Great Planet Debate ends in stalemate
A lively debate over how to define planets failed to forge a common set of criteria on Thursday. Astronomers Neil deGrasse Tyson and Mark Sykes did however agree that the issue is much broader than deciding Pluto's status, with our basic perspective on the solar system in flux.
Pluto was kicked out of the planet club in August 2006, when the International Astronomical Union (IAU) redefined the term planet. Although Pluto met two requirements — it orbits the sun and is massive enough for its gravity to pull it into a round shape — it failed to meet a third stipulation that to be a planet, an object has to have cleared its neighbourhood of other objects.
Pluto's neighbourhood is swarming with other icy objects. In fact, it was the discovery that one of them, the dwarf planet Eris, previously nicknamed Xena, is bigger than Pluto that set astronomers re-examining the planet definition to begin with.
The new IAU definition set off a storm of controversy. An especially prominent critic of the decision was Alan Stern, head of NASA's New Horizons mission to Pluto, who vowed to gather scientists to reconsider the planet question outside the auspices of the IAU.