Photo: Greg Reely
Unique once-in-a-lifetime image of a comet taken by local South Okanagan photographer near Cawston.
If you want to make a comet, an asteroid, a planet, a 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, only part of the material is assembled in one piece. What you end up with is entirely determined by the size of the dough you’re working with. The mass of the lump determines two critical quantities, the pressure and the temperature at the core of this body.
The temperature at the Earth’s core is about 5,200 C and the pressure about 3.6 million times the atmospheric pressure at the surface. The pressure comes from the weight of the rock above it. The internal heat comes from two sources: the energy released by the impacts of incoming objects when the Earth was formed, about 4.5 billion years ago, and from the decay of radioactive elements present in the cosmic material.
For a planet our size, heat escapes very slowly. For smaller worlds, the process is faster.
Imagine that somewhere in a great cloud of cosmic dust and gas, a couple of grains drift in and, thanks to static electricity or something else, stick together. The resulting grain is larger and presents a larger target for other particles, so it has a better chance of catching more particles. Even in these clouds, the density of material is very low, so collisions are rare, but they happen a long, long time.
As the grain grows, it collects samples of all the chemicals that make up the cloud, including hydrogen and other volatiles. Eventually, it goes from being a grain to a lump, and after more time it becomes massive enough that a new force takes over to hold the lump together and increase its rate of growth by dragging more and more of the surrounding material: gravity.
The impact of the new material on the growing lump causes it to heat up, melt so that when it gets big enough and its gravity is strong enough, it is stretched into a sphere, perhaps a thousand kilometers in diameter. It is now a large asteroid. Continued impacts produce more heat. Of course, the formation process can stop at any time, allowing the object to cool and eventually solidify throughout the process. However, in our case the growth continues. When it reaches a diameter of several thousand kilometers, it has graduated as a planet.
If our new planet is close enough to a star, the star’s heat will evaporate and expel most of the gas and other volatile material, so we end up with a rocky planet, like Mercury, Venus, the Earth or Mars
On the other hand, if the planet manages to hold on to its gas and volatiles, it can become a gas giant planet, like Jupiter, Saturn, Uranus and Neptune. During their formation, these planets collected a large amount of internal heat, so even today their cores are extremely hot.
Now things get very interesting. If our planet collects material to the point where it exceeds about 20 times the mass of Jupiter, the central pressure and temperature are 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, which gets its energy by fusing hydrogen.
Objects like this, a star not very bright, are known as brown dwarfs. These objects show some aspects of star 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 you can do with one recipe, one ingredient and just changing the amount.
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• Saturn rises shortly after sunset, followed a couple of hours later by Jupiter. After two hours or so, Mars comes into view, followed, just as the sky begins to light up with dawn, by Venus.
• The Moon will be full on the 11th.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.