Our local neighbourhood - The Solar System

Dr Nicola LoaringSALT/SAAO

nsl@saao.ac.za

Concept: The Scale of our Solar

SystemIf the Sun were a grapefruit (10cm)Earth, grain of sand 1mm, 15 m away Jupiter, marble 1.5cm, 80 m awayPluto, tiny grain of sand 0.2mm, 700 m away

And the NEXT CLOSEST sun (or star) would be in ... Nairobi !

DEMO

Concept: Two types of Planet

Terrestrial planets:Rocky with molten cores

Jovian planets: Mainly gas and liquid with rocky cores

The rocky worlds are the 4 inner planets plus our Moon

They have a solid rock surface with an iron core and a weak or no atmosphere.

Rocky Planets

There are 4 gas giant planets in our solar system.

These planets have NO solid surfaces – just gas and clouds that get denser as you move to their centre.

Gas Giants

Rocky worlds

are close to the Sun

Gas giant worlds are far from the Sun

Relative distribution of the two types of Planets

Wikipedia

Jupiter – largest gas giant world

Earth – largest rocky world

Gas giant worldsare much larger than rocky worlds

Relative sizes

NASA/JPL

Activity opportunity: Powers of 10

Body RadiusSurface

AreaVolume

Earth 1 1 1

Jupiter 10x [101]100x [102]

1000x [103]

Sun 100x 10,000x1,000,00

0x

Rocky worlds have no rings and no, or few, moons.Gas Giant worlds have

rings and many moons.

(From left to right: Enceladus and shadow, Dione and shadow. Titan and Mimas are off the limb to the right).

Relative numbers of rings and moons

www.hubblesite.org

Why are there two types of planet?

Solar System Formation

All orbits are in the same direction and in the same plane.

Suggests a common origin.

Solar system formed when a cloud of gas and dust in space was disturbed. Gas and dust drawn together, forming a solar nebula.

The cloud began to spin as it collapsed and therefore flattened.

As the disk got thinner particles formed clumps, planetisimals eventually forming planets or moons.

As the cloud continued to fall in, the centre eventually got so hot that it became a star, the Sun. Solar wind then blew away excess material.

Why are there 2 types of planet?

Inside the frost line: Too hot for hydrogen compounds to form ices.Outside the frost line: Cold enough for ices to form.

Inner parts of disk are hotter than outer parts. Only materials that solidify at high temperatures can condense to form solid particles. Rock can be solid at much higher temperatures than ice.

Density and Composition

Earth 5.5 g/cm3 composition- iron, rock

Saturn 0.7 g/cm3 composition- some rock, volatiles and lots H & He

Callisto 1.9 g/cm3, Titan 2 g/cm3 composition -rock and ice

DEMO

Asteroids and Comets

Leftovers from the accretion process

Rocky asteroids inside frost line

Icy comets outside frost line

The inner rocky Planets- MercuryHas the largest temperature

extreme in the solar system from -183C to 430C.

Second densest planet after the Earth, so must have a large iron core.

Has a very thin atmosphere consisting of atoms blasted off its surface from the solar wind. Atmosphere is constantly being replenished. Heavily cratered surface because its atmosphere is so thin. DEMO

Mission Launch Year

Mariner 10 1973

Messenger 2004 (to orbit 2011)

BepiColombo 2013 (to arrive 2019)

The inner rocky Planets -Venus

Venus is a similar size to the Earth.It atmosphere is mainly Carbon dioxide and Nitrogen.Its very hot there due to the ‘Green house effect’ a whopping 462C.

Recent Missions Launch Year

Galileo 1989 (flyby 1990)

Magellan1989 (in orbit 1990-

1994)

Cassini1997 (flyby 1998,

1999)

Venus Express 2005 (arrive 2006)

Messenger2004 (flyby 2006,

2007)

Planet C 2010

Our home the Earth

Earth is at a distance of 150 million kilometres from the Sun. Sunlight takes 8 minutes to reach us.

Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents.

71% of the Earth’s surface is covered by water!

Earth is the only planet in the solar system known to harbour life.

Picture taken by Apollo 17 astronauts

The Moon

Heavily cratered.

Evidence for water.

