how old is the universe?? 12 billion years based on the age of the oldest observable stars based on...

How Old is the Universe??

12 Billion Years

Based on the age of the oldest observable stars

Based on the rate of expansion of the universe (Hubble constant)

The Big Bang

The Universe is expanding.Galaxies are observed to be moving away

from each other…There is no center, however…Space itself is expanding!

The Big Bang

Space was created at a single point and “inflated from there”.Massive explosion of matter and energy

coming into existence!The “afterglow” can still be detected, now

as weak microwave energy…

Formation of Solar SystemFormation of Solar System Nebular Hypothesis (Laplace, 18Nebular Hypothesis (Laplace, 18thth century) century)

Rotating sphere of gas flattens into spinning diskRotating sphere of gas flattens into spinning disk Contraction produces a protostar at the centerContraction produces a protostar at the center Material in surrounding disk becomes the planetsMaterial in surrounding disk becomes the planets

Problem: angular momentum…Problem: angular momentum… Sun is 99% of mass of solar systemSun is 99% of mass of solar system Planets have 99% of angular momentumPlanets have 99% of angular momentum Shouldn’t be that way… Sun should be spinning Shouldn’t be that way… Sun should be spinning

faster than once every 25 days (because it’s at faster than once every 25 days (because it’s at the center)the center)

Formation of Solar SystemFormation of Solar System

Where did all the stuff come from?Where did all the stuff come from?How old is all the stuff?How old is all the stuff?


Where did all the stuff come from?Where did all the stuff come from?Stars come from clouds of molecular Stars come from clouds of molecular

gas and dust.gas and dust.Masses from 0.08 Ms to 90 MsMasses from 0.08 Ms to 90 MsSolar systems like our own probably Solar systems like our own probably

limited to 1-3 Mslimited to 1-3 MsToo big – too violent and short-livedToo big – too violent and short-livedToo small – unlikely to ever form planets Too small – unlikely to ever form planets


How old is all the stuff?How old is all the stuff?

Age of meteorites = Age of meteorites =

Age of solar system = Age of solar system =

Age of earthAge of earth

How Old is the Solar System??

• 4.5-4.6 Billion Years

• Based on the age of meteorites made at the same time as the Sun and the planets

• Based on the age of the oldest rocks on the Earth and the Moon


Star forming nebula and circumstellar disksStar forming nebula and circumstellar disks

Birth of the Solar System

• Nebulae – clouds of gas and dust in interstellar space…


Dust to protostarsDust to protostars Dense clouds litter the galaxyDense clouds litter the galaxy Low temperature (10 K)Low temperature (10 K) High density (1000 to 1 million times greater than High density (1000 to 1 million times greater than

interstellar medium)interstellar medium) Rich collection of molecules (but mostly H)Rich collection of molecules (but mostly H) 10101515 km in diameter km in diameter 2000 or so in Milky Way2000 or so in Milky Way Favorable places for star formation (and, Favorable places for star formation (and,

therefore, perhaps planetary formation)therefore, perhaps planetary formation)


Dense clouds Dense clouds associated with associated with young stars young stars (“stellar (“stellar nurseries”)nurseries”)


Problem…Problem…Gravity. What does it do?Gravity. What does it do? ATTRACTSATTRACTS

So all clouds should eventually contract under So all clouds should eventually contract under their own gravity.their own gravity.

But they all don’t!But they all don’t!


Solution…Solution…Jean’s MassJean’s Mass

Gravity is counteracted by Gravity is counteracted by internal pressure of the cloud.internal pressure of the cloud.

