Interstellar Curiosity

Avi Loeb
5 min readMay 29, 2024


(Image credit: LARYTTEN/GETTY)

The unknown is fascinating. We only need to stay curious for our life to be worth living.

Why do some adults lose their curiosity and engage in conflicts rather than exploration? For the same reason that seashells tend to lose their authenticity after rubbing against each other with passing waves on the beach. The recipe for maintaining wonder is simple: social distancing. By staying out of social media, I remain as curious about the world as I was as a farm boy.

These thoughts came to my mind after reading the abstract of a new preprint that was just posted on the arXiv by Hector Socas-Navarro from Tenerife in the Canary Islands of Spain:

This paper investigates the likelihood that the CNEOS 2014–01–08 superbolide (CNEOS14) was caused by an interstellar object. This issue has remained controversial due to lack of information on the capabilities of the classified satellite sensors that recorded the fireball. We critically evaluate previous studies, specifically addressing the reliability of the CNEOS database and the associated measurement uncertainties. With proper statistical analysis of existing data and the addition of a relevant new event (the 2024 Iberian superbolide), we disprove some claims in previous work, such as: a) the existence of a purported correlation between CNEOS velocity errors and bolide speed; b) the presence of large velocity errors of 10–15 km/s in the CNEOS database; and c) the assertion that CNEOS14 is most likely a solar system object with a hyperbolic trajectory due to measurement errors. We present a quantitative estimate of the probability that CNEOS14 is interstellar. If its measurement errors are drawn from the same underlying distribution as the 18 calibrated events, then the probability that CNEOS14 is interstellar is 94.3%. This probability is lower than the 99.7% confidence (3-σ) generally required to claim a scientific discovery. However, it is sufficiently high to be considered significant and, by far, the most likely explanation for the currently available empirical evidence.”

As I pointed out last week, meteors which appear fast relative to Earth are not necessarily interstellar because the Earth moves around the Sun at a speed of 30 kilometers per second which is merely a square-root of 2 smaller than the local escape speed from the solar system, 42 kilometers per second. An object colliding head-on with Earth only needs its velocity to exceed 12 kilometers per second relative to the Sun. This is well below the threshold for escape from the Solar system.

As of last week, we have two examples of meteors documented by sensors on U.S. Government satellites with nearly the same speed relative to Earth: one discovered in the Pacific Ocean on January 8, 2014 with a geocentric speed (relative to Earth) of 44.5 kilometers per second and the second discovered over Spain and Portugal on May 18, 2024 with a geocentric speed of 40.4 kilometers per second. However, the two objects approached Earth from nearly opposite directions relative to its motion around the Sun. As I concluded in a 2022 paper with then my student, Amir Siraj, the first came from behind Earth’s motion and was interstellar in origin with a heliocentric speed of 60 kilometers per second (relative to the Sun), whereas the second came nearly head-on. This second one is bound to the Sun in an elliptic orbit with eccentricity of 0.95 that ranges between 0.12 and 4.95 of the Earth-Sun separation, likely a Jupiter’s Family comet as it touches Jupiter’s orbit around the Sun.

Sketch of the relative orientation of the velocity vector of Earth (green) and the new meteor from May 18, 2024 (red). (Image credit: Peter Veres, Center for Astrophysics)

The measurement error of the U.S. Government data was assessed to be below 0.3 kilometers for the May 18, 2024 event, based on comparison to public ground-based data. This indicates that the U.S. Government errors are not particularly large for meteors of this speed, providing credibility for the interstellar origin of the January 8, 2014 event.

This realization stands in stark contrast to a paper published by Peter Brown and Jiří Borovička in The Astrophysical Journal in August 2023, shortly after I led an ocean expedition that retrieved materials from the fireball site of the interstellar meteor. These authors asserted that “Higher-speed events tend to be overestimated in speed… Appealing to Occam’s razor, we suggest that a significant error in the velocity vector is the most probable explanation for the apparent interstellar nature of USG 20140108 (i.e., it did not have an unbound orbit prior to Earth impact).” The authors argued that the actual speed of the object was less than half of the value reported by sensors aboard U.S. Government satellites and concluded: “we can fit the observed light curve and heights with a low speed (below 20 kilometers per second) using physical parameters consistent with stony impactors.”

This paper was published 18 months after officials from the U.S. Space Command under the Department of Defense issued a letter to NASA, in which they stated that “Dr. Joel Mozer, the Chief Scientist of Space Operations Command, the United States Force service component of the U.S. Space Command, reviewed analysis of additional data available to the Department of Defense … [and] … confirmed that the velocity estimate reported to NASA is sufficiently accurate to indicate an interstellar trajectory.”

By now, our expedition research team analyzed some of the spherules retrieved from the meteor fireball site and concluded in an extensive paper that: “Their chemical composition is unlike any known solar system material.”

If not properly used, Occam’s razor can get you injured. Independently from Dr. Mozer who studied classified data, Dr. Socas-Navarro concluded based on publicly available data for additional meteors in the CNEOS catalog that the January 8, 2014 meteor was interstellar at the 94.3% confidence.

Some scientists choose not to be curious by dismissing the validity of intriguing data. But the rest of us go on expeditions to explore the unknown and live a life worth living.


(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 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.



Avi Loeb

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