A Gift from the Sky

Avi Loeb
4 min readFeb 8, 2024
A 40-gram fragment from the asteroid 2024 BX1 that landed near Berlin, Germany on January 21, 2024. (Credit: Andreas Möller)

The asteroid 2024 BX1 was spotted a few hours before impacting Earth by astronomer Krisztián Sárneczky at Konkoly Observatory in Hungary. Subsequently, it was tracked by NASA’s Near Earth Asteroid Scout and the European Space Agency’s Meerkat Asteroid Guard impact hazard assessment systems. The BX1 asteroid, about 1-meter in diameter , generated a meteor fireball which peaked at an altitude of 34 kilometers as a result of its friction on air and was seen on January 21, 2024 at 00:33 UTC over Berlin, Germany.

The Galileo Project member, Dr. Roald Tagle from the Bruker Corporation in Berlin, went out to collect fragments from the meteorite. He presented his findings over Zoom at our research team meeting last night. Shortly after waking up this morning, I emailed him my interpretation of the report:

“Dear Roald:

Thank you so much for the informative presentation about the meteorite 2024 BX1 that fell in Germany on January 21, 2024. Following the team’s Zoom call last night, I went through the numbers this morning during the half hour I had between waking up and my jog at sunrise. I attach the calculation in the attachment below. Your numbers all make sense.

Despite my initial expectations, the slowdown on air is fast even for the 100-gram fragments. As a result, the vertical fall time for 1-gram fragments is of order ten minutes (given that the effective height for air density is of order 5 km). This time is obtained by balancing air friction against gravity, giving a vertical infall speed of order 9 meters per second for 1-gram (centimeter-scale) fragments.

To get across the horizontal distance of 10 kilometers over 10 minutes requires a wind speed of 17 meters per second for the 1-gram fragments. Indeed, strong winds reach up to ~20 meters per second. It all works out. Physics works once again.

This is very good news for the next expedition to retrieve large fragments from the interstellar meteorite, IM1. The meteorite 2024 BX1 was comparable in size and somewhat slower than IM1. This means that we could potentially find large (centimeter-scale) fragments across a wide region around the meteor fireball path, even for modest wind speeds. The three flares of IM1 mean that there might be three lines of debris, dictated by the wind speed near PNG at 17:05:34 UTC on January 8, 2014.

The notes below summarize the numbers for 2024 BX1.

The Sun will rise shortly, so I need to go out for my jog.

Avi”

My simple calculation implied that BX1’s fragments should be distributed on a line along which the distance of each fragment from the explosion site in units of 10 kilometers scales inversely with the fragment size in units of centimeter. Indeed, this was the way the fragments were ordered perpendicular to the meteor path in Roald’s report.

The meteorite fragments indicated that 2024 BX1 belongs to a rare asteroid family called aubrites. Main belt asteroids like 2024 BX1 are the building blocks that made the rocky planets in the solar system from the debris disk around the newly born Sun 4.6 billion years ago.

Researchers were fortunate to collect BX1’s fragments from the open farm fields along the meteor debris line. Gladly, the German farmers cooperated and did not claim ownership on their gift from the sky. American farmers could have shot those attempting to enter their property without permission. In search for the rocks, Roald took pictures of a small rocket from World War II and old animal bones which were scattered along BX1’s debris path.

BX1’s data will guide our next expedition to the Pacific Ocean in search for centimeter-size pieces of the first reported interstellar meteor, IM1 from 2014. Following the above inferences, I had asked my brilliant team member, Tim Gallaudet: “What is known about the wind near Manus Island, PNG at 17:05:34 UTC on January 8, 2014?” Tim found a wind speed of merely 2.5 meters per second from archival data at the time and location of IM1’s fireball. This wind speed is comparable to my average jogging speed and 7 times smaller than the wind speed inferred for BX1. This suggests that centimeter scale fragments of IM1 might have been shifted only by 1–2 kilometers from IM1’s explosion site. Mild ocean current would have added a small shift on top of that.

Thanks to the BeLaU spherules we traced at IM1’s site, we now know where to search for IM1’s bigger relics. If we find them, we could infer the origin and nature of IM1, and potentially learn something new about the backyard of another star in our cosmic neighborhood.

ABOUT THE AUTHOR

Image credit: Chris Michel (October 2023)

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.

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Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".