Interstellar Affairs Are Not the Pentagon’s Day Job

Avi Loeb
5 min readNov 1, 2023
Space debris around Earth. Image credit: Pixabay

Today, the All Domain Anomaly Resolution Office (AARO) at the Pentagon announced a new reporting mechanism for current and former military members, federal employees and contractors to come forward with direct knowledge of unidentified anomalous phenomena dating back to 1945. This would help AARO fulfil its Congressional mandate. However, anecdotal reports by those who happened to be at the right time and the right place are of limited scientific value because they are not based on well-calibrated and controlled instruments. This makes it difficult to interpret or validate old anecdotal data. A better approach is to use audio and video instruments that monitor the entire sky in many locations at all times and provide well-calibrated data of scientific quality. This is the agenda of the Galileo Project. We already assembled one functioning observatory of this type at Harvard University and its data is now being analyzed with machine learning software. The sky is not classified and we hope to notice anomalous objects if they exist. The Pentagon’s day job is national security and not interstellar affairs. To find out whether we have a cosmic neighbor, we better use the scientific method and not rely on government data. Any item that enters the solar system from interstellar space is labeled an interstellar object, and abbreviated ISO.

ISOs are fast moving objects, identified by their speed exceeding the threshold needed to escape from the gravitational pull of the Sun. At the Earth’s distance from the Sun, this escape speed is 42 kilometers per second or 94,000 miles per hour — more than a thousand times faster than the speed limit on a highway. The escape speed scales inversely with the square root of the distance from the Sun and is always larger than the circular speed of solar-system planets by the square-root of 2.

Next year, the Rubin Observatory in Chile will start surveying the entire Southern sky every 4 days with a 3.2-billion-pixel camera. According to the latest estimate, this sky survey could discover new ISOs up to once per week. The first reported ISO was `Oumuamua, which had roughly the size of a football field.

There are about a thousand solar system asteroids for every ISO of similar size. Finding a needle in a haystack requires removing the hay. The challenge is to find out if among the solar system rocks in our backyard, there might be a tennis ball thrown by a neighbor. In other words, is there any ISO of technological origin?

The anomalies of `Oumuamua led mainstream astronomers to suggest that it is an object of a type that we had never seen before, like a nitrogen iceberg, a hydrogen iceberg or a dust bunny. But even in such a case, we learn something new about ISO birth sites. However, in case an ISO appears to be of technological origin, we will learn that there is intelligent life in our cosmic neighborhood.

The population of ISOs is a mixed bag. For example, the ISO Borisov appeared to be a comet with familiar properties. Two other ISOs that preceded `Oumuamua and Borisov, the meteors IM1 and IM2, are meter-scale objects that were detected by US government satellites as a result of the fireball they generated after colliding with Earth. There are about a million objects like IM1 or IM2 per `Oumuamua-size ISO. However, we cannot detect the reflection of sunlight from them because they are too small. In the darkness, it is easier to notice a bird than a bug near a lamppost.

The data collected on `Oumuamua was limited. By the time astronomers realized that this ISO is anomalous, this ISO was too faint for further observations. But for new ISOs harvested by the Rubin Observatory, we could benefit from using the Webb telescope which could detect the heat emitted by ISOs. The detected infrared radiation would allow us to infer the emitting area of the ISO, given that its surface temperature is dictated by its distance from the Sun. Also, since the Webb telescope is located a million miles away from Earth, its simultaneous operation along with terrestrial telescopes would allow us to measure the motion of ISOs in three-dimensions and decide whether they exhibit any non-gravitational acceleration, as `Oumuamua did.

The main limitation of using the Webb telescope is that it can only point away from the Sun. To compensate for this limitation, one could imagine using the Hubble Space telescope or perhaps even launching a small new telescope to a low-Earth orbit, dedicated to monitoring ISOs harvested by the Rubin Observatory. For an ISO distance of roughly the Earth-Sun separation, a satellite in a low-Earth orbit will have a parallax of order ten arcseconds every couple of hours. This parallax can be resolved by a small optical lens with a diameter bigger than a few centimeters. The actual size of the telescope’s aperture would be dictated by its flux-sensitivity requirement that the number of detectable ISOs will be significant for the duration of the mission.

The worst future would be that in which we raise dust and say that we cannot see anything. A related challenge in identifying ISOs is to remove the thousands of artificial satellites moving through our sky from the Rubin Observatory’s images.

The Rubin Observatory is likely to harvest hundreds of ISOs in the coming decade. When a reporter asked me what I wish for in this new discovery era, I replied that I hope we will get as much data about ISOs as possible. With all the telescopes in the world, we should be able to tell beyond a reasonable doubt whether any of these ISOs is of technological origin and not a natural rock of a type never seen before. Galileo Galilei taught us four centuries ago that we should keep our eyes open and look through our telescopes if we wish to gain new knowledge.


Credit: Chris Michel

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. 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".