MadSci Network: Astronomy

Re: Swapping Enceladus with our Moon

Date: Mon Aug 2 10:30:58 2004
Posted By: Carolyn Ernst, Grad student, Planetary Geology
Area of science: Astronomy
ID: 1089589194.As

Saturnís moon Enceladus is the most reflective object in the Solar System with a reflectivity of 0.99 (meaning 99% of the light that reaches its surface is reflected). By comparison, the reflectivity of the Moon is 0.12 (12%). Enceladus is so highly reflective because its surface is very smooth and composed of water-ice. If youíve ever been outside on a sunny day after a snowfall, you know how bright ice can be, due to its high reflectivity!

For a given surface area, Enceladus would appear to be ~8.25 times brighter than the same- sized patch of the Moon at the same distance from the Earth. So, a given point on Enceladus in a lunar orbit would be much brighter than the Moon. However, if youíre curious about the total reflected light, we need to take the surface areas of both moons into account. The Moon is 1738 km (1030 mi) in diameter. Compared to this, Enceladus is very small, with a diameter of only 499 km (310 mi). The ratio of the surface area of Enceladus to the surface area of the Moon is ~0.02, so the area of Enceladus is ~2% that of the Moon. So, although a given area of Enceladus is 8.25 times brighter than the Moon, the total reflected light off of Enceladus would only be 0.17 times (or 17%) as bright as the Moon. Therefore, Enceladus would appear brighter and smaller, but would reflect less total light.

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