BALTIMORE (WJZ)— A world of fire and ice. It turns out the planet Mercury has both.

Alex DeMetrick reports Johns Hopkins Applied Physics Lab is a key player in the discovery, which will rewrite the science books.

The Messenger Spacecraft was designed with heat in mind. Headed to the planet closest to the sun, it has to withstand what Mercury endures: days that can reach 800-degrees Fahrenheit at the equator.

So what it found is surprising.

“Water ice on Mercury.  Who knew?” said Dr. David Lawrence, Johns Hopkins Applied Physics Lab.

But at the Hopkins Applied Physics Lab, Messenger was assembled with discoveries in mind.

“That’s one of the fun things when you go exploring. You find stuff you didn’t expect in hidden little places,” Lawrence said.

In this case, in craters at Mercury’s North Pole.

Highlights show ice concentrations. Another highlight shows why. It outlines areas of perpetual shadow.

“It doesn’t tilt, so you can have craters deep enough at both poles that never see the sun.  They get very, very cold,” Lawrence said.

Cold enough to deep freeze the water ice that make up comets.

Mercury is pock-marked with impacts from collisions. Most from comets boiled off long ago. But not those pockets at the poles.

Ice piled up over millions of years, “100 billion to maybe a trillion metric tons,” Lawrence said.

Scanning the surface, Messenger found ice after it detected hydrogen, a dead giveaway for water.

The Mercury mission could continue into 2015, and if there is enough fuel, it might fly closer to the planet.

“Closer is better for us.  Absolutely.  Skim the mountain tops if we could,” Lawrence said.

But so far the view has been just fine.

As hot as Mercury is, its cold spots are really cold, as low as 370 degrees below zero.