The solar system

Our knowledge even of the basic constituents of our solar system is ever widening, with technological progress affording wondrous new perspectives. Pluto was identified only in 1930, and it was as recently as 1978 that it was discovered that it has a moon. In 2006, new information led scientists to conclude that it is not, indeed, the ninth planet of our solar system, but rather an enormous comet ... Ever more detailed investigation with increasingly sophisticated instruments is pushing back its outer limits – the familiar schoolroom charts of the ‘topography’ of the solar system, showing nine planets orbiting the sun at neat intervals, is only a tiny inner portion. Pluto is, according to latest estimates, only one fifty-thousandth of the way to the system’s edge: far beyond Pluto – extending for two light years into the cosmos – is believed to be the Oort cloud, a vast zone of drifting comets (its existence is still hypothetical, the ‘cloud’ being too distant for any instrument so far to access).

Pushing back the frontiers

Space travel has opened a new era in space science. Since the first exploratory missions in the 1960s, all the planets (except Pluto) have been visited by space probes, providing a host of data on the composition and dynamics of the celestial bodies to confirm, refine or challenge theoretical assumptions. For example, interplanetary spacecraft have discovered that various planets have satellite moons, some with atmospheres (Saturn’s Titan) and even magnetic fields (Jupiter’s Ganymede). Comets, wanderers through space which are a source of intense interest as they are believed to contain material from the birth of the universe, the very beginning of time, have been viewed at close quarters – the Giotto craft passed Halley’s comet at 600 kilometres from its core in 1986, continuing its mission to approach to within 200 kilometres of Grigg-Skjellerup’s core in 1992; the Stardust mission collected ‘dust’ from the Wild-2 comet which is due to be returned to Earth in 2006, and more recently the Deep Impact probe, in the first direct-contact study of a comet, hurtled to the surface of Tempel-1. In 2014, after a 10-year voyage, the Rosetta mission craft will rendezvous with Churyumov-Gerasimenko, where it will put down a lander on the comet’s surface.

The ability to gather in-situ information about our companions in the solar system has brought about a new science, comparative planetology, the study, essentially, of how and why the planets, formed under the same conditions, have evolved so differently. What we have discovered and are continuing with each mission to discover not only gives greater understanding of the mechanisms of our neighbours, but has also revolutionised our perception of our own Earth, heightened awareness of its fragilities and with it our ecological responsibilities.

Are we alone?

But the search for life on other planets goes on. We may have left the notion of encountering the builders of the putative ‘canals’ on Mars (striations on the planet’s surface first observed by Schiaparelli in 1877) far behind, but the possibility of uncovering ‘signatures’ of traces of life, past or present elsewhere on than our home planet is a driving force in space exploration. The principal scientific objective of the European Mars Express mission is to scrutinise the Martian subsurface, surface and atmosphere for traces of water, the fundamental requirement for life as we understand it. Data supplied by the mission has confirmed the presence of water ice and carbon dioxide ice at Mars’ south polar cap, exciting the scientific community and the general public alike. A manned mission to the red planet is under study, with a date of 2030 pencilled into the diary.

After all, the theory that life on Earth was seeded by a comet carrying organic matter crashing into it – panspermia – has not been fully discounted …