Kuiper Belt, Oort Cloud and TNOs

Transcription

1 Kuiper Belt, Oort Cloud and TNOs Gerhard Weihs Folie 1

2 Content Small Solar System body (SSSB) Short history TNOs (Trans-Neptunian Objects) Kuiper belt (engl. Edgeworth-Kuiper belt ) scattered disk Oort cloud Forming (NICE-model of migration) Folie 2

3 Small Solar System body (SSSB) Definition of SSSB IAU 2006 describes objects in the Solar System that are neither planets nor dwarf planets, nor satellites of a planet or dwarf planet: All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies"... These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.[1] * the classical asteroids, with the exception of Ceres; * the centaurs and trojans; * the Trans-Neptunian Objects, with the exception of Pluto, Haumea, Makemake and Eris; * all comets. Folie 3

4 short history Significant Dates 1943: Astronomer Kenneth Edgeworth suggests that a reservoir of comets and larger bodies resides beyond the planets. 1950: Astronomer Jan Oort theorizes that a vast population of comets may exist in a huge cloud on the distant edges of our solar system. 1951: Astronomer Gerard Kuiper predicts the existence of a belt of icy objects just beyond the orbit of Neptune. 1992: After five years of searching, astronomers David Jewitt and Jane Luu discover the first KBO, 1992QB : Scientists using the 48-inch Oschin telescope at Palomar Observatory find Quaoar, the first large KBO hundreds of kilometers in diameter. This object was photographed in 1980, but was not noticed in those images. 2004: Astronomers using the 48-inch Oschin telescope announce the discovery of Sedna (2003VB12). 2005: Astronomers announce the discovery of 2003UB313. This object, later named Eris, is slightly larger than Pluto. 2008: The Kuiper Belt object provisionally known as 2005FY9 ("Easterbunny") is recognized in July as a dwarf planet and named Makemake (pronounced MAHkeh-MAHkeh) after the Polynesian (Rapa Nui) creation god. In September 2003EL61 ("Santa") was designated a dwarf planet and given the name Haumea after the Hawaiian goddess of fertility and childbirth. Folie 4

5 TNOs TNOs (Trans-Neptunian Objects) are classified in two large groups, according to their distance from the Sun and their orbit parameters, : Kuiper belt (engl. Edgeworth-Kuiper belt ) Scattered disk Folie 5

6 Kuiper belt a torus-shaped region called Edgeworth-Kuiper belt too contains objects usually having close-to-circular orbits with a small inclination from the ecliptic extending from the orbit of Neptune at 30 AU to 55 AU consists mainly of small bodies, or remnants from the Solar System's formation The belt is home to at least four dwarf planets Pluto, Haumea, Eris and Makemake called plutinos The belt ist home of short-range comets Folie 6

7 Scattered disk Scattered disk contains objects further from the Sun average distance from 55 to about 100 AU usually with very irregular orbits (i.e. very elliptical and having a strong inclination from the ecliptic). A typical example is the most massive known TNO - Eris. The belt ist home of short-range comets Folie 7

8 Kuiper belt objects (KBOs) Kuiper belt objects (KBOs) are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. They are further classified into the following two groups: Resonant objects are locked in an orbital resonance with Neptune. - Objects with a 1:2 resonance are also called twotinos, and - objects with a 2:3 resonance are called plutinos, after their most prominent member, Pluto. Classical Kuiper belt objects (also called cubewanos, CKBOs)) have no such resonance, moving on almost circular orbits, unperturbed by Neptune. - Examples are 1992 QB1, Quaoar and Makemake. Folie 8

9 Trans-Neptunian objects (TNOs) Folie 9

10 Trans-Neptunian objects (TNOs) Folie 10

11 Largest Trans-Neptunian Objects Folie 11

12 Centaurs (no TNO) Groups an object is classified as a centaur if its semi-major axis lies between Jupiter and Neptune There is no clear orbital distinction between centaurs and comets. Plutinos similar orbits as Pluto Kuiper Belt Scattered disk Folie 12

13 Colours of TNOs Folie 13

14 Physical characteristics of TNOs Studying colors and spectra provides insight into the objects' origin and a potential correlation with other classes of objects, namely centaurs and some satellites of giant planets (Triton, Phoebe), suspected to originate in the Kuiper Belt. the interpretations are ambiguous as the optical surfaces of small bodies are subject to modification by intense radiation, solar wind and micrometeorites Consequently, the thin optical surface layer could be quite different from the regolith underneath Small TNOs are thought to be low density mixtures of rock and ice with some organic (carbon-containing) surface material such as tholin, detected in their spectra. On the other hand, the high density of Haumea, g/cm3, suggests a very high non-ice content (compare with Pluto's density: 2.0 g/cm3). The composition of some small TNO is similar to that of comets. Some Centaurs undergo seasonal changes when approaching the Sun Folie 14

