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Using the Arecibo 430 MHz incoherent scatter radar located in Puerto Rico, we report the characteristics of the smallest meteors observed by any ground-based instruments. Coupled with an efficient pulse coding technique, the radar detects over 40 meteors min−1 in the dawn hours. The typical mass of these meteors is estimated to be 10−13 kg and the corresponding radius is about 2 μm. The velocity of the meteors is concentrated within a narrow range at a given time from mid-night to noon. Numerical simulations show that such a characteristic is most consistent with meteoroids having circular orbits in inclined planes. The orbital evolution of these meteoroids is most significantly affected by Poynting–Robertson and solar wind drags. They are captured by the Earth on their way to spiral into the Sun. At the mass range where drag forces dominate, Earth-crossing meteoroids are mostly expected to be in quasi-circular orbits because they can be produced anywhere outside the Earth's orbit. Our observation demonstrates this is indeed the case for retrograde meteoroids. [ABSTRACT FROM AUTHOR]