Two Are Better Than One

Avi Loeb
4 min readJun 24, 2023

Diary of an Interstellar Voyage, Report 26

(June 24, 2023)

The largest spherule is a merger of a few droplets just before they solidified. It measures a length of 700 microns and contains a total mass equivalent of all other 18 droplets so far.

“Two are better than one … for if either of them falls, one can help the other up,” according to Ecclesiastes 4:9–10. Could droplets of molten iron merge during their fall through air? This was the question that I asked myself following a new delivery from the fireball of the first recognized interstellar meteor, IM1?

The question was triggered when Ryan Weed and Jeff Wynn showed me the largest spherule so far, derived from the latest Run 14 that we collected at 7AM today. The delivery bed of this baby, our magnetic sled, appeared no different from all previous sled runs. The spherule measuring 700 microns in length looked like the merger of at least two spheres with the characteristic size of a few hundred microns seen before. A quick test at the X-ray Fluorescence analyzer implied the same composition as our previous spherules, dominated by iron but with a surprisingly negligible abundance of nickel.

Both iron and nickel are produced together in supernovae and natural astrophysical environments do not separate them because of their similar atomic weights. However, humans remove nickel from iron alloys in order to make them stronger. Indeed, the material strength of IM1 was larger than all 272 solar system meteors in the CNEOS catalog of NASA. Could the deficiency of nickel in IM1 be the result of technological design?

The largest spherule so far, measuring 700 microns in length, was collected early this morning in Run 14 of the magnetic sled.

By now, we have 19 spherules altogether. The discovery of the new spherule implies a chance of roughly 1 in 19 for two iron droplets to merge just before they solidify. If the two iron droplets merge too early, they would make a single spherical droplet. If they collide after they crust, their surface would not stick.

I immediately performed a back-of-the-envelope calculation. Adopting the crusting temperature to be of order 1000 degrees Kelvin, I estimated that the cooling time of a droplet measuring 300 microns in size through blackbody radiation is tens of seconds. As the droplets move out, they slow down to a terminal speed similar to that of rain drops, resulting from a force balance between friction on air against gravity. Since the friction scales with area (size squared) and gravity scales with mass (size cubed), larger droplets fall faster and can catch up with smaller droplets. This allows for droplets to stick together just before they develop a crust.

Based on the requirement that 1 out of 19 droplets collide at the right time, I have found that the collision must occur within a hundred meters from IM1.

As we get more statistics on merged spherules relative to the global population, this model can be refined to constrain the properties of IM1's fireball.

The most intriguing question remains: was IM1 of natural or technological origin? We hope to find the answer within a week by studying all our spherules with the best instruments that the world has to offer as soon as we return to the US.

It is a great pleasure and privilege to figure things out. There was never a more exciting time in my scientific career than the coming week.

This is the first time in history that humans put their hands on the materials of a large object from outside the solar system. The possibility that an electronic gadget might be lying under our feet is mind blowing. The heroic effort needed to bring these sub-millimeter spherules from a depth of 2 kilometers to the deck of Silver Star is a testimony to the inspiration that science could bring to our lives.

Science does not need to be boring, if we only dare to explore the unknown without pretending to know it in advance.

Many are better than one. Cheers to the exceptional team of individuals that came together to form the Interstellar Expedition team.


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".