Astronomy ch.19

Earth has passed through four stages as it has evolved: (1) _______________________________; (2) ___________________________; (3) __________________________ by lava and water; and (4) slow ______________________ ______________________

1. differentiation, 2. cratering 3. flooding 4. surface evolution

How old is the earth

4.6 billion years old

catastrophic hypothesis.

Buffon later suggested that a passing comet pulled matter out of the Sun to form the planets

Earth is the standard of ______________planetology in the study of the Terrestrial planets because we know it best and because it contains all of the phenomena found on the other Terrestrial planets.

Comparative

Evolutionary Hypothesis

Descartes proposed that the solar system formed from a contracting vortex of matter

The Terrestrial planets may have formed slowly from the accretion of planetesimals of similar composition. Later, radioactive decay plus heat of formation melted each planet's interior to cause

Differentiation, the seperation of materials according to density

Earth's magnetic field is generated by the ______________ effect in the liquid, convecting, rotating, conducting core. The magnetic field shields Earth from the solar wind by producing a bow shock and a magnetosphere around the planet. Radiation belts called the Van Allen belts, as well as auroral displays, are also produced by the magnetic field.

Dynamo

Once a protoplanet approaches about 15 Earth masses, it can begin growing by

Gravitational collapse, as it pulls in gas from the solar nebula

Which planets are Jovian planets

Jupiter, Saturn, Uranus and Neptune

Maria's on the moon

Large, smooth dark plains on the Moon are old lava flows that fill the lowlands. Evidence of lava is seen as sinuous rilles that once carried flowing lava, faults where the lava plain cracked, and wrinkles in the surface

Meteorites

Larger and stronger meteoroids may survive to reach the ground

passing star hypothesis.

Later astronomers modified Buffon's comet with a star. Matter ripped from the sun by a passing star made the planets.

nebular hypothesis

Leplace required a contracting nebula growing smaller with increasing angular momentum. the fast spinning star was to leave behind rings that formed each planet

the angular momentum problem.

Leplace's nebular hypothesis could not explain the Sun's low angular momentum,

resonance

Mercury tides being pulled by the sun have slowed the rotation of mercury and coupled its rotation to its revolution

Which planets are the terrestrial planets

Mercury venus earth and mars

Meteors

Meteoroids that fall into Earth's atmosphere are vaporized by friction and are visible as streaks of light

hot Jupiters

Nearly all extrasolar planets found so far are massive, Jovian worlds orbiting close to their parent stars Lower-mass Terrestrial planets are harder to detect but may be common. Because planets can migrate as they form and can interact to distort orbits, Jovian planets orbiting very close to their suns or moving in elliptical orbits are not objections to the solar nebula theory

The solar system is disk shaped with all the planets ________________ nearly in the same plane. The orbital revolution of all the planets, and the rotation of most of the planets on their axes, and the revolution of most of their moons are all in the same direction, counterclockwise as seen from the north.

Orbiting

Extrasolar Planets

Planets orbiting other stars,have been detected by the way they tug their stars about, creating small Doppler shifts in the stars' spectra

In addition to intense light from hot nearby stars and the gravitational influence of passing stars, the solar nebula was eventually cleared away by ________________ pressure, the _________ wind, and the sweeping up or ejection of debris by the ________________.

Radiation pressure, when the sun became a luminous object, light streaming from its photosphere pushed against particles of the solar nebula. Solar Wind, the flow of ionized hydrogen atoms away from the suns upper atmosphere. Close encounters with planets and their gravity.

Composite volcanoes on Earth have steep slopes and are associated with subduction zones. _________________volcanoes have shallow slopes and are associated with hot spots. The volcanoes on Venus are associated with hot spots

Shield Valcanoes

ordering of the planets from the Sun.

Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Condensation Sequence

The sequence in which different materials would condense from the gas as a function of nebular temperature. Inner Nebula was hot and only rock and metal could condense. the colder outer nebula could form lots of ice along with rock materials.

Planets have also been detected in ___________________ as they cross in front of their star and partly block the star's light. A few planets have been detected when they orbited behind their star and their infrared radiation was cut off. .

