500th Alien Planet Could Be Discovered This Month

This artist's conception shows the inner four planets of the Gliese 581 system and their host star, a red dwarf only 20 light-years from Earth.
This artist's conception shows the inner four planets of the Gliese 581 system and their host star, a red dwarf only 20 light-years from Earth. The large planet in the foreground is Gliese 581g, whose discovery was announced in September 2010. The planet is in the middle of the star's habitable zone and is only three to four times as massive as Earth.
(Image: © Lynette Cook)

Less than 20 years

As of Tuesday (Oct.

"Where we are,

And the 1,000th

Alien worlds

Most of these

Astronomers can

Astronomers first

Since then, however,

That trend will

The Kepler mission,

Researchers are

When such work is

"One could

The number of

Recent discoveries

"We have a

Reaching other

Other important

The rocky, roughly

When a planet

So the discovery of

"I wouldn't be

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