The Asteroids and Gas Giant

Planets

The Asteroid BeltBetween Mars and Jupiter is a belt of rocky materials orbiting the sun. They range in size from 950 km in diameter (Ceres – could it be classified as a planet?) to just fractions of a meter. There are over 200 asteroids that have a diameter of 100 km or more. There are 1.7 million asteroids with a diameter of 1 km or more.

The Origin of the Asteroid BeltA number of theories exist about what caused the asteroid belt. The one most favoured today is that the asteroids would have clumped together into another terrestrial planet but the planet Jupiter was too close and its large gravity force prevented the asteroids from clumping together and instead made them collide and break into more pieces.

Three Different Kinds of AsteroidAsteroids tend to be metallic or silicate (rocky or glassy with the element silicon) or carbonaceous (like carbonates – carbon and oxygen) in composition.

Metallic Silicate Carbonaceous

The Asteroid Belt : Low DensityAsteroids are spaced very far apart. Nine spacecraft have been sent through the belt without any collision. It is calculated that there is a one in a billion chance of hitting an asteroid when sending spacecraft through the belt.

The Largest AsteroidsThe asteroid Ceres may be a planet with a diameter of 950 km. 4 Vesta has a diameter of 529 km and 2 Pallas has a diameter of 544 km.

The Hazards of AsteroidsThe planet, Jupiter, is able to disturb the orbits of asteroids which then may collide and change their path of motion. Some asteroids may take a path that goes towards Earth and if large enough may collide with Earth, causing limited or extensive damage to living things.

JupiterJupiter, the first of the Gas Giant planets, is the largest planet, having a mass that is 2.5 X more than all the other planets combined (318 X Earth’s mass). Jupiter’s “Great Red Spot” is a storm (the size of three Earths) raging in the clouds of hydrogen and helium on the outer surface of the planet.

Jupiter : Almost Became a StarIf Jupiter had come from a nebula that had 100 X more mass, it would have become a small star. Jupiter emits as much radiation and heat as it receives from the sun. The temperature of Jupiter’s core is 35,700 C.

sunlight

Jupiter light

Jupiter’s Revolution and RotationJupiter takes 12 Earth years for one revolution around the sun. It rotates one every 10 hours. At its equator, Jupiter is traveling at 35,200 km/h (Earth’s equator is traveling at 1670 km/h).

Jupiter’s Composition and StructureJupiter’s is mostly made up of hydrogen with some helium. It’s atmosphere is 75% hydrogen and 25% helium. Jupiter is thought to have a solid core surrounded by liquid metallic hydrogen with an outer layer of gaseous molecular hydrogen.

Jupiter’s RingsWith Earth-based telescopes, Jupiter’s very thin rings of dust can not be seen. Space probes flying past Jupiter sent pictures of Jupiter’s rings back to Earth.

Jupiter’s Surface, Gravity and TemperatureJupiter has no defined surface as its outer gases merge with the liquid layer below. The gravity of Jupiter at its outer clouds is 2.4 X the gravity of Earth, increasing up to 318 X as one passes deeper through its clouds. Jupiter’s temperature at its outer clouds is -110 C and rises to 35,700 in its core.

Jupiter’s Magnetic FieldJupiter has a magnetic field that deflects and traps solar wind particles.

Jupiter’s MoonsFrom a simple Earth telescope, four moons of Jupiter can be seen. These are called the Galilean moons since Galileo in the 1600s was the first to record their existence. We now know that Jupiter has 63 moons of various sizes.

Jupiter’s Moon, IoIo is a very active moon with sulfur (yellow) lava flows, lava lakes, 500 km high sulfur geysers and volcanoes and 16 km high mountains.

Jupiter Moons : Europa, Callisto and GanymedeEuropa has a smooth icy crust. Callisto is heavily cratered with a 200 km crust lying over a salty ocean beneath. Ganymede is the largest moon of Jupiter and our Solar System. Ganymede would be a planet if it were orbiting the sun.

