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Tested Explains: Why We Have No Good Images of Pluto

By Matthew Braga

Real pictures of Pluto just don't exist – none more than a few pixels in size, at least. Even with the best and most modern technology at our disposal today, we still can't produce a decent picture of the dwarf planet from here on Earth.

When was the last time you saw an image of Pluto? Think about it. You've probably seen renders and simulated images – but what about an actual, high-quality picture of the minor planet's surface? Don't feel bad if you're drawing a blank. Real pictures of Pluto just don't exist – none more than a few pixels in size, at least. Even with the best and most modern technology at our disposal today, we still can't produce a decent picture of the dwarf planet from here on Earth.

Artist's rendition of the surface of Pluto. Credit: ESO

But around this time next year, thanks to the New Horizons spacecraft launched in 2006, we'll finally catch our first high-quality glimpses of how the solar system's most distant celestial object actually looks.

The best pictures we currently have of Pluto date from 1994.

If you can believe it, the best pictures we currently have of Pluto date from 1994. And, really, they're only pictures in the most liberal sense: blurry, blown-up surface maps made from source images mere pixels across. Taken with the Hubble Space Telescope, the orbiting camera is only just powerful enough to resolve the planet's surface colour – "a complex-looking and variegated world with white, dark-orange and charcoal-black terrain" – making geological observations out of the question.

"To a close approximation, Pluto and the moon are the same size." explains Dr. Marc Buie, a staff scientist at the Southwest Research Institute, and part of the team that captured the planet's first Hubble images. "[But] Pluto is an awful lot farther away."

Image credit: NASA

In fact, from our planet's surface, Pluto is about 180,000 times smaller on the sky at that distance than the Earth's moon.

That hasn't given researchers much to go on – not in the visual wavelength, anyhow. But as you read this article, the New Horizons spacecraft is nearly 30 astronomical units from the sun – or, about the distance from the sun to earth multiplied by 30. Travelling at a rate of about 1 million miles each day, it is the fastest spacecraft ever built. Its primary mission is to image the surface of Pluto, its moons, and beyond, and it is now about 90% of the way to its long-awaited flyby in July 2015.

"Once we get up close, we'll be able to resolve the geology," says Buie. "We'll see craters if they exist. We'll see all the tectonic and weathering patterns on the surface. Everything that's sculpted the landforms on Pluto and [Pluto's moon] Caron is going to be revealed to us for the first time."

In early 2015, the images taken by New Horizons will still be no better than what we've captured with the Hubble Space Telescope or ground-based telescopes on Earth – a mere few pixels wide at most. But come next spring, those images will begin to grow larger, and the resolution of Pluto's surface increase.

New Horizons. Image credit: NASA

By July 2015, just a few days before New Horizons completely passes Pluto by, the spacecraft will be close enough for a "complete global map of the illuminated part of the surface of Pluto to 1 kilometre resolution or better," says Buie, who helped the spacecraft's team prepare its cameras for contact.

At New Horizons' closest point, Buie expects a few images with as much resolution as 50- to 100m. With quality that good, it might not be long before you too can visit Pluto via Google Maps.

But what, exactly, those photos will reveal is still up for debate.

"One of the more fun speculations I've been putting out there is I think you're going to see a strong correlation with topographic elevation and albedo," says Buie. While it's generally accepted that a hemispherical-sized mass of obliterating nitrogen frost moves slowly from pole to pole – one possible explanation for Pluto's presumed lack of craters – how this impacts the planet's topology is unknown. He believes the planet's lower regions will have more of this reflective frost than regions higher up.

"We have an Earth bias that says all the snow is at the top of the mountains, so it's going to kind of look like an inverted landscape," Buie predicts.

It's sort of like being asked to take a picture of an object you can't actually see, based on a description that's been given to you by someone else.

What's particularly amazing about New Horizon's flyby is that all of its imaging tasks have been pre-programmed ahead of time. In other words, the team has spent years on complex calculations to determine the planet's approximate diameter – give or take 6 miles – and brightness, to ensure that exposure levels, bracketing and dynamic range are correct. There's not much opportunity to change things once New Horizons' final approach begins.

It's sort of like being asked to take a picture of an object you can't actually see, based on a description that's been given to you by someone else. But Buie is confident that, after all these years of studying the distant planet, his calculations are correct.

"We know that we're going to get good data as long as we point in the right direction," he says. And they better. There are no second chances for a spacecraft hurtling along at 1 million miles per day.