Pluto and Charon on June 27, 2015. Image credit: NASA/JHUAPL/SwRI

Jun 30, 2015 Watch Pluto Grow In New Horizons’ Eye

Sen—Pluto is growing ever larger in New Horizons’ camera. Finally! After more than nine years, and five billion kilometers, New Horizons is more than 99 per cent of the way in its journey to this distant world. As of June 30, 2015, New Horizons is about 16 million kilometers from Pluto, and just two weeks away from closest encounter.

From that distance, Pluto would just be a dot to your naked eye—about a half arcminute across, where there are 60 arcminutes to a degree. Values vary, but roughly speaking an object has to be about an arcminute across before it starts to look resolved by your eye.

But the Long Range Reconnaissance Imager, or LORRI, is a telescope, and magnifies the view. It has a resolution of about 1/60th of an arcminute per pixel, so right now LORRI sees the 2400-km-wide Pluto as a disk a couple of dozen pixels across. That’s not much, but it’s enough to see features on the surface even without magnifying the raw image.

As I described in an earlier article, the New Horizons team can apply a lot of fancy mathematics to process the images and sharpen them up, but now we’re seeing Pluto better in the raw images than we did then in the sharpened ones taken just a few weeks ago!

You can see this for yourself. The raw images from the camera are beamed back to Earth and are accessible online on the Johns Hopkins University Applied Physical Laboratory website. It’s pretty amazing, truth be told; the images are sometimes only hours old, fresh off the camera an entire solar system away.

Currently, two types of images are being taken: Short (0.1 second) exposures that generally only show Pluto and its moon Charon, and longer (1 second) exposures that are being used to look for any materials that might pose a potential hazard to the spacecraft, including smaller as-yet undiscovered moons and even rings.

Yes, rings. No one knows if Pluto has a ring system, but it’s possible. One likely hypothesis for the origins of its moon system is that Pluto suffered a big collision, and that material coalesced into its moons. If true, it’s possible that some of that debris never settled down to become a moon, but instead stayed orbiting in a thin annulus: a ring.

If New Horizons finds that, scientists back on Earth will probably explode with excitement.

Until then, it’s a lot of fun to look at the raw short images and watch Pluto grow. For example, here’s Pluto as seen on May 27, compared to June 27, one month later:


Pluto as seen by New Horizons on June 27, 2015 (left) and May 27, 2015 (right). Both images have been scaled the same, so the difference in size reflects the actual difference seen by the spacecraft as it approaches. Image credit: NASA/JHUAPL/SwRI

I did a very minor bit of processing here; I expanded the image by a factor of 7 (using bicubic interpolation for those keeping score at home, a standard setting in Photoshop) and dropped the brightness a bit to give the images a little more contrast.

A few things are really obvious: In the older image, when Pluto was still 55 million km away, it’s smaller, and few features are visible. However, the mysterious bright spot near the north pole can be seen. In the newer image, taken from 20 million km, more features are coming into focus. Particularly intriguing is the oval feature near the top and a bit to the right (first brought to my attention by Ron Baalke). Is that a crater? If so, it’s a big one. It’s a real feature, since it appears in multiple images, but I can’t quite convince myself it’s a real crater. It may be a roundish feature tricking our eyes.

But here’s the cool part: In a few days, we’ll know. In a week Pluto will look twice as big in LORRI pictures, about 50 pixels across. Four or so days later it’ll be 100 pixels, and two days after that 200! At that point Pluto will grow visibly in the camera hour by hour. And LORRI’s not alone: New Horizons has other cameras that will take images at even higher resolution, mapping the surface as the probe screams by a dozen times faster than a rifle bullet. Features only a few hundreds meters across will be visible!

It may be some time before we get those images; the spacecraft can only send data back to Earth at an average of 2000 bits/sec—that’s roughly a megabyte per hour. So every image is precious.

And every one from now until the encounter will display Pluto in higher resolution and in more detail than human eyes will have ever seen before… and you can follow along as history is made.

[Note: I originally misstated the data rate from New Horizons. Thanks to Alexis Coudeyras for pointing this out.]