Transitional Disks as Signposts of Young, Multiplanet Systems

TL;DR

This paper argues that wide, optically thin inner holes in accreting transitional disks are best explained by multiple orbiting planets, making these disks prime targets for studying young planetary systems.

Contribution

It demonstrates that multiple planets can create wide, optically thin inner holes in transitional disks, challenging other clearing mechanisms like photoevaporation.

Findings

Multiple planets can clear wide inner holes exceeding 15 AU.

Confined, non-axisymmetric accretion flows allow mass transfer without infrared excess.

Photoevaporation cannot explain the observed properties of these disks.

Abstract

Although there has yet been no undisputed discovery of a still-forming planet embedded in a gaseous protoplanetary disk, the cleared inner holes of transitional disks may be signposts of young planets. Here we show that the subset of accreting transitional disks with wide, optically thin inner holes of 15 AU or more can only be sculpted by multiple planets orbiting inside each hole. Multiplanet systems provide two key ingredients for explaining the origins of transitional disks. First, multiple planets can clear wide inner holes where single planets open only narrow gaps. Second, the confined, non-axisymmetric accretion flows produced by multiple planets provide a way for an arbitrary amount of mass transfer to occur through an apparently optically thin hole without over-producing infrared excess flux. Rather than assuming the gas and dust in the hole are evenly and axisymmetrically distributed, one can construct an inner hole with apparently optically thin infrared fluxes by covering a macroscopic fraction of the hole's surface area with locally optically thick tidal tails. We also establish that other clearing mechanisms, such as photoevaporation, cannot explain our subset of accreting transitional disks with wide holes. Transitional disks are therefore high-value targets for observational searches for young planetary systems.