Summary of the Successful Interstellar Expedition

Avi Loeb
13 min readJul 3


Diary of an Interstellar Voyage, Report 35

(July 3, 2023)

For the official press release of the Interstellar expedition, click here

We did it. I led a Galileo Project expedition to the Pacific Ocean to retrieve spherules of the first recognized interstellar meteor, IM1, and brought back to Harvard College Observatory more than 50 spherules which lay on the deep ocean floor for nearly a decade. These sub-millimeter-sized spheres, which appear under a microscope as beautiful metallic marbles, were concentrated along the expected path of IM1 — about 85 kilometers off the coast of Manus Island in Papua New Guinea. Their discovery opens a new frontier in astronomy, where what lay outside the solar system is studied through a microscope rather than a telescope. That 83% of the matter in the universe is apparently composed of dark matter which was not found yet in the solar system should teach us modesty in forecasting the nature of interstellar objects.

A collection of photos, including the microscope (top left) and the sled (top middle) with the effort to scoop the material from its magnets (remaining photos).

It took us a few days on board the aluminum ship, which is fittingly called `Silver Star’, to get the magnetic sled on the ocean floor and a few more days to understand what we collected. As we scooped the magnets, the most abundant material attached to them was a black powder of volcanic ash. It was everywhere, including the control regions far from IM1’s site. I was frustrated by this background to the extent where I titled one of my 34 diary reports: “Where are the spherules of IM1?”

The magnetic sled (right) was connected by a cable to a winch on Silver Star’s deck. Every morning at sunrise, I jogged on the deck. Initially I was surprised at the jogging speed measured by the workout app on my Apple watch, but then I realized that the GPS system and the Starlink-WiFi baseline are affected by the motion of the platform on which I jog. A filming crew recorded one of my morning jogs (bottom left).

And then came the breakthrough. After a week at sea we used a filter with a mesh size of a third of a millimeter to sift through the tiny volcanic particles and examine the remaining larger particles under a microscope. Shortly thereafter, the team’s geologist Jeff Wynn came running down the stairs to tell me that the team’s analyst Ryan Weed saw through the microscope a beautiful metallic marble of sub-millimeter size and sub-milligram mass. I rushed up to the top level of our ship. When Ryan showed me the image, I asked him to place this spherule in the X-ray Fluorescence analyzer. He responded: “Sure, we can do it later.” I hugged him, thrilled by the finding, and said: “Please do it right now.” The composition analysis implied 84% iron, 8% silicon, 4% magnesium and 2% titanium, plus trace elements. I knew immediately that we would find many more spherules. When you find a single ant after surveying a small part of the kitchen, you know that there are many more ants out there. Sure enough, we found more spherules within a few hours.

Examples of spherules from IM1’s path.

The startling finding of IM1’s spherules was enabled by a team of exceptional individuals, each representing the best of their profession. They complemented each other in harmony like members of a well-trained orchestra. The discovery of spherules felt like a miracle. When the remarkable Rob MacCallum visited the porch of my home a year ago and suggested helping in coordinating the expedition, I never imagined a more successful operation.

The expedition required 1.5 million dollars. A few months after mentioning our funding needs in various podcasts, my wish materialized through a Zoom call with the brilliant mathematician and entrepreneur Charles Hoskinson, who simply said: “You have the funding.” Charles joined us on the ship and helped in all aspects of the operation. In addition to enabling the expedition, he and his assistant J.J. Siler were a delightful addition to our research team and I resonated with all his views on all matters even though we never met before. When I boarded his private jet, the pilot said: “Welcome onboard professor Loeb”, to which I replied: “Please call me Avi. I am just a curious farm boy. All other titles are unimportant.”

I still find it mind boggling that we managed to retrieve milligram-mass spherules of sub-millimeter size from a 2-kilometer depth in the Pacific Ocean using a meter-wide sled scanning a 10-kilometer-wide region. This accomplishment is testimony to the ingenuity and professional skills of all team members.

The critical feat of keeping the sled on the ocean floor was mastered by team members Rob Millsap and Art Wright, who demonstrated the `art of being right’ by following the ocean current and minimizing the vertical force of the winch cable which counteracted gravity and caused a lift akin to a kite.

IM1’s fireball was detected by the US Government on January 8, 2014 and indicated that this meteor was speeding beyond the value required to escape from the Solar system. Based on the air ram-pressure that it sustained before disintegrating in three flares 20 kilometers above the ocean surface, this half-meter-sized object was tougher in material strength than all other 272 meteors in the CNEOS catalog of NASA. Its interstellar origin was formally confirmed at the 99.999% confidence in an official letter from the US Space Command under DoD to NASA on March 1, 2022. Two years earlier, my discovery paper of IM1 with my undergraduate student Amir Siraj showed that IM1 was moving outside the solar system faster than 95% of all stars in the vicinity of the Sun. The possibility that IM1’s excess speed benefited from propulsion and the fact that it was tougher than all known space rocks, raise the possibility that it may have been technological in origin — similar to NASA’s New Horizons craft colliding with an exoplanet in a billion years and burning up in its atmosphere as an interstellar meteor.

