Only 400 years ago – before Galileo – the stars and planets were thought to be pure orbs of light set in perfect crystal spheres. By disproving that ancient view, Galileo’s observa- tions pulled down the curtain between heaven and earth. Venus exhibited phases, Jupiter had its own satellites, and Saturn, far from being a perfect orb, had a sort of collar. Although it would be some time before the collar was recognised as a disc, the implications were clear: the supralunary realm was not a supranatural one where things existed in a different reality.
Saturn’s rings are majestic and wonderful, communicating something perhaps more profound than any scientific story. But suppose, after contemplating them a while, we ask how they came into being: does the beauty imply that they must be the Creator’s direct handiwork, as the astronomers before Galileo would have believed? Looking up, they understood themselves to be peering into a mode of reality where things never changed. The night opened out on a world still in its original state. If the truth is that these particles of ice were not originally rings round the planet, is the sense of a transcendent power lost? Saturn is not the only planet to have rings. Jupiter, Uranus and Neptune also have them – faint, unspectacular ones that evoke no wonder. Almost certainly, they consist of fragments left by small-moon collisions. One of the rings around Saturn is fed by vapour ejected from the moon Enceladus.
The idea that the world is only 6,000 years old imposes a taboo on looking too deeply. Any appearance of history must be dismissed as a consequence of creating the world, or as the prerogative of an arbitrary Creator who could make things appear however he chose. It seems futile to ask, “How did this state come into being?” Inquiry is shut down – very often at the first fence. There is a fear that if one asks open-ended questions about the history of the solar system, the majesty will vanish, and one will end up concluding that nothing was created.
As the following pages seek to demonstrate, rejection of creationist dogma need not imply that the solar system could not have originated in creation, even though it must once have looked very different and been chemically simpler. Here we look as far back as we can go. The oldest known objects are meteorites, and it has long been assumed that the least altered are remnants of a primeval cloud of dust and gas, called the ‘solar nebula’. However, recent research has shown this to be incorrect. Meteorites and the asteroids from which they derive are fragments of larger bodies, not smaller ones, and some of these parental bodies originated from still larger ones – objects the size of planets. The solar system seems older than its oldest datable objects. But how can that be?
The first article [headings above the summaries give links] considers whether what we know about the planets accords with the belief that they came into existence naturally. The second focuses on the origin of asteroids, moons and comets.
- Regions such as the main asteroid belt and the Kuiper Belt have too little mass to be consistent with the hypothesis that everything originated from a solar nebula.
- Before gas could have formed into a giant planet, gravity would have sucked it into the central star. This is also a problem for small bodies. At one Earth-distance from the Sun, metre-size particles surrounded by gas will spiral into the star within 100 years.
- The gas in our galaxy is nearly all located in the spiral arms. But the stars which formed in the arms are rotating round the galactic centre faster than the gas, so would take only 10 million years to pass into the regions between the arms (which they have not yet done). This suggests that the stars are less than 10 million years old – a tiny fraction of the Sun’s supposed age.
- The process leading to the formation of embryonic planets is murky. Asteroids composed of accreted rubble show that dust and boulders can stick together, but beyond a certain size they are as likely to come apart again as cohere into bigger units.
- Evidence that the solar system suffered a heavy asteroidal bombardment at the end of the Hadean era is difficult to reconcile with models indicating that by then interplanetary space should have been mostly clear of asteroids.
- While the nebula hypothesis has been boosted by the discovery that elsewhere in the Galaxy entire solar systems have formed from rotating gas clouds, creation theory does not exclude the natural formation of either stars or planets. The critical question is whether any other system is sufficiently similar to support the belief that our own formed naturally. So far, we know of none.
- Chondritic meteorites. These are the oldest datable objects in the solar system, but their constituents are not at all what the nebula hypothesis presupposed. They consist of melt droplets, condensates, metal grains and dust – all but the last showing evidence that they formed at very high temperatures. These particles were produced in planetary explosions, not a primordial nebula.
- Piecing asteroids back together. Meteorites stem from asteroids, and asteroids come in diverse shapes and sizes along with diverse histories. None of them appear to be first-generation conglomerations from the nebula. They originate from larger bodies, and the oldest of the larger bodies are surprisingly mature. Iron meteorites had grandparents older than the canonical age of the solar system itself.
- Asteroids, comets and moons. Asteroids, most of them lying in a belt between Mars and Jupiter, are the sparse, much altered remains of rocky planets – as are comets and rocky moons. The rest of the debris was swallowed up by the gravitational pull of Jupiter, Saturn and the Sun.
- Water in the heavens. Interplanetary space in the early solar system era seems to have been wet, for evidence of ubiquitous water abounds. Saturn’s rings are made of water ice, the Moon retains substantial traces of water, the composition of most meteorites has been altered by it, and in the outer solar system the substance occurs in increasing abundance all the way out to the Kuiper Belt. The Kuiper Belt is more probably the remnant of a created nebula around the solar system – the ‘waters above the heavens’ of Hebrew tradition and the celestial ocean of Egyptian and Indo-European tradition. Much of Earth’s water is likely to have come from outer space.
- Impacts or explosions from within? That the early solar system was dominated by debris from exploding planets and planetesimals has become part of astronomy’s explanation tool-kit. The question is whether the explosions were the result of collisions or of heat generated from within. Here we suggest that the main heat source was (i) the thermonuclear production of radioisotopes within terrestrial planets, followed by (ii) heat from the radioactive decay of those isotopes.
- Events in real time. Are the oldest datable objects in the solar system truly 4.6 billion years old? Only if rates of radioactivity have always been the same. At that earliest datable period, there is a huge discrepancy between isotope dates and direct evidence of lengths of time. Radioactivity appear to have been much faster than now, in which case the objects dated by radioactivity are much younger.
The solar system that we see now cannot be understood as reflecting its original state. The interior of every terrestrial planet melted, the elements dissolving in fire. The largest of these planets exploded. The original Mercury was intermediate in size – bigger than Earth but not as big as the planets which completely disintegrated – for its unusually small and dense body suggests that it shed part of its mantle. The smaller planets – Venus, Earth and Mars – were blanketed with upwelling magma and pounded by asteroids. The giant gas planets underwent equally transformational convulsions.
It was thermonuclear heat from within the Earth that caused the land to rupture and the subterranean deep to break out onto the surface. When the windows of heaven opened, what they let in was debris from the ruptured bodies of other planets. The rain that fell also came from space. Having suffused inwards from the edge of the solar system, the accumulated water was prevented from reaching the Earth’s surface by its atmosphere. As the asteroids ripped through, the envelope of water collapsed. The Earth emerged, in the early Archaean period, a baptised reborn planet.