Today’s Wonder of the Day was inspired by Anish from Marlboro, NJ. Anish Wonders, “Exoplanets” Thanks for WONDERing with us, Anish!

Are you a dreamer? In the dark of night, do you like to sit under the stars and just gaze up at them, WONDERing what those other worlds are like? Do you ever imagine that there might be other planets with life out there somewhere in the universe?

When astronomers discovered the other planets in our solar system, it was only natural to be curious about whether or not any of those other planets hosted any form of life. Over time, as scientists learned more about the other planets that orbit the Sun, it became clear that Earth was an exceptionally-special place and indeed featured the only environment hospitable enough for life.

For some, learning that we're alone within our solar system might have ended the inquiry. Astronomers, however, tend to be a curious bunch that's not satisfied with staying within the confines of just our solar system. Instead, they know that there are billions of other stars like our Sun spread across the universe.

With so many other stars out there, they began searching the neighborhoods around those stars for planets like Earth. Could there be an Earth-like planet orbiting some other star with all the perfect conditions to support life? Maybe!

Astronomers call these planets that orbit other stars "exoplanets," which is short for extrasolar planets. To date, scientists have found exoplanets in a wide variety of sizes. Some are much larger than Jupiter, while others are much smaller than Earth.

Scientists have learned that other solar systems share similarities with our own solar system. For example, they've learned that exoplanets can orbit their stars at different distances. Some exoplanets are so close to their stars that they have surface temperatures that could melt iron.

Other exoplanets might orbit at just the right distance that they fall in their star's habitable zone, which is the zone in which an exoplanet would enjoy temperatures that would permit liquid water to exist at its surface. The existence of liquid water at the surface is one of the key factors scientists believe would permit life to form.

Unfortunately, exoplanets are not easy to see from Earth. Exoplanets tend to be relatively small and dim compared to the bright glare from the stars they orbit, which makes them hard to spot. Clever scientists have developed an indirect method of discovering exoplanets that they call the "transit method."

Knowing that exoplanets orbit their stars just like Earth orbits the Sun, scientists reasoned that exoplanets would pass between their stars and Earth on a regular basis. By measuring the brightness of stars over long periods of time, scientists can identify periodic decreases in the brightness of stars that correspond to exoplanets orbiting them.

Although astronomers have long believed that exoplanets existed, the first exoplanets weren't confirmed until the 1990s. Since that time, over 2,000 exoplanets have been identified. Over 1,000 exoplanets have been identified by one device alone: NASA's Kepler space telescope.

The Kepler space telescope reached orbit in 2009 and searched for exoplanets using the transit method for four years. Even though its original mission has ended, the Kepler space telescope collected a tremendous amount of data, and scientists are still making new discoveries from that data even today.

Wonder What's Next?

Join us in Wonderopolis tomorrow to examine a disease that plagued many.