Ronald Lemon, age 14, of Milwaukee, Wis., for his question:
What is the protoplanet hypothesis?
Our Earth is estimated to have had at least 4 billion birthdays, and the Solar System is thought to be several million years older. The creation of the planets is a challenging problem, but so far science can offer only theories and hypotheses to explain the dramatic event.
The probing instruments of science have revealed other solar systems, and perhaps most of our galaxy's 100 billion stars may have planet families. The birth of a planetary system seems to be a common cosmic occurrence. So far we cannot prove how this happens, but science offers several theories that suggest explanations, most experts now favor a theory called the protoplanet hypothesis.
It seems logical to suppose that the sun and its family condensed from a vast cloud of cosmic gases, and there is much evidence to support this idea. The protoplanet hypothesis is one of several theories that outline the stages by which the gaseous nebula gave birth to a seething sun with a family of orbiting planets and their moons.
It suggests that certain cosmic forces caused the cloudy nebula to condense and surround itself with an immense, flat halo. Gravitational attraction within the material of the halo caused the huge saucer to pull apart into separate units of whirling gas.
The unborn sun at the center of the cloud may have worn nine or so necklaces, each made from perhaps five gaseous whirlpools. These were the unborn planets. Their particles of matter, whirling at thousands of miles an hour, crashed and merged. Smaller fragments were captured and held by the gravity of larger fragments, and the gaseous whirlpools formed bigger and bigger solid protoplanets and their protomoons. They were more massive than the present planets and moons, and each eas enveloped in a vast atmosphere of gases.
The theory suggests that the protoplanets were formed in darkness before the birth of the radiant sun. Their sizes and orbits, their materials, rotations and moons were dictated by cosmic forces operating naturally within the original cloud. Meantime, other forces within the central core reached a balance that set it blazing with the nuclear furnace of a star. At last the cold, dark protoplanets were bathed in heat and light. Pressure from solar radiation drove off their huge gaseous halos, and they must have looked like super comets. After a short spell of this glowing glory, the young protoplanets became the solid, settled planets of the present orderly solar system.
At one time in its history our own protoplanet may have been 1000 times more massive than the Earth. Most of this extra material was its immense halo of gases such as hydrogen and helium, methane and ammonia, neon and water vapor. Its life as a protoplanet was very short when compared with its 4 billion years as a planet. Scientists estimate that it took only 100 million years for the original nebula to give birth to the present planets.