Astronomer Galileo Galilei may have discovered Neptune in 1613 -- 234 years before the planet was officially found, according to a new theory.
Prof David Jamieson of the University of Melbourne has claimed in his theory that the notebooks of Galileo from some 400 years ago contain concrete evidence that he had discovered a new planet in 1613, which is now known as Neptune.
And, according to him, if correct, the discovery would probably be the first new planet, identified by humanity since deep antiquity.
Galileo was observing the moons of Jupiter in 1612 and 1613 and recorded his observations in his notebooks. Over many nights he had also recorded the position of a nearby star that does not appear in any modern star catalogue.
"It has been known for several decades this unknown star was actually 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.
"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. If this is correct Galileo observed Neptune 234 years before its official discovery," Prof Jamieson said.
Moreover, there is also a mysterious unlabelled 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," Prof Jamieson said.
But he said there could be an even more interesting possibility still buried in Galileo's notes and letters.
"Galileo was in habit of sending a scrambled sentence, an anagram, to his colleagues to establish his priority for the sensational discoveries he made with his new telescope.
"He did this when he discovered the phases of Venus and the rings of Saturn. So perhaps somewhere he wrote an as-yet undecoded anagram that reveals he knew he discovered a new planet," Prof Jamieson speculates.
The theory has been published in the latest edition of the Australian Physics journal.