Astronomers have detected an entire family of Pluto-size objects swarming around a star which is an adolescent version of our own Sun, located approximately 90 light-years from Earth.
By making detailed observations of the protoplanetary disk surrounding the star known as HD 107146, the astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) detected an unexpected increase in the concentration of millimetre-size dust grains in the disk’s outer reaches.
This surprising increase, which begins remarkably far – about 13 billion kilometres – from the host star, may be the result of Pluto-size planetesimals stirring up the region, causing smaller objects to collide and blast themselves apart.
Dust in debris disks typically consists of material left over from the formation of planets. Very early in the lifespan of the disk, this dust is continuously replenished by collisions of larger bodies, such as comets and asteroids.
In mature solar systems with fully formed planets, comparatively little dust remains.
In between these two ages – when a solar system is in its awkward teenage years – certain models predict that the concentration of dust would be much denser in the most distant regions of the disk. This is precisely what ALMA has found.
“The dust in HD 107146 reveals this very interesting feature – it gets thicker in the very distant outer reaches of the star’s disk,” said Luca Ricci, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author on a paper accepted for publication in the Astrophysical Journal
“The surprising aspect is that this is the opposite of what we see in younger primordial disks where the dust is denser near the star.
“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,” said Ricci.
The new ALMA data also hint at another intriguing feature in the outer reaches of the disk: a possible “dip” or depression in the dust about 1.2 billion kilometres wide, beginning approximately 2.5 times the distance of the Sun to Neptune from the central star.
Though only suggested in these preliminary observations, this depression could be a gap in the disk, which would be indicative of an Earth-mass planet sweeping the area clear of debris.
Such a feature would have important implications for the possible planet-like inhabitants of this disk and may suggest that Earth-size planets could form in an entirely new range of orbits than have ever been seen before.
The star HD 107146 is located approximately 90 light-years from Earth in the direction of the constellation Coma Berenices. It is approximately 100 million years old.