Meteoroids coming from outer space come in all shapes and sizes, but those which land on earth as meteorites, are found to be carved into a typical conical shape. The reason behind this has been something of a mystery.
Meteoroids coming from outer space are randomly shaped, but many of these, which land on earth as meteorites, are found to be carved into cones. To explore the forces that produce cone-shaped meteorites, researchers replicated meteoroids travelling through outer space: clay objects, attached to a rod, served as ‘mock meteorites’ that erode while moving through water. ( NYU’s Applied Mathematics Laboratory)
Scientists have determined that the physics of flight in the atmosphere is responsible for this characteristic shape and the circumstances that lead to the transformation of randomly shaped meteoroids to conical meteorites that land on Earth.
Meteoroids coming from outer space are randomly shaped, but many of these, which land on earth as meteorites, are found to be carved into cones. To explore the forces that produce cone-shaped meteorites, researchers replicated meteoroids travelling through outer space: clay objects, attached to a rod, served as ‘mock meteorites’ that erode while moving through water. ( NYU’s Applied Mathematics Laboratory)
In a series of replication experiments in New York University’s Applied Mathematics Lab, scenarios involving melting and erosion during flight found the conditions that ultimately result in an ideal shape as meteoroids hurl through the atmosphere.
Leif Ristroph is an assistant professor in NYU’s Courant Institute of Mathematical Sciences, who led the study — the results of which are reported in the journal Proceedings of the National Academy of Sciences (PNAS).
He points outs: “Slender or narrow cones flip over and tumble, while broad cones flutter and rock back and forth, but we discovered between these are cones that fly perfectly straight with their point or apex leading.
“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.”
The research shows how the shape of an object affects its ability to fly straight, and thus sheds some light on this long-standing mystery about why so many meteorites that arrive on Earth are cone-shaped.
Ristroph continues: “The shapes of meteorites are not as they are in space since they are actually melted, eroded, and reshaped by atmospheric flight.
“While most meteorites are randomly shaped ‘blobs,’ surprisingly many — some say about 25%— are ‘oriented meteorites,’ and complete samples of these look almost like perfect cones.”
To further explore the forces that produce cone-shaped meteorites, the researchers, including Jun Zhang, a professor of physics and mathematics at the Courant Institute and NYU Shanghai, replicated meteoroids travelling through outer space. This meant clay objects, attached to a rod, serving as “mock meteorites” that eroding as they move through water.
The clay objects held in the water current were eventually carved into cones of the same angularity as conical meteorites — not too slender and not too broad.
The researchers recognise the limitations of this unique and creative experimental design. For example, unlike the clay objects, actual flying meteoroids are not held in a fixed position and can freely rotate, tumble, and spin.
This distinction raised the following question, what allows meteorites to keep a fixed orientation and successfully reach Earth?
The team conducted additional experiments in which they examined how different shaped cones fell through water — discovering that narrow cones flip over while broad cones flutter.
However, in between these two are “just right” cone shapes that fly straight.
Ristroph points out: “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.”
ournal Reference:
Khunsa Amin el al. The role of shape-dependent flight stability in the origin of oriented meteorites. Proceedings of the National Academy of Sciences, 2019 DOI: 10.1073/pnas.1815133116
