Cataclysm in the Cosmos: Princeton Researchers Unmask the Violent Origins of the Geminids 
Meteor Shower
Illustration of the Parker Solar Probe spacecraft approaching the sun. Princeton scientists used NASA’s Parker Solar Probe data to deduce a violent, catastrophic event—such as a high-speed collision or a gaseous explosion—likely created the Geminids meteoroid stream, which unusually originates from an asteroid rather than a comet. Credit: Johns Hopkins University Applied Physics Laboratory
Princeton researchers used data from NASA’s Parker Solar Probe to deduce that a catastrophic event likely created the prolific Geminids meteoroid stream.
Unlike most meteor showers which originate from comets, the Geminids appear to stem from the asteroid 3200 Phaethon. The researchers modeled three potential formation scenarios and compared these to models developed from Earth-based observations. The data from the Parker Solar Probe led them to discount the traditional cometary model and conclude that a violent event likely created the Geminids stream, deepening our understanding of the composition and history of asteroids.
The Geminids meteoroids light up the sky as they race past Earth each winter, producing one of the most intense meteor showers in our night sky.
Mysteries surrounding the origin of this meteoroid stream have long fascinated scientists because, while most meteor showers are created when a comet emits a tail of ice and dust, the Geminids stem from an asteroid — a chunk of rock that normally does not produce a tail. Until recently, the Geminids had only been studied from Earth.
Each winter, the Geminids meteoroids light up the sky as they race past Earth, producing one of the most intense meteor showers in our night sky. Until now, the Geminids had only been studied from Earth.
Now, Princeton researchers used observations from NASA’s Parker Solar Probe mission to deduce that it was likely a violent, catastrophic event — such as a high-speed collision with another body or a gaseous explosion — that created the Geminids. The findings, which were published in the Planetary Science Journal on June 15, narrow down hypotheses about this asteroid’s composition and history that would explain its unconventional behavior.
“Asteroids are like little time capsules for the formation of our solar system,” said Jamey Szalay, research scholar at the Princeton University space physics laboratory and co-author on the paper. “They were formed when our solar system was formed, and understanding their composition gives us another piece of the story.”
An unusual asteroid
Unlike most known meteor showers that come from comets, which are made of ice and dust, the Geminids stream seems to originate from an asteroid — a chunk of rock and metal — called 3200 Phaethon.
“Most meteoroid streams are formed via a cometary mechanism, it’s unusual that this one seems to be from an asteroid,” said Wolf Cukier, undergraduate class of 2024 at Princeton and lead author on the paper.
“Additionally, the stream is orbiting slightly outside of its parent body when it’s closest to the sun, which isn’t obvious to explain just by looking at it,” he added, referring to a recent study with Parker Solar Probe images of the Geminids led by Karl Battams of the Naval Research Laboratory.
When a comet travels close to the Sun it gets hotter, causing the ice on the surface to release a tail of gas, which in turn drags with it little pieces of ice and dust. This material continues to trail behind the comet as it stays within the Sun’s gravitational pull. Over time, this repeated process fills the orbit of the parent body with material to form a meteoroid stream.
But because asteroids like 3200 Phaethon are made of rock and metal, they are not typically affected by the Sun’s heat the way comets are, leaving scientists to wonder what causes the formation of 3200 Phaethon’s stream across the night sky.
“What’s really weird is that we know that 3200 Phaethon is an asteroid, but as it flies by the Sun, it seems to have some kind of temperature-driven activity,” Szalay said. “Most asteroids don’t do that.”
Some researchers have suggested that 3200 Phaethon may actually be a comet that lost all of its snow, leaving only a rocky core resembling an asteroid. But the new Parker Solar Probe data show that although some of 3200 Phaethon’s activity is related to temperature, the creation of the Geminids stream was likely not caused by a cometary mechanism, but by something much more catastrophic.