Internal pressure comes Internal pressure comes about by temperature and about by temperature and density of a spherical clouddensity of a spherical cloud

There will be a balance There will be a balance between pressure and between pressure and gravity…gravity…

Until you exceed a certain Until you exceed a certain mass (Jean’s mass)mass (Jean’s mass)

Formation of Solar SystemFormation of Solar System Contracting dense cloud…Contracting dense cloud…

Becomes a disk because of angular momentumBecomes a disk because of angular momentum In plane of rotation, centripetal and gravitational forces In plane of rotation, centripetal and gravitational forces

are in equilibriumare in equilibriumNormal to plane of rotation, gravity and pressure Normal to plane of rotation, gravity and pressure

compete. Gravity wins, pulling material into diskcompete. Gravity wins, pulling material into disk Heats upHeats up

Gravitational energy converted to kinetic energy (and Gravitational energy converted to kinetic energy (and temperature) via collisionstemperature) via collisions

After few kyr, edge of cloud ~2000-3000 KAfter few kyr, edge of cloud ~2000-3000 KCloud becomes opaque at center (due to density), Cloud becomes opaque at center (due to density),

radiation is trapped, and gets hotterradiation is trapped, and gets hotterStar ignition temperature ca. 10Star ignition temperature ca. 1066 K achieved in 10 K achieved in 1088 yr yr

Formation of Solar SystemFormation of Solar System Violent early Violent early

phase…phase… Young protostars Young protostars

go through the “T-go through the “T-Tauri” phase where Tauri” phase where strong, bi-polar strong, bi-polar outflows of 50 km/s outflows of 50 km/s jets of material jets of material form.form.

protostar can loose protostar can loose up to 0.5 Ms within up to 0.5 Ms within 101066 yr yr


1.1. Dense cloud collapse (0.1 – 0.5 Ma)Dense cloud collapse (0.1 – 0.5 Ma)

2.2. Disc dissipation: some material Disc dissipation: some material transported toward protostar (0.05 Ma)transported toward protostar (0.05 Ma)

3.3. T-Tauri phase (1-2 Ma)T-Tauri phase (1-2 Ma)

4.4. Gas dissipation: planetary accretion & Gas dissipation: planetary accretion & residual nebula removed (3 – 30 Ma)residual nebula removed (3 – 30 Ma)

• What about angular momentum problem…?Viscous drag: particles in disc interact, stealing/transferring

some angular momentum from star (slowing its spin) towards edges


Star with a disk around it… now what?Star with a disk around it… now what?


CondensationCondensationCoagulationCoagulationPlanetesimalsPlanetesimalsPlanetary growthPlanetary growthPlanetary migrationPlanetary migrationSatellites, rings, asteroids, cometsSatellites, rings, asteroids, comets

Formation of Solar SystemFormation of Solar System CondensationCondensation

Away from star, disk will be relatively cool (400 K at Away from star, disk will be relatively cool (400 K at 4.5 AU, 3000 K at 1 AU) and material will form 4.5 AU, 3000 K at 1 AU) and material will form compounds/minerals (not necessarily solid, though)compounds/minerals (not necessarily solid, though)

HH22OOCHCH44

FeSFeSAlAl22OO33

CaMgSiCaMgSi22OO66


Temperature Temperature is key…is key…Refractory: Refractory:

condense at condense at high Thigh T

Volatile: Volatile: condense at condense at low Tlow T

A Planetary Nursery

• Protoplanetary disk cools over time...• The temperature also decreases away from

Sun…• Elements condense depending on

temperature…1. Ca, Ti, Al (first and close to the sun)2. Fe, Ni, Si3. water, ammonia, methane (last and further

away)

• …Inner planets are rocky & outer planets are gas and ice.


Now we have particles of condensed stuff Now we have particles of condensed stuff colliding with one another. What colliding with one another. What happens?happens?

Formation of Solar SystemFormation of Solar System They break.They break.

If collisions violent enoughIf collisions violent enough

They bounce.They bounce. Elastic interactionsElastic interactions

They stick.They stick. This is coagulationThis is coagulation By magnetism? Static electricity? Friction? Fluffy By magnetism? Static electricity? Friction? Fluffy

particles with lots of cavities (e.g. velcro effect)?particles with lots of cavities (e.g. velcro effect)?

Formation of Solar SystemFormation of Solar System Coagulation will occur rapidly…Coagulation will occur rapidly…

10 mm particles at 1 AU in 2 kyr10 mm particles at 1 AU in 2 kyr 15 mm particles at 5 AU in 5 kyr15 mm particles at 5 AU in 5 kyr 0.3 mm particles at 30 AU in 50 kyr0.3 mm particles at 30 AU in 50 kyr

What limits rate (so that takes longer to happen What limits rate (so that takes longer to happen further out)?further out)?