SaturnThe rings of Saturn, composed of ices rather than rocks, are easily seen with telescopes on Earth. Saturn is about 95 X as massive as the Earth.

Saturn’s Revolution and Rotation RateSaturn takes 29.5 Earth days for one revolution around the sun. Saturn revolves around once in 10 hours and 40 minutes.

Saturn’s Composition and StructureSaturn is 96% hydrogen and 4% helium. It has an inner rock core surrounded by liquid metallic hydrogen and an outer layer of liquid molecular hydrogen.

Saturn’s SurfaceLike Jupiter, Saturn has no definite surface. Its outer clouds merge with the outer liquid molecular hydrogen layer. The temperature of the outer clouds is -178 C and warms up to 11 700 C in the core. Saturn radiates out 2.5 X as much energy as it receives from the sun. Storms and winds up to 1 800 km/h sweep across Saturn’s surface.

sun radiation

Saturn radiation

Saturn’s Magnetic FieldSaturn has a magnetic field that is slightly weaker than the Earth and helps to deflect solar wind particles.

Saturn’s RingsSaturn has a very large and complex ring structure. The rings are very thin in comparison to their width. The rings are made up of dust and ice with few rocks. The rings may be remnants of the nebula that formed Saturn or the remains of a moon(s) that disintegrated.

Saturn’s MoonsSaturn has 62 moons, five which are very large. Titan, the second largest moon in our Solar System, is larger than the planet Mercury but is a moon because it is orbiting a planet.

The Saturn Moon TitanSaturn’s moon, Titan, has an atmosphere made up of nitrogen and hydrocarbons that is denser than Earth’s atmosphere. It appears to have lakes and rivers of ethane and methane.

The Saturn Moon EnceladusEnceladus is ice covered. Water spouts have been observed near its south pole, probably due to interior heat within the moon.

Uranus

The Gas Giant (Sometimes called an Ice Giant), Uranus, is similar in composition to Jupiter and Saturn and also has rings. It has a mass that is 14.5 X that of Earth.

UranusUranus’ axis of rotation is pointed towards the sun so one pole is in light 42 years while the other pole is in the dark for 42 years. Near the equator, days are 8.5 h long followed by 8.5 h nights. Uranus’ equator is hotter than its poles, something unexpected since its poles get more sunlight.

Revolution and Rotation of Uranus

It takes 84 Earth years for Uranus to make one revolution of the sun. Uranus rotates once in 17 Earth hours and 14 minutes.

Uranus Composition and StructureUranus is composed mostly of hydrogen, helium, and ices of water, ammonia and methane. Uranus has small icy/rocky core, a hot fluid mantle and gas atmosphere that is 83% hydrogen, 15% helium and 2 % methane. The methane gas is mostly in the upper atmosphere and gives the planet a blue look because it absorbs red from the sunlight falling on it. The hot liquid mantle generates electric currents, helping make the planet’s magnetic field.

Uranus’ SurfaceWinds up to 900 km/h have been observed on the outside clouds surrounding Uranus. The surface has an average temperature of -224 C while its core has a temperature of 5000 C.

Uranus’ MagnetosphereUranus has a magnetic field that protects its atmosphere from solar wind particles.

Uranus’ Rings

The thin and dark rings of Uranus are made up of dust and ices.

Uranus’ MoonsUranus has 27 moons. Many are heavily cratered, a number have deep rift valleys and faults that point to movement of moon parts. Umbriel has a spot called the florescent cheerio (probably a crater).

Uranus Seen From One of

its Moons

This is an artist’s conception of a view of Uranus from one of its moons.

NeptuneThe planet Neptune is 17 X Earth’s mass and is on average at a distance of 30 AU from the sun. It takes 165 years to revolve once around the sun and takes 16.11 hours to rotate once. Neptune’s surface has a temperature of -200 C.

