Science
Watch the Chelyabinsk Meteor Breakup in this Detailed Simulation
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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.”
Science
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In a remarkable development, NASA has given the green light to the Dragonfly mission, a revolutionary rotorcraft designed to investigate the complex chemistry of Saturn‘s moon Titan.
This confirmation allows the mission to proceed with the final design, construction, and testing of the spacecraft and its scientific instruments.
Deciphering the prebiotic chemistry on Titan
The Dragonfly mission, led by Dr. Melissa Trainer of NASA’s Goddard Space Flight Center, will carry a cutting-edge instrument called the Dragonfly Mass Spectrometer (DraMS).
This powerful tool will help scientists delve into the intricate chemistry at work on Titan, potentially shedding light on the chemical processes that led to the emergence of life on Earth, known as prebiotic chemistry.
“We want to know if the type of chemistry that could be important for early pre-biochemical systems on Earth is taking place on Titan,” explains Dr. Trainer, a planetary scientist and astrobiologist specializing in Titan.
Titan: Dragonfly’s target
Titan, the largest moon of Saturn, is shrouded in a dense nitrogen-rich atmosphere, bears a striking resemblance to Earth in many ways. With a diameter of 5,150 kilometers, Titan is the second-largest moon in our solar system, surpassed only by Jupiter’s Ganymede.
Dense atmosphere and unique climate
One of Titan’s most distinctive features is its thick atmosphere, which is composed primarily of nitrogen and methane. This dense atmosphere creates a surface pressure 1.5 times higher than Earth’s, making it the only moon in our solar system with a substantial atmosphere.
The presence of methane in Titan’s atmosphere leads to a fascinating hydrological cycle, similar to Earth’s water cycle, but with methane as the primary liquid.
Titan’s surface is dotted with numerous lakes and seas of liquid hydrocarbons, predominantly methane and ethane. These liquid bodies, some of which are larger than the Great Lakes on Earth, are the result of Titan’s unique climate and atmospheric conditions.
The Cassini mission, which explored the Saturn system from 2004 to 2017, provided stunning images and data of these extraterrestrial lakes and seas.
Dragonfly mission to search Titan for prebiotic chemistry and life
The complex chemistry occurring on Titan’s surface and in its atmosphere has drawn significant attention from astrobiologists.
With its abundant organic compounds and the presence of liquid methane, Titan is considered a prime candidate for studying prebiotic chemistry and the potential for life to emerge in environments different from Earth.
Beneath Titan’s icy crust lies another intriguing feature: a global subsurface ocean of liquid water and ammonia. This ocean, which is believed to be salty and have a high pH, may potentially host microbial life.
The presence of this subsurface ocean, along with the unique chemistry on Titan’s surface, makes this moon a fascinating target for future exploration and scientific research.
Pushing the boundaries of rotorcraft exploration
Nicky Fox, associate administrator of the Science Mission Directorate at NASA Headquarters, emphasized the significance of the Dragonfly mission, stating, “Exploring Titan will push the boundaries of what we can do with rotorcraft outside of Earth.”
Titan’s unique characteristics, including its abundant complex carbon-rich chemistry, interior ocean, and past presence of liquid water on the surface, make it an ideal destination for studying prebiotic chemical processes and the potential habitability of an extraterrestrial environment.
Innovative design and cutting-edge technology
The Dragonfly robotic rotorcraft will leverage Titan’s low gravity and dense atmosphere to fly between different points of interest on the moon’s surface, spanning several miles apart.
This innovative approach allows the entire suite of instruments to be relocated to new sites once the previous one has been thoroughly explored, providing access to samples from diverse geological environments.
DraMS, developed by the same team responsible for the Sample Analysis at Mars (SAM) instrument suite aboard the Curiosity rover, will analyze surface samples using techniques tested on Mars.
Dr. Trainer emphasized the benefits of this heritage, stating, “This design has given us an instrument that’s very flexible, that can adapt to the different types of surface samples.”
Dragonfly mission challenges and funding
The Dragonfly mission successfully passed its Preliminary Design Review in early 2023. However, due to funding constraints, the mission was asked to develop an updated budget and schedule.
The revised plan, presented and conditionally approved in November 2023, hinged on the outcome of the fiscal year 2025 budget process.
With the release of the president’s fiscal year 2025 budget request, Dragonfly is now confirmed with a total lifecycle cost of $3.35 billion and a launch date set for July 2028.
This reflects a cost increase of approximately two times the initially proposed cost and a delay of more than two years from the original selection in 2019.
Despite the challenges posed by funding constraints, the COVID-19 pandemic, supply chain issues, and an in-depth design iteration, NASA remains committed to the Dragonfly mission.
Additional funding has been provided for a heavy-lift launch vehicle to shorten the mission’s cruise phase and compensate for the delayed arrival at Titan.
Rigorous testing and validation
To ensure the success of the Dragonfly mission, researchers on Earth have conducted extensive testing and validation of the designs and models for the nuclear-powered, car-sized drone.
The mission team has carried out test campaigns at NASA’s Langley Research Center, utilizing the Subsonic Tunnel and the Transonic Dynamics Tunnel (TDT) to validate computational fluid dynamics models and gather data under simulated Titan atmospheric conditions.
Ken Hibbard, Dragonfly mission systems engineer at APL, emphasized the importance of these tests, stating, “All of these tests feed into our Dragonfly Titan simulations and performance predictions.”
As the Dragonfly mission progresses, it marks a new era of exploration and scientific discovery. Dr. Trainer expressed her excitement, saying, “Dragonfly is a spectacular science mission with broad community interest, and we are excited to take the next steps on this mission.”
Turning science fiction into fact with the Dragonfly mission
In summary, the Dragonfly mission embodies the essence of human curiosity and the relentless pursuit of knowledge. As NASA prepares to send this revolutionary rotorcraft to the alien world of Titan, we stand on the brink of a new era of exploration and discovery.
With its innovative design, cutting-edge technology, and the unwavering dedication of the mission team, Dragonfly will unlock the secrets of prebiotic chemistry and shed light on the potential for life beyond Earth.
As we eagerly await the launch of this titanic mission, we can only imagine the wonders that await us on Saturn’s enigmatic moon. The Dragonfly mission is a testament to the indomitable human spirit and our boundless capacity to push the frontiers of knowledge.
In the words of Ken Hibbard, “With Dragonfly, we’re turning science fiction into exploration fact,” and that fact will undoubtedly inspire generations to come.
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Science
Marine plankton could act as alert in mass extinction event: UVic researcher – Langley Advance Times
A University of Victoria micropaleontologist found that marine plankton may act as an early alert system before a mass extinction occurs.
With help from collaborators at the University of Bristol and Harvard, Andy Fraass’ newest paper in the Nature journal shows that after an analysis of fossil records showed that plankton community structures change before a mass extinction event.
“One of the major findings of the paper was how communities respond to climate events in the past depends on the previous climate,” Fraass said in a news release. “That means that we need to spend a lot more effort understanding recent communities, prior to industrialization. We need to work out what community structure looked like before human-caused climate change, and what has happened since, to do a better job at predicting what will happen in the future.”
According to the release, the fossil record is the most complete and extensive archive of biological changes available to science and by applying advanced computational analyses to the archive, researchers were able to detail the global community structure of the oceans dating back millions of years.
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Next, the team plans to apply similar research methods to other marine plankton groups.
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