Astronomers have long taken the view that the Solar System
has a planet that nobody has seen but which might offer an explanation for some
of the phenomena that have been discovered and which present as-yet-unanswered
questions. This planet is believed to be of substantial size and therefore unlike
any of the dwarf planets that are known to exist in the outer reaches of the
Solar System. However, it is the very size and mass of this planet that is
believed to cause the phenomena in question, such as the elongated orbits of
the dwarf planets and the existence of comets that are sent hurtling towards
the inner Solar System from their natural orbits way beyond that of Pluto.
The planet has been given the title Planet X – the X can either
be taken to signify “unknown” or the Roman numeral for ten. It would have been
the tenth planet when Pluto was still regarded as the ninth.
In October 2015 a new dwarf planet was discovered that might
help in the search for Planet X. The dwarf is about 300 kilometres in diameter
and probably consists of a ball of ice. It was nicknamed “The Goblin” thanks to
its discovery at around Halloween.
Work done since the initial discovery has shown that the
Goblin has an extremely elongated orbit that takes it about 2300 times further away
from the Sun than Earth. A complete orbit would take about 40,000 Earth years.
The Goblin would appear to be orbiting as one of a cluster
of similar objects, which poses the question of why such a cluster might form.
The intriguing thought is that Planet X, if it exists, would have precisely the
effect that is being seen, namely providing a gravitational tug that herds
objects including the Goblin into their extreme orbits.
This suggests that Planet X has a similarly elongated orbit
and might therefore be so far away from the Sun at present that it is unlikely
to be seen from Earth any time soon. But at least the discovery of the Goblin gives
astronomers hope that they are looking in the right direction.
(The illustration is an artist’s impression of another dwarf
planet, namely Sedna)
©John Welford
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