The Transit Method: How to Detect Exoplanets

If you had $550 million US dollars, what would you do with it?

Maybe you’d buy a house, new car, take a vacation, buy a small island, host the Olympics or possibly something else extravagant.

Well, not too long ago NASA and the Laboratory for Atmospheric and Space Physics found themselves asking that same question and decided they would launch a 95 megapixel telescope weighing 2,291 pounds up into space to spend all of its time searching for Earth-like planets orbiting around other stars.

Fast forward to March 7th, 2009, the Kepler Space Telescope was launched into space and immediately went to work searching for exoplanets. The telescope was named after the famous Astronomer: Johannes Kepler and is designed to continuously monitor 145,000 main sequence stars and detect exoplanets orbiting around these stars.



Photo by Nasa


How Does the Kepler Telescope Find Other Planets?

That’s a great question and it’s not as simple as just looking for a planet orbiting around a star in another solar system out in the voids of space. It’s also not as easy as jumping aboard the USS Enterprise and cruising through space looking for other planets, even though that would be awesome!

Imagine you’re on a boat just off the coast in the water and you’re looking towards land. Now imagine you’re looking directly into the blazing light of the Lighthouse (in this example, this is the Sun). Now, imagine someone is standing next to it shining a household flashlight in the same direction (in this example, this is the planet).

Do you think you’d be able to see the flashlight in the midst of the power of the Lighthouse’s massively bright light? It’s not very likely since the small and pretty powerless light of a little household flashlight would be lost in the brightness next to it.



Photo by, Marcus Oh


This is the problem that Astronomers face when searching for Exoplanets orbiting Suns in other solar systems. The incredible power and brightness of a star totally overpowers the light being reflected off the planet orbiting around it.

So with the help of the Kepler Space Telescope, Astronomers use what’s referred to as the Transit Method to find planets orbiting around stars in other solar systems.

What is the Transit Method?

The transit method relies on the Kepler Space Telescope to be pointed in the direction of a distant star and capture the light being emitted from it.

Here’s something to keep in mind. The Kepler Space Telescope isn’t actually only observing 1 star at any given time. The direction the telescope is pointed and the amount of objects in its observable view contains well over 100,000 stars at any given time.

This means that the telescope is actually recording and collecting data on over a hundred thousand potential exoplanets solar systems at the same time!

The transit method monitors the level of brightness that a star is putting out. Think back to our lighthouse example; because of the awesome brightness of a star, any planet orbiting it would be nearly undetectable since its level of light reflection would be so dim compared to the star’s light output.

The transit method looks for almost impossibly small drops in the brightness of a star and can infer that a planet (or object) is passing between our telescope and the light being emitted from the star we’re monitoring.

These drops in brightness can sometimes be between 0.01% and 1% of the brightness of a star (depending on the size of the planet passing between the two of us). The sensitivity required to determine this drop in a star’s brightness is mind boggling. Think back to our example of the lighthouse, imagine being on your boat looking directly into the blasting power of the lighthouse’s light and being able to detect when a spec of dust passes in front of it!

Here is an example of what a transit method graph looks like when the Kepler Space Telescope is sending data down to Earth. It’s recording the brightness of the star it’s observing by the colored line across the graph. It detects a drop in the brightness as the planet orbits between the sun and our telescope’s lens, shown by the drop in the green line near the mid point of the horizontal axis in the graph.



Photo by Nasa


Here is an Interactive Model of the Kepler Space Telescope:

NASA has created a wonderful interactive model of how the Kepler Space Telescope operates and what data it collects, how it collects it and what it does with it. This is kid-friendly and only takes a moment to complete: Interactive Kepler Mission.



Photo by NASA


Can I Hunt for Exoplanets Myself?

You sure can, even from the comfort of your own home. NASA has a kid-friendly version of what using the Transit Method is like to observe distant stars and recording their drops in brightness. It walks you through finding a star to observe, determining what class the star falls into, what the star’s mass and radius is, the decrease in brightness over time, the distance the star is from us and where the habitable zone would given the mass of the star.

With this data in hand, you calculate the surface temperature of any exoplanets orbiting around the star you selected, the radius of the planet (in Earth radii) and then you get to see your planet and what it’s like relative to that of Earth. Check out the Interactive Transit Method Model here.



Photo by NASA

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