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Search for strange new worlds beyond our solar system reaches new milestone

Until 30 years ago, humans had never found a planet outside our own solar system. We've found a bunch more since then of all different types and sizes.

NASA announced a new milestone in its search of the stars. It has now found more than 5,000 exoplanets -- those outside of our solar system.

“It’s not just a number,” Jessie Christiansen, a researcher with the NASA Exoplanet Science Institute at Caltech, said in a statement. “Each one of them is a new world, a brand-new planet. I get excited about every one because we don’t know anything about them.”

Humans had never discovered another planet outside of our solar system until 1992. That's when, NASA said, scientists measures a slight change in the timing of radiation pulses from a type of neutron star known as a pulsar. Three planets were found around the star, giving astronomers a primer on how to find others.

Thirty years later, NASA just added 65 more discoveries to the Exoplanet Archive, putting the list at over 5,000. And that's the tip of the iceberg. NASA said our Milky Way galaxy alone likely has hundreds of billions of planets.

Of the ones that have been found, only 4% are considered to be "terrestrial" -- rocky and about the size of Earth or smaller.

Thirty percent are gas giants like Jupiter or Saturn. Some are several times larger than Jupiter, our largest planet. They can also be incredibly hot, such as one found in 1995 that is so close to its star, it orbits once every four days.

Then there are super-Earths -- about 31% of exoplanets found. They range in size between Earth and Neptune -- about four times larger than Earth -- and might be rocky.

The largest number -- 35% -- are considered Neptune-like. They are similar in size to Neptune or Uranus and, like those planets, can be ice giants. But there are some rare "warm" Neptunes.

Telescopes being launched over the next decade will not only help find exoplanets but also teach scientists more about what they are made of.

That will start with the James Webb Space Telescope, which just provided its first image since reaching distant orbit. NASA said it will capture light from the atmospheres of exoplanets, "reading which gases are present to potentially identify tell-tale signs of habitable conditions."

RELATED: NASA scientists giddy as 'gorgeous' image arrives from space telescope

To be included in the archive, NASA said planets have to appear in peer-reviewed scientific papers and have to be confirmed using multiple detection methods or other forms of analysis.

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