Transit

Ice Line

a boundary further from the sun where water vapor could freeze to form ice particles, between mars and jupiter

Planets begin growing by _________________ of solid material into protoplanets

accretion, or the sticking together of solid particles Example: the way snowflakes stick to form a snow ball

Cold dust disks

also known as debris disks, appear to be composed of dust released by collisions among comets, asteroids, and Kuiper belt objects. Such disks may be signs that planets have already formed in these systems

intercrater plains

appear to be later lava flows on mercury

Comets

are icy bodies that pass through the inner solar system along long elliptical orbits. As the ices vaporize and release dust, this object develops a tail that points approximately away from the Sun.

The Moon is small and has only one-sixth the gravity of Earth. It has such a low escape velocity that it is unable to retain an atmosphere. Observers on Earth see sharp shadows on the Moon's surface, especially near the terminator, and stars disappear behind the limb of the Moon without dimming. Both observations are evidence of the lack of an _________________________

atmosphere

Landers have analyzed the surface rock and found it to be similar to _______________ on Earth

basalts

the green house effect

can warm a planet if gases such as carbon dioxide in the atmosphere are transparent to light but opaque to infrared. This effect warms Earth and makes it comfortable for life, but greenhouse gases added by industrial civilization have probably contributed to global warming. Measurement of carbon isotope ratios and carbon dioxide versus oxygen abundances make it clear that the CO2 added to the atmosphere since 1800 is predominantly from

Because Venus formed closer to the Sun, it was initially warmer, and whatever oceans it may originally have had were not able to persist and remove ____________ _______________ from the atmosphere. The accumulating gas produced an intense greenhouse effect, made the planet very hot, and evaporated the remaining water in a runaway greenhouse effect.

carbon dioxide

The atmosphere of Venus is 95 times thicker than Earth's and composed almost entirely of ______________ ____________. Venus is heated by a runaway greenhouse effect. The temperature at the surface of Venus is about 470ºC (880°F), hotter than Mercury even though it is farther from the Sun.

carbon dioxide

Because Earth formed in a molten state, its first atmosphere was probably mostly carbon dioxide, nitrogen, and water vapor. Most of the _______________ _____________ eventually dissolved in seawater and was added to ocean sediments. Plant life has added _____________ to the atmosphere

carbon dioxide oxygen

The motion of a plate across a hot spot can produce a ________________ of volcanic islands such as the Hawaiian islands. Hot-spot volcanism is not related to subduction zones

chain

coronae

circular buldges, form where rising currents of magma push the crust up and then withdraw, forming circular faults with associated volcanoes and lava flows

What are terrestrial planets

close to the sun, small orbits, small mass & size, rock & metal solid surface, high density, slow rotation, weak magnetic fields, few moons, no rings

Venus is Earth's twin in size but is slightly __________________ to the Sun.

closer

Like Earth, Mercury formed in the inner solar system and contains a larger proportion of dense metals. It is possible that a large impact shattered and drove off some of the planet's crust. This could explain why it has a larger metallic core, even than would be predicted by the __________________ sequence

condensation sequence

Comparative Planetology of terrestrial planets,

considers Earth, the Moon, Mercury, Venus, and Mars. Earth's Moon is included because it is a complex world and makes a striking comparison with Earth

Lava, flowing up from below the crust, filled the lowlands to form smooth maria plains. The maria formed after the end of the heavy bombardment and contain few ___________.

craters

The Terrestrial worlds differ mainly in size, but they all have low-density _______________, _______________ of dense rock, and metallic ________________.

crust, mantles, and cores

Because the Moon is small, it has lost its internal heat and is geologically ___________. The only slow surface evolution occurring now is the blasting of micrometeorites

dead

At some point early in its history Earth was hot enough to be completely molten, which caused it to ___________________________ into layers of different density.

differentiate

When a meteorite strikes the Moon, it digs a large round impact crater and throws out debris that falls back as _____________ and can form rays and secondary craters.

ejecta

Describe Jovian planets

far from the sun, wide orbits, large mass & size, gas surfaces, low density, faster rotation, strong magnetic fields, many moons and rings

Some plates carry continents and where they collide, they can form _________________ ranges. Volcanism and earthquakes are common along the edge of the plates

folded mountain ranges

The age of a rocky body can be found by radioactive dating, based on the decay _______-_______ of radioactive atoms. The oldest rocks from Earth, the Moon, and Mars have ages over 4 billion years. The oldest objects in our solar system are some meteorites that have ages of 4.6 billion years. This is taken to be the age of the solar system

half-life

Evidence that the condensation sequence was important in the solar nebula can be found in the high _______________________ of the Terrestrial planets relative to the Jovian planets

high densities

Van Allen belts of radiation

high energy particles from the solar wind leak into the magnetosphere and become trapped within earths magnetic field

