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Exploring Our Solar System and Its Origin
Chapter 4: Exploring Our Evolving Solar System
SN solar system..\..\..\astronomy\animations\starry night files\solar system.snf
The planets are tiny compared to the distances between them (a million times smaller than shown here), but theyexhibit clear patterns of composition and motion.
The patterns are far more important and interesting than numbers, names, and other trivia
Sun
• Over 99.9% of solar system’s mass• Made mostly of H/He gas (plasma)• Converts 4 million tons of mass into energy each second
Mercury• made of metal and rock; large iron core • desolate, cratered; long, tall, steep cliffs• very hot and very cold: 425°C (day), –170°C (night)
Venus• nearly identical in size to Earth; surface hidden by thick clouds • hellish conditions due to an extreme greenhouse effect:• even hotter than Mercury: 470°C, both day and night• atmospheric pressure equiv. to pressure 1 km deep in oceans• no oxygen, no water, …• perhaps more than any other planet, makes us ask: how did it end up so different from Earth?
Earth• An oasis of life• The only surface liquid water in the solar system; about 3/4 of surface covered by water• A surprisingly large moon
Earth and Moon to scale
Earth and Moon to scale
Mars• Looks almost Earth-like, but don’t go without a spacesuit!• Giant volcanoes, a huge canyon, polar caps, more…• Water flowed in the distant past; could there have been life?
Jupiter
• Much farther from Sun than inner 4 planets (more than twice Mars distance)• Also very different in composition: mostly H/He; no solid surface.• Gigantic for a planet: 300 Earth mass; >1,000 Earth volume. • Many moons, rings…
Great Red Spot
SATURN Giant and gaseous like Jupiter• most spectacular rings of the 4 jovian planets• many moons, including cloud-covered Titan• currently under study by the Cassini spacecraft
Uranus
• much smaller than Jupiter or Saturn, but still much larger than Earth• made of H/He gas, and hydrogen compounds (H2O, NH3, CH4) • extreme axis tilt — nearly tipped on its “side” — makes extreme seasons during its 84-year orbit.• moons also tipped in their orbits…
Wispy white clouds are thought to be crystals of methane.
Neptune
• Very similar to Uranus (but much smaller axis tilt)• Many moons, including unusual Triton: orbits “backward”; and is larger than Pluto.
Pluto• A “misfit” among the planets: far from Sun like large jovian planets, but much smaller than any terrestrial planet.• Comet-like composition (ices, rock) and orbit (eccentric, inclined to ecliptic plane, long -- 248 years).• Its moon Charon is half Pluto’s size in diameter• Best current photo above;
New Horizons mission launch Jan 2006, arrival at Pluto in 2015…
*100,000+ rocky objects within the orbit of Jupiter *Also called minor planets*The largest, Ceres, has a diameter of about 900 km or ~ (560 mi) *Orbit the Sun in the same direction as the planets*Most orbit the Sun at distances of 2 to 3.5 AU, in the asteroid belt
Asteroids
TNOs - Trans-Neptunian Objects
*1,000+ small bodies orbiting beyond the orbit of Neptune *The largest of these are known as dwarf planets *Include Pluto, Eris, Charon, Makemake, etc.*Orbit the Sun in the same direction as the planets*Most orbit within the Kuiper belt at 30 AU to 50 AU
Comets
•Objects that result when Kuiper belt objects collide•Fragments a few kilometers across, diverted into new and elongated orbits •The Sun’s radiation vaporizes ices, producing tails of gas and dust particles•Astronomers deduce composition by studying the spectra of these tails created by reflected sunlight•Oort cloud comets orbit out to 50,000 AU
Clues to the Formation of Our Solar System
Our Goals for Learning• What features of our solar
system provide clues to how it formed?
• What theory best explains the features of our solar system?
Common Properties of Planet Orbits in Our Solar System
As viewed from above, all of the planets orbit the Sun in a counter-clockwise direction.
The planets orbit in nearly the same plane. All planets except Pluto have an orbital inclination of less than 7°.
