U.S. astronomers using the Atacama Large Millimeter/submillimeter Array have discovered an entire family of Pluto-size planetesimals around a nearby young Sun-like star HD 107146.
This is an artist impression of the protoplanetary disk around HD 107146. Image credit: A. Angelich / NRAO / AUI / NSF.
HD 107146 is a yellow main sequence star located in the constellation Coma Berenices, about 90 light-years away.
It has a magnitude of about 7 and cannot be seen with the naked eye but is visible through a small telescope.
The star is 100 million years old and is of particular interest to astronomers because it is in many ways a younger version of our own Sun.
It also represents a period of transition from a Solar System’s early life to its more mature, final stages where planets have finished forming and have settled into their billions-of-years-long journeys around their parent star.
Now, a group of astronomers led by Dr Luca Ricci of the Harvard-Smithsonian Center for Astrophysics has detected an unexpected increase in the concentration of mm-size dust grains in the outer reaches of the HD 107146’s protoplanetary disk.
This increase, which begins remarkably far – about 13 billion km – from the host star, may be the result of Pluto-size planetesimals (up to 2-3 thousands) stirring up the region, causing smaller objects to collide and blast themselves apart.
“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 Dr Ricci, who is the first author of a paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).
“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.”
The new observations also revealed another intriguing feature in the outer reaches of the disk – a possible dip or depression in the dust about 1.2 billion km 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.
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L. Ricci et al. 2014. ALMA observations of the debris disk around the young Solar Analog HD 107146. ApJ, accepted for publication; arXiv:1410.8265
