A fireball in the night sky
Every day, more than 100 tons of space dust and rock fall into Earth’s atmosphere, producing meteors like the one spotted over Kyoto in 2017. Credit: Science@NASA and NASA’s Goddard Space Flight Center; image courtesy of Howard Edin, Oklahoma City Astronomy Club

On 28 April 2017, a fireball exploded over Kyoto, Japan. New research has tied the meteor to a near-Earth asteroid that could one day collide with Earth, though not for another 10 million years or so. Still, the close orbit of the asteroid is allowing scientists a peek at how meteors are born.

Using the SonotaCo network database, a collection of more than 100 cameras spread across 27 sites in Japan, researchers were able to calculate the properties of the meteoroid’s orbit, connecting it to the bright asteroid 2003 YT1. They found that the tiny meteor had a total mass of 29 grams and a diameter of 2.7 centimeters. That’s small potatoes compared to some fireballs, such as the Chelyabinsk meteor that exploded over Russia in 2013. But tiny meteors like the Kyoto fireball can provide insights into the larger bodies they came from.

“The longtime unsolved problem is that nobody knows when and where hazardous objects might impact the Earth. By using meteor science, we may be able to make a guess.”

As asteroids near Earth slowly fall apart, they create dust streams made up of meteoroids that can cross the path of our planet. Burning up in our planet’s atmosphere, their fiery trails signal meteors streaking through the sky. Only a small number survive to reach the ground as meteorites. But even ablaze, the tiny space rocks can provide insights into a class of near-Earth objects (NEOs) that could one day collide with Earth.

“We can consider ejected meteoroid-particles…as demising signs of parental near-Earth objects,” said Toshihiro Kasuga, a researcher at the National Astronomical Observatory of Japan. “This idea can further make an intensive synergy for spotting potentially hazardous NEOs.”

“The longtime unsolved problem is that nobody knows when and where hazardous objects might impact the Earth,” Kasuga said. “By using meteor science, we may be able to make a guess.”

Changing the Game

The near-Earth asteroid YT1 was first spotted in 2003, almost 15 years before the fateful fireball burned in the sky over Japan. The asteroid was one of several spotted by the Catalina Sky Survey, a large-scale project based out of Arizona with a mission to catalog the bulk of NEOs. Most of the larger asteroids are thought to have been identified, but smaller asteroids are more challenging to spot. Previous studies suggest that YT1 has less than a 6% chance of colliding with our planet in the next 10 million years.

YT1 is a binary system, two kilometer-sized asteroids that likely formed as one object. Like most asteroids, the original object is thought to have been a rubble pile, a collection of small materials tightly bound by gravity. As heat from the Sun created a small push on the surface of the asteroid, it began to spin faster and faster. Eventually, YT1 found itself rotating so quickly that it split into two pieces, creating a binary object still held together by gravity.

When the asteroid split in half, it released a stream of fine particles. Streams of dust have a lifetime of only a few thousand years, suggesting that YT1 only recently became a binary. The asteroid and its meteoroid stream are both traveling near our planet. “Both the fireball and 2003 YT1 practically cross the Earth orbit,” the authors wrote in their research, published in the Astronomical Journal.

It’s also possible that impacts from other rocks in space could blow material from the asteroid and create fireballs above Earth. “If an asteroid is hit by another body, it can experience a catastrophic destruction,” said Jose Madiedo, a meteorite scientist at the Institute of Astrophysics of Andalusia in Spain who was not part of the study.

Although YT1 doesn’t appear to show signs of a large impact, smaller micrometeoroids could have slammed into the asteroid, blowing off small particles of debris that could eventually reach Earth. “Rocks detached from the asteroid can be large enough to become meteorites when they cross our planet’s path in the solar system,” Madiedo said.

Because it is part of a stream of material, the Kyoto fireball is probably not alone. Other meteors from YT1 may yet slam into our planet’s atmosphere; many may already have. “Fireballs on Earth are not rare at all, since our atmosphere is being continuously hit by…meteoroids coming from different bodies in the solar system,” Madiedo said. “Nevertheless, very bright fireballs occur less often than less luminous ones.”

Although the odds are slim of YT1 itself making a gigantic fireball in Earth’s sky, Kasuga and his colleagues intend to continue hunting for other meteoroids that might impact Earth’s atmosphere. They hope that these tiny streams might lead to hard-to-spot, smaller NEOs that may have been missed by large surveys.

“We are aiming at characterizing much more numerous and smaller—tens of meter scale—potentially dangerous objects well in advance of any close approach,” Kasuga said.

—Nola Taylor Redd (@NolaTRedd), Science Writer


Redd, N. T. (2020), Tiny fireballs may one day reveal unseen asteroids, Eos, 101, https://doi.org/10.1029/2020EO137232. Published on 20 February 2020.

Text © 2020. The authors. CC BY-NC-ND 3.0
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