A violent collision likely created the Geminids meteor shower

By Ashley Strickland, CNN

(CNN) — The Geminid meteor shower, which lights up the sky each December, is one of the most active and dependable celestial displays of the year.

But the actual origin of the winter light show is something of a mystery. Now, astronomers using NASA’s Parker Solar Probe have gained more insight into the underlying cause of the Geminids.

The meteor shower was first recorded in 1862 and appears to radiate from the Gemini constellation. During the meteor shower’s peak in mid-December, 120 bright yellow meteors can be seen per hour if skies are clear.

Meteors typically originate from the leftover bits and pieces of comets orbiting around the sun. When comets, which originate in the icy outskirts of the solar system, pass close to the sun, they shed trails of particles. Meteor showers appear in Earth’s skies when our planet passes through the debris trails. As the particles collide with Earth’s atmosphere, they blaze up and disintegrate, leaving fiery streaks behind, according to NASA.

The Geminids, however, are unusual in that they have been traced to the asteroid 3200 Phaethon. Scientists have debated the very nature of what Phaethon is. It’s possible that Phaethon is a “dead comet,” with an icy shell that eventually melted away. The closely tracked near-Earth asteroid has been likened to comets, so it’s been called a “rock comet.”

“What’s really weird is that we know that Phaethon is an asteroid, but as it flies by the Sun, it seems to have some kind of temperature-driven activity. Most asteroids don’t do that,” said Jamey Szalay, a research scientist at Princeton University, in a statement. Szalay is the coauthor of a study about the asteroid published on June 15 in The Planetary Science Journal.

Although the Parker Solar Probe, launched in 2018, is on a mission to “touch” and study the sun, the spacecraft’s increasingly close proximity to our star is useful for scientists wanting to study the dust swirling around the inner solar system. The probe’s instruments have provided scientists with a detailed view of the dust particles shed by comets and asteroids on their treks around the sun — and in doing so shed new light on the Geminids-Phaethon connection.

How an asteroid sparked a meteor shower

While the spacecraft doesn’t actually carry a dust counting instrument to measure the grains, the particles impact the Parker Solar Probe as it orbits the sun. As dust hits the spacecraft, it creates electrical signals that can be picked up by the probe’s instruments, including one that measures electric and magnetic fields near the sun.

Data collected by the Parker Solar Probe was used by scientists to model three different scenarios for the Geminid meteor shower, which were then compared with models based on observations from Earth.

The data revealed that the most probable cause of the meteor shower was a sudden, violent event, likely a rapid collision of the asteroid with another space rock or even some kind of gaseous explosion that caused the Geminids to first appear in our skies in 1862.

Phaethon was discovered on October 11, 1983, by astronomers using the Infrared Astronomical Satellite.

After Phaethon’s discovery, astronomer Fred Whipple realized that the asteroid and the Geminid meteor shower stream had nearly identical orbits, and he made a connection between the two.

It’s the first asteroid to be associated with a meteor shower, and it measures about 3.17 miles (5.10 kilometers) across. Astronomers have studied the space rock for years in an attempt to determine why it behaves like a comet.

The space rock was named after the Greek myth about the son of Helios, the sun god, because it closely approaches our sun.

Phaethon orbits the sun closer than any other asteroid and takes 1.4 years to complete its orbit.

Even before studying dust in our solar system with Parker Solar Probe, astronomers determined that the asteroid heats up to about 1,300 degrees Fahrenheit (704 degrees Celsius) on its closest approach to the sun, which causes Phaethon to shed more dusty debris.

These particles cause the meteor shower each year when they plunge into Earth’s atmosphere at 79,000 miles per hour (127,000 kilometers per hour), vaporizing in the streaks we call “shooting stars.”

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