Photos: Delta 4-Heavy launch gallery

Boosted to an altitude of 3,604 miles by a Delta 4 rocket, NASA’s Orion deep space exploration vehicle fell back to Earth Friday in the program’s maiden voyage, slamming into the atmosphere at nearly 20,000 mph, enduring a hellish 4,000-degree re-entry and settling to a Pacific Ocean splashdown to wrap up a critical unmanned test flight.

Three years and a billion miles past Pluto, NASA’s New Horizons probe is on the verge of at least one more pioneering, once-in-a-lifetime milestone: a New Year’s Day flyby of a small body known as 2014 MU69, unofficially dubbed Ultima Thule — “beyond the known world” — in a NASA naming contest.

Images from NASA’s New Horizons probe show Pluto is a surprisingly active world in the deep freeze of the outer solar system, with jagged 11,000-foot-high mountains of frozen water dusted with a veneer of nitrogen, methane and carbon monoxide ice amid smooth plains and jumbled terrain.