Michael Rowan-Robinson, Emeritus professor of astrophysics at Imperial College London, and a former President of the Royal Astronomical Society, found his candidate for a new world in historic observations made by an early space telescope.
The Infrared Astronomical Satellite (IRAS) was launched in 1983 as the first orbiting observatory to look at the entire night sky in the infrared region of the spectrum, which lies just beyond the rainbow of visible light.
Over ten months, the mission observed more than a quarter of a million infrared sources in the sky, by detecting their heat against the cold sky background.
Professor Rowan-Robinson, who is famous for supervising Queen rock star Brian May in the belated completion of his PhD in astrophysics in 2007, decided to look back at data from IRAS to check if anything was lurking undiscovered in the data.
He was particularly interested to find objects that had been observed to move slowly between one observation and another. That would rule out more distant sources, such as galaxies as well as faster moving bodies like comets and asteroids within our Solar System.
The main cause of a planetary candidate’s shift in position against the cosmic background would be due to parallax, as the Earth orbited the Sun causing IRAS to observe from a different angle.
Professor Rowan-Robinson, 79, examined hundreds of sources in the data. He became interested in three observations by IRAS, made in June, July and September, 1983, that had moved slightly over that time.
In a research paper describing his search for Planet 9, the professor admits that the observations are not of high quality and were made in a region of sky full of filaments of galactic gas known as cirrus because of their cloud-like nature.
He also concedes that a more recent comprehensive survey of the night sky by Pan-STARRS telescopes in Hawaii have failed to record the object, suggesting it is not real.
But Professor Rowan-Robinson says: “Given the great interest of the Planet 9 hypothesis, it would be worthwhile to check whether an object with the proposed parameters and in the region of sky proposed, is inconsistent with the planetary ephemerides.”
He also suggests checking the orbits of dwarf planets in the Kuiper Belt beyond Pluto to see if its presence could account for their clustering.
The mystery object, if it exists, lies in the constellation of Cepheus, a part of the sky well away from the plane of the orbits of the other planets, which all lie close to the Ecliptic.
Planetary scientist Professor Mike Brown, who rejoices under the Twitter handle @plutokiller, and has been making his own search for another planet, tweeted: “The candidate is on an orbit utterly inconsistent with our predictions for Planet Nine, and would not be capable of gravitationally perturbing the distant Solar System in the ways that we have suggested. But, of course, that doesn’t mean it isn’t real!
“It just means that it would be a serendipitous discovery of something while searching for Planet Nine. Pluto happened the same way. Tombaugh was searching for Lowell’s Planet X (which didn’t exist) and accidentally found Pluto. Pluto was not the predicted Planet X.”
Pluto itself was once regarded as the ninth planet following its discovery in 1930, but it was relegated to the class of dwarf planet by a controversial vote at the International Astronomical Union in 2006.
The newly suggested planet candidate is in a different part of the sky to a ninth planet proposed by other astronomers in 2016.