Both the first and second interstellar meteors, IM1 and IM2, are outliers in material strength and may have originated in supernova explosions, according to new research by Harvard University astrophysicists.
A fireball. Image credit: Urikyo33.
IM1 was detected by U.S. government sensors in 2014, identified as an interstellar object candidate in 2019, and confirmed in 2022.
Also known as CNEOS1 2014-01-08, the object had an estimated diameter of 0.45 m (1.5 feet), a mass of 460 kg, and a pre-impact velocity of 60 km per second (37.3 miles per second).
“IM1, detected by U.S. Department of Defense (DoD) sensors through the light that it emitted as it burned up in the Earth’s atmosphere off of the coast of Papua New Guinea in 2014, was determined to be an interstellar object in 2019, a conclusion that was confirmed by independent analysis conducted by the DoD in 2022,” explained Harvard University researchers Amir Siraj and Abraham Loeb.
“The object predated the interstellar object ‘Oumuamua by 3.8 years, and the interstellar object 2I/Borisov by 5.6 years.”
“The measured peak are apparent in the light curve of IM1 at an altitude of 18.7 km (11.6 miles) implies ambient ram pressure of 194 MPa (Megapascals) when the meteor disintegrated,” they added.
“This level of material strength is over 20 times higher than stony meteorites and 2 times larger than iron meteorites.”
“IM1 was also dynamically unusual — its speed relative to the Local Standard of Rest is shared by less than 5% of all stars.”
The second interstellar meteor, IM2 or CNEOS 2017-03-09, was identified in data from the CNEOS fireball catalog.
The object was detected on March 9, 2017, at an altitude of 23 km (14.3 miles) over Atlantic Ocean near Portugal.
It was roughly a meter (3 feet) in size, 10 times more massive than IM1, and was moving at a speed of 40 km per second (24.9 miles per second).
The researchers also compared the material strength of IM1 and IM2 with that of other CNEOS objects.
“IM1 and IM2 are ranked 1 and 3 in terms of material strength out of all 273 fireballs in the CNEOS catalog,” they said.
“This implies that interstellar meteors come from a population with material strength characteristically higher than meteors originating from within the Solar System.”
“Additionally, we find that if the two objects are representative of a background population on random trajectories, their combined detections imply that approximately 40% of all refractory elements are locked in meter-scale interstellar objects.”
“Such a high abundance seemingly defies a planetary system origin.”
“We assume that IM1 and IM2 are composed of refractory elements, even though their material strengths imply that they were primarily metallic in composition,” they added.
“Interestingly, there is a paucity of refractory elements observed in the gas phase in the interstellar medium, an observation which could potentially reflect refractory elements being locked in interstellar objects.”
“Supernovae have been observed to produce iron-rich ‘bullets,’ which could be a possible origin of IM1 and IM2.”
The team’s paper will be published in the Astrophysical Journal Letters.
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Amir Siraj & Abraham Loeb. 2022. Interstellar Meteors are Outliers in Material Strength. ApJL, submitted for publication; arXiv: 2209.09905
