DSCOVR EPIC/NASA Earth Observatory As a species, we have long looked to the stars. They have provided navigational guidance, spurred our imaginations, and inspired us to explore.

We are explorers who have spread around the world and are now reaching into space — to Mars soon, we hope, and beyond. Some of our most popular fiction focuses on life spread across the universe, including "Star Wars" and "Star Trek" as well as video games like "Mass Effect" and the coming "No Man's Sky."

So it's perhaps no surprise that when people find out about the 100 Year Starship project, designed to push humanity toward achieving what's needed to actually be capable of interstellar travel within 100 years, many are excited — and want to sign up to go.

But Dr. Mae Jemison, the astronaut in charge of the NASA- and DARPA-funded 100 Year Starship, has some bad news for those eager to join an interstellar voyage.

"There's maybe perhaps an unpleasant truth I have to tell everyone," Jemison tells Tech Insider. "Most of us are going to be on this planet — we're not going to go."

In this case, we should point out that the 100 Year Starship isn't planning on actually constructing such a ship. It just wants to help make sure that it becomes possible to do so.

But even if we do meet the immense technological challenges blocking us from interstellar travel within the next 100 years, Jemison says, most of us will still be living on this planet.

We might send a group of humans out to colonize a new star system, but even if that group includes thousands of people, we're certainly not going to send everyone who might be interested on such a journey. We just don't know that there is another planet out there that's suited for our unique biology, another place that might be a home for us.

Even if we soon become capable of traveling the stars, it will most likely be far longer before we find a place as perfect for us as Earth.

"We're going to be on this planet," Jemison says.

And though it might seem counterintuitive, that's exactly why she argues we need to figure out interstellar travel. Because if we can figure out the technology we'd need to live sustainably in space, we can probably figure out how to live sustainably on Earth as well.

And that's a clear and immediate challenge we all face, whether we'd be interested in an interstellar journey or not.