Night Sky Gaze

What Is an Exoplanet?

It sounds like something out of science fiction, but exoplanets are science fact! Simply put, they are planets orbiting around stars other than the sun. Astronomers are searching for exoplanets—especially those that might be similar to Earth—throughout the galaxy.

Decades of Discovery

The first exoplanet wasn’t discovered until 1995! Since then, astronomers have identified at least 4000 more—doubling the number of known exoplanets every 2 years. They are very difficult to see, even with sophisticated telescopes, so astronomers look instead for the effects exoplanets have on their star systems.

For example, when a planet orbits a star, it can cause what appears to be a wobble in the star itself. However, only the largest planets—we’re talking Jupiter or even bigger—can cause a visible wobble. Earth-sized exoplanets don’t have enough mass to cause a stellar wobble.


Scientists are most interested in planets similar to Earth, where recognizable life might flourish. That’s the mission of TESS, the Transiting Exoplanet Survey Satellite. So far, TESS has assembled a catalogue of almost 2000 stars where Earth-like planets might exist. On March 31, TESS identified the first confirmed exoplanet of the mission, which astronomers nicknamed “hot Saturn.” Its official designation is TOI 197.01—but we like Hot Saturn better!

Hot Saturn isn’t likely to host life. It’s so close to the star it orbits that the temperature is extremely high. It orbits that star in just 2 weeks! The key criteria to finding an Earth-like planet is not just size but also distance from the star it orbits. That distance indicates whether water might be present on the planet—something that’s absolutely essential for life as we know it.

Searching for Life

“Life could exist on all sorts of worlds, but the kind we know can support life is our own, so it makes sense to first look for Earth-like planets,” said Lisa Kaltenegger, director of Cornell’s Carl Sagan Institute and the lead author on a recent paper about TESS’s discoveries.

TESS has been able to pinpoint 408 stars that could be orbited by Earth-like planets at the right distance to have water. That data will make it possible for future missions to survey those stars and discover whether the predicted exoplanets do, in fact, exist.

The James Webb Space Telescope, slated to launch in 2021, will use TESS’s data to study exoplanets. Its focus will be on the atmosphere of those planets—another key piece in whether the planet might support some form of life.

Johnny Rodgers