617 Patroclus and MenoetiusA Binary Minor Planet

Outline

1. Introduction

2. Patroclus and Menoetius1. Detection and parameters

2. Composition

3. Orbital angular momentum

3. Conclusion and Outlook

Patroclus a Trojan Asteroid

• The Trojans are in the astronomieasteroids around the Lagrangianpoints L4 and L5 of Jupiter

• They are named after the warriors ofthe trojan war and sperated in thetwo camps

• Two exceptions: Patroclus and Hector who were discovered before theconfession and are therefore in theoposite Lagrangian point

Discovery of Patroclus

• Patroclus was discovered on the 17th of October in 1906 by Kopff, A. at Heidelberg

• It was the secound trojan asteroid discovered after Hector

• It has a diameter of 122±3 km and the mass of the total system is 1.36 ± 0.11 × 1018 kg and therefore a density of 0.88 ± 0.17

𝑔𝑐𝑚3

• It has a absolute magnitude of 8.19 mag

Discovery of Menoetius

• Menoetius was discovered on 22nd of September in 2001 from: William J. Merline, Laird M. Close, N. Siegler, D. Potter, Clark R. Chapman, Christophe Dumas, François Menard und David C. Slater

• It was discovered with the 8.1 meter-Gemini-North-Telescope in Hawaii

• With a diameter of 112.6 ± 3.2 km it is about 7% smaller than Patroclus

The binary system parameters

Period (days) 4.283 ± 0.004

Semi-major axis (km) 680 ± 20

Eccentricity, e 0.02 ± 0.02

Orbit pole solution ECJ2000 (λ and β in degrees)

λ = 236 ± 5, β = -61 ± 1

Pericentre argument (degrees) 139

Time of passage (Julian days, JD) 2453171.1 ± 0.1

Total mass (kg) (1.36 × 1018) ± 0.11

Bulk density of the system* (g 𝑐𝑚−3) 0.8± 0.17 𝑔 𝑐𝑚3

The orbital angular momentum

• The origin of this tightly bound, small-eccentricity and large angular-momentum binary system remains unclear

• Could be the reuslt of a capture, with subsequent circularization ofthe orbit by tidal effects

• Other explination could be a low velocity impact of large projectile(less probable)

• Could also be formed by tidal effects after low-velocity encounterwith large planet

• Spin periods of components unknown

• Probable a unsynchronized system

Composition of the Asteroids

• Similiar distant to Sun like Galileansatallites → mixture of ice and androck (≜ 50% porosity )

• With the low density of 0.88 ± 0.17

𝑔𝑐𝑚3 it is quite probable that they

consist of water/ice (≜ 15%porosity).

• Referring to Dynimical simulations itis possible that they were formed in the outer solars system

Conclusion and Outlook

• Formation unclear

• Simulations show that several distant planetesimals have a close approach with Jupiter before their final capture at the Lagrange points

• a special programme of photometric observations should be undertaken to attempt to derive the spin poles and rates.

Thank you for your attention!