Voyage To Pluto

At long last, we’ve seen distant Pluto and its many moons.

- Ken Croswell, Ph.D.

In July 2015, a spacecraft named New Horizons sped past Pluto, the farthest world NASA has ever visited. The spacecraft found tall mountains on Pluto and deep canyons on its largest moon. “I think the solar system saved the best for last,” said Pluto scientist Dr. Alan Stern.

Pluto is billions of miles from the Sun and Earth. It is so far away that our telescopes can’t see it well. So no one knew what the spacecraft would see.

Pluto vs. Eris

Pluto belongs to a belt of objects beyond the orbit of the distant planet Neptune. If Pluto were as big as a basketball, the typical object in this belt would be smaller than a marble.

But in 2005, astronomers found a similar world, Eris, which is much farther than Pluto. “If it’s not larger than Pluto, then I’ll eat my telescope,” the discoverer claimed. In 2010, Eris passed in front of a star and blocked its light. How long this event lasted revealed how big Eris is: 1,445 miles across.

The New Horizons spacecraft measured Pluto’s size: 1,477 miles across. So Pluto is bigger than Eris. In fact, Pluto is the largest object in the solar system beyond Neptune.

A Cold World with a Heart