LONDON: We're living in something of a golden age for space exploration, with a fleet of robotic explorers currently orbiting, landing on or roving across most of the planets in the solar system, and more planned for the near future. In A Space Traveller's Guide to the Solar System, Mark Thompson draws upon much of this up-to-date knowledge to serve as our tour guide to the archipelago of planets and moons that share our Sun with us.
Starting with the Earth, the book takes us on a grand tour of the solar system: the rocky inner worlds, and out to the churning gas giant planets and the icy outer realm inhabited by Pluto. Thompson discusses not just the characteristics of the worlds encountered, but also deals with the mechanics of spacecraft and what it takes to keep astronauts alive and healthy on long-duration missions in space.
He employs evocative turns of phrase to illustrate what he means. The pummelling of the Moon by rocks has pulverised its surface into a fine, dusty "lunar regolith", like a chef pounding spices with a pestle and mortar. The ground on Saturn's moon Titan has a thin, hard crust with a softer, wetter consistency underneath, like creme brulee. The shape of our galaxy is like two fried eggs stuck back to back - the yolks representing the bulging core of the Milky Way, and the flattened, circular egg whites the rotating disk of the galaxy. (In retrospect, perhaps I've just been drawn to the culinary references).
And fascinating gems of information glitter from the text. At launch, the Saturn V rocket had a fuel economy of just 17.7cm to the gallon, such is the immense power required to loft astronauts to the Moon. The tallest mountain in the solar system, Olympus Mons on Mars, has such a gentle slope that, standing at the bottom, you wouldn't even be able to see the summit as it would be wrapped around the curvature of the planet and hidden behind the horizon. Theory predicts that diamond rain falls deep in the methane-rich atmosphere of Uranus.
Unfortunately, though, for a book intended to inform as well as entertain, it's marred by errors in the planetary science. Many of these can be attributed to mistypes, lapses in fact-checking or the inappropriate use of specific
words. The reason that water cannot exist in its liquid form on the surface of the Moon is not chiefly because of exposure to solar radiation. The retrograde looping-back motion of Mars across the night sky does not demonstrate that the Earth isn't at the centre of the solar system. The Mars500 study did not involve a mini self-contained ecosystem. The rings of Saturn don't disappear from view every 15 years because of Saturn wobbling on its axis like a child's spinning top. Jupiter does not take 16.7 days to rotate on its axis; Uranus does not rotate prograde. These errors matter, but are not the crux of the problem.
Far more serious are mistakes that betray a writer who has not properly understood the science. For example, when trying to explain how the energy released by fusion reactions escapes the core of our Sun to shine as heat and light onto the Earth, Thompson says: "Heat has the easier job as it simply finds its way to the photosphere of the Sun through radiation and then convection... Light, on the other hand, has a much harder job of it because of the density of the solar material. Instead of travelling in a straight line, light weaves around like a drunk staggering home." What he's missing here is that heat, radiation and light are all the same thing in this situation. Heat is transferred out of the core as radiation in the form of photons of light. These photons haphazardly bounce around in the dense matter inside the sun and so make very slow overall progress outwards. In this sense, it takes heat and light exactly the same time to escape through the radiative zone in the deep interior.
Patrick Moore was an amateur astronomer, and one of the finest popularisers of astronomy since the start of the space age. His great skill lay in combining enthusiasm for the subject with diligence in the clarity and accuracy of his explanations. Mark Thompson, who has appeared on the BBC's Stargazing Live, as well as on The One Show, has the potential to develop his career along similar lines. But Moore understood that popular science must be based on a secure knowledge of your subject matter, and you must talk to experts in the respective fields when you're extending beyond your own expertise. Thompson would do well to learn this lesson.
