Dear Ia,

I looked through a high-power telescope for the first time in college. I couldn’t believe how many stars I saw. It’s hard to imagine all the planets orbiting all those stars.

I talked about how we know those planets are out there with my friend Jose Vazquez. He’s an astronomer at Washington State University.

He told me that scientists look for planets outside our solar system using a number of instruments—like a photometer. That’s a tool that attaches to a telescope and measures light.

The sun and eight major planets make up our solar system. All the planets outside our solar system are called extrasolar planets or exoplanets. Some of them are called hot Jupiters. Exoplanets orbit other stars—just like we orbit the sun.

The closest exoplanet is nearly 25 trillion miles away. Scientists can’t point a telescope and look directly at a planet that distant. They can’t send a rover that far. Instead, they look for clues that a planet is there.

One clue is called a light curve. Imagine you’re facing a distant star with a planet. As the planet orbits its star, sometimes it will pass between you and the star. The star’s light will get dimmer as the planet passes by. Then it will get brighter again.

Scientists measure a star’s light using a photometer. They take lots of measurements over time. Then they plot them into a graph called a light curve. Any time the light dims, there’s a dip in the graph. The dip shows when the planet passed in front of the star. Generally, the deeper the dip, the bigger the planet.

Scientists also use a light curve to tell how long it takes the planet to orbit its star. They can even tell how hot the planet is and how thick its atmosphere is.

A blue light curve graph showing a dip when an asteroid passes a star
Here’s what a light curve looks like, credit: KuriwaObs


In 2009, NASA wanted to see how many Earth-sized exoplanets they could find. They wanted to learn more about the universe. They wanted to see if there were other planets that could support life.

So, they launched a giant space telescope called Kepler. Its main instrument was a photometer. It zoomed around measuring the light from different stars. Then, scientists made light curves and looked for exoplanets.

So far, scientists have found more than 5,500 exoplanets. They’ve found many more possible exoplanets. Scientists are still combing through the Kepler data. Plus, another space telescope called TESS took over when Kepler ran out of fuel.

You don’t have to be an astronomer to hunt for exoplanets. Anybody can use robot-powered telescopes online to look for planets and other objects in space. Or you can look through the data from Kepler yourself.

“The MicroObservatory Telescope Network is for anybody who’s interested in extrasolar systems,” Vazquez said. “With just a few clicks, students can take pictures and try to make contributions to finding these planets.”

That’s an invitation to do community science that’s out of this world.


Dr. Universe