Despite the fact that planetary rings are extremely common in the solar system, they have proven to be very difficult to detect on worlds orbiting other stars. Studies of ring systems around younger, distant planets could help clarify what the giant planets of our nearly 5 billion solar system looked like in the first few million years.
For more than twenty years of searching, scientists have only managed to find an exoplanet with rings once, it turned out to be super-Saturn J1407 B, orbiting its star in a 10-year orbit. The next observations of J1407 B will be possible only in the early 2020s. But now, perhaps a second ringed giant has been found, half hidden in a disk of gas and dust that surrounds the young star.
How it all began
Several years ago, a graduate student from the University of Warwick (England) Hugh Osborne discovered an unusual feature in the dark haze around the star PDS 110. For almost two years, data on the mysterious object lay on his desk. Later, another astronomer, observing the same star with another instrument, obtained similar data. “At that moment it became clear that it was much more interesting than I originally thought,” says Hugh Osborne.
The observations, separated by more than 800 days, were nearly identical. Both showed a strange 25-day darkening of the star - too long to be attributed to a planetary shadow passing through the PDS 110 disk. Osborne and his colleagues concluded that the unusual signal could be a ring system around a previously invisible companion moving through the disk that remained after the star's formation. gas and dust. These rings stretch about 50 million kilometers (nearly 200 times wider than Saturn's rings, which are about 280,000 kilometers). Such a huge ring system, according to Osborne's estimates, could only be held by a massive central object - a potential giant planet larger than Jupiter. Alternatively, the invisible companion could be a brown dwarf.
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The orbit of the ringed planet suggests the following observations in September 2017. Even a medium-sized telescope should be able to detect the deep shadow of the rings illuminated by the star, allowing amateur astronomers to observe and study the system. The third set of observations should provide scientists with data that will confirm or disprove the existence of the rings. “One time is not enough to convince someone. Even two observations may not be related. But three identical numbers are unlikely to be statistically random,”said Joel Kastner, an astronomer at the Rochester Institute of Technology.
Unlike Saturn's rings, which are in nearly the same plane as the planet's orbit, the supposed rings around companion PDS 110 are tilted perpendicularly, like Uranus, protruding above the circumstellar disk. Osborne says that such a distortion may be the result of interaction with another, invisible planet.
Not so simple
However, not all astronomers are convinced that it is the rings. While they agree on the likely presence of material surrounding the exoplanet, they are unsure about the stability of the ring system. When the world crosses a star's disk twice in each revolution, the material surrounding the star must pull out any rings of gas and dust around the planet, distorting them. “It will most likely be a cloud of debris instead of rings, not resembling the structure around Saturn,” says astronomer Jeffroy Lesour from the Institute of Planetology and Astrophysics in Grenoble (France).
It is also possible that the data obtained has nothing to do with the planet, but relate to one or more debris clusters falling back into the circumstellar disk. Such discs tend to be filled with turbulent currents that eject material from the disc, only to pull it back in. Debris thrown out in this way can stick together into pieces of size consistent with observations. Then a particularly long-lived group, or two independent groups that happened by chance at the right time, could explain the observed repetition.
Although such scenarios are possible, they are unlikely to produce two independent, yet identical signals, over such a large time interval. The rings would be gravitationally held in place by the planet, and free clusters would be loosely coupled and subject to a change in orbit. It is difficult to see how they could have had the same shape at the same time after 800 days.
Detailed September observations should help distinguish rings from boulders and even show structures and gaps within them. If the rings are confirmed it will be awesome!
The first few million years after their formation, Saturn and Jupiter may have had huge rings that somehow separated, merged into moons, or fell on planets. Observing ring worlds around young stars will help scientists better understand what might have happened in the early solar system.
Roman Zakharov