The International Astronomical Union considers Pluto to be a dwarf planet, and not a full-fledged planet, because it has not "cleared the neighborhood around its orbit." Stern told NBC News last week that Pluto deserved full planetary status, and he wanted to debate the issue with Tyson. "I am challenging him to the equivalent of the 'Thrilla in Manila,'" Stern said.
"As a general rule, I don't debate people," Tyson wrote. "Done it once or twice before, but abandoned the effort. What's behind it is that I don't have opinions that I require other people to have. So debates don't interest me for this reason."
On his own Facebook page, Stern criticized Tyson's no-debate policy. "All scientists engage in debate over competing ideas," Stern wrote. "If he persists in not supporting his position by engaging in debate, I'll consider it evidence he knows the position isn't supportable."