BBC: "In 2009 Prof McDowell & other astronomers performed an experiment in which a similar-sized rocket was crashed into the Moon." Really? Which one?

Question

The line following the title of BBC's Elon Musk SpaceX rocket on collision course with moon reads:

A rocket launched by Elon Musk's space exploration company is on course to crash into the Moon and explode.

and later:

Falcon 9's projected demise was identified by journalist Eric Berger on the space website Ars Technica and by data analyst Bill Gray in his blog.

The collision is due to happen on 4 March when the rocket will explode as it makes contact.

In 2009 Prof (Jonathan) McDowell and other astronomers performed an experiment in which a similar-sized rocket was crashed into the Moon. Sensors gathered evidence of the collision so they could study the crater.

That means scientists are unlikely to learn anything new from this crash, Prof McDowell explains.

To me the article suggests that McDowell's view of the current crash is "been there, done that".

Question: In 2009 did Prof Jonathan McDowell and other astronomers perform an experiment in which a similar-sized rocket was crashed into the Moon? If so, which rocket? How did they crash it? What did they measure, and what (if anything) did they learn?

Answer 1

"2009 impact" would probably be when the LCROSS/LRO upper stage was crashed into a crater at the Moon's south pole. The LCROSS Centaur upper stage had a mass at impact of around 2300 kg; an empty Falcon 9 upper stage is about twice as heavy, at around 4000 kg.

Jonathan McDowell is an astronomer at the Harvard-Smithsonian Center for Astrophysics. I can't find any indication that he was on the LCROSS team, but he might have had a telescope of his own pointed at the Moon to try to spot the debris plume.

Analysis of the debris plume indicated that the regolith at the point of impact was about 5% water by mass, confirming Chandrayaan-1's indirect observations of water in the Moon's polar regions.