One of the greatest questions of our time is whether we are alone in the universe. And if there is some sort of extraterrestrial life out there, what are those aliens like?

Neil deGrasse Tyson thinks we may have at least a glimpse within the coming decades, because we are likely to find out whether life has ever existed anywhere else in our solar system.

Read: Here’s How Black Holes and Supernovas Kill You In Space

In a recent “ask me anything” post on Reddit, the astrophysicist answered questions about aliens in our galactic neighborhood as well as in outer space in general. He said it’s entirely possible we will know “in the next couple of decades” whether Mars ever hosted life, and within the next century for the rest of the solar system as a whole, which includes moons in the outer reaches like Europa, Titan and Enceladus.

But he has bad news for the people alive today who hope to have intelligent conversations with alien life forms that are more complex than a microorganism: Earth is probably not close enough to where those extraterrestrials live.

“It’s all about our capacity to travel interstellar distances,” Tyson wrote. “And that’s surely not happening in the next 50 years. Not the rate things are going today.”

Until technology advances, scientists are looking for life on other planets in the ways they know how. That includes searching for the things that sustain us on Earth, like water, oxygen and a temperature that is not too hot and not too cold. Although that seems like a biased approach, since other life forms could live under entirely different conditions, Tyson pointed out that the most crucial elements that sustain life on our planet — which include carbon, oxygen and hydrogen — are also among the most common elements in the universe. So maybe we are onto something after all.

And if the idea of the universe’s vastness and all the potential aliens it holds makes you feel small, Tyson has a remedy for that.

“Why not instead think of how awesome it is that our [3-pound] human brain matter actually figured all this out,” he said. “Why not look up to the clear night sky, and reflect on the fact that we don’t simply live in this universe, but the universe lives within us — through the atoms and molecules of our bodies, forged in the hearts of stars that long-ago gave their lives to the galaxy ... and to us.”

See also:

The Signs of Life on Other Planets

Supermassive Black Hole Farts Out a Baby Star