Just over 76 years ago, the 11-year-old Venetia Burney was having breakfast with her grandfather in Oxford when he looked up from The Times to note that a new planet had been found. “What should it be called?” he asked. Her suggestion was cabled to the Lowell Observatory in Arizona, where the planet’s dim outline had been spotted. The suggestion stuck.

Pluto’s name should stay stuck for a millennium or two, but its status is to be downgraded even as the solar system miraculously expands to include three new lesser planets. What to call them? After toying contemptuously with “ice dwarf”, “planetoid” and even “historic planet”, astrophysicists in foetid conclave in Prague appear to have settled for “pluton”.

Miss Burney, as she then was (now Mrs Venetia Phair), says she is “relaxed” about the relegation. The rest of us need not be. Pluto is the quintessential planet. It is spherical. It orbits around the Sun. It wanders magnificently, as the Greeks said planets should (in this case along a 12-billion-mile elliptical orbit). Above all, it is a full-blown planet because our planet embraced it as one in the bleak 1930s, when planets may have needed each other more than they do now. We cannot abandon it to the cosmic second division simply because we think we know more than we did, or because telescopes are a little more precise.

The real problem is 2003 UB313, known by its discoverer as Xena. He thinks it deserves the same status as the original nine because it, too, moves around the Sun. The name has possibilities even if the planet doesn’t: “There was a planet called Xena, You really should have seen her . . .”