A portrait from the New Horizons' final approach of Pluto and its moon Charon. Image credit: NASA/JHUAPL/SWRI

DIGEST [Wall Street Journal, NBC News, Washington Post]

After 9.5 years and $728 million spent, it came down to a few critical hours. That’s the timeframe in which NASA's New Horizons mission was either going to send back breathtaking images of Pluto from the farthest reaches of our solar system, or instead go unsettlingly silent as it passes by that enigmatic once-upon-a-planet, nearly 3 billion miles away.

The fear that the mission would not--and still might not--survive its final hours is all too real. The Washington Post reported, “[t]he New Horizons team, based at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., won’t know whether the spacecraft successfully passed through the Pluto system until 8:53 PM Tuesday.” This is due to the fact that “it will take 4.5 hours of travel time at the speed of light for the all-clear signal to reach Earth,” according to NBC News.

The New Horizons mission via Flickr user Bruce Irving

A failsafe was built into the nearly decade-long project should it not cross the finish line in its final hours. NASA understands that the Plutonian system may have its fair share of debris, “and even a small rock could disable a spacecraft going upward of 31,000 mph.” New Horizons sent one final transmission before the flyby, sharing the system-wide telemetry of Pluto from its approach, before it marks a 22-hour radio silence period. Mission leaders are feeling good.

“It’s a rock-solid spacecraft,” principal investigator Alan Stern told the Washington Post. “We’ve flown this bird for 3,500 days and change. I’m very confident about tomorrow.”

First Image Reveals Curious and Beautiful Heart Shape on Planet

Around 7:49 EDT on Tuesday, NASA received a final image of Pluto right before the moment of closest approach, around 16 hours before it would pass around 7,750 miles above the planet's surface. Social media exploded with the image, fueled by what many see as a "heart" on the planet's surface.

image courtesy of NASA

After snapping this photo, New Horizons plunged closer to the planet, where it will collect and beam back vast amounts of data before its planned continued trip into the Kuiper Belt, a region many scientists believe is filled with thousands of similar astronomical objects. Writing in the Wall Street Journal, astrophysicist Michio Kaku noted that the data that New Horizons collected from this region could wind up saving our planet:

"[O]ccasionally something nudges [these objects] from their orbit, and they come tumbling toward the inner solar system. If one of them struck our planet, it would be a catastrophe unequaled in human history. One theory holds that a renegade Kuiper-belt object about 6 miles wide slammed into Mexico 65 million years ago, so altering the planet that dinosaurs became extinct. Unfortunately, the dinosaurs didn’t have a space program."

Planet of Mystery

There is still much we don’t know about Pluto--a planet first dubbed “Planet X” that overtook the imaginations of scientists and science fiction writers alike from the early 1900s on.

Thanks to the New Horizons spacecraft, launched by NASA in 2006, we are learning more about Pluto--its composition, atmosphere, and moons--with more information every single hour. At the time of publication, the craft is in the throes of its closest approach to Plutonic planetoid, and the data that it is gathering is quite literally out of this world.

Based on New Horizons’ imagery, Pluto is 2,370 kilometers (1,473 miles) across, plus or minus some 20 kilometers (12.4 miles). That puts it about 30 miles wider than Eris, the dwarf planet whose discovery led to Pluto's downfall as the "ninth planet" back in 2006, according to NBC News.

NASA confirmed the composition of Pluto’s atmosphere and its ice caps within the last few

days. We also now know that the ground is made up of more ice, and less rock, than originally thought. It truly is a “dirty snowball.”

But there is still so much we don’t know. Why are some patches bright orange and others very dark? Are the dark patches valleys of frozen methane? Is it possible that Pluto’s radioactive core is heating the inside enough to melt the ice, forming liquid oceans beneath the surface? Could it be the home to a race of aliens, as suggested in the 1951 cult film The Man from Planet X?

OK, probably not aliens. But according to scientists interviewed by the Wall Street Journal, the new data collected so far suggest as many new questions as they do answers, and new numbers are pouring in every hour.

Seasons on Pluto

With some of the things we've been learning, we can get a clearer picture than ever of what it might be like to some day visit that world… If you stood on the surface of Pluto with a friend, trying to guess which point of light in the pitch-black sky was the sun, it would look merely like a fat star: a little larger and much brighter than the others. But a star, nonetheless.

“Day” and “night” don’t mean a lot on Pluto. The planet rotates every 6.4 Earth days, but because of the weird way it wobbles and spins, the speck of light we call the Sun traces tiny circles in the sky and only “rises” and “sets” once each season over the course of Pluto’s roughly 250 year-long year. On the other hand, Pluto’s largest moon, Charon, is a large looming disc standing dead still overhead. It never moves in the sky while the sun, the stars, and the planet’s other four weirdly-shaped elongated moons twist and spin in a wacky dance around it.

via Wikipedia

Spring isn’t that much fun on Pluto. In spring, the solid nitrogen and methane ice caps begin to vaporize (or “sublimate” to use the language of chemistry). As the air pressure builds, you might see clouds form in the sky, and might feel wind on your face. It would be a weak wind, since the atmospheric pressure is a tiny fraction of that on Earth. And you wouldn’t enjoy that very much, since it would be made almost entirely of nitrogen and would be about 369 degrees Fahrenheit below zero.

You might enjoy the summers on Pluto, relatively speaking at least. You’d be able to hike along the pale orange rocks and dirt, looking down into dark rippling valleys of frozen methane, nitrogen and carbon dioxide ice. There is ice underfoot as well, mixed with the dirt and frozen so solid that it hasn’t existed in liquid form for millions of years.

That summer would last about 20 Earth years. After that, the Plutonian autumn would come, refreezing the methane and nitrogen. Perhaps it would appear as beautiful crystal snow falling around you. The atmosphere would become thinner and thinner, and would eventually disappear entirely as Pluto shoots back outward into winter, into the coldest, most distant part of its orbit.

Make sure you stay tuned as the New Horizons craft, if all goes well, delivers a clear picture of one of our most remote and enigmatic neighbors in this planetary system.