15 Other properties of TNOs Folie 15

16 Oort Cloud The Oort cloud is a hypothesized spherical cloud of comets which is thought to occupy a vast space from between 2,000 or 5,000 AU (0.03 and 0.08 ly) to about 50,000 AU (0.79 ly) from the Sun. The outer extent of the Oort cloud defines the gravitational boundary of our Solar System. The Oort cloud is thought to comprise two separate regions - a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hill cloud. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane. the Oort cloud was formed closer to the Sun and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System's evolution. Folie 16

17 Oort Cloud A cloud population of 1.4 trillion comets brighter than an absolute magnitude of 11 The total mass of comets in the Oort cloud is calculated according to a derived relationship between brightness and nucleus mass. The estimated total mass is 1.9 earth masses. The probable error in the estimate is about one order of magnitude. Most of the mass of the Oort cloud is concentrated in the size range of the observed long-period comets. Folie 17

18 Oort Cloud Folie 18

19 Kuiper Belt, Oort Cloud Folie 19

20 Origin of comets Short-period comets (those with orbits of up to 200 years) are generally accepted to have emerged from the Kuiper belt or scattered disk Comets pass from the scattered disc into the realm of the outer planets, becoming what are known as centaurs. These centaurs are then sent farther inward to become the short-period comets. There are two main varieties of short-period comet: Jupiterfamily comets (those with semi-major axes of less than 5 AU) and Halley-family comets. Long-period comets, such as comet Hale-Bopp, whose orbits last for thousands of years, are thought to originate in the Oort cloud. Folie 20

21 Oort cloud as source of comets Oort cloud is the source of all long-period and Halley-type comets entering the inner Solar System and many of the Centaurs and Jupiter-family comets as well. The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way Galaxy itself. These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System. Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud. Folie 21

22 cometary fading Oort noted that the number of returning comets was far less than his model predicted, and this issue, known as "cometary fading", has yet to be resolved. No known dynamical process can explain this undercount of observed comets. Hypotheses for this discrepancy include the destruction of comets due to tidal stresses, impact or heating; the loss of all volatiles, rendering some comets invisible, or the formation of a non-volatile crust on the surface. Dynamical studies of Oort Cloud comets have shown that their occurrence in the outer planet region is several times higher than in the inner planet region. This discrepancy may be due to the gravitational attraction of Jupiter, which acts as a kind of barrier, trapping incoming comets and causing them to collide with it, just as it did with Comet Shoemaker- Levy 9 in Folie 22

23 NICE model of planetary migration The Nice model is a scenario for the dynamical evolution of the Solar System. It is named for the location of the Observatoire de la Côte d'azur, where it was initially developed, in Nice, France (2005): It proposes the migration of the giant planets from an initial compact configuration into their present positions This planetary migration is used to explain: - the Late Heavy Bombardment of the inner Solar System, - the forming of the Oort cloud, and the - existence of small Solar System bodies including - the forming of the Kuiper belt and scattered disk, - the Neptune and Jupiter Trojans, and - the numerous resonant trans-neptunian objects dominated by Neptune. Folie 23

24 NICE model of planetary migration Proposals: The NICE model proposes that after the dissipation of the gas and dust of the primordial Solar System disk, the four giant planets (Jupiter, Saturn, Uranus and Neptune) were originally found on near-circular orbits between ~5.5 and ~17 AU, much more closely spaced and more compact than in the present. A large, dense disk of small, rock and ice planetesimals, their total about 35 Earth masses, and extended from the orbit of the outermost giant planet to some 35 AU. Folie 24

25 NICE model of planetary migration Migration: Planetesimals at the disk's inner edge occasionally pass through gravitational encounters with the outermost giant planet, which change the planetesimals' orbits. The planets scatter inwards the majority of the small icy bodies that they encounter, exchanging angular momentum with the scattered objects so that the planets move outwards in response, preserving the angular momentum of the system. These planetesimals then similarly scatter off the next planet they encounter, successively moving the orbits of Uranus, Neptune, and Saturn outwards. This process continues until the planetesimals interact with the inmost and most massive giant planet, Jupiter, whose immense gravity sends them into highly elliptical orbits or even ejects them outright from the Solar System. This, in contrast, causes Jupiter to move slightly inward Folie 25

26 NICE model of planetary migration Forming of Kuiper Belt and Oort Cloud: objects scattered by Jupiter into highly elliptical orbits formed the Oort cloud; objects scattered to a lesser degree by the migrating Neptune formed the current Kuiper belt and scattered disc. This scenario explains the Kuiper belt's and scattered disc's present low mass. Some of the scattered objects, including Pluto, became gravitationally tied to Neptune's orbit, forcing them into meanmotion resonances. Eventually, friction within the planetesimal disc made the orbits of Uranus and Neptune circular again. In contrast to the outer planets, the inner planets are not believed to have migrated significantly over the age of the Solar System, because their orbits have remained stable following the period of giant impacts. Folie 26

27 References Wikipedia Comets: Coming inside from the Cold Ice Worlds at the Outer Limit ESO Messenger 141-Sep 2010, Folie 27