Tiny impact event

is tiny

South Korean officials stated that the Korea Pathfinder lunar orbiter Danuri began observations thirty minutes before a discarded Falcon 9 upper stage struck the Moon. They conducted eight imaging sessions to confirm “changes in the terrain around the impact site and traces of ejecta spread.” Korea aerospace administration functionary Oh Tae-seok noted that capturing before and after views “serves as a crucial foundation for expanding future lunar research and space exploration strategies.”

The image at the top of this article is from amongst a vast array of largely fantastic (phantasmic) images circulating on the interwebz this week. Apparently there are fireballs and pieces of the broken moon all over our star system which is kinda epic given how little the automated Korean lunar orbiter found on their repeated passes over the impact site.

Let’s see if we can get some perspective on this event. The Falcon 9 upper stage weighs about 4 metric tonnes, which in classical units from thousands of years ago that were worked out by more advanced investigators than those in France’s revolutionary purged academy of sciences in the 18th Century, amounts to about 8,818 pounds. Now, that’s a big object.

It is around half a ton more than the gross fully loaded weight of a Chevy Suburban, just to give you a comparison on which you might “hang your hat” as it were. That is, a 2026 Suburban has a gross vehicle weight rating of 7,700 pounds, max, including cargo, passengers, fuel in the tank, and the whole thing loaded up and sitting there. A Ford F-250 super duty (haha! they said “doody” but no time for that!) has a gross vehicle weight rating of 10,000 pounds. So, 8,818 pounds is about the same as your big American pickup truck or sports utility vehicle with a bunch of stuff in it.

The Earth’s moon has a total mass of 162 quintillion pounds. That is to say 1.62 times 10 to the 23rd power. Or, as we say in the neighbourhood, more.

How do we know? Well, it turns out that the Earth and the Moon orbit a shared balance point or barycentre located about 1,056 miles beneath Earth’s surface. Astronomers measure a tiny monthly wobble in the apparent position of our star, the Sun, against the background stars. This wobble, which they give the fifty-dollar name “parallactic inequality,” is caused by Earth moving back and forth as it orbits the shared centre of mass with the Moon

A French astronomer Jerande de Lalande and later mathematician Pierre-Simon Laplace refined the celestial mechanics by 1798, utilising the gravitational perturbations of our star, the sun, and of the major planets to pin down the mass ratio with true scientific accuracy. So, we’ve had a pretty good idea of how very big the Moon is for 228 years.

There was no great tower of ejecta. There was not, as far as any images we’ve seen here at L5 News, any flare or explosion. There are not, as far as our review has found, any actually good images or videos of the event captured from Earth. Even the Korean lunar orbiter shows only minor changes in the before and after imaging sequences. It was, to use a phrase from Louella Parsons, 1953, a “nothing burger.”

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