On Wednesday, astrophysicist Neil deGrasse Tyson endeavored to explain why space is a vacuum and what exactly we mean when we say that.

Tyson was answering a listener question, "If we take an open jar into space and close it, thereby filling it with the vacuum of space, what would happen if we bring it to Earth atmosphere level and even to the International Space Station?"

"It would be the best vacuum we would ever have encountered on Earth, ever," Tyson said. "Space is a far better vacuum than anything we've been able to create back on Earth."

He then laughed and said that in fact, what's happening if you open a jar in space isn't so much that vacuum is filling it as the air is streaming out of it.

"By the way," he said, "once you put the vacuum in it, and then you bring it back to Earth, what will happen is the inner surface of the glass and presumably a metal lid, will outgas into that volume. There are gases dissolved in the surfaces of all solid objects and it just stays there. It's molecules that are just stuck in the jagged-y surface of every solid object."

"If you would now evacuate the center of that jar," he continued, "it dislodges those gas molecules. And so, then, it'll put some kind of gas pressure back in."

He explained that in trying to create a perfect vacuum, scientists must empty a container and then heat the sides, releasing the gases trapped in the solid surfaces. "Then you vacuum it out again."

To bring a container of vacuum back to Earth, he said, you'd need a container with such smooth interior sides that they trap no gases. Much, much smoother than glass, he said.

He went on to explain that if nature abhors a vacuum, "which it doesn't," he said, "because most of the universe is made of vacuum," the thing that keeps Earth's atmosphere from rushing out into space is gravity, which holds the necessary gases to form an atmosphere close to the planet.

Watch the video, embedded below via Star Talk radio: