THE SOLAR SYSTEM AND THE UNIVERSE

THE SOLAR SYSTEM AND THE UNIVERSE TEACHER INFORMATION SHEETS

MERCURY Gigantic iron core (70% of interior); perhaps partially molten Thin silicate mantle (25%) Thin crust perhaps <100km (60miles) thick Mass (Earth =1): 0.055 Temp (min / max): Min -170 C (-280 F) Max 430 C (800 F) 0.39 AU 0.61 AU 59 days (just under 2 months) 88 days Surface Gravity (Earth=1): 0.38 4,879km (3,032 miles) Volume (Earth=1): 0.056 None Current Missions: Mercury Messenger Orbiter (2004) Closest planet to Sun. Highly cratered in appearance, similar to Earth s moon. Slightly larger than the Moon (diameter X 1.4) Highly elliptical orbit and slow rotation = extreme temp variation. Hot enough to melt lead/cold enough to freeze person.

VENUS Large nickel-iron (solid) core (50% of interior) Thick silicate mantle Thin rocky crust perhaps 50km (30 miles) thick Dense CO2 atmosphere Mass (Earth =1): 0.82 Temp (min / max): 464 C (867 F); little variation 0.72 AU 0.28 AU (closest planet to Earth) 243 days 225 days Surface Gravity (Earth=1): 0.91 12,104 km (7,521 miles) Volume (Earth=1): 0.86 None Current Missions: Venus Express Orbiter (2005) Spins in opposite direction to the other terrestrial planets. Volcano-covered surface; most craters erased by volcanic activity. Dense CO2 atmosphere causing greenhouse effect on planet. Hot enough to melt lead; clouds of sulphuric acid. Atmospheric Pressure is x 92 that of Earth. Can be seen from Earth as bright evening/morning star.

EARTH Only planet with 2 part core: Solid inner core at very high temperature; Outer liquid core is half radius of planet. Both iron-nickel Thick mantle of solid silicate rock Thin outer crust of volcanic rocks Atmosphere: 78% nitrogen; 21% oxygen; 1% argon Water vapour also present Mass: Temp (min / max): Surface Gravity: Volume: 5.974 x 1024 kg Min -88 C (-126 F) Max 58 C (136 F) 149.6 million km (92.9 million miles); 1AU 23.93 hrs 365.25 days 1(g) 12,756 km (7,926 miles) 1.08 trillion km³ One Earth is the only planet we know of that has life. The area in which life occurs is called the biosphere. 71% of Earth is covered by water. Earth s crust is split into 7 large plates which float on the semi-molten mantle below. Where these plates meet are tectonic features such as deep sea trenches, oceanic ridges, high mountain ranges and volcanoes.

THE MOON Small metallic core (<4% total mass) partially molten? Rocky mantle Thick rocky crust (thicker than Earth s as it cooled and solidified much faster) Mass (Earth =1): 0.012 Temp (min / max): Min -233 C (-387 F) Max 123 C (253 F) 384,400 km 27.32 days Surface Gravity (Earth=1): 0.165 3,476 km (2,160 miles) Volume (Earth=1): 0.02 Current Missions: None The Moon is thought to have been formed from material ejected from the Earth during an asteroid collision about 4.5 billion years ago. It is covered in craters caused by heavy meteorite bombardment. The Moon is moving away from us at around 4cm every year. The same side of the Moon (the near side ) always faces the Earth. In 1968, Apollo 8 was first manned spacecraft to leave Earth orbit, carrying 3 men around the Moon. Neil Armstrong and Buzz Aldrin were the first men on the moon on July 20 1969, with Michael Collins in the Apollo 11 command module. Twelve people have walked on the Moon, all American male astronauts.

MARS Iron & iron sulphide (solid) core (30-40% of interior) Mantle of silicate rock Crust thicker than Earth s; 120km (75 miles) Thin atmosphere (95% CO2) Mass (Earth =1): 0.11 Temp (min / max): Min -133 C (-207 F) Max 27 C (80 F) 1.52 AU 0.52 AU 24.62 hrs (v. similar to Earth) 687 days Surface Gravity (Earth=1): 0.38 6,794 km (4,222 miles) Volume (Earth=1): 0.15 2 (Phobos & Deimos) Current Missions: Mars Odyssey Orbiter (2001) Mars Express Orbiter (2003) Spirit & Opportunity Rovers (2003) Mars Reconnaissance Orbiter (2005) Phoenix Lander (2007) Called Red Planet due to rusty rocks of iron oxide. Surface similar to Earth, with mountains, valleys and polar ice caps. Largest mountain in Solar System - Olympus Mons 27 km (17miles) high. Largest canyon in Solar System Valles Marineris 7km (4.5 miles) deep and 3,800 km (2,400 miles) long. Evidence that Mars once had lakes, seas and oceans in distant past; perhaps water still remains in lowest areas? Sandstorms can last for months.

JUPITER Possibly has small solid core of ice and rock Inner mantle (>66% of interior) of dense liquid metallic hydrogen Outer mantle of liquid hydrogen and helium Thin atmosphere 90% hydrogen, 10% helium Mass (Earth =1): 317.8 Temp: Surface Gravity (Earth=1): Volume (Earth=1): Current Missions: -110 C (-160 F) at cloud tops 5.2 AU 4.2 AU 10 hrs 12 years 2.64 (at cloud tops) 142,984 km (88,846 miles) 1,321 (over 1000 Earths could fit inside) 63 known at present None Largest planet in Solar System. Rapid rotation causes banding - bright zones and darker belts. Great Red Spot giant storm system over 400 years old. Could fit three Earths inside it. Thin, dark ring system, invisible to even powerful telescopes. Four Galilean Moons: Ganymede (largest moon in Solar System); Callisto (most cratered moon in Solar System); Io (most volcanic moon); Europa (may have ocean beneath its icy surface).

SATURN Small core of rock and ice Inner mantle of liquid metallic hydrogen Outer mantle of liquid hydrogen (50% of planet) Thicker atmosphere than Jupiter; 96% hydrogen 4% helium Mass (Earth =1): 95.2 Temp: Surface Gravity (Earth=1): -140 C (-220 F) at cloud tops 9.6 AU 8.6 AU 11 hrs 29 yrs 0.92 (at cloud tops) 120,536 km (74,898 miles) Volume (Earth=1): 763.6 60 known at present Current Missions: Cassini Orbiter (1997) Extensive ring system composed of dirty water ice ranging in size from dust grains to boulders several metres across. Rapid rotation causes visible flattening at poles and banding similar to Jupiter. Least dense of all the planets it would float in water. Saturn s moon Titan is the second largest moon in the Solar System, and is also the only known moon to have a substantial atmosphere.

URANUS Small core of rock and ice Slushy inner mantle of ice compounds of water, methane and ammonia Outer mantle of liquid hydrogen and other elements Atmosphere of 83% hydrogen, 15% helium and 2% methane Discovered by: William Herschel in 1781 Mass (Earth =1): 14.5 Temp: Surface Gravity (Earth=1): -214 C (353 F) at cloud tops 19.2 AU 18.2 AU 17 hrs 84 yrs 0.86 (at cloud tops) 51,118 km (31,763 miles) Volume (Earth=1): 63.1 27 known at present Current Missions: None (Only mission- Voyager 2 flyby in 1986) Methane in atmosphere absorbs red light giving the planet a blue-green colour. Uranus orbits on its side, possibly due to a massive collision in the distant past. It has a ring system of eleven dark rings thought to be ice particles covered in sooty organic compounds. All moons named after characters by William Shakespeare & Alexander Pope (e.g. Titania, Oberon are from a Midsummer Night s Dream)

