Meteoroids from the outer space have random shapes, but when many of them land on earth as meteorites, they are found to be carved as cones. Researchers have identified the physics involved in flight in the atmosphere that causes this transformation.
The progression was discovered by a series of replication experiments conducted in the Applied Mathematics Lab of New York University. It involves melting and erosion during the flight which finally results in an ideal shape as meteoroids pass through the atmosphere. The study has been reported in the Proceedings of the National Academy of Sciences (PNAS).
Leif Ristroph, assistant professor in New York University and also the leader of the study said that slender or narrow cones flip over, tumble but the broader ones flutter and move back and forth. They discovered a family of cones which fly perfectly straight with their apex leading. These ‘Goldilocks’ cones with exact right angles perfectly match the shapes of the eroded clays obtained from the experiments and of real conical meteorites. He said that identifying the relation between the shape of an object and its ability to fly straight revealed the cause of why many meteorites landing on Earth are cone-shaped. It has been a mystery for a long period of time about the forces behind the strange shapes of meteorites which survive the flight through the atmosphere and land on Earth.
Ristroph explains that the shapes of the meteorites differ in space since they are melted, eroded and reshaped due to their journey through the atmosphere. Many meteorites are randomly shaped, nearly 25 percent are ‘oriented meteorites’ which look very similar to perfect cones.
Researchers including Jun Zhang, physics and mathematics professor at Courant Institute and NYU Shanghai replicated the travel of meteorites through outer space with the help of clay objects attached to rod as “mock meteorites” which eroded while passing through water. These clay objects were finally carved into cones with the same angularity as the conical meteorites.
The limitations of the experiment were that unlike the clay objects, the real meteoroids are not fixed and they can freely rotate or tumble. This raised the question that what made the meteorites keep a fixed orientation for reaching Earth.
The team included NYU undergraduates, Khunsa Amin and Kevin Hu and a doctoral student, Jinzi Huang. They conducted additional experiments where they examined how cones of different shapes moved through water. Here they found that the narrow cones flip over while the broader ones flutter. The “just right” cones moved straight.
Ristroph says that these experiments reveal the origin behind the oriented meteorites. Aerodynamic forces melt and reshape the meteoroids in their flight, while also stabilizing the posture so that a cone shape is carved on reaching Earth. This interesting message about the composition and structure of meteorites can give us more information about the universe.
Reference: Khunsa Amin el al., “The role of shape-dependent flight stability in the origin of oriented meteorites,” PNAS (2019)