Based on the IM1’s fireball, I forecasted in a paper with the students Amory Tillinghast-Raby and Amir Siraj, that as a result of being exposed to the fireball’s heat, the surface of the object likely disintegrated into tiny spherules, similar in number per unit area to those recovered by the expedition.

The localization of IM1’s likely path (red band) within the DoD error box was aided by data from a seismometer in Manus Island. The fireball signal recorded by the seismometer included reflections from the ocean surface (upper left).

Our latest paper on IM1 focused on localizing the fireball site based on the blast wave signal recorded by seismometers in Manus Island and Australia.

The maximum size of the recovered spherules were dictated by the survey area. We were fortunate to find multiple spherules filtered by our mesh size in a 10-kilometer run through the meteor path. The meter-wide sled covered a surface area of 0.01 kilometers squared, implying that if the meteor was half its size we would not have noticed a concentration of IM1’s spherules relative to the background in control areas. Also, with a power-law size distribution, one expects very few large spherules. For example, if there is an equal amount of mass in big spherules as there is in small spherules, the number of spherules which are twice as large will be down by a factor of 8. This implies that very quickly one runs out of spherules. In the longest Run 8, we found 10 spherules of size half a millimeter. This means that we should not expect more than roughly one spherule with a size larger than a millimeter.

Ship runs through the DoD error box (red). The expected meteor path is marked by the orange band.
Sled tracks through the various runs. The sled cable stretched out to 5 kilometers, longer than the ocean depth of 2 kilometers, introducing a few kilometers difference between the tracks of the ship and the sled.

Over the past few days, I was busy interpreting the preliminary results from the diagnostics of our harvest of spherules. Upon our return to the US, we visited UC Berkeley and used electron microscope scanning to image the spherules. Altogether we collected more than 50 spherules so far which we plan to analyze in the coming week with state-of-the-art instruments at Harvard. My daughter, Lotem, who was admitted to Harvard College, will dedicate a summer internship to finding the population of smaller spherules in the material we retrieved.

By now, we studied five spherules with a scanning electron microscope and laser ablation mass spectroscopy at UC Berkeley. The composition of the spherules along the meteor path are consistently from the same source whereas the background spherules from the control region had a different morphology and composition. The meteor composition is consistent with the results from the X-ray Fluorescence analyzer on the ship (84% iron, no nickel and some trace elements including 8% silicon, 5% magnesium and 2% titanium). Interestingly, the meteor spherules show evidence for a rapid heating event with surface dendrites whose spatial separation can be used to estimate the highest temperature they reached in the fireball. We also noticed an inner structure of spheres within spheres, like Russian dolls, implying hierarchical merger events of droplets during the explosion.

But most interestingly, the mass spectroscopy revealed uranium (U) and lead (Pb). The isotope U238 decays to Pb206 with a half-life of 4.47 billion years and U235 decays to Pb107 with a half-life of 0.71 billion year. This allows us to estimate the age of the spherules in two independent ways.

Based on the measured abundance of U238, Pb206, U235 and Pb207, I calculated that the two spherules from the meteor path (derived from Run 8 and Run 19) have an age of order the age of the universe (14 billion years) whereas the background spherule (found in Run 17 outside the DoD localization box) has an age of order the age of the solar system (a few billion years). In the coming weeks we will examine further any clue for the spherules being different from solar system materials. This will constitute independent evidence for the interstellar origin of IM1 in addition to its measured speed.

The expedition demonstrates how science should be done. Driven by raw curiosity and wonder, on a topic of great interest to the public, while seeking evidence to find the truth and finding it despite all odds after a heroic effort by a team of dedicated professionals.

More than two million readers followed my 34 diary reports from the expedition, and this led to an avalanche of emails. Below are a few examples.

“Hello Avi,

“what a wonderful world” Yes, you are right Avi! I had a heart attack four weeks ago and am now in rehab. I read your IM1 diary every day and it always gives me new courage to face life. There are still so many things to discover and I want to live long enough to see some of them. I wish you and your team all the best.

Life can be damn beautiful!

Best regards…”

“Dear Avi,

Felicidades! I can’t be happier for the success of your mission. Reading your diary has been a source of joy every day.

My son who is six years old and loves space and science, has been excitedly hearing my reports on your progress and your crew’s. Next week he starts a camp at the National Natural History Museum here in Madrid. It will be about the Universe, its origins and mechanics. He will most surely be talking about the spherules of IM1 to everyone he can. He’s very persistent, like you and your crew! :-)

There’s one more thing: Today I read that you say 30,000 read your entries every day and how an Italian reader lamented that mainstream media didn’t cover your expedition in Italy. Well, here in Spain we have been covering it! El Confidencial is the Spanish equivalent to The Guardian, and we have been translating your entries to Spanish in our section Novaceno, Chronicles of the Future, as we usually do with your blog entries but at a higher pace. We packed the entries in chapters and published them every three to four days.

