The people of Chelyabinsk in Russia got the surprise of their lives on the morning of February 15, 2013. That’s when a small asteroid exploded overhead. The resulting shockwave damaged buildings, injured people, and sent a sonic boom thundering across the region.

The Chelyabinsk impactor was about 20 meters across. It broke up in the atmosphere in an airburst and sent a shower of debris across the landscape. The event awakened people to the dangers of incoming space debris. Since we experience frequent warnings about near-Earth objects, scientists want to understand what a piece of space rock can do.

These days, there are many observation programs across the planet. For example, NASA operates its Sentry System and ESA sponsors the NEODyS project. They and others track incoming space rock. The observation data help predict the impacts of all but the very smallest asteroid chunks that come our way. Despite those programs, it’s inevitable that something like the Chelyabinsk asteroid chunk will slip through. So, it’s important to understand what happens during such an impact.

Modeling the Chelyabinsk Meteor

Scientists around the world began studying the event almost as soon as it happened. They collected bits of the debris and studied images of the entire event. Researchers with the Planetary Defense program at the Lawrence Livermore National Laboratory recently released a highly detailed 3D animation of a simulated chunk of space rock modeled after the Chelyabinsk impactor. They based the materials of the object in their animation on meteorites recovered from the ground.

Because people recorded the event with cell phones and security cameras, the team compared their model to what everybody witnessed. It turned out to be very close to what actually happened.

“This is something that can really only be captured with 3D simulation,” said Jason Pearl, lead researcher on the project. “When you combine LLNL’s specialized expertise in impact physics and hydrocodes with the Lab’s state-of-the-art High Performance Computing capabilities, we were uniquely positioned to model and simulate the meteor in full 3D. Our research underlines the importance of using these types of high-fidelity models to understand asteroid airburst events. A lot of smaller asteroids are rubble piles or loosely bound collections of space gravel, so the possibility of a monolith is really interesting.”

So, How Did the Chelyabinsk Object Shatter?

The most often-asked question about the rock that smacked into Earth over Russia was: was it a single chunk of debris? Or was it a flying rubble pile? If it was a monolithic chunk of rock, that would imply specific details about the strength of the rock and how it broke up. If it was a flying rubble pile, it might have broken up earlier and higher in the atmosphere. The LLNL experiment implies strongly that the impact was a single monolithic rock. It broke up under the heat and pressure of atmospheric entry.

To model the impactor and its behavior, the research team used a computational method called “smoothed particle hydrodynamics (SPH).” It models an object in a fluidic flow. In this case, it treats the atmosphere as a fluid. The model also simulates what happens as a Chelyabinsk-sized hunk of rock moves through the simulated air.

In their simulation, the team found that the incoming object started to break up from the rear and the cracks moved from back to front. The timescale of crack propagation toward the front of the asteroid controls the time at which the asteroid splits into smaller fragments while entering Earth’s atmosphere. A collection of fragments lies near the shock front and that shields the rest of the fragmenting rock. Finally, when the impactor reaches about 30 kilometers above Earth’s surface, intact fragments separate. That’s when the debris is exposed to the free stream. Eventually, the debris cloud decelerates very quickly and the remaining fragments continue to break up as they fly through the air toward the ground.

The Physics of the Breakup

The disintegration of the Chelyabinsk object provided scientists with a “physics-rich” event to study. According to LLNL physicist Mike Owen, the coupling of the asteroid to the atmosphere depends on how much surface area it has. The greater the surface area, the more exposure it has to heat, stress and pressure. Those all combine to break it up.

“As the asteroid enters the atmosphere, you start to have sort of a catastrophic failure,” Owen said. “And it tends to compress in the direction of travel. It was like the asteroid was being squeezed in the direction of travel, breaking into distinct pieces that started to separate and break perpendicular to the direction of travel. All of a sudden, you’ve got a lot more material being exposed to the hypersonic interaction with the air, a lot more heat being dumped in, a lot more stress on it, which makes it break faster and you get sort of a cascading runaway process.”

Using Chelyabinsk To Understand Future Impacts

Models of impactors like this one provide insight into future events when chunks of space rock will hit Earth. One long-term goal would be to use such models to assess what will happen to a target region during an impact. Meteoric impacts are natural disasters that affect our planet just as fires and floods do. As such, there’s a need to predict and understand them so that people can be more prepared.

Researcher Cody Raskin points to our increased ability to detect such incoming impactors. “If we can see a small asteroid approaching Earth in time, we could run our model and inform authorities of the potential risk, similar to a hurricane map,” said Raskin. “They could then take appropriate protective actions, such as evacuating residents or issuing shelter-in-place orders, ultimately saving lives.”

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In 2002, Thomas Hertog was urgently summoned to the office of his esteemed mentor, Stephen Hawking. With a sense of excitement radiating from his eyes, the renowned cosmologist communicated to Hertog through his computer-controlled voice system, declaring that he had experienced a change of heart. “My book, A Brief History of Time, is written from the wrong perspective,” Hawking announced. This statement consigned the popular scientific tome, which had sold over 10 million copies worldwide, to the waste bin. According to a report from the Guardia, Hertog, and Hawking then embarked on a new project, aiming to encapsulate their latest ideas about the universe in a fresh way.

Five years following the passing of Stephen Hawking, his final theory, titled On the Origin of Time, is set to be published in the UK next month. At a Cambridge festival lecture on March 31st, cosmologist Thomas Hertog, currently affiliated with KU Leuven University in Belgium, will discuss the origins and themes of the book. According to Hertog, Hawking struggled to comprehend how the universe was able to create conditions that are so perfectly suitable for life. These conditions include a precise balance of particle forces that enable the existence of chemistry and complex molecules, as well as the presence of only three dimensions of space that allow for the formation of stable solar systems and habitats for living organisms. Some cosmologists assert that without these specific characteristics, life as we know it may not have come to fruition in the universe.

A quick glance at Hawking’s life

Stephen Hawking was born on January 8, 1942, in Oxford, England. His father was a medical researcher, and his mother was a secretary. From an early age, Hawking was interested in science, especially physics and astronomy. He attended University College, Oxford, where he studied physics and graduated with honors in 1962. He then went on to pursue graduate studies in cosmology at Trinity College, Cambridge.

It was during his time at Cambridge that Hawking was diagnosed with a rare form of motor neuron disease that left him wheelchair-bound and unable to speak without the use of a computerized voice synthesizer. Despite this debilitating condition, Hawking continued his studies and research, becoming one of the most brilliant and influential scientists of his generation.

In 1974, Hawking proposed the theory of Hawking radiation, which suggested that black holes could emit radiation and eventually evaporate over time. This groundbreaking work established Hawking as a leading figure in theoretical physics, and he continued to make significant contributions to the field throughout his career. He also wrote several popular science books, including the best-selling A Brief History of Time, which helped make complex scientific ideas accessible to a wider audience.

Hawking received numerous awards and honors for his contributions to science, including the Albert Einstein Medal, the Presidential Medal of Freedom, and the Copley Medal, the highest honor of the Royal Society. He also served as the Lucasian Professor of Mathematics at Cambridge, a position once held by Isaac Newton.

Hawking passed away on March 14, 2018, at the age of 76, leaving behind a legacy of scientific achievement and popularizing science for the general public. His work has inspired countless people around the world to pursue careers in science and to explore the mysteries of the universe.

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