Physical Constraints on Unidentified Aerial Phenomena

Brief

Using standard fluid dynamics and meteor physics, the authors calculate that a 10 m² object moving at 10 km/s through air at 10 km altitude must dissipate ~1.5 TW of mechanical power, with ~10% radiated as optical emission (~150 GW). Fireball luminosity scales as the fifth power of inferred distance, meaning range errors in single-sensor FLIR measurements propagate catastrophically into derived velocity. The ionization shell around any such object produces electron densities above 10¹⁰ cm⁻³, making it detectable by L, S, C, and X-band radars before a fireball threshold is even reached. The paper concludes that most reported 'highly maneuverable' UAP cases lacking these signatures are better explained by inaccurate distance estimates than by novel propulsion.

Metadata

Category

Phenomenon

Venue

preprint (Harvard CfA)

Type

Preprint

Year

2023

Authors

Abraham Loeb, Sean M. Kirkpatrick

Access

Open access

Length

237.3 K

Programs

Galileo Project, AARO, Pan-STARRS, Legacy Survey of Space and Time

Instruments

FLIR, Pan-STARRS, James Webb Space Telescope, L/S/C/X-band radar, Space Fence

Data sources

ODNI UAP Report 2021, US Space Command velocity data (IM1), Brown et al. 2002 meteor optical efficiency data, Surzhikov 2018 ionization calculations

Tags

UAP-physics, technosignature, interstellar objects, radar, FLIR, propulsion, SETI

Key points

• Mechanical power dissipated by a 10 m² object at 10 km/s is ~1.5 TW; ~150 GW of that is radiated in the optical band, scaling as L_opt ∝ Av³.p.4
• Fireball luminosity scales with inferred distance to the fifth power because cross-sectional area scales as distance squared and velocity scales linearly with distance, making single-site range errors highly consequential.p.4
• Ionization at high supersonic speeds produces critical electron densities above 10¹⁰ cm⁻³, rendering an object detectable in L, S, C, and X radar bands prior to fireball onset.p.5
• FLIR-based UAP range estimates rely on platform flight dynamics and fixed scene points, introducing human bias and error that can generate spurious supersonic velocity readings.p.5
• The authors propose a 'dandelion seed' scenario: a parent interstellar craft releases cm-scale probes near Earth, which are too small to reflect detectable sunlight but could slow in the atmosphere using a high-area-to-mass parachute configuration.p.2
• Self-replicating probes traveling at 10⁻⁴ c could reach ~10¹⁰ habitable planets around Sun-like stars within ~0.5 Gyr, with the required number dropping from ~10³⁴ to ~10²⁴ if trajectories are targeted rather than random.p.4
• IM1, confirmed by US Space Command velocity measurement, had an estimated diameter of ~0.45 m and velocity of 60 km/s; its detection rate implies a local interstellar meteor density of ~10⁶ AU⁻³.p.4

Verbatim

• “The lack of all these signatures could imply inaccurate distance measurements (and hence derived velocity) for single site sensors without a range gate capability.”

  p.1

Most interesting

• The paper is co-authored by the sitting AARO director (Kirkpatrick) and a Harvard astronomer (Loeb), making it one of the few UAP-physics papers with a named DoD co-author.
• A meter-diameter object reflecting 10% of sunlight at 1 AU would produce ~0.2 nJy, below JWST's detection threshold, meaning cm-scale probes near Earth would be effectively invisible to optical surveys.
• Current first-world radar coverage can detect High-Area-To-Mass (HAMR) objects down to a few centimeters depending on material, according to Frueh et al. (2017), cited here as a detection floor for hypothetical probes.
• The 'dandelion seed' probe scenario is framed as energetically more viable than direct interstellar deceleration: pure liquid hydrogen/oxygen exhaust at 4.5 km/s is insufficient to slow from interstellar free-fall speeds (~40 km/s) without a fuel mass many orders of magnitude larger than the payload.
• The paper notes that interstellar meteor IM2 had an identical speed relative to the Sun and identical heliocentric semimajor axis as 'Oumuamua, but a completely different orbital inclination, ruling out a common origin while still motivating the mothership hypothesis.
• The Galileo Project ocean expedition to recover fragments of IM1 is described as 'fully-funded,' with the explicit scientific goal of determining whether its anomalous material strength indicates an artificial alloy.