Galileo's Mysterious Black Dot: Notebooks May Reveal His Discovery of New Planet

Galileo knew he had discovered a new planet in 1613, 234 years before Neptune's official discovery date, according to a new theory by David Jamieson, Head of the School of Physics at the University of Melbourne. Jamieson is investigating the notebooks of Galileo from 400 years ago and believes that buried in the notations is a mysterious black dot -evidence, it is believed, that he discovered a new planet that we now know as Neptune -the first such discovery of a planet since the ancient Greeks.

The astronomer's championing of Copernicanism, when a large majority of philosophers and astronomers still subscribed to the geocentric view that the Earth remained motionless at the center of the universe. led to his trial by the Inquisition. He was found "vehemently suspect of heresy," forced to recant, and spent the rest of his life under house arrest.

Galileo was observing the moons of Jupiter in the years 1612 and 1613 and recorded his observations in his notebooks. Over several nights he also recorded the position of a nearby star which does not appear in any modern star catalog.

"It has been known for several decades that this unknown star was actually the planet Neptune. Computer simulations show the precision of his observations revealing that Neptune would have looked just like a faint star almost exactly where Galileo observed it," Professor Jamieson says.

"But a planet is different to a star because planets orbit the Sun and move through the sky relative to the stars. It is remarkable that on the night of January 28 in 1613 Galileo noted that the "star" we now know is the planet Neptune appeared to have moved relative to an actual nearby star."

There is also a mysterious unlabeled black dot in his earlier observations of January 6, 1613, which is in the right position to be Neptune. "I believe this dot could reveal he went back in his notes to record where he saw Neptune earlier when it was even closer to Jupiter but had not previously attracted his attention because of its unremarkable star-like appearance."

If the mysterious black dot on January 6 was actually recorded on January 28, Professor Jamieson proposes this would prove that Galileo believed he may have discovered a new planet.

By using the expertise of trace element analysts from the University of Florence, who have previously analyzed inks in Galileo's manuscripts, dating the unlabelled dot in his notebook may be possible. This analysis may be conducted in October this year.

"Galileo may indeed have formed the hypothesis that he had seen a new planet which had moved right across the field of view during his observations of Jupiter over the month of January 1613," Professor Jamieson says. "If this is correct Galileo observed Neptune 234 years before its official discovery."

Posted by Jason McManus. Adapted and edited from materials provided by the University of Melbourne.