Neptune’s Tilted Axis Gives it SeasonsNeptune’s axis of rotation is tilted at 28 degrees which produces seasons. Each season (Spring, Summer, Fall and Winter) of Neptune lasts for about 40 Earth years.

Neptune StructureNeptune has a structure much like Uranus. The core is made of iron and nickel at a temperature of 5 100 C. Around this is a hot liquid mantle made up of water, ammonia and methane which generates electrical currents and a magnetic field. The outer atmosphere layer is made up of 80% hydrogen gas, 19% helium gas and 1 % methane gas (which gives the planet its blue colour).

Neptune Atmosphere : More Stormy than UranusThe atmosphere of Neptune is more active than Uranus with many storms and a very large one, the Great Dark Spot, similar to Jupiter’s large red storm. Cloud winds of 2 100 km/h have been observed.

Neptune MagnetosphereNeptune’s magnetosphere deflects solar wind particles past the planet.

Neptune Rings

Neptune has dark, thin rings made up of ices and dust.

Neptune MoonsTwelve moons have been discovered orbiting Neptune. Triton is the largest and most geologically active moon of Neptune. It shows cracks and nitrogen geysers erupting.

The Kuiper Belt : 30 – 55 AU from the SunThe Kuiper Belt is a flat disc of millions of small bodies that is orbiting the sun beyond the orbit of Neptune. These bodies are thought to be the remains of the formation of our Solar System. The Kuiper belt is like the asteroid belt but Kuiper Belt bodies are more ice-like whereas asteroids are more stony or metallic.

The Kuiper BeltSome of the objects in the Kuiper Belt are called dwarf planets and even have moons that orbit them. Pluto is a Kuiper Belt Dwarf Planet.

The Kuiper BeltOccasionally objects from the Kuiper Belt move into the Solar System. Some of the moons of planets (Neptune’s moon Triton and Saturn’s moon Phoebe) are thought to be Kuiper Belt objects that were captured by the planets.

The Oort Cloud

The Oort Cloud is a three-dimensional cloud of icy fragments and debris that lies around and beyond the Kuiper Belt.

Distance of the Oort CloudThe Oort Cloud is from 2000 – 100 000 AU away from the sun, about ¼ the distance to the star, Proxima Centauri, the star nearest our Sun.

The Oort Cloud and Kuiper Belt : Home of CometsComets are thought to come from either the Oort Cloud or the Kuiper Belt. The Gas Giant planets’ gravity affects objects in the Kuiper Belt and the Oort cloud, sending them into our Solar System towards the Sun.

CometsComets were once referred to as “dirty snowballs”. Comets are composed of ices, rocks and gases. Comets originate in the Kuiper Belt or the Oort Cloud. Through collisions with other objects, they may get “bumped” into our Solar System or they may be pulled by the gravity of the gas giants into our Solar System.

Comets Captured by the Sun’s GravityAs comets move into our Solar System, they are attracted by the Sun’s gravity since the sun has a mass that is 99.89% of our whole solar system.

Comets have “Tails”As comets move towards the sun, the radiation of the sun and solar wind particles start to strip away parts of the icy comet which creates a tail that points away from the Sun.

Comets often ReappearMost comets take up orbits that cause them to return around the Sun. If comets take less than 200 years to reappear they are called short term comets and from 200 to thousands or millions of years to reappear are called long term comets.

A Comet’s Appearance in the Sky

Comets often ReappearHalley’s Comet is a famous short term comet that comes every 74 to 75 years. It was last seen in 1986. It has been observed since 250 BC but persons did not realize that it was the same comet. Historically, comets have been thought to be omens of disaster and generated fear in people whenever they were seen.

Halley’s Comet and the English DisasterHailey’s comet was seen the year that William the Conqueror from France invaded England. The English King Harold was killed in battle by an arrow going into his eye.

Halley’s Comet and the English DisasterWilliam took care of Harold for some time in France and Harold swore an oath of loyalty to William. When the English king died, William had a claim to the throne that Harold then rejected which caused the French invasion.