Phys 214. Planets and Life

Dr. Cristina Buzea

Department of Physics

Room 259

E-mail: cristi@physics.queensu.ca

(Please use PHYS214 in e-mail subject)

Lecture 8.

The scale of time and nature of worlds

(Page 64-74)

January 23

Contents

Textbook: Pages 64-74

• The scale of time - the cosmic calendar

• The Observable Universe

• The nature of worlds

• How do other worlds in the Solar System compare to Earth

• Acknowledgment: images NASA, ESA, Hubble, NOAO, AURA, NSF

The cosmic calendar

The Universe is 14 billion years old.The Universe is 14 billion years old.

14,000,000,000

How do we grasp the meaning of this number?

Let’s imagine we compress the entire history of the Universe, from the Big Bang

to present, into a single year –

THE COSMIC CALENDAR

The cosmic calendar

Jan 1 Jan 1 –– The Big Bang The Big Bang

Feb Feb –– The Milky Way The Milky Way

Many generations of stars livedand died in the subsequentmonths, enriching the galaxywith heavier elements.

Sept Sept –– Solar System & Earth Solar System & Earth

(about 4.5 billion years ago)

Sept 22 Sept 22 –– early life on Earth early life on Earth

(more than 3.5 billion years ago)living organisms remainedmicroscopic in size until Dec17.

The Big Bang is on Jan 1st, and the present is the stroke of midnight on Dec 31.

Each month is a little more than one billion years, each day ~ 40 million years,

each second more than 400 years.

The cosmic calendar

Dec 17 Dec 17 –– Cambrian explosion Cambrian explosion

(545 million years ago)

Incredible animal diversity

Dec 26 Dec 26 –– Rise of dinosaurs Rise of dinosaurs

Dec 30 Dec 30 –– Dinosaurs extinction Dinosaurs extinction

(65 million years ago)

The death of dinosaurs allowed other

species to evolve.

Dec 31, 9 pm Dec 31, 9 pm –– early hominids early hominids

(human ancestors) 60 million years

later after dinosaurs extinction…

The cosmic calendar

Dec 31, 11:58 pm Dec 31, 11:58 pm –– Modern humans evolve Modern humans evolveThe entire history of human civilization fits into just the last half-minute!

The scale of time

The fact that the Universe is so much older than Earth means thatcould be many worlds that had plenty of time for life to ariseand evolve.

These worlds might have had civilizations millions or billions ofyears ago.

The scale of time holds sobering lessons for our own future.

Species have come and gone in the months of the cosmiccalendar, and there is no reason to think that our fate shouldbe different.

How big is the Universe?

The Universe could be infinite, and contain an infinite number of galaxies.

The age of the universe poses some limitations on the portion of the universe that

we can observe with telescopes, due to the limited value of the speed of light.

When we look to great distances, we are also looking far back into the past.

The observable Universe

• Andromeda located 2.5 million light-years away. The photo shows the galaxy

as it was 2.5 million years ago, long before modern humans existed.

• It takes 200 million years to rotate once. Probably looks similar today.

• However, at much greater distances we begin to see back to a time when the

universe looks different than today.

Andromeda (M31)

The observable Universe

Beyond the observable universe: We cannot see anything farther away than 14Beyond the observable universe: We cannot see anything farther away than 14

billions light-years away, because its light has not had enough time to reach us.billions light-years away, because its light has not had enough time to reach us.

FAR:FAR: We see a galaxy 7 We see a galaxy 7

billions light-years away asbillions light-years away as

it was 7 billion years ago,it was 7 billion years ago,

when the Universe was halfwhen the Universe was half

its current age of 14 billionsits current age of 14 billions

years old.years old.

FARTHERFARTHER: We see a: We see a

galaxy 12 billions light-galaxy 12 billions light-

years away as it was 12years away as it was 12

billion years ago, whenbillion years ago, when

the Universe was about 2the Universe was about 2

billions years old.billions years old.

The limit of our observableThe limit of our observable

universe:universe: Light from nearly Light from nearly

14 billion light-years away14 billion light-years away

shows the universe as itshows the universe as it

looked shortly after the Biglooked shortly after the Big

Bang, before galaxiesBang, before galaxies

existed.existed.

