On 18 May 2024, a giant superbolide overflew the Iberian Peninsula, being captured by the video stations monitoring the sky of the Spanish Meteor Network (SPMN). A team led by the Institute of Space Sciences (ICE-CSIC) reconstructed the trajectory of the meteoroid and concluded that its most likely source is the Jupiter-family comet (JFC) region. The study is being published today in the journal Monthly Notices of the Royal Astronomical Society: Letters. 

This is the first time that the orbit of a meter-sized meteoroid is dynamically associated with a Jupiter family comet. Most rocks impacting Earth’s atmosphere come from orbits that originated in the main asteroid belt. On the contrary, Jupiter family comets are short-period comets with orbital periods less than 20 years. They are believed to have formed in the Kuiper Belt, a collection of rock-ice bodies located just beyond the orbit of Neptune.

The meteoroid was registered by 12 video stations from the SPMN network, a professional-amateur (proam) collaboration led by ICE-CSIC researcher and member of the Institute of Space Studies of Catalonia (IEEC), Josep M. Trigo. Among them, the team, led by three researchers of the ICE-CSIC Meteorites, Minor Bodies and Planetary Science Research Group, selected three SPMN videos, another one obtained by Pablo Ramírez-Moreta and Rainer Kresken, co-authors of the study from Planetary Defence Office (OPS-SP) of the European Space Agency (ESA), and observations from space through USA defense satellites. After the trajectory and heliocentric orbit of the meteoroid were computed, the team found out that the orbital elements indicated the most likely source is the Jupiter-family comet region, aligning with the SOHO comet family, as its sun skirting orbit is eccentric and inclined enough to be decoupled from the gravitational action of Jupiter.

“The so-called 2024 Iberian Superbolide was certainly a special event, characterized by unusual atmospheric fragmentation and a near-Sun orbit. Its metric size presents a challenge to our current understanding of disruption processes.”, says Eloy Peña-Asensio, first author of the study, who developed his PhD at the ICE-CSIC and IEEC, and nowadays is a postdoctoral researcher at Politecnico di Milano.

The team found surprising that the closest distance to the Sun in the trajectory of this meter-sized meteoroid was 15 million kilometers, meaning a tenth of the distance between Earth and the Sun. At this distance from the Sun, the surface of the rock was subjected to temperatures of about 1000 Kelvin, so the meteoroid experienced a quite extreme heating in each approach to the perihelion, probably affecting its volatile content. “Once the meteoroid reached Earth’s atmosphere at a velocity of 40 kilometers per second, it started to ablate at a height of about 130 km over the sea level, and followed a near-horizontal path, producing a luminous trail more than 500 kilometers long, until it ended over the Atlantic Ocean”, says Pau Grèbol, predoctoral researcher at ICE-CSIC and IEEC. 

The inferred physical properties of the meteoroid revealed that the superbolide was produced by a relatively fragile carbonaceous meteoroid, but hosting high-strength rocks that reached the lower part of the luminous trajectory at heights above sea level of about 50 kilometers. The team suggests that the meteoroid was a polymict carbonaceous chondrite, containing  alien materials to that of a carbonaceous chondrite in its interior due to the collisional gardening experienced over the time it was in interplanetary space, probably crossing regions abundant in rocks with higher-strength.

However, as explained by Eloy Peña-Asensio, the authors did not reject the hypothesis that the impactor could be a thermally processed C-type asteroid due to close encounters with the Sun. Whether such objects end up in this orbit remains an open question. This study also identifies other similar previous impactors, but none of them were meter-sized. This establishes new limits on the expected super catastrophic disruption of sunskirting objects.

Meter-sized projectiles close to Earth

“Our study exemplifies the need to increase our global telescopic coverage to identify meter-sized asteroids and comets experiencing close approaches with the Earth. The detection of this ‘small comet’ is a case study to learn more about the potential hazard associated with highly eccentric projectiles associated with JFCs, probably contributing between 1 and 5% of the global flux of meteoroids, but rarely being populated by meter-sized projectiles like the one producing this unique superbolide.”, says ICE-CSIC and IEEC researcher Josep M. Trigo Rodríguez. 

After proving that the meteoroid is probably the product of the disruption of an eccentric comet, the team is currently studying the possibility of survival of samples associated with this event. The nature of the rock demonstrates that JFCs might host high-strength materials and end their days as dark bodies crossing periodically the near-Earth region. In addition, meter-sized projectiles from JFCs could be sources of risk, or produce meteorite falls in the right geometrical conditions.