Comparing the uncompressed densities of the Terrestrial planets shows that the innermost Terrestrial planets have the

higher densities than the outer ones because of condensation space

Because Earth formed ________, it never had a primeval atmosphere rich in hydrogen and helium that was later replaced by a secondary atmosphere baked out of the interior

hot

Kuiper belt

icy bodies orbiting the outer fringes of the solar system beyond neptune

Between 1969 and 1972, 12 astronauts set foot on the Moon and returned specimens to Earth. The Moon rocks are all __________________, showing that they solidified from molten rock. Some are vesicular basalts, showing that they formed in lava flows on the surface. Light-colored anorthosite is part of the old crust and helps make the highlands brighter than the maria in the lowlands. Many of the rocks are breccias, showing that much of the lunar crust was fractured by meteorite impacts.

igneous

Condensation

in the solar nebula converted some of the gas into solid bits of matter

Microlensing

in which extrasolar planets passes between earth and a background star, briefly magnifying the distant stars brightness by gravitational lensing

Mercury is a small world that has been unable to retain a true atmosphere and has lost most of its internal heat. It is cratered and geologically ______________

inactive

Mercury was heavily cratered during the heavy bombardment, but lava flows covered some of those craters, and new craters formed the ___________________ plains. Fractures produced by the Caloris impact may have triggered later lava flows that formed the smooth plains.

intercrater

Seismic waves generated by earthquakes can be detected by seismographs all over the world and canreveal Earth's _______________________structue

internal

The Moon differentiated but contains little ____________. Its low-density crust was heavily cratered and shattered to great depth

iron

The Caloris Basin

is a large multi-ringed basin on Mercury that has been partially flooded by lava flows

Disks of gas and dust around protostars may not last long enough to form ______________ planets by accretion and then by gravitational collapse. Some models suggest these planets could have formed more rapidly by direct collapse, skipping the condensation and accretion steps

jovian

The fission, condensation, and capture hypotheses for the origin of the Moon have all been abandoned. The commonly accepted explanation is called the ________ -_________ hypothesis. The Moon appears to have formed from a ring of debris ejected into space when a large planetesimal struck the proto-Earth after Earth had differentiated. This would explain, for example, the Moon's low density and lack of volatiles

large-impact

The surface of Venus appears to be about half a billion years old. Planetary scientists suspect that the entire planet was resurfaced by an outpouring of

lava

Earth is also peculiar in that it is the only known home for

life

Earth is peculiar in that it has large amounts of ________________ _______________on its surface that drives strong erosion that alters the surface geology

liquid water

Pressure (P) waves can travel through a ____________________, but shear (S) waves cannot. Observations show that S waves cannot pass through Earth's core, and that is evidence that the core is liquid. Measurements of heat flowing outward from the interior combined with mathematical models reveal that the core is very hot and composed of _____________ and _________________

liquid, iron and nickel

As the metallic core cooled and contracted, the brittle crust broke to form _______ _________ like wrinkles in the skin of a drying apple.

lobate scarps (great curved cliffs)

There is evidence from lunar crater counts and rock samples of an episode of increased impact rate, labeled the late heavy bombardment, about 4 billion years ago near the end of the heavy bombardment era. Many of the giant impact basins containing __________ were formed during this time. That event may have been caused by Jovian planets migrating and scattering remnant planetesimals across the solar system. The Imbrium basin was formed about 4 billion years ago by the impact of a planetesimal at least 60 km (40 mi) in diameter. Seismic waves traveling through the Moon were focused to the far side and produced jumbled terrain. Later flooding has nearly buried the original basin.

mare or maria

New crust is formed along _________________ rises where molten rock solidifies to form basalt. Crust is destroyed where it sinks into the mantle along __________________zones.