The observable Universe

Our observable universe - the portion of the entire universe that we can potentially

observe – lie within 14 billion light-years of Earth.

Implications:

1) We cannot observe anything more that 14 billion light-years away.

This does not mean that nothing exists beyond that distance or that the universe

might not be infinite.

2) We are the center of our observable universe, since it is defined by a light-travel

distance in all directions from us.

This does not implies we are the center of the Universe.

Every observer in another part of the universe must be at the center of his

observable universe.

Movie

• Hubble 15 years of discovery

• Chapter 9. Looking to the end of time (9 minutes + credits ~15 min)

Number of galaxies in the observable universe

Because the observable

universe has a finite size, it

must contain a finite

number of galaxies.

We do not know how many,

because there are too many

to count and some galaxies

are too faint to be observed.

By counting the galaxies in the

photo, the observable

universe has an estimate of

about 100 billion galaxies.

Hubble Ultra-Deep Field.

More than 10 days of exposure, it shows galaxies some at more than 12 billion light-years away.

Number of stars in the observable universe

The Universe has an estimate of 100 billion galaxies.The Universe has an estimate of 100 billion galaxies.

Milky Way has an estimate of 100 billion stars.Milky Way has an estimate of 100 billion stars.

100 billion x 100 billion =

10,000,000,000,000,000,000,000=

1022 stars

The number of stars in the observable Universe is comparable to theThe number of stars in the observable Universe is comparable to the

number of grains of sand on every beach on Earth.number of grains of sand on every beach on Earth.

Due to the incredible size of the universe, our search for extraterrestrial lifeDue to the incredible size of the universe, our search for extraterrestrial life

will probably be limited to within our Milky Way.will probably be limited to within our Milky Way.

The nature of worlds - solar system

The solar system

(1) All the planets orbit within a few degrees of the equatorial plane(1) All the planets orbit within a few degrees of the equatorial planeof the Sunof the Sun

(2) Most of the planets have a rotation axis roughly perpendicular(2) Most of the planets have a rotation axis roughly perpendicularto the plane of the solar systemto the plane of the solar system

Both Pluto and Uranus have rotations that are highly inclinedBoth Pluto and Uranus have rotations that are highly inclinedto the plane of the solar systemto the plane of the solar system

(3) Planets are divided into rocky (terrestrial), gas giants(3) Planets are divided into rocky (terrestrial), gas giants

Two major type of planets

Terrestrial planets - small, made mostly of rock & ironTerrestrial planets - small, made mostly of rock & ironwith high densities, near the Sun.with high densities, near the Sun.

Jovian Jovian planets -large, made mostly of gases and liquidsplanets -large, made mostly of gases and liquidswith low densities, far from the Sunwith low densities, far from the Sun

Terrestrial planets

• All are similar in overall

composition, however

their surface looks quite

different.

•• Small,Small,

•• made mostly of rock &made mostly of rock &

iron,iron,

•• high densities,high densities,

•• close to the Sun (< 5AU),close to the Sun (< 5AU),

•• no ringsno rings

Jovian planets - gas giants

-- LargeLarge-- Made mostly of gases with aMade mostly of gases with a

rocky corerocky core-- Low densitiesLow densities-- Far from the Sun (> 5AU)Far from the Sun (> 5AU)-- Have ringsHave rings

Jupiter- failed star

-miniature solar system

many moons

Jovian planets - gas giants

The pressure inside is so high that the gases are compressed into liquid andThe pressure inside is so high that the gases are compressed into liquid and

metallic phases = large magnetic fieldsmetallic phases = large magnetic fields

Less likely to be habitable if we assume life needs a solid surface or oceans.Less likely to be habitable if we assume life needs a solid surface or oceans.

When we are looking for habitable planets in other star systems we should lookWhen we are looking for habitable planets in other star systems we should look

for terrestrial planets.for terrestrial planets.

Gas giants - Jupiter

Gas giants - Jupiter

Gas giants - Saturn

Gas giants - Saturn

North pole South Pole

Saturn dragon eye storm

Gas giants - Uranus and Neptune

Dwarf planets and small bodies orbiting the SunDwarf planets and small bodies orbiting the Sun

The Solar Systems goes beyond Neptune -the outermost of the official planets.

