Identifying the Unidentified Using the Rubin and Galileo Observatories

Avi Loeb
4 min readMar 31, 2024
Drone view of the transport of the 8.4-meter Primary/Tertiary mirror from the storage room into the Rubin Observatory on March 7, 2024. (Credit: VRO/LSST)

The Vera C. Rubin Observatory will employ a 3.2-billion-pixel camera to survey the southern sky every four days, starting in 2025. Its Legacy Survey of Space and Time (LSST) will document sources of light all the way to the edge of the observable Universe, but it would also detect interesting objects near Earth. Sources located light-milliseconds away from the telescope might be more interesting than those billions of light years away.

A couple of months ago, I published a calculation showing that LSST would detect objects in Low Earth Orbits (LEO) which are larger than 10-centimeters and reflect more than 10% of the sunlight shining on them. The calculation was refined by the LSST science team in a follow-up paper. It also implies that LSST will document all LEO objects bigger than a meter which reflect more than 0.1% of the sunlight illuminating them. Aside from satellites and space debris, this population of detectable objects could also include Unidentified Anomalous Phenomena (UAPs) in the Earth’s atmosphere. What are these?

We do not know. Over the past three years, the Director of National Intelligence, Avril Haines, delivered three reports (here, here and here) to the U.S. Congress about UAPs spotted by military personnel. I met Avril in the green room of the Washington National Cathedral prior to a public appearance and asked her what she makes of these objects. She frankly confessed: “I don’t know.” Most recently, the All-Domain Anomaly Resolution Office (AARO) studied hundreds of these UAP reports and concluded that about 97% of them can be explained as familiar objects. This might appear as a satisfactory state-of-affairs for government officials whose day job is national security. But my day job as an astronomer is to find what lies outside the solar system. From that perspective, even if only one in a million UAPs in the LSST data pipeline would appear to have originated from an extraterrestrial technological origin, this identification of the unidentified would still carry a great scientific weight.

Given the huge background of human-made objects in space, this search is as daunting as finding a needle in a haystack. The European Space Agency reports that there were 6,500 successful rocket launches of nearly 17,000 satellites into orbit around Earth. Out of these, about 11,500 satellites are still in space and about 9,000 of them are functioning. But there are many more objects orbiting Earth as a result of broken satellites or discarded rockets. The number of debris objects regularly tracked by Space Surveillance Networks is 35,150.

According to a recent report from the United Nations, there are of order 10 million orbiting objects in the size range of 1–10 centimeters and 36,500 pieces larger than 10 centimeters. These fragments orbit the Earth at a typical speed of about 8 kilometers per second. As these fragments move across the sky, their glint produces a flare that typically lasts a fraction of a second at a favorable orientation relative to the Sun. Due to the motion of the objects during the telescope integration time, typically tens of seconds, these flares would be smeared across a streak length of order a degree in the sky.

Large objects would be easiest to detect. The Galileo Project Observatory at Harvard University is sensitive to large communication satellites. Within a year, the Galileo Project will assemble two new observatories, one in Colorado and the second — thanks to a grant from the Richard King Mellon Foundation, in Pennsylvania.

Farther away from Earth, but still within the orbit of the Earth around the Sun, LSST will be sensitive to interstellar objects bigger than Starship or the interstellar object `Oumuamua. Together with my postdoc, Richard Cloete, we are developing software that will help us discover the sunlight reflected from such objects roughly once per month.

If some space debris was created by advanced technological civilizations, the Rubin and Galileo observatories might find them. Our own Voyager spacecraft reached a distance of 24 billion kilometers away from Earth. At a distance that is a hundred thousand times larger representing the edge of the Oort Cloud, there are more interstellar objects than solar system objects.

Elon Musk tweeted on X yesterday: “At 5000 tons, Starship is the largest flying object ever made. Thrust is more than double the Saturn V moon rocket. It is the first spaceship design capable of making life multiplanetary. Goal of the next mission is to make it through the meteorically extreme heat of reentry.”

Elon should have been more careful by referring to “ever made on Earth.” The Rubin and Galileo Observatories could inform us whether there was a more successful space entrepreneur in the Milky-Way galaxy over the past 13.8 billion years since the Big Bang.


Image credit: Chris Michel (October 2023)

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 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. His new book, titled “Interstellar”, was published in August 2023.



Avi Loeb

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