NEPTUNE Small core of rock and ice Slushy inner mantle of water, methane and ammonia (similar to Uranus) Outer mantle of hydrogen and other compounds in icy liquid (similar to Uranus) Atmosphere of 79% hydrogen; 18% helium; 3% methane Discovered by: Johann Galle in 1846 Mass (Earth =1): 17.1 Temp: Surface Gravity (Earth=1): -200 C (-320 F) 30 AU 29 AU 16 hrs 165 yrs 1.2 (at cloud tops) 49,528 km (30,775 miles) Volume (Earth=1): 57.7 13 known at present Current Missions: None (Only mission - Voyager 2 flyby in 1989) Dark ring system similar to that of Uranus. Due to Pluto s eccentric orbit, Neptune is sometimes the furthest planet from the Sun. Cloud belts, zones and turbulent storms similar to Jupiter. Storms have fastest winds in Solar System at 670 m per second. Great Dark Spot observed by Voyager 2 in 1989, disappeared by 1994. Triton is Neptune s only large satellite and is bigger than Pluto. It is the coldest known object in the Solar System at -235 C (-391 F)

PLUTO Giant rocky core makes up most of planet Mantle rich in water ice Thin icy crust Thin atmosphere 98% nitrogen; 2% methane and CO2 Discovered by: Clyde Tombaugh in 1930 Mass (Earth =1): 0.002 Temp: -223 C (369 F) 39.5 AU 29.5AU 6.4 days (almost a week) 248 years Surface Gravity (Earth=1): 0.06 2,390 km (1,485 miles) Volume (Earth=1): 0.006 Current Missions: 3 Charon, Nix and Hydra New Horizons (2006) due to reach Pluto in 2015 Charon s mass is 15% of Pluto s, making it the largest moon in relation to its parent body in Solar System. Pluto and Charon rotate at same speed, so always keep the same face to each other. Nix and Hydra are tiny satellites of Pluto discovered in 2005. They are thought to be between 48-165 km wide. In 2006, the IAU re-classed Pluto as a dwarf planet.

THE SUN The Sun is 71% hydrogen; 27% helium and 2% other elements like carbon, nitrogen and iron. Core nuclear reactions (hydrogen nuclei smashing together to form helium) produce heat and light. Radiation zone energy from core transported outwards. Convection zone energy carried to surface by convection. Photosphere visible surface of Sun where e.g. sunspots are observed. Chromosphere irregular lower atmosphere. Corona outermost layer of atmosphere extending millions of km into space. Can be seen during a solar eclipse. Temp: Axial Rotation Period: Core: 15,500,000 C (28 million F) Surface (photosphere): 5,500 C (9,900 F) 149.6 million km (92.9 million miles); 1 AU 25.38 days Surface Gravity (Earth=1): 28 1,392,000 km (865,000 miles) Volume (Earth=1): 1,304,000 Current Missions: Several missions including: STEREO (2006); Hinode (2006); SOHO (1995) Sunspots are cooler regions which appear as dark patches in the photosphere and can be 80,500 km (50,000 miles) in diameter. They occur in regions where the Sun s magnetic field is concentrated, inhibiting energy flow. The Sun s magnetic field also causes solar flares (huge eruptions); coronal loops (streamers of gas joining two points on the Sun s surface); and prominences (huge strands of cool gas).

ASTEROIDS Asteroids are minor planets, most ( but not all ) of which are located in the Asteroid Belt between the orbits of Mars and Jupiter. The Asteroid Belt is 2.1 3.3 AU from the Sun. There are millions of asteroids here, but their combined mass is only 1/20th the mass of the Moon. Asteroids range in size in the following approximate amounts: 100 asteroids >200km (125 miles) across 100,000 asteroids >20km (12.5 miles) across 1 billion asteroids >2km (1.25 miles) across They were originally divided into three different classes, although there are now many more classes and sub-classes C-type asteroids : carbonaceous; 75% of known asteroids; outer region of belt S-type asteroids : silicaceous (stony); 17% of known asteroids; inner region of belt M-type asteroids : metallic (nickel and iron); 5% of known asteroids; middle of belt Ceres was by far the largest asteroid bigger than Pluto and containing approx 25% of the combined mass of all the other asteroids in the belt. It has now been re-classified as a dwarf planet the only one in the Asteroid Belt. Some asteroids have tiny moons e.g. Ida (above) has a moon called Dactyl. Others comprise two similar-sized asteroids orbiting a common centre of mass. These are called double asteroids. Near Earth Asteroids (NEAs) orbit within 1.3 AU of the Sun and come close to Earth s orbit. Only a few thousand have been found, but over 100,000 which are >100m are estimated to exist. In 2001, the NEAR Shoemaker probe landed on Eros, an NEA. Before landing, the probe orbited and photographed the asteroid.

