This artistic
rendering shows the distant view from Planet Nine back towards the sun.
The planet is
thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning
lights up the
night side. Credit: Caltech/R. Hurt (IPAC)
(January 20, 2016) Caltech
researchers have found evidence of a giant planet tracing a bizarre, highly
elongated orbit in the outer solar system. The object, which the researchers
have nicknamed Planet Nine, has a mass about 10 times that of Earth and orbits
about 20 times farther from the sun on average than does Neptune (which orbits
the sun at an average distance of 2.8 billion miles). In fact, it would take
this new planet between 10,000 and 20,000 years to make just one full orbit
around the sun.
The researchers, Konstantin Batygin and Mike Brown, discovered
the planet's existence through mathematical modeling and computer simulations
but have not yet observed the object directly.
"This would be a real ninth planet," says Brown,
the Richard and Barbara Rosenberg Professor of Planetary Astronomy. "There
have only been two true planets discovered since ancient times, and this would
be a third. It's a pretty substantial chunk of our solar system that's still
out there to be found, which is pretty exciting."
Brown notes that the putative ninth planet—at 5,000 times
the mass of Pluto—is sufficiently large that there should be no debate about
whether it is a true planet. Unlike the class of smaller objects now known as
dwarf planets, Planet Nine gravitationally dominates its neighborhood of the
solar system. In fact, it dominates a region larger than any of the other known
planets—a fact that Brown says makes it "the most planet-y of the planets
in the whole solar system."
Batygin and Brown describe their work in the current issue
of the Astronomical Journal and show how Planet Nine helps explain a number of
mysterious features of the field of icy objects and debris beyond Neptune known
as the Kuiper Belt.