Neighbourhood worlds

Ken Tapping, November 28, 2012

In the sky this week…

  • Jupiter rises around 5 pm.
  • Saturn and Venus lie close together and rise around 5 am.
  • The Moon will be Full on the 28th.

One of the more exciting recent astronomical discoveries was the finding of an earth-sized planet orbiting the nearest star to the Sun.  It lies about 4.3 light years away, which is no distance at all by cosmic standards. The star is usually called Alpha Centauri, but it also has the more poetic name of Rigel Kentaurus. It is a moderately bright star in the constellation of Centaurus, “The Centaur”. 

To the naked eye it looks like a single star, but the telescope reveals it to consist of three stars orbiting each other. These have been artistically labelled A, B and C. The planet orbits Alpha Centauri B. This star is about the same temperature as the Sun, but only half as bright. However, the planet orbits so close to its star that it completes an orbit around it in less than four days.  Being that close to the star it must be red hot and partially molten.

So far astronomers have confirmed about a thousand planets orbiting other stars, with several thousand more having been reported and in the process of being confirmed.  However, as yet the big puzzle is why those other planets don’t seem to be in planetary systems like our Solar System.

The Solar System consists of four rocky planets orbiting relatively close to the Sun: Mercury, Venus, Earth and Mars. Then there is a belt of asteroids, and then four gas giant planets: Jupiter, Saturn, Uranus and Neptune. Then there are many icy bodies and minor planets orbiting the outer reaches of the Solar System, including Pluto.

It all used to make sense. A cloud of cosmic dust collapsed into a disc. The core became the Sun and a lot of the other stuff formed planets. The inner four had a lot of their gassy atmospheres cooked and blown away by the Sun, whereas further out, the planets hung onto them, making them gas giants. The gravity of the giant planet Jupiter interfered with the formation of a planet between it and Jupiter, leaving us with a belt of asteroids. However, other planetary systems do not seem to be following this logical model. We have a lot more to learn about planet and star formation.

One reason we have a special interest in planets orbiting the stars closest to us is that we might be able to visit them. However, in the absence of “interstellar jumps” and “warp drive”, this is very difficult.  A spacecraft of current designs might reach 200 km/sec. However, at that speed it will take 6,450 years to get to Alpha Centauri. There are concept technologies that might get us to 20% of the speed of light. This brings the journey down to 21.5 years, which is still a long time.

Ideas in science fiction for travelling these distances include “generation ships”, where your remote descendants arrive at the destination, and “deep hibernation”, where you sleep the interstellar decades away.  However, there is a story about such a mission to another star, where the crew woke up at their destination and found a human reception committee. While they were asleep someone back on Earth had invented warp drive and colonists had got there ahead of them. The best idea seems to be to stick around home and wait for the right technologies to be developed.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355

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