There are Exoplanets?

Over the last several years astronomers have identified thousands of exoplanets. That is, planets orbiting other stars (our sun is a star remember). You might think, well they look through their telescopes and see them but no. A planet orbiting a star many light years away is too close to that star as seen from here to be detected. Plus the light from the star itself is many times brighter than the light that would be bouncing off the planet.* So all the methods for detecting exoplanets are indirect. You see something that you infer must be a planet. Note that this doesn’t make the conclusions any less valid anymore than indirectly detecting the wind with a wind vane is. Can’t see ‘the wind’ either!

There are 5 methods and NASA has a great site explaining all 5.

I only want to focus on the transit method -the method that has detected the most planets. As a planet passes in front of its star it will block some of the light. If you can monitor the brightness of the star over time you can detect a regular dip in it’s brightness. The amount of dip will tell you some thing about the size of the planet and the periodicity of the dipping will tell you the period of it’s orbit (its ‘year’) which can also tell you it’s distance from it’s star. Most of these are being detected by the Kepler space telescope which can ‘stare’ and a group of stars for long periods of time to collect the data on the brightness of many stars at once.

Notice that for this method to work you have to be looking at another solar system edge on. That’s just luck that we must be seeing some edge-on. It also means that statistically there are many times more planets out there than we can see by this method.

Bonus with this method is that some of the light that comes to us has passed through the atmosphere of the planet telling us the composition of that atmosphere (again via spectroscopy). This data will only get better after the launch of the James Webb space telescope. The exciting thing about analyzing the atmosphere of distant worlds is that abundant life on a planet will leave a unique signature within the atmosphere. Exciting times these are. Stand by!

Let’s GO!

Before we too excited about visiting let’s remember that the closest star with possible exoplanet would be Alpha Centauri and it’s about 4 light years away. If we try to say hello via a radio wave (they travel at the speed of light as well) that signal will get there in 4 years. If some intelligence responds instantly it will take another 4 years for the return hello to get to earth.

Spaceships? The fastest spaceship we’ve ever built was the New Horizons craft which cruised past Pluto at about 60,000 km/hr. Let’s say we work on that and get a craft up to 100,000 km/hr. 4 light years is actually 36 trillion km = 36,000,000,000,000 km. So to cover that distance at 100,000 km/hr would take 360,000,000 hours which is about 40,000 years! Better to wait for warp drive?

*There are methods afoot to cleverly block the stars light and get a snapshot of the planet itself.