Monday, 25 January 2016

Sam Rolfe - Science Correspondent

“Ninth planet”
Researchers Batygin and Brown at CalTech have built on the work of Trujillo and Sheppard
in 2014 to show that a gravitational signature suggests that an object 2 to 10 times the mass
of the Earth orbits the Sun every 20,000 years, at a closest distance of 200 AU (We are 1 AU
from the Sun, Neptune 30 AU and Pluto 39.5 AU (average, as it crosses Neptune’s orbital
path, most distant at 48 AU)).
It belongs to a group of objects called the Kuiper Belt Objects (KBOs). Gravitational
disturbances in Uranus’s orbit lead to the discovery of Neptune.
This object is called 2012 VP
, informally “Phattie”. Other than spotting it directly, which will
be difficult given its distance from the Sun, it will be very faint, another technique could be
used to infer its existence – find more KBOs that have steeply inclined orbits. It is possible
that a new telescope, the Large Synoptic Survey Telescope (LSST), may be able to find it.
However, it is not due to be built until 2022.
Previous searches for Planet X
1846 Johann Gottfried Galle discovers Neptune, guided by predictions from perturbations of
Uranus’s orbit.
1905 Percival Lowell (pictured) starts hunting for a ‘Planet X’, which he predicted would lie
beyond Neptune, just as Neptune lies beyond Uranus. His calculations led astronomers at
Lowell’s namesake observatory to find Pluto in 1930, but the object is not massive enough to
be Planet X.
1984 On the basis of periodic extinctions in the fossil record, scientists propose that a dwarf
star, later named Nemesis, passes through the Solar System every 26 million years, flinging
comets on a path to impact Earth.
1999 Perturbations in comet orbits lead astronomers to propose that a brown dwarf (bigger
than a planet but smaller than a star) exists in the outer Solar System. It is named Tyche, the
good sister of Nemesis.
2014 A search with the Wide-Field Infrared Survey Explorer satellite rules out the existence
of both Nemesis and Tyche. But the discovery of an object in the distant Kuiper belt prompts
Chadwick Trujillo and Scott Sheppard to propose a large planet in the Kuiper belt

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