Is Earth being bombarded by sub-relativistic meteors? A study says yes.

Planet Earth occasionally gets bombarded by space rocks that either vaporizes in the upper atmosphere or sometimes reach the earth’s surface. There is a fundamental difference between the space rocks, in simple terms.

  • Asteroids – A large rocky space body orbiting the sun and occasionally the orbits pass closer to the planet’s orbit. Theories suggest an asteroid impact led to the extinction of dinosaurs
  • Meteoroid – Small rock or particle orbiting the sun
  • Meteor – When a meteoroid enters the earth’s atmosphere, due friction with atmospheric gases it vaporizes and becomes a meteor, commonly referred to as shooting star
  • Meteorite – A small asteroid or large meteoroid if survives the fiery entry through Earth’s atmosphere and reaches Earth’s surface it is called a meteorite

A new study by astronomers Amir Siraj and Prof. Abraham Loeb from Harvard University titled “Observational Signatures of Sub-Relativistic Meteors” submitted to Astrophysical Journal,  suggests that there could be meteors of size 1 mm to 100mm (about 0.04 to 4 inches) that are extremely fast. According to them, these meteors could be the result of nearby supernovae explosion which could accelerate them to near sub or even near relativistic speeds. We are talking about speeds to the tune of several thousand times the speed of sound to a fraction of speed of light. The astronomers’ work addresses the ongoing astrophysics mystery of whether a supernova’s ejecta can be accelerated to near relativistic speeds through the interstellar space and reach Earth. Several astronomers in the past including Lyman Spitzer and Satio Hayakawa proposed the existence of such meteors.

A meteor flashes over the ALMA observatory in Chile. The different colors correspond to different elements vaporizing and glowing at characteristic wavelengths. Credit: ESO / C. Malin

According to Siraj, Supernovae are known to release significant quantities of particles at sub-relativistic speeds. Even if a fraction of these, say just 0.01% is of objects that are 1 mm size or larger, we can expect at least 1 such object to reach Earth’s atmosphere every month, given the number of Supernova in our Galaxy. Typically meteor travels at about 0.01% of the speed of light, current surveys are tuned to track signals from objects moving at this speed range and would miss the meteors from supernovae as they are 100 times faster.

For their study, Siraj and Loeb developed a hydrodynamic and radiative model to track the evolution of plasma cylinders created by sub-relativistic meteors passing through Earth’s atmosphere. In simple terms, when a normal meteor passes through Earth’s atmosphere it decelerates violently and the air behind it cools rapidly when compared to the speed of the meteor, so we see a glowing point moving through the sky. But in case of a meteor moving at sub-relativistic speed through Earth’s atmosphere, there is not enough time for the air behind to cool, resulting in the generation of a cylinder of plasma that cools all at once. This creates an intense shockwave and the air glows along the path of the meteoroid for as little as one-tenth of a millisecond.

Map displaying location and energy of meteor explosions detected by CNEOS. Credit: NASA/CNEOS

Based on this study, Siraj and Loeb outlined that new surveys could incorporate infrasound microphones and optical-infrared instruments to detect the acoustic signature and optical flashes created by these meteors entering Earth’s atmosphere and causing an explosion. They recommend a global network of about 600 detectors with all-sky coverage to detect a few of these types of meteors. Also, there is a possibility of using existing infrastructure, as Siraj explained, is found in NASA’s Center for Near-Earth Object Studies (CNEOS) network and database.

In spite of having a sound theoretical basis, the question still remains – whether or not meteors of size 1 mm to 100mm (about 0.04 to 4 inches) enter Earth’s atmosphere at sub-relativistic or relativistic speed. The payoff for detecting these meteors would be the ability to study an entirely new set of objects that interacts with Earth’s atmosphere on a regular basis. Also, this would allow astronomers to place important constraints on the ejecta which would provide a new perspective in the study of Supernovae

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Source:, UniverseToday

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