Date: January 11, 2010
Title: The New Solar System
Podcaster: Andy Briggs
Organization: Science File: http://www.sciencefile.org
Description: How has our view of the solar system changed since the beginning of the space age, and what can it tell us about solar systems around other stars?
Bio: Andy Briggs is an amateur astronomer living in Spain. He has been observing the heavens for more than 40 years. He is the publisher of sciencefile.org (http://www.sciencefile.org), a website for anybody with any interest in science.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Beth Katz. Beth Katz wishes her father a happy birthday along with a thank you for introducing me to the stars. Also thank you for the Galileoscope birthday present.
When I was young, and finding my feet in astronomy, our view of the solar system was very different to what it is today. I still have a book from 1961 entitled Adventures in Space, in which two very English, very middle-class comic-strip children called John and Pam have all sorts of thrilling escapades with their astronomer uncle, from being shown round his observatory to taking a trip to the Moon in one of the beautifully aerodynamic, winged rocket ships so prevalent in the science fiction of the time. In another comic strip, Pluton the space boy fights off extraterrestrials on Mars to get to the hidden treasure.
But between the comic strips, Adventures in Space has pages of interesting information about astronomy, rocketry and travelling to other worlds. There is a diagram of the planets of the solar system, showing the number of moons they possess. Jupiter has twelve, Saturn nine, Uranus five and Neptune two. It was not until 1978, of course, that Pluto’s moon Charon was discovered, some 17 years after Adventures in Space was published, and so Pluto, according to the book, has no moons. But of course, if the diagram were being published today, Pluto itself would not even be included, something which would have been inconceivable back in 1961.
And listen to what Adventures in Space has to say about our own Moon: “It has been claimed that shadows pass over the Moon’s face, and one suggestion is that these may be swarms of simple insect life.” About Mars, the book states that the existence of artificial Martian canals is still not totally discounted, and that creatures like those from the prehistoric past of Earth may roam the Martian surface.
So I went through my childhood years with a view of the solar system which was unchanging. There were nine planets. Jupiter had twelve moons, Saturn nine. Those numbers would never change – or so my books suggested. The number of moons possessed by each planet was written in stone, and there was absolutely no suggestion that more moons were awaiting discovery. The Moon and Mars would be explored by humans in my lifetime: I myself might be one of the plucky explorers. It was a time of optimism, of exploration, of new discoveries, set against the background of a reliable and unchanging retinue of planets.
But look at the solar system now!! Jupiter and Saturn both have around 60 moons. How did that happen? Pluto is not even a planet. How on earth could that be so? Humans have never got to Mars and have only extremely briefly visited the Moon. There are no winged rockets flying between the planets, no Moon bases, no space stations acting as relays for interplanetary travel. And, sadly, there are no children exploring the solar system with their uncles. It´s all so very different from how I thought it would be when I was young.
But at the same time, there are wonders undreamed of in 1961. Volcanoes and geysers on Io, literally hundreds of them. Ice geysers on Triton and Enceladus. A radically different view of Mars, as a world which once had large volumes of surface water rather than being the dry, dusty planet we see through telescopes. We have discovered an amazing variety of planetary moons, whole populations of bizarre rocky and icy worlds bearing unique features whose origins we can often only guess at. From the 15-mile-high ice cliffs of Miranda to the sponge-like Hyperion, from the equatorial mountain chain extending most of the way around Iapetus to the hidden ocean of Europa, from the ethane lakes of Titan to the frozen wastes of Triton, the moons, not the planets themselves, have often been the stars of the show. They are ciphers of the distant past, telling us stories of the early solar system, if we could only understand those tales writ large across the moons’ ancient surfaces.
And look how the old structure of the solar system has changed too. In 1961, we had the terrestrial zone, comprising the rocky inner planets, and then the gas giant zone. Pluto was an enigma even back in 1961, as nobody quite seemed to know what it was doing there. But now, we have four zones in and around the solar system – the terrestrial planets, the gas giants, the Kuiper Belt, of which Pluto is just one sizeable member along with Sedna and that one beginning with “Q” which nobody can pronounce, and finally the Oort cloud of billions of comets, which may extend halfway to the next star. The solar system is bigger, more complex and certainly a lot more exciting than when I was a child. There are stranger, more alien, more distant places for humans to explore in the far future, stranger than anybody imagined at the beginning of the space age.
And there is something else, of possibly profound significance, about the new solar system. It´s something completely unexpected. When Voyager 2 passed by Neptune’s moon Triton in 1989, it discovered geysers spewing gases and ice hundreds of kilometers upwards. Triton is one of the coldest places in the solar system, with temperatures not that far above absolute zero. And yet, here in this frozen, dark place, where surely there could be no activity, no movement of any kind, something stirred. Weak sunlight, reaching Triton’s surface from a Sun which is just a bright star in the heavens, heats gases trapped under the ice, which then expand, building up pressure until a weak point in the ice cracks open and the gases are vented violently into space as geysers. The lesson for us was that even in places which common sense says should be dead and frozen, there is activity. There is energy. There is movement. And if there is movement on a deep-frozen world like Triton, can there be anywhere in the Universe which is truly dead? What will we see when NASA’s New Horizons spacecraft arrives at Pluto and the Kuiper Belt in 2015? Will there be activity there too? Surely it would be a foolhardy person who answered no.
Fast-forward a couple of decades to Cassini’s exploration of Saturn and its moons, and we find the same type of phenomenon on Enceladus. But this time, it´s not clear what is providing the energy, what is driving the ice geysers which spew water and organic compounds into space from fissures nicknamed Tiger Stripes towards the moon´s south pole. An underground ocean? Tidal heating of the interior by Saturn´s massive gravity, like that which drives the volcanoes of Io? Or some hitherto unsuspected and unobserved mechanism, which may come as much of a shock as what Voyager found on Triton? Only time will tell – that, and more painstaking observation of the fountains of Enceladus.
What emerges from all this is a view of the solar system which is not unchanging and predictable, but evolving, dynamic and full of surprises. I have avidly followed the discoveries of the Mariners, the Pioneers, the Voyagers and the other robotic explorers, and have seen our cosmic neighbourhood change dramatically in ways which Gerald Kepps, the author of Adventures in Space, could surely never have foreseen in 1961. Mr. Kepps, if you are still out there somewhere, I wonder what you make of it all.
Above all, the lesson to be learned is that as we study other solar systems, around other stars, we should remember that things are not always as one would expect, nor as one would necessarily like. Just look at the hundreds of so-called “hot Jupiters” we have so far discovered around other stars. Their orbit and positions are pushing our theories of planetary formation to their limits, and may indeed necessitate a radical reappraisal of some long-held and cherished beliefs. Surely there can be few astronomers who expected other solar systems to be so radically different to our own. It’s now clear that our solar system may be exceptional and certainly not in any way the norm; it may even be unique. There are always going to be surprises and shocks. We must always expect the unexpected: and that, in the end, is the lesson of the New Solar System.
End of podcast:
365 Days of Astronomy
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