LS: Speaking of Science Column January 05, 2009

Let’s find a new planet by gravity, 'mini-eclipse’

If you’re a science fiction fan, you’ve come across stories about relocating the population of Earth to another planet.           

Sometimes it’s because of overpopulation, sometimes because we’ve poisoned the environment, and sometimes it’s just for the adventure.

In fact, this idea crosses the line between science and science fiction, with serious scientists sometimes suggesting we may need to consider colonizing other planets.

Before the late 1980s, the existence of planets outside our solar system was only speculation, although the likelihood of their existence was high, simply because of the billions of stars and galaxies that exist.

Then in late 1988, the first evidence of such a planet was found. These planets have been termed exoplanets.

But how was this discovery was possible, as even the closest stars are so far away that they appear only as pinpoints of light to the most powerful telescopes?

One method is to measure the dimming in light we see from the star when the planet crosses the face of the star (sort of a “mini-eclipse”).

Unfortunately, this method only works if the plane of the planet’s orbit is exactly in line with our line of sight to the star, which doesn’t happen too often.

Another method depends on the gravitational force between the star and the planet. Did you ever play the game “ring around the rosie,” holding hands with a friend and circling around each other? The faster you spin, the more tightly you have to grip, or you will both fly off in opposite directions because of the centrifugal force (caused by the rotation) pulling you apart.

And if your friend is much larger than you, you will do most of the rotating, and your friend will do very little.

This is very similar to two objects orbiting each other in space, such as a star and a planet. The force holding the objects together is gravity (in space) or your grip (for your friend and you).

Because a star is much heavier than a planet, the planet moves in a large circle, but the star moves a little, too.

This movement of the star is called “wobbling” and can be detected by very sensitive measurements of its position. So even when you cannot see the planet, you can detect its presence by the wobbling of the star it circles.

So far, more than 300 exoplanets have been discovered by one of these methods.

Amazingly, this past November, the first exoplanet was directly observed by optical telescopes.

That means the light reflected from a planet, millions of times dimmer than the star it circles, was detected, to the surprise of many.

It is the first time a planet outside our solar system has actually been seen.

Could life exist on one of these planets?

Could we survive on them if we managed to travel to one?

The range of conditions that support life here on Earth seem to be quite broad, with plants and animals living at crushing pressures under the ocean, in subzero temperatures near the poles and in scorching deserts.

But these conditions are fairly uniform when you begin to consider the extremes of temperature and gravity that exist on other planets in our own solar system.

Could life exist where temperatures are too hot for liquid water to exist or too cold for oxygen to exist as a gas?

Unfortunately, the characteristics of the exoplanets that make them easiest for us to detect (large size and nearness to their star) are not conducive to life as we know it.

We will not be able to relocate to a planet with the gravity of Jupiter and the temperatures of Mercury unless we adapt quite a bit.

But maybe forms of life quite different from us could develop there.

It is likely that there are a large number of planets similar to Earth that we cannot detect yet.

So how long will the trip be if we want to visit one of these planets (or if they want to visit us)?

That will have to be the subject of another article.


Vincent King is a certified health physicist who has been involved in radiological sciences for more than 30 years. He is a volunteer at the Western Colorado Math & Science Center.

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