NASA just released a new batch of Pluto photos taken by New Horizons — and they're pretty amazing.
This composite image — a combination of several different photos — shows Pluto's heart-shaped region (technically known as the Tombaugh Regio) in extreme detail. It focuses on the left half of the heart, which is covered in smooth, icy plains.
Here, a closer view shows the so-called "chaos region" bordering the heart. You can see mountain ridges and other sorts of elevated terrain emerging at the edge of the ice:
The dwarf planet also has much darker regions, such as the one shown in the photo below. Scientists still don't really know what they are, or what chemical composition is responsible for their dark color.
NASA also released a new view of Pluto's hazy atmosphere, taken by New Horizons as it looked back at the dwarf planet's dark side after the flyby:
Why it's taking so long to get all the Pluto photos
New Horizons began sending back photos and other scientific data shortly after its July flyby. But even traveling at the speed of light, it takes about 4.5 hours for those signals to reach Earth. On top of that, the huge distance means the signal is extremely faint and must be transmitted very slowly: An image that's 1024 pixels wide takes about 42 minutes to come through.
Scientists initially sent back a small batch of photos for public consumption, but New Horizons then stopped sending photos for a while in order to transmit scientific data on Pluto's temperature, atmosphere, and interactions with the solar wind (the charged plasma released by the sun), as well as the five moons.
Now the probe is back in photo-transmitting mode, and NASA will continue releasing new images regularly. Still, it'll take 16 months in total to relay all the images and data, mainly because the transmission speed is so slow.
What New Horizons has taught us about Pluto so far
We've received less than 5 percent of New Horizons' data — but it's already revealed all sorts of surprises about Pluto, and created a number of mysteries.
The biggest surprise is the fact that parts of Pluto's surface seem relatively young, with little or no craters. It also has ice mountains that are 11,000 feet tall — as high as the Rockies. Together, these observations tell us that some sort of underlying geologic process is going on that's generating fresh terrain and features over time, perhaps even volcanic plumes.
But geologic activity requires some internal source of energy — and previously, scientists assumed Pluto wouldn't have any. Models suggest it's too small to still have a large amount of radioactive materials left over from its creation (these materials decay over time, releasing heat).
And it's not orbiting a large planet, which can lead to tectonic activity in places such as Jupiter's moon Europa. That works through a phenomenon called tidal heating, in which the moon is squeezed by the gravity of the planet that it orbits, generating energy. Ultimately, Pluto's activity remains a big mystery at the moment.
What's next for New Horizons
As the probe beams back data, it'll also begin heading for a new target: a 30-mile-wide chunk of ice called 2014 MU69. This destination, like Pluto, is what's known as a Kuiper belt object — one of the thousand or so pieces of rock and ice that orbit the sun in a cloud beyond Neptune.
Before this mission, we knew vanishingly little about this part of the solar system. But as we get more and more of the data collected on Pluto — and after New Horizons reached 2014 MU69 sometime around 2019 — we'll have a much better understanding of two different Kuiper belt objects. This information will help scientists better model how these objects formed, and what role they played in the creation of the early solar system.