THE SECRET LIVES OF PLANETS

A smooth survey of the planets and satellites.

With nations reviving an interest in human space exploration, this expert overview by Murdin, emeritus professor of astronomy at Cambridge, is a welcome description of what’s out there. The author, who was part of a team that discovered Cygnus X-1, a galactic X-ray source thought to be the first accepted as a black hole, discusses planets (once nine, now eight), some interesting moons, and several miscellaneous bodies. The nearest four planets—Mercury, Venus, Earth, Mars—are small and rocky, while the distant four—Jupiter, Saturn, Uranus, Neptune—are large and gassy. Mercury resembles the moon, airless and cratered but larger and hotter. As hot as melting lead, cloud-covered Venus resembles an Earth with its greenhouse gases out of control. Barren and cold with almost no atmosphere, Mars may be barely tolerable. Hopefully, we will know in a decade or two. Massive Jupiter and Saturn are the “gas giants.” Not so massive but colder, Uranus and Neptune are “ice giants.” Even further, colder, tiny, and with a wacky orbit, Pluto has been demoted to the considerable family of dwarf planets. Earth receives the longest chapter. Many readers take comfort that it orbits in the “Goldilocks Zone,” the distance from the sun where liquid water can exist. But life also requires a large magnetic field to fend off solar radiation—Earth’s won’t last forever—as well as an atmosphere with greenhouse gases. With none, it freezes; with too much, it overheats. Earth’s huge moon stabilizes the planet’s axis and seasons. Since human life requires liquid water, the author focuses intently on that topic. Mars contains almost none, but several moons of Jupiter and one of Saturn contain oceans beneath their surfaces. Another moon of Saturn, Titan, has an atmosphere as well as rivers and oceans of methane. Astronomers, science fiction writers, and Murdin remain fascinated by methane-based life.

Satisfying popular science, just right for the budding astronomer in the household.