Theory 014/Earth & Space /Exoplanets
Obliquity Records Disk Lifetime
Misalignment is explained by two migration routes. It may be a clock on how long the disk lasted.
The obliquity distribution of close-in planets records the lifetime of the protoplanetary disk rather than the migration channel, so systems with short-lived disks should show more misalignment.
01The evidence
Stellar obliquities of close-in planets are broadly distributed, with a population near alignment and a tail extending to retrograde.
02The tension
Two migration channels are invoked, with free mixing fractions fitted after the fact. Disk lifetime is measurable independently and is not used.
03The mechanism
A long-lived disk damps inclination and keeps the planet aligned. A short-lived disk lets the planet retain the misalignment it acquired during formation or later scattering.
That makes disk lifetime the switch, and predicts that clusters with shorter disk lifetimes should show a larger misaligned fraction.
04What this is not
Channel models fit mixing fractions. This predicts the mixture from a measurable stellar property.
05Predictions
- P1Misaligned fraction should rise as disk lifetime falls.
- P2The relation should hold across clusters.
- P3Aligned systems should be older-disk systems.
06Refutation
No relation between disk lifetime and obliquity would leave the mixture model standing.
07What it changes
It would connect exoplanet obliquity to disk demographics.