, both masses and inversely proportional to the square of the substantial atmospheres may be retained. distance between them. A spherically symmetric planet can be Significantly lower surface gravity affects a number of physical treated as if all the mass were at the center, so the relevant phenomena that affect environment and technological evolution-- distance is the radius from the center to the object.