Accretion disk Small bodies in the Solar System

1. Accretion disk Small bodies in the Solar System

2. Small bodies – Definition and inventoriesT.D. - Trojan asteroids • Comets, dust and meteor showers • The thermal history of asteroids (Vesta/Dawn)

3. A brief summary – the formation of the solar system Stage 1 – Collapse of a molecular cloud – Formation of a hot disk of gas. Stage 2 – Cooling of the disk – Condensation of metal, silicates and ices. Planetesimals formation Stage 3 – Formation of planetary embryos (mass comparable to the Moon or Mars). Formation of the core of giant planets (super-Earth). Stage 4 – Formation of the four telluric planets and hydratation of the inner solar system.

4. Small bodies – definition - All material that was not incorporated into the solid and gaseous planets • Moons of planets • Asteroids • Comets • Troyans • Transneptunian objects (Kuiper belts, Centaurs) • The Oort clouds • Dust, meteorites

5. Why do we study small bodies ? • Leftovers from the formation phase of the solar system • Comets and some asteroids are the most primitive objects in the solar system • Study processes and forces which have a signigicant effect only on small bodies (e.g., radiation pressure, non-gravitational forces on comets dynamics)

6. Jupiter : 63 moons (many of them are captured asteroids)

7. Asteroids Small solid bodies (iron, or rocky) of the inner solar system out of the orbit of Jupiter

8. Asteroids

9. Asteroids The mass of all the objects of the asteroid belt is estimated to be about 2.8 – 3.2 *1021 kg, or about 4 % of the mass of the moon.

10. Asteroids – size distribution The mass of all the objects of the asteroid belt is estimated to be about 2.8 – 3.2 *1021 kg, or about 4 % of the mass of the moon.

11. Centaurs The minor planet center (MPC) defines centaurs as having a perihelion beyond the orbit of Jupiter and a semi-major axis less than than of Neptune. Unstable objects – they have dynamic lifetime of a few millions of years

12. The orbits of Centaurs

13. The color of Centaurs

14. Troyans A trojan is a minor planet or natural satellite that shares an orbit with a larger body (planet or satellite) but does not collide with it because its orbit around on of the two Lagrangian points of stability L4 and L5, which lie 60° ahead of and behind the largerer body.

15. Troyan asteroids of Jupiter

16. Troyan asteroids of Saturn’s moons

17. Troyan asteroids of Saturn’s moons Telesto 32.6×23.6×20 km Thetys - 531.1 ± 0.6 km Callipso - 30.2×23×14 km

18. Troyan asteroids of Saturn Helene - 43.4×38.2×26 km Dione - 1128.8 × 1122.6 × 1119.2 km Polydeuces - 1.75 km

19. The first confirmed Trojan for the Earth – 2010 TK7

20. The first confirmed Trojan for the Earth – 2010 TK7

21. Trans-Neptunian Objects (TNO) A trans-Neptunian object (TNO) is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune. - Kuiper’s belt- Oort cloud

22. Trans-Neptunian Objects (TNO) A trans-Neptunian object (TNO) is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune.

23. Kuiper’s Belt - The Kuiper’s belt is a region of the Solar System beyond the planets extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the sun. - Similar to the asteroid belt, although is 20 times as wide and 20 – 200 times as massive • Kuiper objects are composed largel of frozen volatiles (ices) such as methane, ammonia, and water. - The belt is home to at least three dwarf planets : Pluto, Haumea, Makemake. - Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, are also believed to have originated in the region

24. Kuiper’s Belt

25. Oort cloud The Oort cloud is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth of the Oort cloud's distance. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance

26. Oort cloud - hypothesis • To resolve a paradox :(1932, Estonian Astronomer Ernst Opik, Dutch Astronomer Jan Handrick Oort, 1950) • over the course of the Solar System's existence, the orbits of comets are unstable : • Dynamics dictate that a comet must either collide with the Sun or a planet, or else be ejected from the Solar System by planetary perturbations. • Moreover, their volatile composition means that as they repeatedly approach the Sun, radiation gradually boils the volatiles off until the comet splits or develops an insulating crust that prevents further outgassing. • =>Thus, reasoned Oort, a comet could not have formed while in its current orbit, and must have been held in an outer reservoir for almost all of its existence

27. Oort cloud But still no direct or indirect proof of existence !

28. Conclusions Animation of small bodies dynamics in the Solar System Close encounters with the Earth

29. The inner solar system The orbits of the planets Mercury, Venus, Earth and Mars are shown in light blue, with the current locations of each planet being shown by large crossed circles. Main-belt minor planets are shown as green circles, Near-Earth asteroids as red circles. Comets are shown as blue squares (filled for numbered periodic comets, outline for other comets). Source : center for minor planets

30. The middle solar system This animation shows the motion of objects in the inner- to mid-region of the solar system over a two-year period. The animation shows objects out to the orbit of Jupiter and a little beyond. The meaning of the symbols is as for the Inner Solar System animation: additionally, Jupiter and its orbit are now shown and the Jupiter Trojans, which orbit in the same orbit as Jupiter but roughly 60 degrees ahead or behind the planet, are colored blue. Source : center for minor planets

31. The outer solar system The orbits and current locations of the Jovian planets (Jupiter, Saturn, Uranus and Neptune) are shown. The current location of Pluto is indicated by the large white crossed circle. High-eccentricity objects are shown with cyan triangles, Centaurs as orange triangles, Plutinos as white circles, "Classical" TNOs as red circles and Scattered-Disk Objects as magenta circles. Source : center for minor planets

32. Closest encounters with the Earth Objects in red D < 6*106 km Objects in orange 6*106 km < d < 13*106 kmObjects in green D > 13*106 km Source : center for minor planets Only in one year !

33. Near-Earth Objects • Three families of NEOs87 near-earth comets, 7867 near Earth asteroids • Atens (647) – Average orbital radii less than one AU and aphelia of more than Earth’s perihelion (0.983 AU) [Inside the orbit of the Earth] • Apollos (4289) – Average orbital radii more than that of the Earth and perihelia less than Earht’s aphelion (1.017 AU) • Amors (2920) – Average orbital radii in between the Earth and Mars radii and perihelia outside Earth’s orbit. Amors often cross the orbit of Mars, but do not cross the orbit of the earth.

34. Near-Earth Objects

35. Closest encounters with the Earth Source : center for minor planets (diameter with albedo ranging from 0.05 to 0.5)