It’s in the shake and wobble!

It’s in the shake and wobble!

Ever wondered how scientists can tell if there are new planets orbiting in space?

Ever wondered how scientists can tell if there are new planets out there? New stars and planets help scientists learn how planets form. They are called extra solar planets and astronomers know of about just over 400 of them. Extra solar planets orbit stars other than the Sun and some of them are huge, even larger than Jupiter.


It can be very tricky to spot new planets .You can only see them when they are reflecting light from their parent star. When you look at them through a telescope, even the most powerful one, it's very difficult to spot them as they're drowned out by the star's light.

If astronomers can't see the planets, how do they know that they are there at all?  According to astronomers, some stars appear to wobble back and forwards. Yes that's right, wobble! But stars don't move…do they?

Well stars with orbiting planets do, and so this is what astronomers look out for.  When they see a shaky star they know that something near it must be making it move.  So why does a planet make the star wobble, planets go round stars, right?

Wrong! Stars and planets actually orbit each other, even The Earth and the Sun!

The Sun is about 330,000 times bigger than the Earth, which makes it 330,000 times harder to move. But the Earth's pull on the Sun does manage to move it a bit. The Earth's orbit is about 186,000,000 miles from one side to the other. This is how much the Sun's pull moves the Earth. The Earth's pull on the Sun moves it 330,000 times less than this. That is, about 560 miles. Not much in comparison. So all you see from a distance is the Sun wobbling about 560 miles back and forth in year, but this is enough for a clever alien to know that the Earth is there.

By watching for the wobble, a scientist will be able to tell when a new planet forms.  This will give them a better idea of what made it happen, and maybe give us a clue about how our planet formed.

But if they can't even see the planets how are they going to discover anything useful? Scientists can use the wobble to work the planet's mass and distance from the star.  They can measure the wobble using the Doppler effect.

You can hear the Doppler effect change the pitch of a sound waves from the siren as a police car goes past. Waves that come from a moving object seem to change their wavelength. If the object is coming towards you they are all bunched up, the wavelength is shorter. If they are going away from you they are stretched out, the wavelength is longer. When this happens to light, it is known as a blue or red shift.  By measuring this shift in the colour of the light we can work out how big the planet is and how fast it orbits!


It seems that there are a lot more planets out there than we first thought. There are shaky stars everywhere.  But you don't have to be a scientist or own the world's most powerful telescope to find stuff. Amateur's discover things all the time - like this guy.