Pluto-sized planets seen around Sun-like star

These distant objects could reveal how young star systems form planets


Dust in the outer region of the disk surrounding HD 107146 is thicker than at the centre.

Credit: L. Ricci ALMA (NRAO/NAOJ/ESO); B. Saxton (NRAO/AUI/NSF)

A swarm of Pluto-sized objects have been spotted around a star similar to a younger version of our Sun. The Atacama Large Millimeter/submillimeter Array (ALMA) detected a dusty ring at the outer edge of the planetary system that could contains many planetesimals.

The thick dust ring is at a distance of 13 billion km – around 90AU – from the host star, HD 107146, remarkably far out for such a feature. It could give an insight into how our own Solar System was formed.

The discovery gives insight into a key stage in planetary formation, bridging the gap between the system's birth and its maturity. When very young, the protoplanetary disk is extremely dusty, especially in its inner region, as constant collisions between forming planets, comets and asteroids fill the void with debris. Later in the system’s life, when it has formed stable planets, there are few collisions meaning little dust is found.

During the troublesome ‘teenage’ years between these two life stages disks like the one seen around HD107146 can be found at the outer edges of the system.

“It is possible that we caught this particular debris disk at a stage in which Pluto-size planetesimals are forming right now in the outer disk while other Pluto-size bodies have already formed closer to the star,” says Luca Ricci, an astronomer at the Harvard-Smithsonian Centre for Astrophysics.

The gravitational disturbances caused by many bodies would disrupt their motion, resulting in many collisions in the region. These impacts would generate lots of dust, creating a ring around the system.

This star has particularly captivated the attention of astronomers because it is very similar to the Sun in its youth. It could be key in understanding the time in which our Solar System transitioned from a young tumultuous place, to a mature and stable planetary system.

"We are possibly looking back in time here, back to when the Sun was about 2 per cent of its current age," said ALMA Deputy Director and co-author Stuartt Corder. “This system offers us the chance to study an intriguing time around a young, Sun-like star."


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