What We've Learned From Pluto So Far

So. Many. Things.

Pluto And Charon

New Horizons shot this portrait of Pluto and Charon on July 11, just a few days ahead of its closest approach. For some reason, it kind of reminds us of the American Gothic painting of the farmer and his wife.NASA/JHUAPL/SWRI

When the New Horizons spacecraft launched in 2006, scientists had no idea what it would find when it arrived at Pluto nine years later. “We might have seen a cloud-enshrouded nitrogen haze that we'd zip by and say, 'Well, that was fun,'” says John Grunsfeld of NASA's Science Mission Directorate. “Or we might have seen something that looks like an ancient monolithic crater-laden body.”

Now we've finally seen the face of Pluto, and just as expected, it is full of surprises. Here's what we've learned so far.

Pluto Has Had A Change Of Heart

Pluto as seen just before the New Horizons flyby

Pluto As Seen Just Before The New Horizons Flyby

The day before the spacecraft was set to make its closest approach, Pluto sent us this love letter. The image was taken on July 13 from a distance of 476,000 miles, and it has a resolution of 2.5 miles per pixel.NASA

The bright heart-shaped patch of frost visible in the latest images of Pluto hasn't always looked that way. Using ground-based telescopes, “we have been monitoring what we now know as the heart for 60 years,” says New Horizons planetary scientist Bonnie Buratti, “and it does look like that heart thing has been eroding away over time.” Most of the erosion seems to have occurred near the dark “whale” shape, which makes sense since darker materials absorb more sunlight.

But don't worry, Pluto's heart isn't going anywhere anytime soon. If we were to return to Pluto in 100 years, the heart would be smaller, but Buratti says “it's really hard in that cold to sublimate a patch of frost that big.”

It's Active And Complex

Pluto's surface seems to be much younger than Charon's gray facade, New Horizons leader Alan Stern said in a press conference today. Its relative lack of impact craters suggest the dwarf planet's surface is renewing, either by geological or atmospheric activity, such as erosion.

Pluto's highly reflective “heart” is also a good sign, says Buratti. “Bright is good because it means the planet is active.” Although we still don't know whether it has geologic activity such as volcanoes or tectonic, its frost does seem to sublimate and recondense in new ways when the seasons change.

Bunratti noted that it is also quite surprising that Pluto is home to very bright surfaces, like the “heart”, but also very dark surfaces such as the “whale”, which only reflects 10 percent of the light that hits it. Such contrast-y surfaces are rare in our solar system. “It really does seem to be complex compared to what we've seen before,” says deputy project scientist Cathy Olkin.

Pluto Might Not Be Triton's "Sister" After All

Pluto and Triton, Neptune's largest moon, have been considered siblings or cousins--both are small worlds with thin, nitrogen-based atmospheres and icy surfaces.

“We thought Pluto would be a kinder, gentler version of Triton,” says planetary scientist Bill McKinnon. “It's completely the opposite. Pluto is more like Triton on steroids.”

New Horizons Measured Pluto's Waistline, And That Of Its Moons

For the first time, scientists have a precise estimate for Pluto's diameter. It turns out it's slightly bigger than expected, so the former planet can keep its title of "King of the Kuiper Belt". The size data also helped to reveal that Pluto's atmosphere is shallower than scientists expected.

In a press conference this afternoon, planetary scientist John Spencer announced that his team has measured the diameters of two of Pluto's tiny moons, Nix and Hydra, as well.

"We thought Pluto would be a kinder, gentler version of Triton. It's completely the opposite."

“Just last weekend, we first started to see Nix and Hydra as a little bit more than points of light,” says Spencer. “Well, they were still points of light, but they were fat points of light, and that meant that we could start to determine their sizes. We really hadn't any idea before as to how big they were. But it turns out they're 20 or 30 miles across, which is kind of in the range of what we expected, but we're not just guessing anymore, so that's a big step forward.”

Pluto's Heart Is In Pieces, And Charon's Pole Is Red

New, false-color images provide hints as to the chemical makeup of Pluto and Charon's surface. The images suggest that Pluto's heart is composed of two different halves of different composition, and that Charon is crowned in red deposits that may come from Pluto's escaping atmosphere.

The Best Is Yet To Come

Since it will take New Horizons 16 months to beam back all the data it's collecting during today's flyby, you can rest assured that this is just the tip of the (methane) iceberg.