Prospect readers will already know all about our increasingly populous solar-system, thanks to Stephen Eales’s account in the May issue of Pluto’s demotion from proper planet to second-rate dwarf. Today brings final confirmation of the bad news for astronomical reactionaries, as this report in Science explains. Pluto is now officially lighter than its shadowy outer neighbour, Eris (appropriately enough named after the Greek goddess of strife and discord), which at 16.6 billion trillion kilograms is no less than 27% more massive than the object previously thought to be the ninth largest in the solar system.
The image of nine planets orbiting our sun through a pristine void has, it seems, gone the way of the flat earth less than a century after Pluto was discovered. On the other hand, opportunities for scientists to give things silly/portentous names are multiplying. Eris’s tiny moon has already been dubbed Dysnomia, after a Greek demon of lawlessness; and it shares the trans-Neptunian regions with a tongue-twisting cast that includes Varuna (after the Hindu god of the sky), Quaoar (a Native American creation deity), Orcus (a Roman god of the dead), Ixion (a Greek king allegedly bound to a burning wheel for all eternity) and Sedna (Inuit goddess of the sea). Lumps of frozen rock have never had it so good.
CORRECTION: As has been quite rightly pointed out in the comments below, Pluto was never thought to be the ninth largest object in the solar system, even excluding the sun. In fact, Ganymede, Titan, Callisto, Io, Luna, Europa and Triton are all bigger – as well as Eris, of course.
Many thanks for the correction, Charles.