# The journey of Typhon-Echidna as a binary system through the planetary region

## TL;DR

This study investigates the orbital evolution of the Typhon-Echidna binary system, a trans-Neptunian object crossing Neptune's orbit, assessing its stability, potential to reach terrestrial planets, and its history over the past 100 million years.

## Contribution

The paper provides the first detailed numerical analysis of Typhon-Echidna's orbital evolution and binary stability during planetary encounters, highlighting its potential to reach the inner Solar System.

## Key findings

- Only 22% of planetary encounters disrupt the binary.
- Approximately 3.6% chance of reaching terrestrial planetary region in 5.4 Myr.
- Typhon may have spent most of the last 100 Myr crossing Neptune's orbit.

## Abstract

Among the current population of the 81 known trans-Neptunian binaries (TNBs), only two are in orbits that cross the orbit of Neptune. These are (42355) Typhon-Echidna and (65489) Ceto-Phorcys. In the present work, we focused our analyses on the temporal evolution of the Typhon-Echidna binary system through the outer and inner planetary systems. Using numer- ical integrations of the N-body gravitational problem, we explored the orbital evolutions of 500 clones of Typhon, recording the close encounters of those clones with planets. We then analysed the effects of those encounters on the binary system. It was found that only 22% of the encounters with the giant planets were strong enough to disrupt the binary. This binary system has an ~3.6% probability of reaching the terrestrial planetary region over a time scale of approximately 5.4 Myr. Close encounters of Typhon-Echidna with Earth and Venus were also registered, but the probabilities of such events occurring are low (~0.4%). The orbital evolution of the system in the past was also investigated. It was found that in the last 100 Myr, Typhon might have spent most of its time as a TNB crossing the orbit of Neptune. Therefore, our study of the Typhon-Echidna orbital evolution illustrates the possibility of large cometary bodies (radii of 76 km for Typhon and 42 km for Echidna) coming from a remote region of the outer Solar System and that might enter the terrestrial planetary region preserving its binarity throughout the journey.