1.1. Density (e.g. column mass) – decreases outward Density (e.g. column mass) – decreases outward from Sunfrom Sun

2.2. Number of collisions/time (density dependent)Number of collisions/time (density dependent)3.3. Thickness of disk (thicker away from Sun) Thickness of disk (thicker away from Sun)

determines timescale for particles to get to midplanedetermines timescale for particles to get to midplane


Remember T-Tauri stage… it could blow Remember T-Tauri stage… it could blow particles up to 10 m out of the solar particles up to 10 m out of the solar system.system.

So we have to get up to this size and So we have to get up to this size and larger before ca. 1 Ma!larger before ca. 1 Ma!

Coagulation can’t do it, though.Coagulation can’t do it, though.

Formation of Solar SystemFormation of Solar System How do you get 0.1 to 10 km planetesimals?How do you get 0.1 to 10 km planetesimals?

Gather coagulants into turbulent knots in thinning Gather coagulants into turbulent knots in thinning diskdisk

Gravity draws material together (focusing) in Gravity draws material together (focusing) in collisions that have a net effect of collisions that have a net effect of accretionaccretion (rather than dispersal)(rather than dispersal)

At given distance from Sun, runaway growth will At given distance from Sun, runaway growth will promote development of one or two dominant promote development of one or two dominant planetary embryos that sweep up all materialplanetary embryos that sweep up all material


Planetary growth in inner solar systemPlanetary growth in inner solar systemEmbryo growth is self limiting as material Embryo growth is self limiting as material

used upused upEmbryos every 0.02 AU formed by time of T-Embryos every 0.02 AU formed by time of T-

Tauri stageTauri stageEmbryos about 0.1 mass of eventual planetsEmbryos about 0.1 mass of eventual planetsSubsequent interactions (collisions) take 10Subsequent interactions (collisions) take 1077--

101088 yr to complete planet formation yr to complete planet formation

Formation of Solar SystemFormation of Solar System Planetary growth in outer solar systemPlanetary growth in outer solar system

Larger rock-ice embryos up to 5 MeLarger rock-ice embryos up to 5 Me Takes 10x as long to form as in inner solar Takes 10x as long to form as in inner solar

systemsystem Embryos get large enough to gravitationally trap Embryos get large enough to gravitationally trap

volatiles e.g. H, He, etc.volatiles e.g. H, He, etc. T-Tauri stage eventually begins, removing T-Tauri stage eventually begins, removing

remaining, unbound H and Heremaining, unbound H and He Sizes of outer planets determined by amounts of Sizes of outer planets determined by amounts of

H and He present at those distances (and H and He present at those distances (and amount of time available for accumulation before amount of time available for accumulation before removed)removed)

From Grains to Giants

• We need to go from tiny grains to planets…How?

• Accretion, a 4-stage process:

1. Micron-sized particles stick together electrostatically 1 cm sized.

2. Inelastic collisions 1 km sized planetesimals.

3. “Sweep up” by dominant object in an orbit 1000 km size planetesimals.

4. Gravitational accretion observed sizes.

Differentiation

• Sufficient sources of heat for bodies larger than few 100 km to melt interiors (ca. 1000° C):• Internal gravitational pressure• Radioactive decay heating• Residual heat & impact (minor contributions)

• “Fe catastrophe” and magma ocean• Heavy elements fall to center and release huge

amounts of gravitational potential energy.• Raised temps to 2000° C

Formation of Solar SystemFormation of Solar System New, controversial idea… radii of planetary orbits can New, controversial idea… radii of planetary orbits can

change over time!change over time! By 2-30 % (in or out) over 0.1 GaBy 2-30 % (in or out) over 0.1 Ga

Why might this be true?Why might this be true?1.1. Discovery of icy, minor planets out to 60+ AUDiscovery of icy, minor planets out to 60+ AU2.2. Discovery of extrasolar planets size of Jupiter close to their Discovery of extrasolar planets size of Jupiter close to their

starstar3.3. Volatiles in Jupiter atmosphere consistent with formation at Volatiles in Jupiter atmosphere consistent with formation at

lower T (e.g. further from Sun) than present position lower T (e.g. further from Sun) than present position impliesimplies

4.4. Orbits of satellites demonstrably change over time (e.g. Orbits of satellites demonstrably change over time (e.g. Moon), so why not that of planets around Sun?Moon), so why not that of planets around Sun?


