At least once in our lives, we’ve all seen a bright streak of light briefly blaze across the sky and have quickly referred to it as an asteroid, meteor, shooting star, comet, or some other whimsical name we’ve heard others use to describe it. For those calling it a meteor, you would be correct, but we’ll touch upon this later. The time it takes for a space rock, bolide being its scientific name, to travel through Earth’s atmosphere and crash into the ground literally takes only a few seconds. But what happens to a space rock during this very brief travel time, and how can scientists use this to learn about a specific space rock’s origin and the potential damage it could cause if it explodes in mid-air?

Now, a team of researchers from the SETI Institute and NASA Ames Research Center might have shed new light on what happens to space rocks as they blaze through the Earth’s atmosphere. In findings recently published in Meteoritics & Planetary Science, the researchers introduced a step-for-step process regarding what happens to space rocks from the moment they enter the Earth’s atmosphere all the way to ground impact.

The primary motivation behind the study was to fill a longstanding knowledge gap regarding how a space rock’s composition influences what happens if it explodes mid-air like the one that exploded over Chelyabinsk, Russia, in 2013. To accomplish this, the researchers analyzed image and video data from 75 meteorite falls regarding several attributes, including entry angle, spin rate, and mass loss.

In the end, the researchers introduced a seven-stage process that space rocks endure as they enter and travel through the Earth’s atmosphere: Phase 1: Atmospheric entry; Phase 2: Brightness begins; Phase 3: Brightness increases with fireball appearance; Phase 4: Brightness maintains while melting begins; Phase 5: Front of rock begins to break apart; Phase 6: Back of rock breaks apart; Phase 7: Melting and breaking apart continue until glowing stops, followed by melting ending and wind discards crusted pieces.

“We used to think that solid rocks would evaporate from the enormous heat and brilliant light generated in the air collision,” said Dr. Peter Jenniskens, who is a meteor astronomer at the SETI Institute and NASA Ames Research Center and lead author of the study. “We found instead that first melting and then fragmentation controls how a rock loses mass.”

The researchers note that the 75 meteorites they studied went through the seven phases at different altitudes and were also based on the meteorite composition. They specifically emphasized these findings could help better inform Planetary Defense measures and how to prepare if an incoming space rock explodes in mid-air.

Past Exploding Space Rocks

As noted, a recent example of a space rock exploding in mid-air occurred in Chelyabinsk, Russia, on February 15, 2013, when a 20-meter (66-feet) near-Earth asteroid entered the Earth’s atmosphere traveling at 19 kilometers per second/12 miles per hour (68,400 kilometers per hour/42,500 miles per hour) and exploding at an approximate altitude of 30 kilometers (18.5 miles). The blast was equivalent to about 30 times stronger than the Hiroshima bomb and about 1,500 individuals were injured, largely from broken glass that shattered across more than 7,200 buildings and six cities.

One of the most famous exploding space rocks also occurred over Russia, though it occurred more than a century earlier. This was the Tunguska explosion, which occurred on June 30, 1908, though the bolide was much larger at about 50-100 meters (160-330 feet), it exploded at an altitude of about 5-10 kilometers (3-6 miles), and the resulting blast was about 1,000 times stronger than the Hiroshima bomb. This incredible blast resulted in about 80 million trees over an area of more than 2,150 square kilometers (830 square miles).

Cleaning Up Whimsical Names

While this study referred to a space rock as a bolide, space rock just sounds cooler. However, it’s important to provide the real names of astronomical objects to clean up any confusion. For example, an object residing in space that is smaller than 1 meter (about 3.3 feet) wide is called a meteoroid, whereas an asteroid is larger than 1 meter wide. As noted earlier, a meteor is the visual streak of light seen as a meteoroid or an asteroid emits as it blazes through the Earth’s atmosphere. Finally, a meteorite is the piece that survives the atmosphere and lands on the ground.

What new insights into meteorite-forming processes will researchers make in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!