Editor's Note: This story accompanies the Science Journal feature article The Disks that Make Solar Systems Flat.
When planets are difficult to observe directly—for example, because the planets are too dim or are lost in the glare of a bright star—astronomers can instead look to the nearby disk of planetary leftovers.
“Debris disks have been sculpted by the planets that formed within them, so they can be an indirect way to learn about planets in a system,” said Penn State astronomer Rebekah Dawson. “They can also act as a sort of fossil record of the evolution of the planetary system.”
These debris disks contain small protoplanets and asteroid-sized objects that frequently collide due to gravitational forces of nearby planets. These collisions produce dust, which produce emissions that can be detected from Earth.
“Certain features of the debris disk act as signposts for planets,” said Jiayin Dong, a graduate student in Dawson’s lab. “A gap in the debris disk could indicate a planet redistributing the material, for example. A wider gap would indicate a planet with a larger mass.”
Debris disks could also be warped, have an edge that “lifts up,” have a portion that is misaligned with the rest of the relatively flat disk, or be offset from the star, which can give clues to a nearby planet’s mass, orbit, or the tilt of its axis. The closer the planet, the stronger the effect on the disk.
“We use models to infer a variety of planet properties from the disk,” said Dong. “These models often assume only one planet is in the system, but many systems have more than one planet.”
Dong found that properties of planets inferred from a debris disk using a single-planet model could be off by orders of magnitude if multiple planets are actually present. Her work suggests researchers should use caution when interpreting these models. Future technology, like the James Webb Space Telescope or the proposed Large UV/Optical/IR Surveyor (LUVOIR), could allow some direct observations of planets in multiplanet systems, which could help researchers build and refine multiplanet models.
Dong is also interested in understanding how large gas giants called warm Jupiters form. These planets have an orbital period of 10 to 200 days and fill the gap between cool Jupiters, like the one in our solar system, and the hot Jupiters that Dawson studies. These warm Jupiters are much less common, and Dong recently used data from the Transiting Exoplanet Survey Satellite (TESS) to identify 60 additional warm Jupiter candidates beyond the 100 or so already known.
The theorized formation pathways for warm Jupiters are very similar to those for hot Jupiters, including one suggestion that they actually are hot Jupiters at an earlier life stage.
“These large exoplanets are often the most massive component in a planetary system and can be very influential to the rest of the system,” said Dong. “Investigating formation pathways of the range of Jupiters will not only tell us about the different ways planets can form but may also provide important insight about the early evolution of entire planetary systems.”