As Meteorites Slice Through the Atmosphere, They’re Sculpted Into Cones

Since it first formed roughly 4.5 billion years ago, planet Earth has been subject to impacts by asteroids and plenty of meteors. These impacts have played a significant role in the geological history of our planet and even played a role in species evolution. And while meteors come in many shapes and sizes, scientists have found that many become cone-shaped once they enter our atmosphere.

The reason for this has remained a mystery for some time. But thanks to a recent study conducted by a team of researchers from New York University’s Applied Mathematics Lab have figured out the physics that leads to this transformation. In essence, the process involves melting and erosion that ultimately turns meteorities into the ideal shape as they hurl through the atmosphere.

The findings were reported in the journal Proceedings of the National Academy of Sciences (PNAS). The study was led by Leif Ristroph, an assistant professor in NYU’s Courant Institute of Mathematical Sciences (CIMS), and was assisted by Khunsa Amin and Kevin Hu (both of whom are NYU undergraduates) and Jinzi Huang – an NYU doctoral student at the time of the work.

A bright Perseid meteor over the UK on August 13, 2014. Credit and copyright: Richard Fleet.

In essence, the shapes of meteorites change drastically as a result of atmospheric flight. The process creates a ton of air friction, which in turn causes the surface of the meteor to melt, erode and become reshaped. While most become randomly shaped, a surprising 25 percent become “oriented meteorites” that look like perfect cones.

To be sure, there are many types of canonical meteors. Whereas some flip and tumble through the atmosphere and produce slender or narrow cones, others while the other rocks back and forth to broad cones. In between these, you have cones that fly perfectly straight through the atmosphere with their apex leading. As Ristroph explained in recent NYU news release:

“Amazingly, these ‘Goldilocks’ cones of the ‘just right’ angles exactly match the shapes of eroded clay resulting from our experiments and of actual conical meteorites… By showing how the shape of an object affects its ability to fly straight, our study sheds some light on this long-standing mystery about why so many meteorites that arrive on Earth are cone shaped.”

For the sake of their study, the team conducted several replicator experiments using clay objects attached to a rod. These served as their “mock meteorites” whose erosion patterns were examined as they were sculpted by water currents. Eventually, they were carved into cones that had the same shape as conical meteorites.

WT1190F striking the atmosphere over the Indian Ocean, where it broke apart into multiple fireballs against the blue sky. Credit: IAC/UAE Space Agency/NASA/ESA

The clay objects were eventually carved into cones that had the same angularity as conical meteorites. However, the researchers knew that truly simulate the right conditions, they needed more than objects that were fixed in place. When they fly through our atmosphere, meteorites are free to rotate, tumble and spin, thus raising the question – what allows them to keep a fixed orientation?

To answer this, the team conducted additional experiments in which they examined how cones of different shapes cones fared in running water. What the found was that narrow cones flip end over end while broader ones flutter, but the “goldilocks” cones managed to remain flying straight and true.

As Ristroph explained, these findings not only explain an ongoing mystery surrounding meteorites, but could also help with the study of extra-terrestrial bodies:

“These experiments tell an origin story for oriented meteorites: the very aerodynamic forces that melt and reshape meteoroids in flight also stabilize its posture so that a cone shape can be carved and ultimately arrive on Earth. This is another interesting message we’re learning from meteorites, which are scientifically important as ‘alien visitors’ to Earth whose composition and structure tell us about the universe.”

Further Reading: NYU, PNAS