In 2006 officials at the International Astronomical Union decided to change the definition of a "planet" after several objects larger than Pluto were discovered in the Kuiper Belt, an expanse of billions of comets and rocky balls of ice at the furthest reaches of the solar system.
The discovery by astronomer Mike Brown was the death knell for Pluto. Since Pluto did not have a clearly defined orbit (it sometimes careens inside the orbit of Neptune in its journey around the sun), Pluto was relegated to the status of a "dwarf planet."
That certainly didn't make Pluto any less interesting. When the probe New Horizons flew by Pluto in June 2015, scientists and space buffs were treated to some spectacular photos of a strange, beguiling world that a decade later still mystifies us.
Brown was not very popular, even in his own house. His ten-year-old daughter told him the only way he could redeem himself was by discovering another planet.
“When she said that, I kind of laughed,” Brown says. “In my head, I was like, ‘That’s never happening.’”
Brown may now be on the verge of redeeming himself in the eyes of his daughter. Astronomers have been searching for nearly 100 years for another planet orbiting the sun beyond Pluto. They know it exists because "distant subplanetary objects are being found on orbits that look sculpted, and arranged by an unseen gravitational force," according to Scientific American's Robin Andrews.
Brown thinks that "Planet 9" (sometimes referred to as "Planet X") is larger than Earth but smaller than Neptune. And late next year, if all goes well, the hardware that will be able to image such a distant body will see its first light.
On a mountaintop in Chile, 8,800 feet high, workers have lugged an extraordinary scientific instrument up the mountainside.; a digital telescope with a 3.2-gigapixel camera. About the size of a small car, it will be placed on the top of Cerro Pachón in the Andes where the Earth's atmosphere is extremely thin and light pollution is minimal.
There is just one hitch: the delicate, nearly three-metric-ton machine is currently some 10,000 kilometers away in the hills above San Francisco Bay, where its builders have put it through final tests. In the coming weeks the precisely engineered camera will begin a tense intercontinental voyage in which it will be flown by cargo plane, hauled by truck and painstakingly escorted up twisty mountain roads.
The daunting logistics fall to members of an obscure but consequential engineering subfield dedicated to keeping multimillion-dollar astronomy hardware intact in transit. This is “a very obvious and visible moment when things can go wrong,” says engineer Margaux Lopez of the Rubin Observatory and the SLAC National Accelerator Laboratory, who is in charge of the effort.
The Vera C. Rubin Observatory will be able to find Planet 9 or present strong indirect evidence for its existence. It will also be able to see distant supernovae as well as near-Earth asteroids. With telescope time for the James Webb and Hubble space telescopes at a premium, one more instrument capable of unraveling the mysteries of the universe will be a welcome addition.
If it exists, Planet Nine is big compared with Earth—Brown’s best guess is that it hovers around seven Earth masses. But it’s so far away that it’s beyond the detection capabilities of most telescopes. In general, observatories have a choice: have a wide field of view to see more of the night sky in one go or a big mirror to collect more light from a smaller area and see distant, faint objects. Space is rather expansive, so trying to zoom in on one minuscule patch of it in the hope of finding a single object is extremely unlikely to succeed.
The mystery of what is perturbing the orbits of distant bodies will be solved as scientific mysteries are always solved — with hard work and a little luck. Brown is confident that he and his team will succeed — if there is, indeed, a ninth planet. Alternate theories for the disturbed orbits of Kuiper Belt objects point to everything from a Mars-sized planet in the belt to several smaller bodies "shepherding" these distant objects into strange orbits.
It took 80 years to find the object that was disturbing the orbit of Neptune. When Clyde Tombaugh finally found Pluto in 1930, the hunt began immediately for a "Planet X." Brown's optimism notwithstanding, it's best to take the attitude, "I'll believe it when I see it."
