Carl Sagan on Swastika

The swastika appears ubiquitously in pre-historical art and design, sometimes symbolizing good luck, sometimes the sun, and sometimes Brahma (the creator God). The swastika can be found almost everywhere in early human history, with the exceptions being most of Africa and South America. It occurs in Asian, European, African and Native American cultures – sometimes as a geometrical motif, sometimes as a religious symbol. It was used extensively by Hittites, Celts and Greeks, among others.
The ubiquity of the swastika has been explained by three main theories: independent development, cultural diffusion, and external event. The first theory is that the swastika's symmetry and simplicity led to its independent development everywhere. According to the second theory, the swastika symbol spread due to cultural diffusion. It is sacred in Hinduism, which is considered the parent religion of Buddhism and Jainism, both dating from about the 6th century BC, and both borrowing the swastika from their parent. Buddhism in particular enjoyed great success, spreading eastward and taking hold in southeast Asia, China, Korea and Japan by the end of the first millennium. Similarly, the existence of the swastika as a solar symbol among the Akan civilization of southwest Africa may have been the result of cultural transfer along the African slave routes around AD 1500. However, the existence of the swastika symbol in the Americas is a clear challenge to the diffusion theory. While some have proposed that the swastika was secretly transferred to North America by an early seafaring civilization on Eurasia, a separate but parallel development of religious symbolism is considered the most likely explanation.
Lastly, we come to Carl Sagan's reasoning. In his book, "Comet", Sagan reproduces an ancient Chinese manuscript that shows comet tail varieties: most are variations on simple comet tails, but the last shows the comet nucleus with four bent arms extending from it, recalling a swastika.
Sagan suggests that in antiquity a comet could have approached so close to Earth that the jets of gas streaming from it, bent by the comet's rotation, became visible, leading to the adoption of the swastika as a symbol across the world. Very interesting, isn't it?