"Habitability" is a curious phrase. Certainly, large parts of Earth are habitable — and large parts of it are more difficult to live in. Humans have a smaller liveable range of conditions than creatures such as microbes, which can exist in areas of high heat or high acidity, for example.

But here's what astronomers say is a "habitable" planet: It's a rocky world that orbits near its parent star in a region where liquid water could exist on the planet. If the planet is too close to the star, that water evaporates (like on Mercury); if it's too far, the water turns to ice.

Telescopes of the future will tell us even more about these habitable planets. Do they have oxygen in their atmospheres? Can we see clouds of water vapor? These are all indications that the planet might be habitable, at least under the conditions that life needs to exist here on Earth.

TESS launched about a year ago to search out habitable exoplanets (planets outside our solar system) that are close to Earth. A team of astronomers just published a "TESS Habitable Zone Star Catalog," led by astronomy professor Lisa Kaltenegger at Cornell University, in The Astrophysical Journal Letters. The new catalog identifies more than 1,800 stars that could host habitable worlds; more than 400 of those stars could yield planets in just a brief search, too.

Life, of course, could exist under a range of conditions — for example, on Mars, where hardy microbes could bury underground or live in ice despite the cold temperatures and high radiation on the surface. The catalog does identify a few hundred stars where researchers could search a little further out in those solar systems to find worlds that aren't quite like Earth, but more like Mars.

What's more, about 10 percent of those more than 1,800 stars are within the viewing range of the James Webb Space Telescope. That's a next-generation telescope that NASA hopes to send into space by 2021. Once it's in space, Webb can take pictures of some of the planets that are largest and closest to Earth, providing us a glimpse of their atmospheres, perhaps. But that might be more possible for gas giant planets — those ones that are more like Jupiter — than the tiny planets that represent cousins of Earth.

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Learn about the residents of our own solar system in "Solar System: An Exploration of the Bodies that Orbit the Sun" by Marcus Chown. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.