Seeds from An Interstellar “Dandelion”

Avi Loeb
5 min readOct 17, 2022


Dandelion seeds (Credit: Bess Hamiti)

In 2005, the US Congress tasked NASA to find 90% of all Near Earth Objects (NEOs) that are larger than 140 meters, of order the size of a football field. Dinosaurs were not smart enough to look up through telescopes and protect themselves from the catastrophe they encountered 66 million years ago. Apparently, the human brain is more valuable for survival than the huge body of a dinosaur. Let this be a teaching moment to all kindergarten kids who use physical force to bully their fellow nerds.

The Congressional task resulted in the construction of the Pan-STARRS telescopes. On October 19, 2017, the Pan-STARRS sky survey flagged an unusual NEO, the interstellar object `Oumuamua. Unlike Solar system asteroids or comets, `Oumuamua appeared to have an unusually extreme shape and was pushed away from the Sun without showing a cometary tail of gas and dust, raising the possibility that it was artificial in origin. Three years later, Pan-STARRS discovered a definitely artificial object, namely NASA’s rocket booster 2020 SO, which exhibited an extreme shape, a push by the Solar radiation pressure and no cometary tail because it was made of stainless steel.

On March 9, 2017, six months before `Oumuamua’s closest approach to Earth, a meter-size interstellar meteor (IM2) collided with Earth, as shown in a recent paper that I wrote with my student, Amir Siraj. Surprisingly, IM2 had an identical speed relative to the Sun at large distances and an identical heliocentric semimajor axis as `Oumuamua had. But the inclination of IM2’s orbital plane around the Sun was completely different from `Oumuamua’s, implying that the two objects are unrelated.

Nevertheless, the coincidences between some orbital parameters of `Oumuamua and IM2 inspired me to consider the possibility that an artificial interstellar object could potentially be a parent ship that releases many small probes during its close passage to Earth.

These “dandelion seeds” could be separated from the parent ship by the tidal gravitational force of the Sun. A small ejection speed far away could lead to a large deviation from the trajectory of the parent ship near the Sun. The changes would manifest both in arrival time and distance of closest approach to Earth. With proper design, these tiny probes would reach the Earth as the parent ship passes by within 16% of the Earth-Sun separation — as `Oumuamua did. Astronomers would not be able to notice the spray of micro-probes because they do not reflect enough sunlight for existing telescopes to notice them if they are on the scale of our CubeSats or smaller. Equipped with a large surface-to-mass ratio of a parachute, such technological “dandelion seeds” could slow down in the Earth’s atmosphere to avoid burnup and then pursue their objectives wherever they land.

These 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 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.

What would be the overarching purpose of their 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.

Based on the detection rate of interstellar objects, I estimated in a paper with my student Amir Siraj 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, is the target of a fully-funded ocean expedition by the Galileo Project. 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.

Are there any functioning extraterrestrial probes near Earth? We do not know. But the Galileo Project intends to use the scientific method to explore this possibility, following the 2021 report about Unidentified Aerial Phenomena (UAP) from the Director of National Intelligence to the US Congress.

High-quality data is required to separate real UAP signal from noise. The level of noise is elevated in complex environments like the war zone in Ukraine. A report on unidentified objects with uncertain distance estimates muddies the waters of scientific credibility. Analogies with past events or eyewitness testimonies without documented data from well-calibrated instruments, do not constitute scientific evidence. It is necessary to triangulate objects before claiming their distance, travel speed and physical size. This is a prerequisite before “new physics” is contemplated to explain them.

Here’s hoping that 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.


Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".