Astronomer Scott Sheppard runs through his checklist as he settles in for a long night of skygazing at the Subaru telescope atop Mauna Kea, Hawaii. The air above the summit: clear. The telescope: working smoothly. His 3-terabyte hard drive: emptied and ready to accept a flood of fresh data in the hours to come.
On a wall in the observing room, three clocks track the hours in Hawaii, Tokyo and Coordinated Universal Time. Screens display every tic of the weather above the summit: wind direction, temperature and the dreaded humidity levels that could end this November night of observing if they were to rise. But for now, conditions are nearly perfect, especially when it comes to a characteristic known as seeing — a measure of how stable the stars above look. “Seeing is point-five-five,” says David Tholen, an astronomer at the University of Hawaii in Manoa. “It doesn't get much better than that,” replies the third member of this team, Chad Trujillo of the Gemini Observatory in Hilo, Hawaii. Sheppard, the lone mainlander of the group, works at the Carnegie Institution of Science in Washington DC. With the weather looking promising, he pulls out his logbook and begins to outline plans for the next ten hours.
Between twilight and dawn, he will methodically direct Subaru's enormous 8.2-metre mirror — one of the largest in the world — to stare deeply at one patch of the sky, then another and another. Several hours later, he will look at the same areas for a second time, and after that, a third. By comparing the staggered images, the researchers can hunt for objects that move ever so slightly over the course of a few hours. These would be distant worlds beyond Pluto, in the most extreme reaches of the Solar System. This is the realm of the long-sought Planet X.
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