06-01-2007 Solar System in perspective (Article 67)

[Simon Kenny]

Solar System in perspective (Article 67)

To help understand the extremes within our Solar System, it may be useful to compare them to everyday references. If the Sun was the size of a ball 1.8m across, Pluto would be the size of a pea 7.6km away, but our nearest star would be 52 000km distant. If the Sun were the size of an orange, Earth would be a tiny seed 10m away. Light from our Sun takes 8 minutes to reach the Earth, 11 hours to reach Pluto, and over 4 years to reach our nearest star. If you could travel at the speed of light you could go round the Earth seven times in 1 second. Our Sun, a dwarf star, loses 4 million tonnes of hydrogen gas, the equivalent weight of 1 million adult elephants, every second, in a nuclear reaction, while its surface shines with the brightness of 232,500 candles per cm2.

Travelling at 161kph, our Moon could be reached by a train in 99.5 days, and as it spins at the same rate that it orbits us, we never see the “far side”. We saw the far side for the first time in 1959, from a space probe. The largest crater we can see on the Moon, is Bailly, and you could fit Scotland inside it, while the Ocean of Storms is larger than the Mediterranean and dry as dust. As there is no weather on the Moon, the astronaut’s footprints will remain for at least 10 million years. Mercury’s hot hemisphere is 7 times hotter than the hottest temperature recorded in Libya of 57.7C, while its cold side is 7 times colder than a freezer. The largest volcano and longest canyon in our Solar System is on Mars. The volcano Olpmpus Mons is 3 times higher than Everest, while the Valles Marinaris would stretch from New York to San Francisco. Venus rotates backwards, so the Sun rises in the west and sets in the east, and its atmosphere traps heat like a giant greenhouse, with average surface temperatures about 465C.

Jupiter’s Great Red Spot is a storm three times larger than Earth, and if the planet were the size of a ball 18cm across, the Earth would be a 1cm marble. If you rode a bicycle non-stop around the planet at 9.6kph it would take 1935 days to complete, while one of its many moons, Io, turns itself inside out over a period of 3000 years. Saturn would float in a bowl of water, and has winds that blow at 1770 kph, 10 times stronger than any hurricane on Earth. One of Saturn’s tiny moons is the fastest moving in the Solar System, travelling at 113,600 kph, the equivalent of travelling from Bombay to Port Said in just 2 minutes 11 seconds. A baby born on Neptune would never live for one Neptunian year, as it takes 164.8 years to orbit the Sun, while if on Pluto they would have to wait 248 Earth years before their first birthday. Clear skies!