Historical clue formulations

• Question of humanity that has never been answered — 2021-08-20
• What many stargazers wonder — 2017-08-11
• A question of cosmology — 2017-03-10
• "Can anybody hear us?" — 2013-10-07
• What cosmologists wonder — 2012-09-28
• Spy's query at the start of a meeting — 2012-02-25
• Exobiologist's query — 2010-05-22
• Conspirator's cautious conversation starter — 2008-10-25