A young star -- a "teenage" equivalent of our own sun -- is surrounded by a deep layer of dust whose composition suggests the star may be surrounded by a swarm of Pluto-sized dwarf planets, astronomers say.

The scientists say they believe the protoplanetary disk around this star about 90 light years from Earth is at an "in-between" stage of its development.

In early stages, such disks are normally full of dust of uniform size that is replenished continually by collisions between asteroids and comets.

In later solar systems that have matured and finished forming their planets, little dust is remaining.

In contrast, the disk surrounding the star HD 107146 displays an unexpected increase in the concentration of larger-than-normal dust grains in its outer reaches, astronomers have reported 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," says study lead author Luca Ricci of the Harvard-Smithsonian Center for Astrophysics. "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."

Their gravity of such would disturb smaller planetesimals, causing frequent collisions that would generate the dust patterns the astronomers observed using the Atacama Large Millimeter/submillimeter Array (ALMA) observatory in Chile.

The astronomers also noted another intriguing feature: a depression or possible gap in the disk of dust around 750 million miles wide, beginning approximately 2.5 times the distance from the system's central star as Neptune is from our sun.

That could be evidence of an Earth-sized planet sweeping the region clear of dust and debris, the astronomers say.

If so, they add, it may suggest Earth-sized planets can form in an unexpected range of orbits never detected before.

The star HD 107146 is an interested subject for observation, the researchers point out, because it resembles a younger version of our sun existing in a period of transition from a solar system's early beginnings to a more mature, final stage.

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