Terrestrial Jovians
Smaller Mass and size
higher density
made of rock and metal
Have solid surfaces
few moons
no rings
Closer to Sun and closer together
Larger mass and size
low density
mostly H, He, & hydrocarbon compounds
No solid surface
many moons
rings
Farther from sun and farther apart
Rocky asteroids between Mars & Jupiter
Icy comets in vicinity of Neptune and beyond
Asteroids and comets far outnumber the planets and their moons
A successful theory of solar system formation must allow for exceptions to general rules
Summary: Four Major Features of our Solar System
10
Classifying the PlanetsThe planets (except Pluto) fit into two groups:The Terrestrials or Inner Planets:
Mercury
Venus
Earth
Mars
The Jovians or Outer Planets:
Jupiter
Saturn
Uranus
Neptune
Size, Mass, and DensityThe Jovian planets have much bigger diameters and even larger masses than the terrestrial planets.
Though less massive than the Jovians, Terrestrial planets are
much more dense.
Again, with the exception of ODD BALL Pluto, the rotation rates of Jovian planets on their axes are much faster than the Terrestrial planets.
Despite these fast rotation rates, the diameters of the
Jovian planets are tremendously larger than
those of the Terrestrial Planets.
What theory best explains the features of our solar
system?
According to the nebular theory our solar system formed from a giant cloud of interstellar gas
(nebula = cloud)
The lightest and simplest elements, hydrogen and helium, are abundant in the universe. Heavier elements, such as iron and silicon, are created by thermonuclear reactions in the interiors of stars, and then ejected into space by those stars.
Ejection of Matter from StarsEjection of Matter from Stars
FORMATION OF PLANETARY NEBULA
SUPERNOVA EXPLOSIONS
LARGE STAR NEAR THE END OF ITS LIFE
Great clouds of gas and dust ejected from old stars are gathered into regions from which new stars can be made.
This region in the constellation of Orion shows new stars still surrounded by the nebula from which they were formed.
Summary of the Nebular Model for formation of the solar system.
Other Star Systems Forming
We can look at young star systems developing today. The planets orbiting these stars are formed from the surrounding disks of gas and dust, called protoplanetary disks or proplyds.
PLANET FORMATIONPLANET FORMATION
Within the disk that surrounds the protosun, solid grains collide and clump together into planetesimals.
The terrestrial planets are built up by collisions and the accretion of planetesimals by gravitational attraction.
The Jovian-like planets are formed by gas accretion.
Common Properties of Common Properties of Planet Orbits in Our Planet Orbits in Our Solar SystemSolar System
As viewed from above, all of the planets orbit the Sun in a counter-clockwise direction.
The planets orbit in nearly the same plane. All planets except Pluto have an orbital inclination of less than 7°.
Why are there two types of planets?
1. Outer planets get bigger because abundant hydrogen compounds condense to form ICES.
2. Outer planets accrete and keep H & He gas because they’re bigger.
3. Inner planets too hot, gases evaporate
Inside the frost line: too hot for hydrogen compounds to form ices.
Outside the frost line: cold enough for ices to form.
Fig 9.5
Inner parts of disk are hotter than outer parts.
Rock can be solid at much higher temperatures than ice.
Four Unexplained Features of our Solar System
√ Why do large bodies in our solar system have orderly motions?
√ Why are there two types of planets?
--> 3) Where did the comets and asteroids come from?
4) How can we explain the exceptions the the ‘rules’ above?
• Asteroids are rocky because they formed inside the frostline. • Comets are icy because they formed outside the frostline
Comets and asteroids are leftover planetesimals.
Four Unexplained Features of our Solar System
√ Why do large bodies in our solar system have orderly motions?
√ Why are there two types of planets?
√ Where did the comets and asteroids come from?
--> 4) How do we explain the existence of our Moon and other “exceptions to the rules”?
Other large impacts may be responsible for other exceptions like rotation of Venus and Uranus
Earth’s moon was probably created when a big planetesimal slammed into the newly forming Earth
Remember! Early in history of solar system, such impacts far more common
Review of nebular theory
Fig 6.27
Four Features of our Solar System - Explained
√ Why do large bodies in our solar system have orderly motions?
√ Why are there two types of planets?
