Pluto

The papers seek to explain why Sputnik Planitia -- a 1,000 kilometer-wide, nitrogen-covered basin in Pluto's heart-shaped northern region -- is permanently aligned with the dwarf planet's moon Charon.

The first paper, from the University of Arizona,suggests that Sputnik Planitia filled with ice and altered tidal forces between Pluto and Charon.

The team responsible for the New Horizons flyby of Pluto last week released new pictures Friday of the previously unexplored world.

Scientists say layers of haze stretch 100 miles (160 kilometers) into the atmosphere, much higher than anticipated. All this haze is believed to account for Pluto's reddish color.

As for the incredible ice flows, they appear to be relatively recent: just a few tens of millions of years. 

The long-awaited images were unveiled Wednesday in Maryland, home to mission operations for NASA's New Horizons spacecraft.

A zoom-in of Pluto reveals an icy range about as high as the Rockies. To the scientists' great surprise, there are no impact craters. On Charon, deep troughs and canyons can be seen.

The images were collected as New Horizons swept within 7,700 miles of Pluto on Tuesday, becoming Pluto's first visitor in its 4.5 billion-year existence.

On the eve of NASA's historic flyby of Pluto, scientists announced Monday the New Horizons spacecraft has nailed the size of the faraway icy world. Measurements by the spacecraft set to sweep past Pluto on Tuesday indicate the radius of the dwarf planet spans 736 miles, plus or minus six miles. That's 20 miles to 30 miles bigger than previous estimates. The diameter would be twice that.

Principal scientist Alan Stern says this means Pluto has a lower density than thought, which could mean an icier interior.

A computer overload prompted the spacecraft to partially shut down on July 4th — just days before the first-ever close flyby of Pluto. Flight controllers managed to regain contact with the spacecraft in just over an hour and correct the tense situation, occurring after a relatively quiet journey of 3 billion miles and 9½ years.

"We're on to Pluto!" NASA's director of planetary science, Jim Green, assured journalists Monday.