The Origin of Neptune's Unusual Satellites from a Planetary Encounter
(2020) In The Astronomical Journal 159(4).- Abstract
The Neptunian satellite system is unusual, comprising Triton, a large (∼2700 km) moon on a close-in, circular, yet retrograde orbit, flanked by Nereid, the largest irregular satellite (∼300 km) on a highly eccentric orbit. Capture origins have been previously suggested for both moons. Here we explore an alternative in situ formation model where the two satellites accreted in the circum-Neptunian disk and are imparted irregular and eccentric orbits by a deep planetary encounter with an ice giant (IG), like that predicted in the Nice scenario of early solar system development. We use N-body simulations of an IG approaching Neptune to 20 Neptunian radii (R Nep), through a belt of circular prograde regular satellites at 10-30 R... (More)
The Neptunian satellite system is unusual, comprising Triton, a large (∼2700 km) moon on a close-in, circular, yet retrograde orbit, flanked by Nereid, the largest irregular satellite (∼300 km) on a highly eccentric orbit. Capture origins have been previously suggested for both moons. Here we explore an alternative in situ formation model where the two satellites accreted in the circum-Neptunian disk and are imparted irregular and eccentric orbits by a deep planetary encounter with an ice giant (IG), like that predicted in the Nice scenario of early solar system development. We use N-body simulations of an IG approaching Neptune to 20 Neptunian radii (R Nep), through a belt of circular prograde regular satellites at 10-30 R Nep. We find that half of these primordial satellites remain bound to Neptune and that 0.4%-3% are scattered directly onto wide and eccentric orbits resembling that of Nereid. With better matches to the observed orbit, our model has a success rate comparable to or higher than capture of large Nereid-sized irregular satellites from heliocentric orbit. At the same time, the IG encounter injects a large primordial moon onto a retrograde orbit with specific angular momentum similar to Triton's in 0.3%-3% of our runs. While less efficient than capture scenarios, our model does indicate that an in situ origin for Triton is dynamically possible. We also simulate the post-encounter collisional and tidal orbital evolution of Triton analog satellites and find they are decoupled from Nereid on timescales of ∼104 yr, in agreement with Cuk & Gladman.
(Less)
- author
- Li, Daohai LU and Christou, Apostolos A.
- organization
- publishing date
- 2020-04-01
- type
- Contribution to journal
- publication status
- published
- subject
- in
- The Astronomical Journal
- volume
- 159
- issue
- 4
- article number
- 184
- publisher
- IOP Publishing
- external identifiers
-
- scopus:85086599384
- ISSN
- 0004-6256
- DOI
- 10.3847/1538-3881/ab7cd5
- language
- English
- LU publication?
- yes
- id
- 09548e19-c8ea-4e37-a547-9d47651875fa
- date added to LUP
- 2021-01-11 15:34:33
- date last changed
- 2024-04-03 20:56:20
@article{09548e19-c8ea-4e37-a547-9d47651875fa, abstract = {{<p>The Neptunian satellite system is unusual, comprising Triton, a large (∼2700 km) moon on a close-in, circular, yet retrograde orbit, flanked by Nereid, the largest irregular satellite (∼300 km) on a highly eccentric orbit. Capture origins have been previously suggested for both moons. Here we explore an alternative in situ formation model where the two satellites accreted in the circum-Neptunian disk and are imparted irregular and eccentric orbits by a deep planetary encounter with an ice giant (IG), like that predicted in the Nice scenario of early solar system development. We use N-body simulations of an IG approaching Neptune to 20 Neptunian radii (R <sub>Nep</sub>), through a belt of circular prograde regular satellites at 10-30 R <sub>Nep</sub>. We find that half of these primordial satellites remain bound to Neptune and that 0.4%-3% are scattered directly onto wide and eccentric orbits resembling that of Nereid. With better matches to the observed orbit, our model has a success rate comparable to or higher than capture of large Nereid-sized irregular satellites from heliocentric orbit. At the same time, the IG encounter injects a large primordial moon onto a retrograde orbit with specific angular momentum similar to Triton's in 0.3%-3% of our runs. While less efficient than capture scenarios, our model does indicate that an in situ origin for Triton is dynamically possible. We also simulate the post-encounter collisional and tidal orbital evolution of Triton analog satellites and find they are decoupled from Nereid on timescales of ∼10<sup>4</sup> yr, in agreement with Cuk & Gladman.</p>}}, author = {{Li, Daohai and Christou, Apostolos A.}}, issn = {{0004-6256}}, language = {{eng}}, month = {{04}}, number = {{4}}, publisher = {{IOP Publishing}}, series = {{The Astronomical Journal}}, title = {{The Origin of Neptune's Unusual Satellites from a Planetary Encounter}}, url = {{http://dx.doi.org/10.3847/1538-3881/ab7cd5}}, doi = {{10.3847/1538-3881/ab7cd5}}, volume = {{159}}, year = {{2020}}, }