We Recovered Shock-Resisting Steel in the Debris Field of the First Recognized Interstellar Meteor, IM1

Avi Loeb
4 min readJun 19, 2023

Diary of an Interstellar Voyage: Part 15 (June 19, 2023)

Avi Loeb holds shards of corroded iron that he recovered from the magnetic sled from Run 6 in IM1’s debris site. These shards resemble the composition of two types of strong steel.

On Run 6 of the magnetic sled through the likely crash site of the first recognized interstellar meteor, IM1, the expedition research team recovered shards of corroded iron. At first, we thought it may be common industrial iron associated with human-made ocean trash. But when Ryan Weed ran the sample of shards through the X-ray Fluorescence (XRF) analyzer, the most likely alloy it flagged is S5 steel with titanium, which is also known as shock-resisting steel.

The yield strength of S5 steel, 1.7 GPa, is well above that of iron meteorites. This is consistent with the fact that IM1 was tougher in material strength than all other 272 meteors in the CNEOS catalog of NASA.

Most importantly, the shape of the recovered shards is nearly flat — as if they were surface layers broken off from a technological object which experienced extreme material stress. Iron meteorites break into small pieces which are melted by the fireball into spherules that rain down and are recovered in strewn fields as nearly spherical fragments.

It is possible that the fireball of IM1 resulted from the breakup of surface layers and the core of the object survived entry through the atmosphere, as expected for spacecraft. As it turns out, the magnetic sled bumped into a solid object in Run 6, but this encounter was not captured by the sled’s camera because it ran out of batteries.

Today, Run 7 recovered additional iron shards along a path separated from Run 6 by a few kilometers. This indicates that the shards are not associated with a single wreck site but rather constitute a wide debris field, consistent with an IM1 origin.

We noticed two types of shards, that we label `red’ and `gray’ based on their color — which in turn reflects different oxide states. Preliminary XRF analysis implies that the gray-type resembles S5 steel with 93% iron and 0.8% titanium by mass whereas the red-type is 99.3% iron and 0.1% titanium. The red-type shards are labeled by the XRF as close to 1100 Series Carbon-Steel with a yield strength of about 200 MPa, surprisingly close to the ram-pressure at which IM1 disintegrated.

Does this coincidence mean that we have recovered fragments from IM1? And if so, why would an interstellar object be made of steel unless it was manufactured technologically? The technological origin would be consistent with the flat shape of the recovered shards in Runs 6 and 7 on June 18–19, 2023. The speed of IM1 outside the solar system was higher than any human-made spacecraft so far.

A vial full of red-type shards from Run 6 along IM1’s impact path. Image credit: Jeff Wynn.
Avi Loeb (right) and Ryan Weed (left) discussing the preliminary results from the XRF, indicating that the recovered shards are potentially made of steel.

We are currently studying the gray-type shards with our gamma-ray spectrometer. A lack of short-lived radioactive isotopes, like Aluminum-26, could be used to infer an extraterrestrial origin of these shards if they spent much more time than the half-life of these isotopes in interstellar space. Given the known speed of IM1 outside the solar system, its travel time through the Milky-Way galaxy was likely many millions or perhaps billions of years — leaving no trace of short-lived isotopes. In contrast, any trash thrown into the ocean should have the well-known abundances of rare radioactive isotopes on Earth.

The sled was launched into Run 8 this afternoon. In the coming days, we will know more. It is possible that we will conclude that the shards are all human made based on the results from the gamma-ray spectrometer and further analysis of the XRF data. As Richard Feynman noted, the pleasure of doing science is in finding things out.


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".