# Origin and evolution of long-period comets

## TL;DR

This study models the origin and evolution of long-period comets from the Oort cloud, matching observed distributions and predicting future discoveries, with implications for understanding the Solar System's outer regions.

## Contribution

It introduces a comprehensive numerical model of LPC evolution from the trans-Neptunian disk, incorporating fading and orbital dynamics, to better match observations and predict future comet detections.

## Key findings

- The model fits the observed semimajor axis distribution with a specific fading law.
- Perihelion distribution shows a linear plus quadratic trend, with steep increase beyond 15 au.
- Predicted LPC flux is about half of current observational estimates.

## Abstract

We develop an evolutionary model of the long-period comet (LPC) population, starting from their birthplace in a massive trans-Neptunian disk that was dispersed by migrating giant planets. Most comets that remain bound to the Solar system are stored in the Oort cloud. Galactic tides and passing stars make some of these bodies evolve into observable comets in the inner Solar system. Our approach models each step in a full-fledged numerical framework. Subsequent analysis consists of applying plausible fading models and computing the original orbits to compare with observations. Our results match the observed semimajor axis distribution of LPCs when Whipple's power-law fading scheme with an exponent $\kappa= 0.6^{+0.1}_{-0.2}$ is adopted. The cumulative perihelion ($q$) distribution is fit well by a linear increase plus a weak quadratic term. Beyond $q = 15$~au, however, the population increases steeply and the isotropy of LPC orbital planes breaks. We find tentative evidence from the perihelion distribution of LPCs that the returning comets are depleted in supervolatiles and become active due to water ice sublimation for $q\leq 3$ au. Using an independent calibration of the population of the initial disk, our predicted LPC flux is smaller than observations suggest by a factor of $\simeq 2$. Current data only characterize comets from the outer Oort cloud (semimajor axes $\gtrsim 10^4$~au). A true boost in understanding the Oort cloud's structure should result from future surveys when they detect LPCs with perihelia beyond $15$~au. Our results provide observational predictions of what can be expected from these new data.