When did the number of planets last change?
When did the number of planets last change?
24 August 2006
Pluto was reclassified as a dwarf planet, leaving eight
The International Astronomical Union adopted a definition requiring a planet to have cleared its orbital neighbourhood, which Pluto has not — it shares its region with a great many other Kuiper Belt objects. The vote was prompted by the discovery of Eris, which is more massive than Pluto: either Eris was a tenth planet or Pluto was not a ninth. Only about four per cent of the IAU membership was present for the vote, which is part of why the decision remains contested.
- What
- Pluto was reclassified as a dwarf planet, leaving eight
- When
- 24 August 2006
- Category
- Science and measurement
- Could this change?
- Not in any foreseeable way. The event is closed.
Science and measurement
| Question | When |
|---|---|
| When were the SI base units last redefined? | 20 May 2019 |
| When was the last leap second added? | 31 December 2016 |
| When was an element last added to the periodic table? | 28 November 2016 |
| When was the metre last redefined? | 1983 |
This page gives a date and never a "years ago". These pages are built as static files, so a computed interval would freeze at build time and quietly become wrong — which on a reference site is worse than making the reader do the subtraction.
Common questions
- When did the number of planets last change?
- 24 August 2006 — Pluto was reclassified as a dwarf planet, leaving eight.
- What happened?
- The International Astronomical Union adopted a definition requiring a planet to have cleared its orbital neighbourhood, which Pluto has not — it shares its region with a great many other Kuiper Belt objects. The vote was prompted by the discovery of Eris, which is more massive than Pluto: either Eris was a tenth planet or Pluto was not a ninth. Only about four per cent of the IAU membership was present for the vote, which is part of why the decision remains contested.
Related pages
- When were the SI base units last redefined? 20 May 2019
- When was the last leap second added? 31 December 2016
- When was an element last added to the periodic table? 28 November 2016
- When was the metre last redefined? 1983
- When was the last Boeing 747 delivered? Also 31 January 2023
- When did Microsoft Office last change its default font? Also 2023
- When did the London Underground last gain a line? Also 24 May 2022
- When were the SI base units last redefined? Also 20 May 2019
- When was the last leap second added? Also 31 December 2016
- When was an element last added to the periodic table? Also 28 November 2016
- Everything, most recent first 36 last occurrences
Sources
- NASA — National Aeronautics and Space Administration (Public domain (US Government))