About a week after finding the exoplanet that most resembles Earth, NASA scientists reported the nearest Earth-like exoplanet.

NASA stated in a press release last week that astronomers found HD 219134b using the Spitzer Space Telescope. They determined it is a rocky planet a little bigger than Earth about 21 light years away, but its significant caveat is that it orbits its host star way too close.

About a week earlier, NASA reported the discovery of Kepler-452b and called it "Earth 2.0" for being a bit bigger and remarkably similar. While scientists will be studying it further, Kepler-452b apparently orbits its host star at an appropriate distance and has a protective atmosphere, as well as a rocky surface.

But it too has a significant caveat: it is 1,400 light years from Earth. Even HD 219134b, which is clearly inhospitable, would be impossible to get to at 21 light years away.

Jeffrey Bennett, an astronomer who wrote the book, "What Is Relativity?: An Intuitive Introduction to Einstein's Ideas, and Why They Matter," told NBC News just how impossible traveling to Kepler-452b would be.

He said it would take a spacecraft 28 million years to get to "Earth 2.0" if it went at the same pace at which New Horizons reached Pluto. With NASA's in-development Evolutionary Xenon Thruster (NEXT) engines, Bennett said the trip to Kepler-452b could be cut down to 10.5 millions years.

Not that NASA is planning to go these great distances, but the search for Earth-like exoplanets serves as a reminder of the universe's endless reaches. With the Kepler Telescope no longer seeking out distant worlds, NASA is developing the next of its kind to take up the torch.

Meanwhile, Kepler's extensive backlog of data is providing NASA astronomers with plenty of reviewing to do.