Didn’t Alf call that object “Planet Dave?”
The Man from Planet X!!
Planet XWhat this means is that a planet of Earth's mass could exist undetected if it were more than a few 100 AU away, and even a Jupiter (300 Earth mass planet) could exist at distances only slightly greater. The sun could have a companion brown dwarf or even a star if far enough away! It's a nice thought but it will be very tough to do anything about it unless we are lucky. The Pan STARRS telescope now under development in Hawaii will provide the best constraints in the forseeable future... There is no convincing evidence for Planet X but "absence of evidence is not evidence of absence". Such an object could exist provided it is sufficiently far away.
by David Jewitt