√ Where did the comets and asteroids come from?
√ How do we explain the existence of our Moon and other “exceptions to the rules”?
We cannot find the age of a planet, but we can find the ages of the rocks that make it up
We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it
When did the planets form?
The decay of radioactive elements into other elements is a key tool in finding the ages of rocks
Age dating of meteorites that are unchanged since they condensed and accreted tell us that the solar system is about 4.6 billion years old.
Since 2008, the oldest rock on earth has been discovered by McGill University in the Nuvvuagittuq greenstone belt on the coast of Hudson Bay, in northern Quebec, and is dated from 3.8 to 4.28 billion years old, based on isotopes of neodymium and samarium
Other Planetary Systems
Our Goals for Learning• How do we detect planets
around other stars?• What have other planetary
systems taught us about our own?
Extrasolar planets are usually too dim or too close to the stars they orbit to observe directly, however Kepler craft can see many transient events.
Most common
Kepler mission
However, we can detect the effect they have on the spectra from their star to confirm their existence. newest
The gravitational fields of a star and its planet will cause passing light to change direction. The focusing of light by gravity is called microlensing.
We detect planets around other stars by looking for a periodic motion of the stars they orbit.
We measure the motion through the Doppler shift of the star’s spectrum –very small shifts ~ 0.000044 nm
The size of the wobble tells us the planet’s mass
The period of the wobble tells us the radius of its orbit (Kepler’s 3rd law)
Earth mass .00314
We can also detect planets if they eclipse their star
Fraction of starlight blocked tells us planet’s size
These are only a few of the many ways in which our planet is special and perhaps unique1. Orbits in habitable zone (liquid water exists)
2. Has a large, fairly close moon
3. Orbits right type star @ right time
4. Solar system is in right region of the galaxy
5. Planet is right size, not too big or too small
6. Has plate tectonics
7. Solar system has a Jupiter size planet, not too close
8. Stable, nearly circular orbits
9. Etc . . .
We do know there are currently 1056 extrasolar planets found in 802 planetary systems as of Jan.10,2014. Source : www.exoplanet.eu
539 planets in 405 systems by astrometry/radial velocity
430 planets in 327 systems by transiting planets
26 planets in 24 systems by microlensing
46 planets in 42 systems by imaging
15 planets in 12 systems by timing (pulsar planets)Let’s see how many of these are even remotely earthlike.We will observe first of all that the Earth’s orbit and mass are quite unusual
16 planets out of 1056 with masses within 100% of the Earth
Stars with low metallicity (elements > He) are unlikely to have rocky planets. In plot below The sun is the reference @ 0
Earth’s orbit
Earth’s Mass (.00314 MJ)
16 planets out of 1056 with masses within 100% of the Earth
The majority of extrasolar planets orbit inside Earth’s orbit, very close to their host star.
All known extrasolar planets with masses from 0 to 0.01 Mjup
All known extrasolar planets with orbits between 0.8 AU and 1.2 Au and masses between Earth (.00314 MJ ) and at least 100 Earth masses (.314 MJ ).