KUIPER BELT & OORT CLOUD The Kuiper Belt is a region beyond the orbit of Neptune, from 30-55 AU from the Sun, which contains many small icy bodies left over from the formation of the Solar System. There are an estimated 10 million 1 billion deep-frozen Kuiper Belt Objects (KBOs) of which >1000 are known. The belt is named after Gerrard Kuiper, a Dutch American astronomer who had such good eyesight he was able to see stars four times fainter than those visible to normal eyes. The dwarf planet Pluto is the largest known object in the Kuiper Belt. Another dwarf planet, Eris, is found beyond the belt. Neptune s moon Triton is thought to be a captured KBO. KBO s are sometimes disturbed by the gravitational influence of the outer planets. They enter the inner solar system in highly elliptical orbits and become short-period comets (orbit <200yrs) e.g. Halley s Comet which orbits every 75-76 years. A comet is a body of ice, rock and dust (a dirty snowball ). When it enters the inner solar system its nucleus becomes surrounded by a bright cloud of gas called a coma. Large comets also produce a long glowing tail of gas and dust as they come close to the Sun. Long-period comets (orbit >200 yrs) are thought to originate in the Oort Cloud, named after Dutch astronomer Jan H. Oort. This is a cloud of trillions of icy fragments orbiting from the edge of the Kuiper Belt (50 AU) 50,000 AU. Comet Hale-Bopp, which orbits every 2,320 years is a long-period comet.

MILKY WAY A galaxy is a giant rotating island of stars. The Milky Way Galaxy is a spiral galaxy with a central bar of stars - a barred spiral galaxy. It is the second biggest galaxy in our local group of around 30 galaxies, after the Andromeda galaxy. The Milky Way contains about 200 billion stars. The stars at the centre of the galaxy are the oldest and coolest stars and appear yellow/orange in colour. The stars in the outer arms of the galaxy are the younger, hotter stars and appear blue/white in colour. The galaxy is about 100,000 light years in diameter. Our Solar System is found about 26,000 LY from the centre in the Orion Arm. It takes the Sun 225 million years to complete one circuit of the galaxy. In 2004, astronomers in Chile determined that the galaxy was 13.6 billion years old, making it nearly as old as the Universe itself. The main disk of the galaxy is about 1000 LY thick. The central core of the galaxy contains a bulge of stars around 15,000 LY thick. We think that a supermassive black hole may lie here. The Milky Way is named after the faint milky band of light which can be seen stretching across a dark sky. Dark rifts on the band appear to contain no stars, but the starlight here is simply blocked out by interstellar dust.

EXOPLANETS An extra solar planet or exoplanet is a planet existing outside our Solar System. To date, over 250 exoplanets have been discovered. In 1995, the first exoplanet was discovered orbiting a star called 51 Pegasi. Unexpectedly, the planet appeared to be a gas giant like Jupiter. Astronomers were amazed to discover the planet orbiting so closely to its star that one orbit took only four days (Jupiter s orbit takes twelve years!) This illustrated that exoplanets are quite different to those in our Solar System, and prompted much more research into finding these strange worlds. In April 2007, Gliese 581c was reported in the press as being a potential New Earth. This planet may be located within its host star s habitable zone, meaning that water could exist in liquid form on the planet. Gliese 581c is thought to be 50% larger than Earth and almost 5 times its mass. We have no images of exoplanets as they are too distant, but astronomers can detect their presence by various means e.g. the wobbling effect the planet has on its parent star; and also by the transit of the exoplanet across the star, causing its light to dim slightly. These micro-eclipses will be observed by telescope on the COROT mission, launched in 2006, as it searches for rocky planets beyond our Solar System.