Asteroids, Trans-Neptunian Objects, Oort Cloud & Comets

Asteroids: the “minor planets” (The Asteroid Belt) - There are 100,000s of relatively small rocky bodies orbiting around the Sun between the orbit of

Mars and the orbit of Jupiter the Asteroid Belt - At a distance of 2-3.5 AU mainly with large eccentricity and inclination

- These are “left-over” from the objects (“planetesimals”) that formed the planets, but will never form a planet

- Their combined mass is about that of the Moon or a little less - There are a few large objects, more smaller objects and plenty of tiny objects. - These were planetesimals which never formed a planet due to the strong gravitational pull of

Jupiter. - These planetesimals lost most of their “ice” and are made mainly of rocky materials. - There are gaps in the belts due to Jupiter gravitational pull (resonance).

The Main Asteroids: Ceres: almost 1000km in diameter, eccentricity=0.08, i=10deg (“dwarf planet”)

Pallas: 550km, e=0.23, i=35deg

Juno (300km), Vesta, Astraea, Hebe, Iris, Flora, Metis, Hygiea,….

Mathilde

Ida & its moon Dactyl Mainly 3 types of Asteroids:

- Carbon-rich (C-type) - Stony (S-type) - Metallic (M-type)

Close view of Gaspra

Trans-Neptunian Objects – The Kuiper Belt - Pluto “used to be the last planet”, with a diameter of 1,150km “dwarf planet”

- Eccentricity of 0.25, inclination of 17.15degrees…

Pluto is now considered a dwarf planet, part of a large collection of small objects beyond the orbit of

Neptune – the Trans-Neptunian Objects

Small icy objects beyond Neptune have recently been discovered, similar to Pluto in orbit, size and

composition.

These Trans Neptunian Objects are the inner portion of the Kuiper Belt and Pluto is the largest object in

the Kuiper Belt.

The Kuiper Belt is between 30 and 50AU, the combined mass of the objects is about one Jupiter Mass,

and these are also “left-over” from the planetesimal that never formed a planet.

Due to their distance these objects contain ice as well as rock.

The Kuiper Belt is the source of comets due to collision between objects in the belt.

The Kuiper Belt:

Some Kuiper Belt objects can go as far as 100AU from the sun, that outer region of the Kuiper Belt is

sometimes called the farther “scattered disk” and it is from there that comets originate.

The Oort Cloud

It is a hypothesized spherical cloud of comets some 50,000AU from the sun (about 1 light year away;

1,000 times further away than the Kuiper Belt).

There is a disk-shaped inner Oort cloud and

A spherical outer Oort cloud

The matter in the Oort cloud was formed closer to the Sun and was scattered by the migration of the

giant planets during the evolution of the solar system.

The Nice model:

It is the source of very long period comets. The largest known object in the Oort cloud: Sedna, 1200-1800km in diameter, 76-892AU!

Comets - A comet is an icy small solar system body that, when close enough to the Sun, displays a visible

fuzzy coma and a tail, due to the solar radiation and wind, on the nucleus of the comet. - The comets are icy/rocky bodies coming from the Kuiper Belt (scattered siks) or from the Oort

Cloud. - Comets range in size between a few 100m to a few km - Orbital periods range from a few yrs to 1,000s of yrs - Comets that have passed many times close to the sun have lost their volatile (ice, water,

methane, ammonia) and are similar to asteroids (rocky material). - A comet has a Nucleus, a Coma, a gas tail and a dust tail.

The Nucleus Composed of rock, dust, water ice and frozen volatiles CO, CO2, NH3, CH4

Nucleus of Comet Tempel 1 (5-7km).

The Coma - The solar radiation causes the volatile of the comet to vaporize and stream out of the nucleus

carrying dust away with them. - The streams of dust and gas ejected from the nucleus forms the coma (it is like a very tenuous

atmosphere around the nucleus), which reflects the sunlight and also glows due to ionization. The coma of Comet Holmes

The dust and gas escaping are blown away by the Sun radiation and wind forming the tails of the comet. The comet has a dust tail and a gas or ion tail. The Tails of the comet: The gas in the tail is ionized “ion” tail The dust tail reflects sunlight The ion tail glows due to ionization The dust tail is always behind in the comet’s orbit (trailing behind) The ion tail always points away from the Sun, as it is blown away by solar wind.

Ion tail in blue…