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At a press conference on Wednesday astronomers working on the New Horizons space probe revealed new images that show surface features on Pluto for the first time!
The probe was just over 100 million kilometers from Pluto when the images were taken on April 12–18 (the Earth is 150 million km from the Sun, for comparison). Hubble images taken over the years have shown the diminutive world has darker and lighter patches on its surface, and these images match that.
In fact, these images are now at higher resolution than Hubble can produce! And they'll be getting better every day ...
Pluto looks lumpy in the animation, but that’s certainly an illusion; darker spots near the edge make it look like Pluto has chunks taken out of it. It’s expected that Pluto will be quite round; its gravity should compress it enough for it to be mostly spherical. I wonder if it’ll be oblate (slightly flattened) due to tides from its moon Charon. We’ll know pretty soon.
Charon can be seen in the animation as well, orbiting Pluto once every six days or so. Actually, it’s about ¼ the diameter of Pluto, and massive enough that it pulls on its parent pretty hard, hard enough that it’s more correct to say they both orbit their common barycenter, their center of mass.
I’ll note these images have been deconvolved; that means they’ve been sharpened using techniques that help bring them into better focus. The raw images look like blurs, but by combining them and using these techniques, the surface features can be detected.
The rotation axis of Pluto is labeled in the animation. Pluto’s spin is tilted compared with its orbit, so the probe is coming into the system nearly “face-on”. Interestingly, as NH Principal Investigator Alan Stern points out, there’s a bright spot on Pluto at the lower right, right at the pole. Is that some sort of ice cap? Maybe. It’s too soon to tell, but in a few months we’ll know better once New Horizons can see features better, and analyze their composition.
Pluto is tiny, just 2,370 km across—our own Moon is far larger (3,470 km). That’s why it still appears so small to New Horizons. The probe is closing in on Pluto rapidly, though, moving at about 14 km/sec. Right now, New Horizons is about 90 million kilometers from Pluto, and 4.7 billion km from Earth. It takes the radio signals from the probe nearly 4.5 hours to get here!
Closest approach occurs at noon UTC on July 14. Even in early June Pluto will only be a little over 10 pixels across, and 100 pixels four days before the encounter. Things will happen rapidly starting then. New Horizons flies through the system in only a few hours, and it’ll take months to send all the data back to Earth. Bandwidth is limited when you’re that far from home.
I'll note that the raw images off the probe are being posted online, too. I suggest checking in on them every day or two, and watch them get better and better as time goes on, and New Horizons approaches Pluto.
I’m very excited about this mission. If they’re getting detail like this now, imagine what we’ll see in July!