On 8 January 2014, US government satellite sensors detected three atmospheric detonations in rapid succession about 84 kilometers north of Manus Island, outside the territorial waters of Papua New Guinea. Analysis of the trajectory suggested an interstellar origin of the meteor. The object, labeled IM1 for Interstellar Meteor 1, arrived with a velocity relative to Earth of more than 45 kilometers per second and originated from outside the plane of the ecliptic. On 1 March 2022, the US Space Command issued a formal letter to NASA certifying a 99.999% likelihood that the object was interstellar in origin. Along with this letter, the US Government released the fireball light curve as measured by satellites, which showed three flares separated by a tenth of a second from each other. The bolide broke apart at an unusually low altitude of about 17 kilometers. The object was substantially stronger than any of the other 272 objects in the CNEOS catalog of fireballs compiled by NASA, including the 5%-fraction of iron meteorites from the solar system. Calculations of the fireball light energy suggest that about 500 kilograms of material was ablated by the fireball and converted into ablation spherules with a small efficiency. The fireball path was localized to a kilometer-wide strip based on the delay in arrival time of the direct and reflected sound waves to a seismometer located on Manus Island.
The expedition team of the Galileo Project conducted an extensive towed-magnetic-sled survey during the period 14–28 June, 2023, over the seafloor north of Manus Island, Papua New Guinea, centered around the calculated path of IM1. The expedition was mounted from Port Moresby to search for remnants of IM1. It utilized a 40-meter catamaran workboat, the M/V Silver Star. A 200-kg sled was used with 300 neodymium magnets mounted on both of its sides and video cameras mounted on the tow-bridle. Approximately 0.06 km2 were sampled in the target area. The fine material collected on the neodymium magnets was extracted and brought in a wet slurry up to a laboratory set up on the bridge of the vessel for further examination. There, an initial wet-magnetic separation took place. Subsequently, both magnetic and non-magnetic separations were processed through sieves and dried. Spherules were handpicked with tweezers using a binocular zoom microscope. They ranged in size from 100 microns to 2 mm. We obtained a total of 850 spherules by this method.
Our research team used state-of-the-art instruments to analyze the retrieved spherules at the Geochemistry laboratory of Professor Stein Jacobsen at Harvard University and the analysis laboratory of Dr. Roald Tagle at the Bruker Corporation in Berlin, Germany. Most spherules were first analyzed by micro-XRF with a Bruker Tornado M4 for their bulk major element composition, followed by imaging with a scanning electron microprobe and chemical mapping, as well as spot chemical analyses of about 100 spherules with an Electron Probe Microanalyzer. Measurements of elemental abundances for about 60 major and trace elements were performed for 70 spherules with an iCAP TQ triple quadrupole ICP-MS. We described our new findings in a new preprint, with the main details as follows.
Cosmic spherules are often sub-divided into three compositional types. These are the silicate-rich spherules or S-type, the Fe-rich spherules or I-type and glassy spherules or G-types. Relatively rare spherules have been called differentiated as they have similarities to achondrite meteorites and have been treated as a subgroup of S-type spherules. Differentiated spherules have major-element compositions with higher Si/Mg and Al/Si ratios, and higher refractory lithophile trace element contents relative to chondritic spherules.
The major element compositions of 745 spherules from the IM1 site, measured by micro-XRF, were plotted in a Mg-Si-Fe ternary diagram, since such a diagram has been shown to effectively distinguish the S-, I- and G-type groups. About 78 % of the spherules fall along the trend of S, G and I-type spherules. These are referred to as primitive spherules as they are thought to be related to primitive chondritic meteorites and represent materials that have not gone through planetary differentiation. The remaining 22% of the spherules have low Mg and plot close to the Si-Fe side of the diagram. These spherules are thus called differentiated, meaning they are likely derived from crustal rocks of a differentiated planet. Since they are clearly different from the differentiated subgroup of S-type spherules we gave them a new name: D-type spherules. The primitive and differentiated spherules are divided based on their Mg/Si ratio. Primitive spherules have Mg/Si >1/3, while differentiated spherules have Mg/Si < 1/3, so this ratio can be used to distinguish the two groups.
The high Si varieties of D-spherules appear close to or within the range of terrestrial igneous rocks, while the low Si groups do not. Thus, the D-type spherules have been divided into four distinct groups. This results in 8 distinct spherule groups that are all shown in the triangular diagram below.
We use a different diagram to identify spherules with particularly high contents of refractory lithophile elements, based on the enrichments of Be, La and U relative to Mg and Fe. This procedure identifies 10 of D-type spherules as BeLaU/low-Si spherules and 2 as BeLaU/high-Si spherules. While these spherules clearly appear to be derived from material formed by igneous fractionation, their chemical composition is unlike any known solar system material, the KREEP component of the lunar crust being closest.
It has been claimed a few months ago in a paper and a preprint by authors who had no access to the spherules, that the compositions of BeLaU spherules are consistent with coal ash, disfavoring their meteoritic origin. The National Institute of Standards and Technology (NIST) has provided multiple standards of coal fly ash. These standards all have very similar compositions. The best documented standard for many elements is SRM 1633a, and its composition is given on the GeoReM website. We compared the average composition of BeLaU spherules for 55 elements with the SRM1633a coal ash standard in the figure attached below. Many volatile elements (Zn, As, Se, Cd, Tl, Pb and Bi) are enriched in the coal fly ash by factors of about 10 to 100 compared to the BeLaU spherules. Some refractory elements (Be, Ca, Cr, Fe, Y, Tm, Yb, Lu and W) are depleted by factors of 3 to 10 in coal fly ash when compared to BeLaU spherules. Thus, BeLaU spherules do not have the composition of coal ash, making the aforementioned claims invalid.
Scientific knowledge should be based on empirical evidence and not opinions. It took our exceptional team a year to plan the expedition and six months to conduct a thorough analysis of the materials retrieved from IM1’s site in the Pacific Ocean. It took critics much less time and effort to voice their opinions and get the attention of reporters or colleagues. But at the end, professional integrity must lead the way, irrespective of the temporary distortions created by social or news media. To be regarded as an intelligent civilization, we better follow the rigorous scientific path pursued by the research team of the Galileo Project.
ABOUT THE AUTHOR
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.
