Photo: Greg Reilly
A once-in-a-lifetime photo of a once-in-a-lifetime comet by a local South Okanagan photographer near Causton.
If you want to make a comet, asteroid, planet, star, or many other bodies, the recipe is the same. There is only one ingredient: cosmic clouds of gas and dust.
The procedure is the same, just collect some of the material in a lump. What you end up with depends entirely on how big a lump you work. The mass of the lump determines two critical quantities, the pressure and the temperature at the core of this body.
The temperature in the Earth’s core is about 5200 C and the pressure about 3.6 million times greater than the atmospheric pressure at the surface. The pressure comes from the weight of the overlying rock. The internal heat comes from two sources – the energy released by the impacts of incoming objects when the Earth formed, about 4.5 billion years ago, and from the decay of radioactive elements present in the cosmic material.
For a planet the size of ours, heat escapes very slowly. For smaller worlds, the process is faster.
Imagine that somewhere in a big cloud of cosmic gas and dust, a few grains wander into each other, and thanks to static electricity or something else, they stick together. The resulting grain is larger and presents a greater target for impact than other particles, so it has a better chance of capturing more particles. Even in these clouds, the density of material is very low, so collisions are rare, but there are many, many times.
As the grain grows, it samples all the chemicals that make up the cloud, including hydrogen and other volatiles. Eventually, it turns from a grain into a lump, and after more time becomes massive enough to take on a new force to hold the lump together and increase its growth rate by attracting more and more of the surrounding material: gravity.
The impact of new material on the growing clump makes it hot, melting it, so that when it gets big enough and its gravity strong enough, it is pulled into a sphere perhaps a thousand kilometers in diameter. Now that’s a big asteroid. Continued impacts produce more heat. Of course, the formation process can stop at any time, allowing the object to cool and eventually solidify. In our case, however, growth continues. When it reaches a diameter of several thousand kilometers, it has become a planet.
If our new planet is close enough to a star, the heat from the star will evaporate and expel most of the gas and other volatile material, so that we end up with a rocky planet, like Mercury, Venus, Earth, or Mars.
On the other hand, if the planet manages to hold on to its gas and volatiles, it can grow into a gas giant planet, like Jupiter, Saturn, Uranus, and Neptune. During their formation, these planets collected a huge amount of internal heat, so even today their cores are extremely hot.
Now things get really interesting. If our planet collects material to the point where it exceeds about 20 times the mass of Jupiter, the pressure and temperature in the core become high enough for some elements, such as deuterium and lithium, to undergo nuclear fusion, producing energy. It’s no longer a planet, and it’s not yet a star that gets its energy through hydrogen fusion.
Objects like this, not quite a graduated star, are known as brown dwarfs. These objects show some aspects of stellar behavior, such as flaring. Astronomers are very interested in them. If the material keeps coming and our star reaches 100 or more Jupiter masses of material, we have a new star.
It’s amazing what can be done with one recipe, one ingredient and just changing the amount.
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• Saturn rises soon after sunset, followed a few hours later by Jupiter. After another two hours or so, Mars creeps into view, followed, just as the sky begins to lighten for dawn, by Venus.
• The moon will be full on the 11th.
This article was written by or on behalf of an outside columnist and does not necessarily reflect the views of Castanet.
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