mid-ocean rises subduction zones

The Moon rocks show that the Moon formed in a ___________ state

molten

smooth plains

more recent lava flows that contain few craters on mercury

The __________ side of the Moon has a thin crust, possibly due to tidal forces. The __________ side has a thicker crust and little lava flooding

near side back side

albedo

of a planet is the fraction of sunlight hitting it that it reflects into space. Small changes in this quantity caused by changes in clouds and atmospheric currents can have a dramatic effect on climate of Earth

All of the _______ surfaces in the solar system were heavily cratered during the heavy bombardment by debris that filled the solar system when it was young

old

Comparative planetology warns you to expect that cratered surfaces are ____________, that heat flowing out of a planet drives _______________________________ activity, and that the nature of a planet's atmosphere depends on the size of the planet and its ______________________.

old, geological, temperature

The Moon is tidally coupled to Earth and rotates on its axis ______________ each orbit, keeping the same side facing Earth.

once tidally coupled - a moon locked to its planet

In that scenario, Earth's early atmosphere was probably supplied by a combination of ___________________________ from Earth's interior and planetesimal impacts

outgassing

Ultraviolet photons can break up water molecules in a planet's atmosphere, but as soon as Earth had enough oxygen, a/an ________________ layer could form high in Earth's atmosphere. This layer absorbs ultraviolet photons and protects water molecules

ozone layer

Hot disks of gas and dust have been detected in early stages of star formation and are believed to be the kind of disk in which _____________ could form.

planets around young stars

Although Earth's crust is brittle and breaks under stress, the mantle is ____________________ and can deform and flow under pressure.

plastic

bow shock- the surface where the solar wind is first deflected

plate tectonics

Most geological features on Earth, such as mountain ranges and the Grand Canyon, have been formed recently. The first billion years of Earth's geology are almost entirely erased by ____________ ______________ and _____________________.

plate tectonics and erosion

The solar nebula theory

proposes that planets formed in a disk of gas and dust around the protostar that became the Sun. Observations show that these disks are common

Tectonic plates are made of low-density, brittle rock that floats on the hotter plastic upper layers of the mantle. Rift valleys can be produced where plates begin __________ _______ from each other

pulling away

Although it is perpetually hidden below thick clouds, the surface of Venus can be studied by _________ mapping, which reveals higher uplands and low rolling plains. Volcanoes, lava flows and channels, and impact craters are detectable. Volcanism is apparently common on Venus, and much of the surface is solidified lava flows. Volcanoes are probably still active on Venus. Radar maps can measure altitude, roughness, and in some cases, composition of the surface

radar mapping

Astronomers can find relative ages for lunar features by looking to see which lies on top and which lies below. Ages in years can be found by counting craters on a surface and comparing the result with an estimate of the rate of crater formation, calibrated using ________________________ ages of lunar rock samples.

radioactive

The surface of the Moon is covered by rock crushed and powdered by meteorite impacts to form a soil called

regolith

The highlands on the moon are...

saturated with craters. Rare meteorite impacts continue to form new craters, and micrometeorites constantly grind the surface down to dust, but most of the craters on the Moon are very old. Most of the craters on the Moon were formed during the heavy bombardment at the end of planet building about 4 billion years ago. No crater is known with certainty to have been formed on the Moon in historic times.

Venus rotates so ____________ that solar heat at the subsolar point produces strong atmospheric circulation that circles the planet in only 4 days

slowly

Asteroids

small irregularly shaped rocky worlds, which orbit the sun in a belt between mars and jupiter

The surface of Venus is so hot that compounds have cooked out of the crust to form traces of sulfuric, hydrochloric, and hydrofluoric acids in the atmosphere. The very high clouds on Venus are composed of small droplets of __________ __________ and sulfur crystals.

sulfuric acid

Magnetosphere

the cavity dominated by earths magnetic field

Uncompressed densities

the density a planet would have if gravity did not compress them

Bow shock

the surface where the solar wind is first deflected

Mercury is ____________ locked to the Sun and rotates 1.5 times per orbit in a resonance relationship between its rotation and its revolution.

tidally locked

The ozone layer high in Earth's atmosphere protects the surface from ultraviolet radiation, but certain chemicals called chlorofluorocarbons released in industrial processes attack the ozone layer and thin it. This is allowing more harmful __________________ radiation to reach Earth's surface

ultraviolet radiation

The Messenger space craft

will go into orbit around Mercury in 2011 and provide more extensive photography of its surface and detailed measurements of its physical properties.