Historical clue formulations

• Almost spherical in shape — 2023-10-22
• Shaped like a clementine — 2020-05-09
• Not perfectly round — 2019-10-01
• Like Earth — 2017-12-30
• Shaped like Saturn — 2016-01-16
• Shaped like Skittles — 2015-07-25
• Depressed at the poles — 2013-02-03
• Like M&M's — 2010-12-31
• Flattened at the poles — 2008-11-12
• Squeezed at the ends, as leaves — 2007-09-02
• Not quite spherical — 2006-08-29
• Flattened at the poles — 2006-05-26
• Flattened at the poles — 2006-01-10
• Layperson in a monastery — 2003-12-06
• Flattened at the poles — 1999-03-17
• Flattened at the poles — 1998-05-03
• Flattened at the poles — 1997-07-12
• Not quite spherical — 1993-11-29