Mission Launch Year

Apollo manned missions 1968 - 1972

Lunar Prospector 1998

SMART-1 2003

SELENE (JAXA) 2007

Chandrayaan-1 2008

LRO 2009

LCROSS 2009

The inner rocky Planets - Mars

Mars is 1/10th the mass of Earth

Average temp is –63C

Rock are made of silicates (like sand) and also a dash of iron oxides to give it that reddish colour (Mars is rusty!)

Surface is dry now, but scientists believe there were once rivers, lake and maybe oceans of water

Water exists in “permafrost” a few metres below the surface (Mars Express / Mars Odyssey). Maybe even liquid water down there! (MGS).

No landers have detected water in soil, but have found evidence of past water.

Mars

Mars has the highest (extinct) volcano in the Solar System: Olympus Mons at 24 km high 2.7 times Everest!

Recent Missions Launch Year

Viking 1 1975 (landed 1976)

Viking 2 1975 (landed 1976)

Mars Global Surveyor 1996 (arrived 1997)

Mars Pathfinder 1996 (arrived 1997)

Mars Express 2003 (still active)

Spirit / Opportunity 2003 (still active)

Phoenix 2007 (till 2008)

ExoMars 2016?

Mars Sample Return Mission 2020?

The gas giants -JupiterLargest planet in the solar system – its diameter is 11x the Earth’s diameter.

Jupiter takes about 12 years to orbit the sun and rotates in about 10 hours.

Jupiter is a ball of dense hydrogen, helium, water, nitrogen and other gases over a rocky core. ~90% H, ~10% He.

Above core is the main bulk of the planet which is liquid metallic hydrogen. (Huge pressure). Ionized protons and electrons in liquid form.

Powerful winds, jet streams, lightning and huge hurricane-like storms like the Great Red Spot.

This storm has been raging for over 300 years and is twice the size of Earth!

Mission Launch

Pioneer 11 1974 (arrived 1979)

Voyager 1 1977 (arrived 1980)

Voyager 2 1977 (arrived 1981)

Galileo1989 (arrived 1990, still

operational)

This image shows, from left to right, the outer portion of the C ring and inner portion of the B ring. The B ring begins a little more than halfway across the image. The general pattern is from "dirty" particles indicated by red to cleaner ice particles shown in turquoise in the outer parts of the rings.

Cassini and Saturn

95 times the Earth’s mass.

Saturn, famous for its rings. These are made up of trillions of icy particles.

1015 tons of material in the rings, enough for a small moon!

No more than 50 million years old (MUCH younger than the planet) - continually replenished

Mission Launch Date

Pioneer 11 1973 (flyby 1979)

Voyager 1 1977 (encounter 1980)

Voyager 2 1977 (encounter 1981)

Cassini-Huygens1997 (orbiting 2004, Titan descent 2005 - orbiter still

operational)

Titan's surface in2004-2005!

Titan

Liquid ethane/methane on surfaceLots of hydrocarbons

Uranus Primarily composed of rock and ices with only 15% H (much less than Jupiter and Saturn).

No rocky core like Jupiter and Saturn, but material is more evenly distributed.

No liquid metallic hydrogen envelope.

Atmosphere of 83% H, 15% He, 2% methane.

Mission Launch Date

Voyager 21977 (encounter 1985-

1986)

NeptuneComposed of ices and rock with about 15% H and a little He

Atmosphere mainly H and He with a little methane which gives it its blue colour as methane absorbs red light

Small solid core, the size of the Earth

No distinct layers like Uranus (unlike Saturn and Jupiter)

Neptune has the fastest winds in the solar system reaching 2000 km/hr

Mission Launch Date

Voyager 2 1977 (flyby 1989)

The IAU definition of a planet (2006): is in orbit around the Sun, has sufficient mass so that it is nearly round has "cleared the neighborhood" around its orbit.

What Counts as a Planet?

Mission Launch

New Horizons 2006 (to arrive 2015)

The IAU currently recognises five dwarf planets—Ceres, Pluto, Haumea, Makemake, and Eris.

Ceres is in the asteroid belt others in the Kuiper belt.

Many Kuiper Belt objects, exist in what is believed to be a vast shell of icy and rocky objects that live at the very edge of our solar system.

Dwarf Planets