Earth
Earth
Earth Mass
Planet △Mass Radius a
(MEarth) (REarth) (AU)
PSR 1257 12 b 0.022248 — 0.19
KOI-1843 b 0.31783 0.582867 —
Kepler-70 c 0.667443 0.8743 0.0076
KOI-2700 b 0.86 1.06 —
Kepler-42 d 0.95349 0.571658 0.0154
alf Cen B b 1.144188 — 0.04
Kepler-307 c 1.207754 2.802245 —
Kepler-78 b 1.69 1.2 0.01
Kepler-177 b 1.700391 2.903126 —
Kepler-88 b 1.756456 4.219845 —
Kepler-11 b 1.9 1.8 0.091
Kepler-42 c 1.90698 0.728584 0.006
Gl 581 e 1.938763 — 0.028
KOI-115 d 2 1.91 0.077
Kepler-65 d 2 1.513212 0.084
Kepler-11 f 2 2.49 0.25
HD 20794 c 2.415508 — 0.2036
Kepler-307 b 2.510857 3.205768 —
HD 20794 b 2.701555 — 0.1207
GJ 667C f 2.701555 — 0.156
GJ 667C e 2.701555 — 0.213
HD 215152 b 2.765121 — 0.0652
Kepler-42 b 2.86047 0.784629 0.0116
Kepler-11 c 2.9 2.87 0.106
KOI-117 b 3 1.58 0.045
KOI-82 c 3 1.34 0.086
KOI-111 c 3 2.05 0.15
Kepler-20 e 3.082951 0.8743 0.0507
HD 215152 c 3.082951 — 0.0852
MOA-2007-BLG-192-L b
3.1783 — 0.66
HD 40307 e 3.49613 — 0.1886
HD 85512 b 3.49613 — 0.26
HD 39194 b 3.718611 — 0.0519
PSR 1257 12 d 3.81396 — 0.46
KOI-82 d 4 0.69 0.067
HD 40307 b 4.004658 — 0.0468
Kepler-62 c 4.004658 0.538031 0.0929
Kepler-79 e 4.100007 3.497202 0.386
PSR 1257 12 c 4.13179 — 0.36
HD 156668 b 4.163573 — 0.05
GJ 667C c 4.258922 — 0.1251
Kepler-70 b 4.44962 0.762211 0.006
GJ 676A d 4.44962 — 0.0413
Kepler-36 b 4.46 1.48 0.1153
Kepler-10 b 4.6 1.46 0.01687
GJ 667C g 4.608535 — 0.549
Kepler-68 c 4.76745 0.907927 0.09059
HD 20794 d 4.76745 — 0.3499
Kepler-114 d 4.799233 2.533229 0.09
KOI-115 C 5 4.819861 0.066
50 lightest planets known
50 planets with lowest masses from 0.86 to 5 MEHow many of these have a mass between 0.1ME and 10ME ? Exactly 29 planets
3 lightest planets in ME
PSR 1257 12 b, 0.0225 Orbits at 0.19 AU KOI-1843 b 0.3178 orbits at ?? AU Kepler-70 c 0.6674 orbits at .0076 AU
www.exoplanet.eu
Of these 29 planets how many have an orbit radius between 0.8 to 1.2 AU ? 0
4 planets closest to ME
KOI-2700 b, 0.86ME at ??? Kepler-42 d, 0.953 at 0.015 AU alf Cen B b, 1.144 at 0.04 AU Kepler-307 c, 2.80 at ??
Typical Extrasolar system compared with our solar system
a b c d e
Mercury a = .00017
Venus b = .00256
Earth c = .00315
Mars d = .00034
Jupiter e = 1.0
Solar system masses in terms of Jupiter mass
Our solar system
6 x MEI would weigh more than 900 pounds
First, most are more massive than Jupiter and closer to their star than Earth is to Sun. Our solar system is unusual.
Revisions to the nebular theory are necessary! Planets can apparently migrate inward from their birthplaces.
Highly eccentric orbits are the norm
Based on the 1056 known extrasolar planets as of Jan. 2014, what can we conclude?
Secondly, the sun is not an average star, it ranks in the top 10% of all stars in size. The average star is a small, very cool M class star.
The sun also has a high metal content. Stars with low metal content will not have rocky planets.
The sun is also unusually stable for a main sequence star, whose luminosity (brightness) has increased only a few % over the last 2 billion years, providing a very long term stable environment for life to flourish and develop
Our Sun
Survey of stars in the solar neighborhood
Very few have masses greater than the sun
heavier
lighter
Mass weighted avg. of the 319 stars is 0.45 M/Mo most common stars are 0.1 to 0.2 M/M0`
Is Earth Unusual?• No Earth-like
planets found yet.• Data aren’t good
enough to tell if they are common or rare
• Kepler mission has provided more data on Earth size planets.
• Earth probably IS unusual
conclusion
Based on the multiple lines of evidence from a variety of scientific areas ( and I have only presented a very small sample of a large body of evidence) what is one to conclude ?
Based on almost any reasonable criteria that one could devise, the existence of intelligent life on Earth
and perhaps in the Universe as well
is an ENIGMA....
without GOD