Pluto's Best Portrait Yet Reveals Complex World, Surface Features

7-14-15 Pluto before closest approach
Pluto nearly fills the frame in this image from the Long Range Reconnaissance Imager aboard NASA's New Horizons spacecraft, taken on Monday, when the spacecraft was 476,000 miles from the surface. NASA/JHUAPL/SwRI

Years of excitement bubbled forth among NASA scientists, administrators and onlookers just before 8 a.m. EDT Tuesday. They were gathered at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, to celebrate a moment nearly 10 years in the making—since the launch of the New Horizons spacecraft in January 2006 (and even longer if you consider the years of preparation that went into the mission ahead of the launch). New Horizons was scheduled to make its closest approach at 7:49 a.m. as it zoomed past the Pluto system.

Shortly after its live broadcast counting down to the approach, NASA held a press conference during which it released and discussed the most recent image it had received from the spacecraft prior to the flyby. Because of the vast distance between the spacecraft and Earth, it takes more than four hours to send an image back.

During the crucial hours around the flyby, the spacecraft is programmed not to be in contact with mission control, but rather to focus all its capabilities on gathering data. It is scheduled to send a short burst of data on Tuesday afternoon letting NASA know the flyby went as planned and that there were no debris strikes along the way. This data indicating a successful mission, which the New Horizons team calls the "phone home" data, will take several hours to reach Earth.

"That view is just the first of many, many rewards that the team will get," said John Grunsfeld, former astronaut and now the associate administrator for the Science Mission Directorate, referring to the image that had just been shown on a large screen behind him, taken at roughly 4 p.m. on Monday. It's especially rewarding, he explained, since Pluto has "turned out to be an extraordinarily complex and interesting world."

A sneak peek of that image was posted on NASA's Instagram page Tuesday morning even before the flyby. Just a few hours later, it had garnered nearly a quarter of a million likes and more than 8,000 comments. With a resolution of about 2.5 miles per pixel, principal investigator Alan Stern explained at the Tuesday press briefing, the image is approximately 1,000 times clearer than what could be captured with a telescope as powerful as Hubble.

"How about a round of applause for that beautiful planet?" Stern said to the crowd. He also shared a video of the New Horizons team's reaction to the photo when it first came in.

7-14-15 NASA reaction
Members of the New Horizons science team react to seeing the spacecraft's last and sharpest image of Pluto before closest approach on Tuesday at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Bill Ingalls/NASA

In a Q&A session following the remarks, Stern was asked to describe what he and his colleagues were noticing in the most recent image. He replied:

OK, so this image is oriented with north to the top. And so the dark regions that you see are near Pluto's equator. The planet is about 1,500 miles across to give you a scale. It's got a thin, or a rarefied, nitrogen atmosphere, which you can't see in this image because it's clear, just like looking through other tenuous atmospheres….

You can see regions of various kinds of brightness, very dark regions near the equator, very bright regions just to the north of that, a broad intermediate zone over the pole. And what we know is that on the surface we see the history of impacts. We see a history of surface activity in terms of some features that we might be able to identify as tectonic, indicating internal activity in the planet at some point in its past or maybe even in its present.

And what we also know is that this is clearly a world where geology and atmospheric climatology play a role, because Pluto has strong atmospheric cycles. It snows on the surface, the snows sublimate and go back into the atmosphere each 248-year orbit.

They're waiting, however, for all the supporting data about topography, composition, temperature and more, Stern said, to get a better understanding of what they're seeing.

Meanwhile, the images are only going to improve. This latest image was taken about 16 hours before the New Horizons spacecraft's closest approach, when it was about 476,000 miles from the surface of Pluto. After the "phone home" message is received at approximately 9 p.m. on Tuesday evening, it will begin sending data, including higher resolution images, from the hours surrounding closest approach.

"Our data tomorrow (Wednesday, July 15) will have 10 times the resolution of what we see today," Stern is quoted as saying in a NASA press release. "And it will knock your socks off."

Stay tuned here for new images as they're released.