Since NASA’s Kepler telescope launched in 2009, the planet-hunting spacecraft has changed our conception of space over and over again. Our galaxy, it turns out, is rife with exoplanets, or planets orbiting other stars—some of them perhaps even habitable. Today, NASA announced Kepler has identified 500 more possible planets, bringing the total to 4,175. And one newly discovered exoplanet, Kepler 452b, may be the most Earth-like ever.

That’s great and all, but still...kind of meaningless. We know of these planets now, but a more interesting question is: Could any of them really harbor life? And if they do, could any of them know of us?

Humankind, after all, has been inadvertently broadcasting electromagnetic waves since the invention of radio a century ago. Those early radio transmission were weak—too weak to even make it through Earth’s ionosphere, says Seth Shostak, senior astronomer at the SETI Institute. With World War II came military radar and then television and FM radio. Those waves, which are all electromagnetic like light, would have since traveled about 70 light years away from Earth. The newly confirmed Kepler 452b, at 1,400 light years away, will not be seeing I Love Lucy for more than a millennium.

So how many planets are in this 70 light-year radius? Astronomers have found evidence of over 100. And how many are potentially habitable? Just thirteen.

But potentially habitable doesn’t mean there’s life—intelligent or otherwise—and actually, potentially habitable doesn’t mean, uh, very much at all. “It’s quite literally anyone’s guess what those planets are like,” says Greg Laughlin, an astronomer at the University of California, Santa Cruz.

Kepler finds exoplanets by detecting how a star dims as its planet transits across it. The change in luminosity is miniscule—one part in 10,000 for an Earth-like planet passing in front of a sun-like star. That dimming and how often it happens lets astronomers estimate the exoplanet’s radius and distance from its star. That’s about it. “Habitable” is a label applied to any planet not too close to its star to get fried or too far to be frozen. Whether a planet like Kepler 452b is bathed in liquid water like Earth or seething like Venus is unknown.

In fact, exoplanets are so hard to detect, we’ve likely only found a tiny fraction of them. Shostak estimates there are 10,000 star systems in the 70 light year radius from Earth. Perhaps 10 to 20 percent will have a habitable planet, which comes to 1,000 to 2,000 maybe-possibly life-harboring rocks. Remember, astronomers have only found evidence of thirteen. Our telescopes are biased toward big planets close to their stars. The rest are left in the dark.

To confirm whether planets are habitable, astronomers have to look for an atmosphere. “There’s not a lot we can do now,” says Sara Seager, an astrophysicist and planetary scientist at MIT. Seager is waiting for the launch of the James Webb Space Telescope, which will be powerful enough to detect the atmospheres of some planets as they transit across their stars. The jackpot would be an atmosphere like Earth’s, with carbon dioxide, water, and oxygen that could support life.

So suppose there are habitable planets out there and there’s even intelligent life living on them. Could they sense us? Television and radio signals will have dramatically weakened as they dissipated through space. If those aliens had our technology, they would need an array of radio telescopes covering the state of Vermont. And that’s just to pick up intermittent signals. “If you really want the picture and sound, you’d need something bigger than that,” says Shostak.

It’s not impossible that somewhere within 70 light years, aliens with huge-ass radio telescopes arrays—or just way more advanced technology—know of our existence. But we don’t know the first thing about their planet yet.