"This intriguing, distant world gives us even greater hope that a second Earth lies among the stars, waiting to be found," said an associate administrator at NASA.
The work was famously described by Albert Einstein as "perhaps the greatest intellectual stride that it has ever been granted to any man to make."
The exoplanet is 110 light-years from Earth and was discovered by NASA's Kepler spacecraft in 2015.
A year on these planets flies by, lasting between five and 10 Earth days.
The planet is likely the densest Earth-sized planet ever found.
The spacecraft has spotted almost three-quarters of the alien planets scientists have identified to date.
The news is under tight wraps, but spoiler alert: It's definitely not Nibiru.
The lipstick-shaped satellite has already done incredible science, whatever news Thursday's announcement brings.
The device will look for stars like our own sun and examine planets similar to Earth.