On the Way Back from IM1’s Site

Avi Loeb
6 min readJun 28


Diary of an Interstellar Voyage, Report 34

(June 28, 2023)

Silver Star’s captain, Joko (left), with Avi Loeb at sunrise, just before the expedition team’s departure back to the US (June 28, 2023).

Just before leaving Silver Star, I hugged its captain, Joko, for guiding us skillfully towards the fireball path of the first recognized interstellar meteor, IM1.

As I approached the exit door from the kitchen to the deck, the expedition’s cook, Tom, who made amazing meals during the journey approached me and said: “You are doing the best science in the world” and I did not hesitate to reciprocate: “You are making the best meals on our planet.”

Silver Star’s cook, Tom (left), with Avi Loeb near the exit door to land from Silver Star.

On our flight from Manus Island to Port Moresby, I could see through my passenger’s window the seismometer station on Manus Island which provided us with the most likely path of IM1 based on the blast wave signal that IM1's fireball generated.

A view of the seismometer site on Manus Island which helped us localize the likely path of IM1 within the DoD error box.

Amazingly, we recovered 50 spherules along IM1's path but not in control regions far from it, confirming the association of the spherules with IM1 and not with background events from the past as they would be uncorrelated with the specific length and direction of IM1’s path.

During the flight I sat across the aisle from Art Wright who drank whiskey with a silver ball cooler in his glass. With the expedition in my mind, the silver ball appeared like a giant spherule. It celebrated the success of our scientific mission as Art skillfully navigated Silver Star through IM1’s path.

Art Wright drinking whisky on the flight with a giant silver spherule in his glass.

But common sense should not be taken for granted. As a result of news reports about the interstellar expedition in the BBC, New Scientist and Forbes, I became aware of a new paper by Peter Brown and Jiri Borovicka, who argue that modeling IM1 as a familiar solar-system meteoroid does not fit the US Government data on IM1’s fireball unless its speed is reduced considerably — making the object bound to the Sun and not interstellar.

We should keep in mind that the US Space Command under the Department of Defense (DoD) has already double-checked its data carefully for a few years and issued an official letter to NASA in March 2022, confirming the interstellar origin of IM1 at the 99.999% confidence. Nevertheless, Brown & Borovicka favor the notion that the network of sensors developed by DoD to mitigate the risk to national security from ballistic missiles cannot be trusted more than their theoretical model for solar system meteoroids.

The argument is akin to an astronomer suggesting that data on the rotation curve of the Milky Way galaxy is invalid because it cannot be explained by types of matter found in the solar system. With the rationale that we should have seen the light emitted by any form of matter and therefore the data must be invalid, dark matter would have never been part of the vocabulary of cosmologists.

There are many other examples from the history of astronomy where revisions in theoretical modeling were prudent given the anomalous data on a new class of objects. The lesson to be learned from these examples is that our knowledge is incomplete and we must allow for the possibility that anomalous data suggests new knowledge.

We often complain about politicians ignoring evidence that contradicts their narrative. Similarly, scientists should not dismiss data that violates their models. Reality stays whatever it is, irrespective of whether we choose to ignore it. In the long run, it is better to adapt to reality than to ignore it. Ultimately, other people beyond Galileo Galilei would have realized that the Earth is not at the center of the solar system, so there is no point in denying it. In fact, acknowledging Galileo’s insight allowed humanity to design successful space missions.

Brown & Borovicka argue that the DoD data must be wrong because their model for solar system meteoroids is unable to reproduce the measured fireball properties at IM1’s speed. However, an open-minded approach would consider materials of different composition than solar system rocks, just because the first interstellar meteor could have originated from an environment very different from the solar system. As it turns out, this argument was already made in a paper that I published in The Astrophysical Journal Letters last year with Amir Siraj. Brown & Borovicka do not acknowledge this earlier paper or contrast their conclusions with it.

The new wrinkle in this debate is that by the time the Brown & Borovicka paper appeared, our expedition to the Pacific Ocean recovered spherules at the location of IM1’s path. We now know that the DoD localization is correct, casting doubt on their conclusions.

Brown & Borovicka argue: “While an iron interpretation is attractive, the modeling … strongly argues against an iron object. This is because an iron would have much higher ablation coefficients than used in our modeling and even at low speeds such high mass loss rates would cause the fireball to be visible much earlier than is observed. The object would also have to be much larger than modeled, further increasing the difficulty in matching the light curve. Moreover, irons do not typically show flares but rather have smooth light curves as would be physically expected.”

They dismiss an iron composition of IM1, but we already know from the X-ray Fluorescence analyzer on the expedition ship that iron is the dominant constituent of the spherules found at IM1’s location. If further analysis were to reveal additional differences from solar system meteoroids, the composition data alone would suggest an interstellar origin independently of the DoD data on IM1’s velocity.

Brown & Borovicka conclude that: “light curve modeling using the measured speed can only reproduce the observed light curve/flares for an extremely unusual (high density, low ablation coefficient) object with extremely low drag.”

In the coming weeks we will analyze the spherules we collected and report the results in a paper submitted to a peer-reviewed journal. Given that IM1 was moving faster than 95% of the stars in the vicinity of the Sun and that it had an anomalous material strength, its source may have been a natural environment different from the solar system, or an extraterrestrial technological civilization.

Yes, science can be exciting, if we could only allow ourselves to learn something new!


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”, is scheduled for publication 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".