A letter written by Galileo Galilei that defended the heliocentric model of the solar system and challenged religious doctrines has recently been discovered.

The 7-page letter addressed to a friend and was penned on Dec. 21, 1613 is believed to be the beginning of the renowned astronomer's battle with the Catholic Church.

An Important Artifact Rediscovered

The letter that historians long thought has been lost was discovered by a postdoctoral science historian Salvatore Ricciardo of the University of Bergamo in Italy. He visited the Royal Society in August for a different purpose but found an important artifact in history instead.

"I thought, 'I can't believe that I have discovered the letter that virtually all Galileo scholars thought to be hopelessly lost,'" he said to Nature. "It seemed even more incredible because the letter was not in an obscure library, but in the Royal Society library."

Galileo Galilei's Battle With Catholic Church

Two differing version of the letter exist: one was sent to the Inquisition in Rome by a Dominican friar while the other, with less accusatory language, is now kept in the Vatical Secret Archives. Because the original was thought to be lost, historians had no way of knowing if one of the letters was edited by the clergymen to help their heresy case against the astronomer.

However, the original letter found by Ricciardo while browsing the Royal Society's online catalog proved that Galileo edited his own words to appear less critical of the Catholic Church. The newly discovered letter contains amendments.

In the letter, Galileo explained that the heliocentric model of the Earth orbiting the Sun, which was first proposed by Nicolaus Copernicus in the book On The Revolutions of the Heavenly Spheres, did not actually go against theological doctrine. He said the references of astronomical events to the Bible should not be taken literally because descriptions within the scripture were oversimplified to be understood by the public.

Moreover, the astronomer argued that there should be a separation between scientific research and theological doctrine.

Copernicus himself did not live to see the impact of his theory that the Earth is not the center of the universe. His book had been published just before he died in 1543.

However, Galileo did. The Church accused the astronomer of heresy and warned him to abandon his controversial claim.

Notably, 16 years after his first bout with the Church, Galilei published Dialogue on The Two World Systems, a book that once again discussed the Copernican model of the solar system. He was once again investigated and was forced to testify about himself in a trial. He was convicted with "vehement suspicion of heresy."

Galileo was under house arrest for the remainder of his life.