Physical Constraints on UAP: The Loeb-Kirkpatrick Draft Paper, 2023

Most coverage of this paper focused on its “mothership” passage. The part with the most practical consequence is a single scaling law. If an object really crossed the sky at the speeds some UAP reports imply, the air around it would glow brightly, and the glow would grow with the fifth power of how far away the observer thought it was.

What this record is

This is the draft of an astrophysics-style paper, set in the American Astronomical Society’s LaTeX template and dated 1 March 2023. It is six pages long. Its authors are Abraham (Avi) Loeb, head of Harvard’s Galileo Project, and Sean M. Kirkpatrick, writing from the All-domain Anomaly Resolution Office (AARO) at the Pentagon. The acknowledgements say the work was supported in part by the Galileo Project and “conducted in partnership with” AARO. The Department of Defense prepublication office cleared it for open publication on 8 March 2023. AARO’s Chief of Staff reviewed it again on 5 February 2025 under the FY2024 National Defense Authorization Act and released it in full as case number 330UAP000002. The authors posted the paper publicly in early March 2023, when it was widely reported. It was not a formal AARO finding and had not been peer reviewed.

What it says

The introduction is Loeb’s argument, in compressed form. It covers the interstellar object ‘Oumuamua, found by Pan-STARRS on 19 October 2017; the rocket booster 2020 SO, which the paper cites as a definitely artificial object that behaved in a similar way; and a meter-sized “interstellar meteor” (IM2) that the authors say struck Earth on 9 March 2017. From these the paper builds a hypothesis. An artificial interstellar object could be “a parent craft that releases many small probes” as it passes the Sun, and these “dandelion seeds” would be too small and dim for survey telescopes to spot. It argues that such probes would more likely carry artificial intelligence than living crews, and that any purpose would “more likely” be scientific exploration unrelated to humanity. It closes the introduction with “Are there any functioning extraterrestrial probes near Earth? We do not know.”

The propulsion section uses the rocket equation to argue that chemical rockets can leave the Sun’s habitable zone but cannot slow down from interstellar speeds without help. On that basis the authors call a mothership-and-probe arrangement “more energetically viable.”

The core of the paper is physics that applies to any explanation. An object of known matter moving faster than sound must form a bow shock and shed mechanical power in proportion to its cross-section and the cube of its speed. Using meteor data, the authors estimate that about 10 percent of that power comes out as visible light, which for a 10-square-meter object at 10 km/s would be about 150 gigawatts. Because the size inferred from an image grows with the square of the assumed distance, and the inferred speed grows in direct proportion to it, the expected fireball brightness scales “with inferred distance to the 5th power.” Such an object would also ionize the air around it and leave an ionized trail, and both would reflect radar in the L, S, C and X bands.

The conclusion is aimed at military sensor data. Forward-looking infrared (FLIR) pods produce sharp relative thermal images but usually no range, so range is estimated from the platform’s flight path and fixed points in the scene, a method the paper says is “subject to human bias and error.” Claims of transonic or faster motion should therefore be checked for the fireball, ionization, radar return, heating and sonic boom that such motion would produce. If those signatures are missing, the paper says, that “could imply inaccurate distance measurements (and hence derived velocity).”

Context

The paper arrived early in AARO’s public life, about seven weeks before Kirkpatrick’s first open Senate testimony. Its co-author led a Harvard group set up to test, in public, whether some UAP could be extraterrestrial technology. Coverage in March 2023 focused on the mothership idea, and some articles described it as a Pentagon theory. The document itself is more modest. Its speculative sections are Loeb’s framework, and its physics sections do most of the work of limiting what UAP can be. The same reasoning runs through AARO’s later information papers: if a single sensor with no range data sees an object that looks impossibly fast, the distance estimate is the first thing to question. AARO later set that point out for general readers in its paper on forced perspective and parallax. For the Galileo Project itself, see the Galileo Project entry.

Status

This is a draft research paper, not an investigative finding, and it reports no incident. The interstellar-probe material is hypothesis, and the paper labels it as such. The physical argument is conventional aerodynamics and meteor science, and its practical conclusion is deflationary: a report of a fast object with no fireball, radar trail or sonic boom is more likely a mistake about distance than evidence of unknown propulsion. The National Archives copy is the cleared draft of 1 March 2023. Readers citing it should note that its authors describe it as a draft.

Sources

• National Archives catalog entry: https://catalog.archives.gov/id/499915934
• PDF of the record: https://catalog.archives.gov/medialz/electronic-records/rg-615/493468580/02_Physical_Constraints_Paper.pdf
• Series: Records from the Office of the Secretary of Defense Relating to Unidentified Anomalous Phenomena: https://catalog.archives.gov/id/493468580
• National Archives, Record Group 615 UAP records: https://www.archives.gov/research/topics/uaps/rg-615
• Military Times, “Pentagon UFO chief says alien mothership in our solar system possible” (9 March 2023): https://www.militarytimes.com/off-duty/military-culture/2023/03/09/pentagon-ufo-chief-says-alien-mothership-in-our-solar-system-possible/