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NASA/Jim Ross

I Chased Pluto’s Shadow Across the Southern Pacific Ocean

Last night, I joined several teams of scientists as they chased Pluto’s shadow across the southern Pacific ocean. We were riding aboard NASA’s flying infrared telescope, SOFIA, and needed to get that Boeing 747 to the exact right place at the exact right time.

Just before 5 a.m. New Zealand time, Pluto would slide in front of a bright star in the constellation Sagittarius and cast a Pluto-size shadow along a swath of Earth. Called an occultation, the relatively rare celestial alignment lets astronomers use the distant star’s light to probe the structure of Pluto’s atmosphere, which has been behaving a bit oddly since its discovery in 1988.

This would be the brightest star Pluto had yet occulted – and given next month’s Pluto flyby, astronomers were particularly keen to gather the most precise observations possible.

The closer we were to the center of the shadow’s path, the better those observations would be. Early predictions had put the center line somewhere between southern Australia and northern Antarctica. Scientists from around the world had gathered at the region’s ground-based observatories and were eagerly training their eyes on the sky.

We would be trying to observe the occultation from 39,000 feet up, which eliminated the possibility of problematic clouds crashing the party.

But the shadow’s path is a shifting, elusive target that can be hard to nail down—and it’s sweeping across the Earth’s surface at more than 53,000 miles per hour. Fall behind on your flight path, and you’ll miss it. Miscalculate the shadow’s track, and you’ll miss it. Don’t quite hit that center line? You’ll miss some important data.

As it turned out, the best predictions of the shadow’s track were proven wrong at the last possible hour. Luckily, teams on board SOFIA were able to work with the revised predictions and recalculate a flight path (not once, but twice!) that would intercept the shadow’s center… IF it ended up falling along the dramatically different new coordinates. To say mission scientists were worried would be a bit of an understatement.

Yet off we zoomed through the night, zigzagging over the ocean for about six hours as teams calibrated their instruments and got preliminary data on both Pluto and the star.

Then, for about 90 seconds in the early winter morning, we watched as Pluto dimmed the face of that distant star. A brief flash of brightness toward the midpoint of Pluto’s passage revealed that SOFIA had hit its target bang on and provided astronomers with a beautifully precise set of data.

Soon, I’ll have a longer report for you about the flight and the occultation data, perhaps with such interestingness as the magical bone brought aboard for good luck, and maybe a bit about what it’s like to see the southern aurora from the cockpit of a 747.

For now, I’ll leave you with this little piece of information: The whole thing almost didn’t happen. Midway through the afternoon, a rogue blast of absurdly strong wind had hurled a piece of equipment at the plane that ended up leaving a gash near one of the windows. Without proper repair, the mission would be scrapped. So, a huge thank you to the engineers who fixed the plane and made last night’s flight possible!