Accretion diskSmall bodies in the Solar System

I. Small bodies – Definition and inventoriesT.D. - Trojan asteroids

II. Comets, dust and meteor showers

III. The thermal history of asteroids (Vesta/Dawn)

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.

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

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)

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

Asteroids

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

Asteroids

AsteroidsThe 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.

Asteroids – size distributionThe 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.

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

The orbits of Centaurs

The color of Centaurs

TroyansA 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.

Troyan asteroids of Jupiter

Troyan asteroids of Saturn’s moons

Troyan asteroids of Saturn’s moons

Callipso - 30.2×23×14 km

Telesto 32.6×23.6×20 km

Thetys - 531.1 ± 0.6 km

Troyan asteroids of Saturn

Helene - 43.4×38.2×26 km

Polydeuces - 1.75 km

Dione - 1128.8 × 1122.6 × 1119.2 km

The first confirmed Trojan for the Earth – 2010 TK7

The first confirmed Trojan for the Earth – 2010 TK7

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

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

- 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

Kuiper’s Belt

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

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

Oort cloud

But still no direct or indirect proof of existence !

Conclusions

Animation of small bodies dynamics in the Solar System

Close encounters with the Earth

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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).

The inner solar system

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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.

The middle solar system

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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.

The outer solar system

Closest encounters with the Earth

Objects in red D < 6*106 km

Objects in orange6*106 km < d < 13*106 km

Objects in greenD > 13*106 km

Only in one year !

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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.

Near-Earth Objects

Closest encounters with the Earth

Source : center for minor planets (diameter with albedo ranging from 0.05 to 0.5)