Pluto counted as a ninth planet until 2006; orbits at a distance about a third farther

from the Sun than Neptune.

There are thousands of icy objects sharing Pluto’s region.

An object larger than Pluto was discovered in 2005 – Eris (Xena).

Dwarf planet - object large enough for their own gravity to make them round.Dwarf planet - object large enough for their own gravity to make them round.

Small body Small body –– object low enough in mass to take any other shape than round. object low enough in mass to take any other shape than round.

True Colours of Pluto

Small bodies orbiting the Sun - asteroids

Asteroids Asteroids –– made mostly of metal and rock. made mostly of metal and rock.Asteroids resemble a terrestrial planet in

composition, but are too small to count as aplanet itself.

Eros (image 12 m across)

Gaspra (Galileo spacecraft 1991)

Small bodies orbiting the Sun - asteroids

Asteroids Asteroids –– made mostly of metal and rock. made mostly of metal and rock.Asteroids resemble a terrestrial planet in

composition, but are too small to count as aplanet itself..

Asteroid Itokawa, copyright ISAS, JAXA

Small bodies orbiting the Sun - comets

Comets Comets –– made mostly of rock and ice. made mostly of rock and ice.

Comets grow tail when they come close

to the Sun.

Comet Neat, 2004

Comet Machholz

Small bodies orbiting the Sun - comets

Comet Neat, 2004

Comet Wild 2's Heart

Comet C/2002 T7

Small bodies orbiting the Sun

Most asteroids orbit in the region called the asteroid belt, whichMost asteroids orbit in the region called the asteroid belt, which

lies between the orbits of Mars and Jupiter.lies between the orbits of Mars and Jupiter.

Comets come from theComets come from the Kuiper Kuiper belt and thebelt and the Oort Oort could.could.

Small bodies orbiting the Sun

TheThe Kuiper Kuiper belt isbelt is

immediatelyimmediately

beyond the orbit ofbeyond the orbit of

the planetthe planet

Neptune.Neptune.

The Oort cloud – is ar

from the Sun in a

spherical cloud

surrounding the

solar system.

Small bodies orbiting the Sun

Small bodies orbiting the Sun

Pluto is a member of thePluto is a member of the

Kuiper Kuiper belt, along withbelt, along with

many of other moderatelymany of other moderately

large objects.large objects.

These objects are unusually

large comets, having the

same composition with

smaller comets that

occasionally fall inward

towards the Sun.

Small bodies orbiting the Sun

• Jupiter role in reducing space debris in the inner solar system - cosmic vacuumcleaner

• discovered in March 24, 1993 by the Shoemakers and Levy

• Unlike all other comets, it was orbiting Jupiter rather than the Sun

Could dwarf planets or small bodies be habitable?Could dwarf planets or small bodies be habitable?

Probably not. They are too far away from

the Sun and are too cold for liquid

water to exist.

They are important to life because they

occasionally crash into planets and

moons and have a profound effect on

the living organisms that inhabit the

planet.

Moons

Terrestrial planets havefew moons.Mercury andVenus have nomoons at all. Marshas two very smallmoons, probablycaptured asteroids.

Moons are common forJovian planets,totalling at least150 moonstogether.

Moons

Jupiter moon Ganymede andJupiter moon Ganymede and

Saturn moon Titan areSaturn moon Titan are

larger than planet Mercury.larger than planet Mercury.

Saturn’s moon Titan (2,575 km) Mercury (2,440 km radius)

Jupiter Moons: Ganymede (2,634 km), Callisto (2,403 km), Io (1,821 km), Europa (1,565 km)

Moons

Io (1,821 km), Europa (1,565 km), Titan (2,575 km)

Many moons are planetlike in almost every way except their orbits.Some moons are geologically active, others have water, other atmosphere.

Io is the most volcanically active world in the Solar System.Europa has occasionally water or ice floating on its surface.

Titan has an atmosphere thicker than the Earth.

Large moons aroundLarge moons around jovian jovian planets offer a second category (after terrestrialplanets offer a second category (after terrestrialplanets) of potentially habitable worlds.planets) of potentially habitable worlds.

Next lecture

• Nebular theory - the formation of the solar system

• + movie