A decade ago Mike Brown helped get Pluto demoted from a
“planet” to a mere “dwarf planet.” Now the astronomer and one of his CalTech
colleagues may have plotted the orbit of a new ninth
planet in our solar system, dramatically larger than Pluto and much, much farther away.
Astronomers have been hunting for an undiscovered “Planet X”
for nearly two centuries, generally without success.
In 2006, when Pluto was demoted, Brown recalls telling many
people, “That’s it. That’s the end of planets. We get eight in this solar
system and that will have to be enough.” A survey by NASA’s Widefield Infrared
Survey Explorer (WISE) satellite essentially proved that there couldn’t be
anything Saturn-sized or larger hiding out beyond Pluto.