Office of the Secretary of Defense: 02_Physical_Constraints_Paper

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Space Telescope. In contrast, the radar signatures of a meter class object would be detectable with our deep space
radars and space fence, much like IM2 was, out to beyond geosynchronous orbit at an altitude above 36,000 km. Such
objects could also become optically detectable as they get close to Earth, especially if they create a fireball as a result
of their friction with air.
Equipped with a large surface-to-mass ratio of a parachute, technological “dandelion seeds” could slow down in the
Earth’s atmosphere to avoid burnup and then pursue their objectives wherever they land. Current radar coverage
of the majority of first-world countries gives detectability of this High-Area-To-Mass (HAMR) objects down to a few
centimeters depending on material, making detectability possible (Frueh et al. 2017).
Within a close range to a star, extraterrestrial technological probes could use starlight to charge their batteries
and liquid water as their fuel. This would explain why they would target the habitable region around stars, where
liquid water may exist on the surface of rocky planets with an atmosphere, like the Earth. Habitable planets would
be particularly appealing to trans-medium probes, capable of moving between space, air and water. From a large
distance, Venus, Earth or Mars would be equally attractive for probes. But upon closer inspection, Earth would show
spectral signatures of liquid water (through reflection of blue light) and vegetation (through its red edge) that might
attract selective attention (Seager et al. 2005).
What would be the overarching purpose of the journey? In analogy with actual dandelion seeds, the probes could
propagate the blueprint of their senders. As with biological seeds, the raw materials on the planet’s surface could also
be used by them as nutrients for self-replication or simply scientific exploration. It is important to note, that given
the time scales associated with the propulsion scheme discussed here, it is unreasonable to assert that the intention of
any such probe launched in the far distant past, has anything to do with the human species. More likely, and similar
to NASA’s missions – the goal would be scientific and exploratory in nature.
Based on the detection rate of interstellar objects, Siraj & Loeb (2022b) estimated that for every interstellar NEO
there are a thousand Solar system NEOs of the same size. Searching for interstellar meteorites among the many
more meteorites from the Solar system without information about impact velocity, is like searching for a needle in a
haystack.
This is why the first interstellar meteor (IM1), confirmed by velocity measurement of the US Space Command (Siraj &
Loeb 2022c), is the target of a fully-funded ocean expedition by the Galileo Project (Siraj et al. 2022; Tillinghast-Raby
et al. 2022). Hopefully, by retrieving IM1’s fragments within the coming year we will know whether its extraordinary
material strength resulted from it being made out of an artificial alloy, like stainless steel or materials not yet developed
by humans.
Are there any functioning extraterrestrial probes near Earth? We do not know. But the Galileo Project (2021) (Loeb
2021) intends to use the scientific method to explore this possibility, following the 2021 report about Unidentified Aerial
Phenomena (UAP) from the Office of the Director of National Intelligence to the US Congress (ODN 2021). The state-
of-the-art suite of instruments and computer algorithms of the Galileo Project will be able to study such data in the
near future (Loeb & Laukien 2023).
The search for UAP, and the characterization of UAP, requires bounding the search plan with physics-based con-
straints on what we are searching for. This paper aims to constrain one aspect of the UAP hypothesis with parameters
that govern the movement and interaction of a UAP with Earth’s atmosphere to eliminate or bound observational
uncertainties. Some data collected to date, while arising from multiple sensors, have uncertainties in one or more
dimensions, leaving the exploitation of the data with a significant range of interpretations. This inevitably leaves open
the debate on what some objects are, and whether or not they exhibited truly anomalous behavior. Specifically, if
some observed UAP are of extraterrestrial origin, there are some practical limits on the interpretation of observed and
measured data resulting from physics-based constraints.
2. THE EXTRATTERIAL POSSIBILITY
The academic interest in UAP stems from their potential non-human technological origin. Extraterrestrial equipment
could arrive in two forms: space trash, similar to the way our own interstellar probes (Voyager 1 & 2, Pioneer 10 &
11 and New Horizons) will appear in a billion years, or functional equipment such as autonomous devices equipped
with Artificial Intelligence (AI). Electronic probes employing conventional chemical propulsion and refueling that we
currently understand, would be a likely choice for travel within a planetary system. Some combination of conventional
propulsion, ion propulsion, or lightsail propulsion would provide good choices for crossing the tens of thousands of02Page determined to be Unclassified
Reviewed by Chief of Staff, AARO
IAW FY24 NDAA, Section 1841(a)(1)(C)
Date: 2/5/2025