Hypersonic breakthrough could enable planes that fly 10 times the speed of sound

"It really shrinks the planet," says Professor Nicholaus Parziale, whose work centers on turning hypersonic travel from aspiration into reality. Parziale recently received the Presidential Early Career Award for Scientists and Engineers in recognition of his research into fluid mechanics at extreme speeds. "It will make travel faster, easier and more enjoyable."

The Challenges of Flying at Mach 10

Covering half the world in just one hour may seem impossible, yet the technology is not as far away as it appears. Some military aircraft already reach speeds of Mach 2 or Mach 3, which means two or three times the speed of sound. Mach 1 equals about 760 miles per hour. To travel from Los Angeles to Sydney in sixty minutes, an aircraft would need to reach Mach 10. The major obstacles are the extraordinary turbulence and heat produced during flight at these extreme speeds.

There is a fundamental difference between how air behaves around an aircraft at lower speeds and how it behaves at higher speeds. Engineers describe these conditions as incompressible flow and compressible flow. In incompressible flow, which occurs at lower speeds (below about Mach 0.3 or 225 miles per hour), the density of the air stays nearly the same. This consistency simplifies aeronautical design. Once an aircraft moves faster than the speed of sound, the airflow becomes compressible instead. "That's because a gas can 'squish,'" Parziale explains, meaning it can compress.

Why Airflow Behavior Matters for Hypersonic Design

When air compresses, its density changes in response to variations in both pressure and temperature. These shifts influence how an aircraft interacts with the air around it. "Compressibility affects how the airflow goes around the body and that can change things like lift, drag, and thrust required to take off or stay airborne." All of these factors play a major role in aircraft design.

Engineers already understand airflow fairly well for aircraft that fly below or near the speed of sound, a range called "low Mach" numbers. Creating hypersonic aircraft requires a much deeper understanding of how air behaves at Mach 5, Mach 6, or even Mach 10. Much of that behavior is still uncertain, except for guidance provided by Morkovin's hypothesis.

Morkovin's Hypothesis and the Mystery of Hypersonic Turbulence

Developed by Mark Morkovin in the mid 20th century, the hypothesis proposes that when air moves around Mach 5 or Mach 6, the fundamental nature of turbulence remains surprisingly similar to turbulence at lower speeds. Although high-speed airflow involves larger shifts in temperature and density, Morkovin suggested that the general pattern of turbulent motion stays mostly consistent. "Basically, the Morkovin's hypothesis means that the way the turbulent air moves at low and high speeds isn't that different," Parziale says. "If the hypothesis is correct, it means that we don't need a whole new way to understand turbulence at these higher speeds. We can use the same concepts we use for the slower flows." This also suggests that future hypersonic aircraft may not require a completely different design philosophy.

Despite its importance, the hypothesis has lacked solid experimental validation. That gap led to Parziale's recent research, described in his study Hypersonic Turbulent Quantities in Support of Morkovin's Hypothesis, published in Nature Communications on November 12, 2025.

A Laser and Krypton Experiment Eleven Years in the Making

In the study, Parziale's team introduced krypton gas into a wind tunnel and used lasers to ionize it. This process briefly created a straight, glowing line formed by the krypton atoms. High-resolution cameras then captured how this illuminated line bent, twisted, and distorted as it moved through the airflow, similar to how a leaf drifts and spins within small swirling currents in a river."As that line moves with the gas, you can see crinkles and structure in the flow, and from that, we can learn a lot about turbulence," Parziale says. He notes that developing the experimental setup required 11 years of effort. "And what we found was that at Mach 6, the turbulence behavior is pretty close to the incompressible flow."

Parziale's group received early support from the Air Force Office of Scientific Research Young Investigator Research Program (YIP) in 2016 and from the Office of Naval Research (ONR) YIP in 2020, with the latest work also funded by ONR.

What the Findings Mean for Future Flight and Space Access

While Morkovin's hypothesis is not yet completely proven, the new results move scientists closer to understanding how to design aircraft that can withstand hypersonic speeds. The findings indicate that engineers may not need to reinvent the fundamental approach to aircraft design for these extreme conditions, which simplifies the challenge significantly.

"Today, we must use computers to design an airplane, and the computational resources to design a plane that will fly at Mach 6, simulating all the tiny, fine, little details would be impossible," Parziale explains. "The Morkovin's hypothesis allows us to make simplifying assumptions so that the computational demands to design hypersonic vehicles can become more doable."

Parziale adds that the same principles could transform future access to space. "If we can build planes that fly at hypersonic speed, we can also fly them into space, rather than launching rockets, which would make transportation to and from low Earth orbit easier," he says. "It will be a game-changer for transportation not only on earth, but also in low orbit."