Satellites, rings, asteroids, cometsSatellites, rings, asteroids, cometsPresence of Jupiter and orbital resonance Presence of Jupiter and orbital resonance

greatly affected distribution of asteroidsgreatly affected distribution of asteroidsJupiter (and other giant planets) affected Jupiter (and other giant planets) affected

orbits of cometsorbits of cometsGravitational focusing affected impact Gravitational focusing affected impact

histories of all planetshistories of all planetsProtosatellite disks, capture, and giant Protosatellite disks, capture, and giant

impacts lead to formation of moons and ring impacts lead to formation of moons and ring systemssystems

Birth of the Solar System

1. Gravity causes gas and dust to contract.

2. Temperature increases and cloud begins to rotate.

3. Cloud eventually flattens into disk.

4. 90% of mass concentrates to center.

5. Sun ignites (106 °C).

6. Planets form…

The Solar System

Includes the Sun, the planets, satellites of Includes the Sun, the planets, satellites of the planets, small bodies (comets, the planets, small bodies (comets, asteroids, KBOs, etc.asteroids, KBOs, etc.

The Solar System

Comparisons

The Sun

• 1 million km wide ball of H, He undergoing nuclear fusion. Contains 99% of the mass in the whole solar system! Would hold 1.3 million earths!

• 386 billion billion megawatts of power produced. 15 minutes of this is equivalent to all the energy consumed by humans in 1 year.

• 4 million tons of H are consumed every second, but there is enough to burn for another 5 billion years!

The Sun

• Surface temperature about 5800 degrees• Core temperature about 15 million degrees• Core pressure about 150 billion atmospheres

The Sun

• Intense magnetic field extends all the way to outer solar system!

• Magnetic fields get twisted by differential rotation of Sun…

• Causes intense solar activity.

The Sun

• In addition to light and heat energy, the Sun produces a stream of plasma (charged particles) called the solar wind.

The Inner Planets

The Asteroid Belt Rocky (93%) and metallic Rocky (93%) and metallic

(7%) objects left over from (7%) objects left over from solar system formation.solar system formation.

Most confined to a belt Most confined to a belt between Mars and Jupiter. between Mars and Jupiter. Some are in Jupiter orbit. Some are in Jupiter orbit. Some cross Earth’s orbit.Some cross Earth’s orbit.

Many of them, but lots of Many of them, but lots of empty space between them. empty space between them. All combined would be an All combined would be an object only 1500 km across.object only 1500 km across.

Largest is Ceres (1000 km)Largest is Ceres (1000 km)

The Outer Planets

Comets Icy objects with highly Icy objects with highly

elliptical orbits that elliptical orbits that bring them close to the bring them close to the Sun and then far out Sun and then far out beyond Pluto.beyond Pluto.

Solar radiation causes Solar radiation causes the ice to volatilize in the ice to volatilize in the inner solar system.the inner solar system.

Tail is blown by the Tail is blown by the solar wind and points solar wind and points away from the sun.away from the sun.

The Kuiper Belt and Oort Cloud

What is a Planet?

Kuiper Belt and Oort cloud may contain Kuiper Belt and Oort cloud may contain objects larger than Pluto!objects larger than Pluto!

Pluto’s orbit is strange and it is very small.Pluto’s orbit is strange and it is very small.

Some debate about whether Pluto should be Some debate about whether Pluto should be classified as a planet at all!classified as a planet at all!

How does one define a planet??How does one define a planet??

how old is the universe?? 12 billion years based on the age of the oldest observable stars based on...

Documents

age of solar system

mass of solar systemplanets

age of meteorites

age of earthhow old

protostarsdense clouds

clouds of molecular

internal pressure

galaxylow temperature