The success has been phenomenal. Our internal measurements, which rigorously discount any duplicates and are extremely conservative, give a total readership of more than half a million unique readers from all over the world (573,028 to be exact). Spanish speakers mostly from Spain, all of Latinamerica, and the United States. So add those to your tally of excited people who share a common passion for discovery.

Your expedition has reminded me of a poem, “The Diamond of a Star” by the great Spanish writer Federico García Lorca, who was killed by the fascists for the mere fact that he thought differently:

The diamond of a star

has cut strips into the deep sky,

The bird of light that wants,

can escape from the universe

It can fly away from the huge nest

where it was a prisoner for ages

without knowing that it is tied to

a chain around the neck.

Extraterrestrial hunters

are hunting the stars,

The solid silver swans

bathing in the water of silence.

Can’t wait to read your new papers and for the next expedition to sail in search of new fragments.

Buen viaje!

Kindest regards…”

“Dear Dr. Loeb,

I am writing to you to express the great pleasure I had reading your daily diary entries of this amazing expedition you and your team have put together.

Every day bringing its share of breakthrough discoveries mixed with a sense of adventure. It would make a great book! How wonderful it must have been.

I couldn’t help but think about great scientists the likes of Darwin, Wallace and Galileo as I was reading.

In many regards I think you might have just invented a new kind of astronomy, an adventurous kind, by bridging the gap between field observation the way Darwin made it and pioneering spirit the way Galileo did. No small feat don’t you think?

Perhaps that is the real reason you and your team have experienced so much push back from fellow scientists, not so much the (still for now) fringe subject of this research. But the simple jealousy of being the first to think of it and manage to source the funding and team to actually pull it off and do some hard science.

The most important is that you had great pleasure in doing what you love, you communicated that in your diary and I think everyone who followed you shared that pleasure in seeing you and your team finding out new and exciting things. Thank you for that.

Now just before I conclude, I had a question regarding the spherules your team found.

It is my understanding that their diameter is quite small compared to what was found on the previous expedition which found spherules in the bottom of the ocean.

Given the unusual composition of those spherules I was wondering if their was maybe a link between composition and resulting size of spherules. Should a meteorite devoid of nickel produce spherules of comparable size to classical iron-nickel one ?

Thank you again doctor for your time and I am eager to learn more about your findings in the coming weeks. Let’s hope it will inspire younger people in doing science, perhaps in a different way even…”

“Hello Dr. Loeb,

I wanted to reach out and say how exciting your work on determining the origin of IM1 is. Even if, ultimately, an intelligent origin has to be discounted, the idea that human beings are physically interacting with objects that once experienced the heat of different stars is mind-boggling to me. What a time to be alive! I hope to read your first papers on the composition of the spherules soon.


“Dear Professor Avi Loeb,

I am writing to you today after watching your recent interview on The Hill. I was so impressed by your enthusiasm for your research and your passion for teaching. I am currently a third-year student at The Technical University of Kenya (TUK) majoring in Information Science.

I have always been fascinated by Astrophysics, and your work has really inspired me. I find your findings to be very insightful, and I’m eager to learn more about your research.

I am writing to you today to express my interest in working with you on your research. I am a hard worker and I am eager to learn. I am also a good communicator and I am confident that I would be a valuable asset to your team.

I understand that you are very busy, but I would be honored if you would consider me for an opportunity to work with you. However, I’m currently in Kenya and would be available to meet with you at a later date to discuss my qualifications and my interest in your research.

Thank you for your time and consideration. I look forward to hearing from you soon…”

There is no greater reward than reading these messages.

The “babies” delivered by the expedition (left) are spherules. They were stored in vials, serving as “beds” in the plastic container of their “delivery room.” An electron scan image of one of them (right) shows beautiful structures on their surface.

In my last class of the spring semester at Harvard University, I asked my students for advice on what to do if we find an extraterrestrial gadget. Half of the class recommended pressing buttons on it and the other half expressed caution. When one of the students asked: “What would you do, Professor Loeb?”, I replied: “I will bring it to a laboratory and study it before engaging with it.”

Art Wright (left) and Avi Loeb looking at the sunset on the deck of Silver Star.

We are starting to make plans for the next expedition in the spring of 2024. The spherules serve as romantic rose petals leading us to a partner, which in on our case is a possible large relic of IM1. Finding it will be of great value to reveal its natural or technological origin.

Throughout my career I focused on theoretical astrophysics. I chose to lead this expedition because it addresses a fundamental question of great importance to the future of humanity: “Are we alone?” This is not a philosophical question. A technological device might be lurking 2 kilometers under the ocean surface with the answer. If so, we shall find it!


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".