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 observations 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 realm 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 astronomers before Galileo would have presumed? Looking up, they thught they were peering into a heaven where things never changed, a universe still in its original state. But the truth is that these ice particles were not originally rings round the planet but, almost certainly, fragments left by small-moon collisions. One of the rings is fed by vapour ejected from the moon Enceladus. Jupiter, Uranus and Neptune also have rings – faint, unspectacular ones that evoke no wonder. Rings can form naturally: they are not in themselves evidence of creation, however beautiful. That said, the bright purity of Saturn’s rings is partly why astronomers have concluded in surprise that they must be relatively young.
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 inevitable consequence of creation. It seems futile to ask, “How did this state come into being?” Inquiry is shut down – very often at the first fence. The fear is 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. In a way, astronomers used to thinking on timescales of billions of years have the same mental block. “Geologists like things to be the same as they ever were,” a NASA scientist told Nature. The unchanging world is “philosophically comforting because you don’t have to assume you’re living in special times” (McKee 2013).
Rejection of creationist dogma is not the same as giving up on the possibility that the solar system originated in creation, even though it may have looked very different and been chemically simpler. In the following pages we look as far back as we can go. The oldest known objects are meteorites, and it has long been assumed that these 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. How can that be?
The first article 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. The particles were produced in planetary explosions, not a primordial nebula.
- Piecing asteroids back together. Meteorites stem from asteroids, and asteroids have diverse shapes and sizes along with diverse histories. None of the asteroids 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. Mostly lying in a belt between Mars and Jupiter, asteroids 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. The Moon retains substantial traces of water, the composition of most meteorites has been altered by it, Saturn’s rings mostly consist of water ice, and it 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 and (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 passing 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, dissolving in fire. The largest of these planets exploded. Mercury is now the smallest terrestrial planet, but its unusually dense body suggests that it shed part of its mantle and was originally intermediate in size, bigger than Earth but smaller than the planets which completely disintegrated. The other rocky 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 for 40 days and 40 nights was a rain of asteroids. When, in the early Archaean, the Earth emerged from the waters, it was a baptised reborn planet.