Nasa’s New Horizons spacecraft will be flying past the moon next month, and could solve the mystery

Pluto’s moon, Charon, has a huge dark patch at the top — and nobody knows why.

Nasa hopes that some of the mystery will be solved when its New Horizons spacecraft flies past the moon next month. But until then, scientists can only speculate about what might be the reason for dark terrains at the moon’s pole.

The scientists have also found new detail about Pluto itself, which contains more varied terrains than they had expected to see. It also has a bright fringe, which scientists think might be frost from an ice cap that is in the process of melting in Pluto’s summer.

"This system is just amazing," said Alan Stern, New Horizons principal investigator, in a statement. "The science team is just ecstatic with what we see on Pluto’s close approach hemisphere: Every terrain type we see on the planet—including both the brightest and darkest surface areas —are represented there, it’s a wonderland!”

"And about Charon—wow—I don’t think anyone expected Charon to reveal a mystery like dark terrains at its pole," he said. "Who ordered that?"

The piano-sized New Horizons craft is now about 2.9 billion miles from Earth. It’s just 16 million miles from Pluto, and is expected to fly past the dwarf planet in mid-July.