(CNN) NASA's new planet-hunting TESS telescope has found an exoplanet three times the size of Earth only 53 light-years away. It has also discovered a super-Earth and a rocky world, making three exoplanet discoveries in the first three months since it began surveying the sky in July.

The nearby exoplanet, HD 21749b, orbits a bright neighboring star in the Reticulum constellation, with a 36-day orbit and a surface temperature of 300 degrees Fahrenheit. That's actually quite cool, considering how close the planet is to its star.

The discovery was announced Monday at the 233rd meeting of the American Astronomical Society in Seattle.

"It's the coolest small planet that we know of around a star this bright," said Diana Dragomir, a postdoctoral researcher in the Massachusetts Institute for Technology's Kavli Institute for Astrophysics and Space Research. "We know a lot about atmospheres of hot planets, but because it's very hard to find small planets that orbit farther from their stars and are therefore cooler, we haven't been able to learn much about these smaller, cooler planets. But here, we were lucky and caught this one and can now study it in more detail."

Its size, three times that of Earth, makes it a sub-Neptune. But despite the exoplanet's size, it has 23 times the mass of Earth. This means it is most likely a gaseous planet, rather than rocky like Earth. But the gas that makes it up it is probably more dense than that of Uranus or Neptune.

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