Rice University astronomers and their colleagues have for the first time mapped gases in three dark rings around a distant star. The rings mark spaces where planets are thought to have formed from dust and gas around the star.
All the rings around HD 163296 are devoid of dust, and the international team of researchers led by Rice astronomer Andrea Isella is sure that planets, probably gas giants with masses comparable to Saturn, are responsible for clearing the outermost ones.
But the inner ring has far more carbon monoxide than the other two, leading them to believe no planet exists there. That remains unexplained, he said.
“The inner gap is mysterious,” Isella said. “Whatever is creating the structure is removing the dust but there’s still a lot of gas.” The work appears this week in Physical Review Letters.
The outer rings are 100 and 160 astronomical units from HD 163296. (One unit is the distance from the center of the sun to Earth.) That’s much farther from the star than previously thought possible for planet formation.
The star is too far from Earth for direct observation of the planets, yet evidence from the new study shows they are likely to be there, clearing dust and gas from the outer rings much like orbiting asteroids called shepherd satellites clear space between the rings around Saturn, Isella said.
The inner ring, 60 astronomical units from its star, showed a much greater concentration of the three carbon monoxide isotopes measured relative to dust.