Astronomers detect alien planet with rings that dwarf Saturn’s

Astronomers believe they have found a giant new planet, orbiting another star, which has rings so wide that they would stretch a third of the way from Earth to the Sun.

Giant ringed gas planet
Artist’s impression of the giant alien planet orbiting the star PDS 110. Image credit: University of Warwick.

The disk of rings measures 50 million km (30 million miles) from one edge to the other. By comparison, those encircling our own spectacular ringed planet, Saturn, are just 270,000 km (170,000 miles) wide.

The discovery team say that a ringed world, 50 times more massive than Jupiter, is the best explanation for a regular dimming by the star every 2.2 years.

The alien sun, labelled PDS-110, lies 1,000 light-years away in the constellation of Orion the hunter. It is a rare young star, only 10 million years old, and the dust could be forming moons around the planet.

Over two or three weeks, PDS-110 becomes only a third as bright before regaining its normal luminosity, with rapid fluctuations due to individual rings of dust crossing the face of the star. Such fades have been recorded for 15 years.

Dr Hugh Osborn, who was working as a researcher from the University of Warwick’s Astrophysics Group, first noticed the unusual pattern of light variations by the star. He led the international team that identified the ringed planet using telescopes around the world.

The team, which also included researchers from Harvard University, Vanderbilt University, and Leiden Observatory, are now preparing for the next due eclipse, in September this year, to confirm their findings.

Position of PDS-110
The position of the star PDS-110 in Orion is indicated in this screenshot using the planetarium software Stellarium

The eclipses were first seen in data collected by a planet-hunting survey called WASP (the Wide Angle Search for Planets), and KELT (the delightfully-named Kilodegree Extremely Little Telescope). Both WASP and KELT use commercial camera lenses with science-grade CCD detectors to monitor stars and check for transiting exoplanets.

Dr Osborn said in a statement: “We found a hint that this was an interesting object in data from the WASP survey. But it wasn’t until we found a second, almost identical eclipse in the KELT survey data that we knew we had something special.

“September’s eclipse will let us study the intricate structure around PDS 110 in detail for the first time, and hopefully prove that what we are seeing is a giant exoplanet and its moons in the process of formation.”

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Colleague Matthew Kenworthy, of Leiden University in the Netherlands, said: “What’s exciting is that during both eclipses we see the light from the star change rapidly, and that suggests that there are rings in the eclipsing object, but these rings are many times larger than the rings around Saturn.”

Though a ringed planet is the favoured cause of the star’s fades, Dr Osborn admits that astronomers are not yet certain. He told Skymania: “Well, the ring system is one explanation – alternatively we’re being fooled by two random dust events that happened to look nearly identical, so we need to observe in September to confirm that!

WASP cameras
A photo of the cameras forming one of the WASP arrays, on La Palma. Image credit: David Anderson

“A similar ring system was actually found around the so-called J1407, also a young star, but that one was on an undetermined orbit and has yet to repeat. So if confirmed PDS-110 this would be the first exoring system on a known orbit.

“If it’s real we can say that it is 0.3 – 0.4 AU across, (an AU, or Astronomical Unit is the distance of the Earth from the Sun) making it about 350 – 400 times larger than Saturn’s rings.

“Saturn’s rings form very close to the planet because rock and ice has been disrupted by the gravity. Rings around young bodies are primordial remnants, and can therefore extend much larger distances from the planet.”

The astronomers’ paper announcing the discovery is being published by the Monthly Notices of the Royal Astronomical Society. A preprint can be viewed here.

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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