A man in his early 20s received a transplant of his own sperm-producing stem cells, which had been frozen since his childhood, in an attempt to regain fertility. Doctors are waiting to see if the treatment works.

Researchers analyzed the ancient DNA of two mummies from what is now Libya to learn about people who lived in the "Green Sahara" 7,000 years ago.

SpaceX's Starship has been awarded a NASA contract that will allow it to be considered for future missions. However, recent explosive tests have shown the supersized spacecraft is still far from mission-ready.

A roughly 100-year-old western Santa Cruz Galápagos tortoise has become a mom for the first time after reproducing with a male of the same age at Philadelphia Zoo.

A sudden stratospheric warming event reversed the winds that make up the northern polar vortex on March 9. A new animation shows the vortex also moved away from the Arctic towards Europe.