Reclaiming Pluto: to the Kuiper Belt and beyond

Jamie Carter visits Lowell Observatory and its Discovery Channel Telescope during the #yearofpluto

Credit: Jamie Carter

By Jamie Carter

You don't think Pluto is a planet? Try telling that to the people of Flagstaff, Arizona, where a young astronomer called Clyde Tombaugh discovered the so-called 'Planet X' in 1930 up at Lowell Observatory.

Seventy-six years later, Pluto was famously stripped of its status as a 'proper' planet – and relegated to being a dwarf planet – by the International Astronomical Union (IAU). Ironically, that was just eight months after the New Horizons Pluto-Kuiper Belt Mission had launched.

After a journey of three billion miles at an astonishing 31,000mph, New Horizons is already taking photos of Pluto and its moons as its prepares to flyby on 14 July. So does it matter if Pluto isn't officially a planet? Not to Lowell Observatory, which has made 2015 its #yearofpluto.

Clyde Tombaugh discovered Pluto using this 13-inch astrograph. Pic: Jamie Carter

The underdog 'planet'

“This year we are focusing heavily on Pluto, but since New Horizons has identified a Kuiper Belt object that it could fly on to in 2019 – if an extended mission is approved – we're using it as an opportunity to talk not only about Pluto, but about Solar System objects in general,” says Jeffrey Hall, Director, Lowell Observatory. “The Kuiper Belt is a very interesting region in its own right – we're not shying away from the 'is it a planet?' debate.”

Jeffrey Hall, Director at Lowell Observatory, worries about the current definition of a planet. Pic: Jamie Carter

So is Pluto a planet? “We don't have an institutional position on that, because as a research organisation it would be inappropriate to say 'Lowell Observatory believes…'," says Hall. "But there is obviously disagreement among astronomers about how to classify things.”

Back in 2006 the IAU concluded that since Pluto hadn't cleared the neighbourhood around its orbit, it was merely a dwarf planet like Ceres, Eris and around 45 others. “Personally, I like the simplest possible definition of a planet, which is: it's a ball, which means it's round as a result of its own gravity, and it's not a star, it doesn't shine,” says Hall. “That omits not only Pluto, but a whole slew of things not only in our Solar System, but also all the things around other stars that we're finding. By the current definition of planets, you can't call them planets. This seems to be scientifically to me a very narrow definition.”

The IAU has since decided that dwarf planets are special kinds of Trans-Neptunian Objects that deserve their own name: Plutoids. However, Hall tells me that he's not trying to be “macho or weepy” about Pluto, and sees no reason to wallow. “Much more exciting to our scientific staff is what we are going to learn when we finally get our first close-up look at Pluto,” he says.

The New Horizons mission to Pluto includes 7g of Clyde Tombaugh ashes. Pic: NASA/JHU APL/SwRI/Steve Gribben

New Horizons: this generation's Voyager?

“Pluto is the only planet in the Solar System that we haven't got a close-up look at yet, so it's a tremendous opportunity for us even if we argue Pluto is a Kuiper Belt object,” says Hall. “It was discovered here 62 years before the rest of the Kuiper Belt. Will Grundy, a planetary scientist at Lowell and a member of the New Horizons team, will tell you that he has no idea what we're going to see, but we know it will surprise us.”

Such excitement recalls the Voyager missions of the 1970s and 1980s that were able – thanks to a geometric arrangement of the outer planets – to visit Jupiter, Saturn, Uranus and Neptune. “Those pioneering Voyager missions gave us our first look at moons like Europa, Titan, Triton and Miranda … there is always something weird and we're bound to learn a lot scientifically about Pluto, the Kuiper Belt and about and the origin of the Solar System,” says Hall. “The science buried in all of that is really a lot more interesting than arguing what you call Pluto.”

Pluto was the first planet to be 'discovered' during daylight.

The daylight discovery

Legend has it that around 4pm on 18 February 1930, observing assistant Clyde Tombaugh found Pluto – from a distance of three billion miles – on the photographic plates he'd exposed the night before. He found it after lunch, making it the only planet to be found in daylight. Tombaugh had just eaten at the Black Cat Café along Route 66 in nearby Flagstaff, a fact celebrated by the present-day occupants, Karma Sushi. The Pluto Roll – tempura lobster with snow crab – has a dot of puree on it that resembles the dwarf planet – and it's been devised in honour of the New Horizons mission and Lowell Observatory's #yearofpluto.

Tombaugh might not have eaten sushi back in 1930, but later that day he found something fishy in the results of the blink comparator: the famed 'Planet X' that astronomers had (wrongly, as it turns out) theorised must exist to 'balance' the gravitational positions of the outer planets.

Karma Sushi's Pluto Roll celebrates New Horizons and #yearofpluto. Pic: Jamie Carter

Pluto … and beyond!

Hall wants to use the Pluto story to tell the world about other worlds. “Eighty-five years ago, right up the hill at the Pluto telescope, we discovered a world here at Lowell, and now we are very heavily into discovering other worlds around other stars,” he says, describing the private money now pouring in to the space industry and astronomy as a 'wave' that's enabling new discoveries.

Part of that wave – and Lowell Observatory's 'new toy' – is the 4.3-metre Discovery Channel Telescope (DCT), which BBC Sky At Night Magazine was able to pay a visit to. Situated 40 miles to the south of Flagstaff, at a breathless 8,000ft and surrounded by very dark national forest, the DCT is a completely private venture. As part of a capital US$16 million deal (though it cost US$53 million in total), the Discovery Channel gets the rights to use the images in its broadcast and online programming, though this arrangement has no impact on how it's used for research.

The Discovery Channel Telescope boasts a 4.3-metre mirror. Pic: Jamie Carter 

Modular magic

The DCT is unusual in that it is a modular telescope that can be augmented and added to over time. “Often you take a great big instrument and then just mount it at the back focus of the telescope. This is a Ritchey-Chrétien design, like a Celestron or a Meade, but instead of one instrument stuck directly on the back we built a cube, which has five faces, so you can put five instruments on it and switch between them within a minute.” This helps astronomers react quickly, which can be decisive. “If something happens like a supernova, or a gamma-ray burst goes off, we can be right on it.”

During our visit the enormous dome was surrounded by snow, with wind buffeting the giant panels and ice on the top quickly melting. Since first light in 2012, the DCT has been used to image Comet ISON, to study the light curves of asteroids, track near-Earth asteroids and by astronomer Deirdre Hunter for deep imaging surveys of dwarf galaxies. An upgrade later this year will add an infrared spectrograph specifically intended to enable Kuiper Belt studies.

Call Pluto what you like – a dwarf planet, plutoid or a Trans-Neptunian Object – but its 'birthplace' and the New Horizons mission are making #yearofpluto just the beginning.

The enormous telescope will soon be used to study Kuiper Belt objects. Pic: Jamie Carter
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