Will Falcon 9 upper stage impact on Moon be observable in RF?
monroe....@gmail.com
Curious – Given AL+Li alloy of SpaceX Falcon 9 upper stage, will this week’s lunar impact exhibit any sort of RF emission, e.g. observable short-lived spike in RF spectrum? Propulsion liquids have been drained, explosion not expected, just impact, ejecta, short lived dust plume, small crater.
If impact were to emit RF, given booster and lunar materials (Si), what might be frequency range?
Would RF emission be sufficiently strong that larger amateur RA observatories might be able to observe/record it? Might make for an unusual observation report or conference paper.
Given nearby proximity of Moon, such an RF spike amplitude might be too much for highly sensitive large professional or array observatories (GBO, VLA, ALMA, DSN, etc.).
Even if it is initially believed to not be observable in RF it wouldn’t be a big waste of time to point at Western limb of Moon in vicinity of crater Einstein on Wed Aug 5 at 2:30AM ET and record over broad a bandwidth as possible for about 10 minutes and see what gets recorded.
Regards,
Monroe Pattillo
Adrian
I am afraid the impact observations planned are all in the optical or near‑IR spectrum, and several observatories are scheduled to attempt monitoring the resultant emission. See https://arxiv.org/html/2607.14625v1.
Theoretically, the impact will heat the surface to ~3000° K and release ~12.4 gigajoules of kinetic energy upon impact, or the equivalent of ~3 tons of TNT. At this temperature, the peak blackbody radiation is at 1000 nm, or in the near‑IR region of the electromagnetic spectrum, thus the reason for the planned observations being mostly in the optical range.
As far as radio detection, although a very small portion of the blackbody radiation at frequencies at or below 300 GHz—such as those detectable by the ALMA observatory—would be ~0.00000057% of the total energy released, the incredible sensitivity of the ALMA observatory theoretically could observe this weak signal, as it would amount to ~40 milli‑Janskys at Earth, and ALMA can easily measure micro‑Janskys.
The inherent problem, however, is not sensitivity but beam dilution of the signal. The Moon’s daytime surface temperature is around 400 Kelvin. A tiny, 0.5‑arcsecond ALMA beam looking at the Moon will encompass a patch of land several hundred meters wide. That tiny piece of normal lunar background constantly radiates roughly 5 to 10 Janskys of thermal noise at 300 GHz. Therefore, attempting to detect a temporary 0.04 Jy signal spike on top of a constant, fluctuating up to 10 Jy background is like trying to spot a firefly landing on a stadium floodlight from miles away.
The only signal other than blackbody radiation that the impact could produce would be coherent emission from the ensuing brief plasma generated at those temperatures, and the frequencies here could peak in the 10–30 MHz region at even several Janskys intensity. But of course most of the signal would be severely attenuated by Earth’s ionosphere and would be detectable only as a sub‑millisecond pulse.
The last remaining potential mechanism would be very weak free‑free electron emission at micro‑Jansky continuum intensities extending up to maybe 30 GHz, and below any detectability again from anything other than SKA, VLA, or ALMA‑type observatories.
I am sure most of the observatories in the class of potentially being able to observe any such radio emissions woulld have greater priorities than to attempt to utilize valuble observation schedules to divert to this event as its scientifc return value is likely to be of little or no significance.
Adrian
Alfred Aburto
The optical spectra could be interesting though!
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Adrian
Alfred Aburto
Yes :-(
But "Einstein" is right on the limb so maybe a plume of ejected material?
Al
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Adrian
Alfred Aburto
No, but I'm interested to learn if there will be an easily visible plume. A mile high plume? I'm trying to image the scale. Probably will be very hard to see. I'm thinking some stuff may escape the Moon's gravity?
Al
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Scott Elliott
On Aug 1, 2026, at 6:17 PM, Alfred Aburto <abu...@san.rr.com> wrote:
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