astro 5 Flashcards
Our atmosphere protects us from
dangerous UV & X-ray radiation.
X-ray photons _____
ionize (knock e–s free from) almost
any atom or molecule»> can damage living tissue
UV light:
absorbed by ozone (O3)→ resides
mainly in the stratosphere
Visible Light:
passes straight through, but
some is scattered randomly around the sky
Reason why the sky in the day is bright
Reason why the sky in the day is blue:
Rayleigh scattering:
short wavelengths are scattered much more strongly than long ones by gas
molecules/particles
IR light:
The relatively small amount coming
from the Sun does NOT have a significant effect on the atmosphere
What happens to the visible light that reaches the ground?
Part is
reflected, the other part absorbed → Planetary surfaces emit
energy primarily in the IR
what does our atmos to do some of the IR light
Our atmosphere temporarily traps some of the IR light emitted by the planetary surface, slowing its return to space = Greenhouse effect The greenhouse effect keeps Earth’s surface much warmer than it would be otherwise water remains mostly liquid over most of the surface
Not all the regions of the Moon’s surface_____________
look the same.
what do the moon’s surfaces look like
Some are heavily cratered, while others look smoother & darker
what is lunar maria
Some moon’s surfaces are heavily cratered, while others look smoother & darker. Their smooth & dark appearance
suggests they were made by a flood of molten lava b of years ago when the Moon’s interior was heated by radioactive decay
Craters covered Moon’s entire surface during
the Heavy Bombardment and the largest impacts fractured the lithosphere
Heat from radioactive decay on the moon
melted the mantle a few 100 m of
years later & lava flooded the largest craters Dark colour from dense iron-rich rocks (basalt) that rose up as molten lava
Moon’s interior cooled quickly &
& there was never again enough
radioactive heat to cause further melting
The dark side has a higher altitude, is heavily cratered and with very few
maria → nobody knows the reason for this stark difference
Interior cooled completely since formation
were very few craters were made by impacts within maria after the
latter’s formation.
yes man yes
Moon’s era of geological activity is long gone and __________
Impacts are very rare now
Today it is a desolate & nearly unchanging place
describe moon getting blasted by space sand
Slow but constant “sand-blasting” of surface by micrometeorites
from space pulverized it, leaving behind powdery “soil”.
why didn’t earth get space-sand blasted like the moon
These tiny particles burn up in the atmospheres of Earth, Venus & Mars
Mercury looks very much like the
Moon
Mercury and moon
Also had many similar geological processes
what’s a World of extremes
due to its closeness to the Sun & its slow
rotation: day & night are about 3 Earth months each!
describe impact craters on the moon
Impact craters are visible almost everywhere, but less crowded together than most ancient regions of the Moon. This suggests that flowing lava later covered up some of them Lava flow probably due to radioactive heating Lesser crater crowding & many smaller lava plains suggest that Mercury had at least as much volcanism as the Moon.
where is the Caloris Basin
Mercury
describe the caloris basin
Caloris Basin is the largest impact crater on Mercury: it spans
more than half of the planet’s radius
describe the caloris basin’s impact
The impact must have reverberated throughout the planet.
The impact’s shock wave on the opposite side of the planet jumbled the crust
& broke it into a series of complex blocks large area of hilly, grooved
terrain produced
Few craters in Caloris Basin
must have formed when the Heavy
Bombardment was subsiding
what is Mercury – Tectonic evidence of planetary shrinking
mercury’s core and mantle shrank, causing merc’s crust to contract. Some portions of the crust were forced to sluide under other’s. Today we see long steep cliffs created by this crustal movement
describe merc’s tremendous cliffs
Vertical faces more than 3 km high & typically run for100s of km
Evidence of past tectonics
describe lack of stretch marks indicate that Mercury must have shrunk
It has a large Fe core gained & retained more internal heat from accretion & differentiation than the Moon it swelled in size
As it cooled, the core contracted by as much as 20 km in radius
describe what happened as merc cooled
, the core contracted by as much as 20 km in radius
Mantle & lithosphere contracted with the core, generating tectonic stresses that created the great cliffs.
The contraction probably also closed off any remaining volcanic vents
merc’s atmosphere
no atmosphere. The only ongoing feeble
source of gas = the micrometeorites, solar wind particles or high-energy photons that knock free surface atoms & molecules
this gas never
accumulates and is lost as quickly as it is gained
Both Mercury & the Moon have modest amounts of
water frozen in
craters near their poles–> their bottoms lie in perpetual shadow–> water
from comets may have condensed, accumulated and been preserved there
Crater counts on Mercury suggest
t that all its
volcanic & tectonic activity ceased within the first b y after its formation. It may still have a small inner core that is molten and
has (some) convection, to account for its present MF
Like the Moon, Mercury
has been geologically dead for most of its history.
Venus & Earth
have similar size & composition,
but they are different in many other aspects:
how are venus and earth different
No MF ! Rotates (much slower!) in the opposite direction! (Axial tilt≅ 177o) Thicker atmosphere made largely of CO2 very strong greenhouse effect
venus thick cloud cover prevents its surface to be seen →
radar mapping
allowed its geological features to be studied
describe venus geological features
Geological features include: impact craters, volcanoes & a lithosphere contorted by tectonic forces.
As expected for a planet of similar size to Earth.
Few impact craters & cloud composition indicate that Venus
s must
still be geologically active.
Thick atmosphere of CO2 & high clouds with H2SO4 droplets prove intense recent volcanic outgassing which seems to still be on-going.
venus lack of erosion due to
o the hot environment & slow rotation. Hot rain & snow not possible Slow rotation no wind or weather yet very strong high-altitude winds → nobody knows why they blow
Venus Counting of uniformly-distributed craters suggest a
surface age of 750m years everywhere on Venus.
how was the venus surface formed
Entire surface must have been “re-paved” at that time, erasing previously
formed features
Probably due to tectonic & esp. volcanic processes.
Present-day Venus shows no evidence of Earth-like plate tectonics because
e either mantle convection is weak OR it has a thicker & stronger lithosphere that is resisting fracture.
Its high surface temperature baked out
the crust & mantle → evaporated H2O in
rocks that can soften & lubricate them
No direct evidence (yet) but most strongly
supported hypothesis.
Venus (cont’d) – Why is it so hot
Venus’s thick CO
2 atmosphere creates an extremely strong
greenhouse effect that makes it so hot.
Earth has as much CO2 as on Venus, but it is locked away in
rocks
On Venus outgassed water was decomposed by UV radiation and
the molecules stripped away by the solar wind due to the lack of a MF!
Venus retained CO2 in its atmosphere due to a lack of
oceans to dissolve & lock it away in rocks—>runaway
greenhouse effect!
why Venus does not have oceans
Gradual but relentless heating up–>↑ temperature–> More H2O vapors retained
in atmosphere–> ↑↑ greenhouse effect–> Even more H2O evaporated and, hence,
less atmospheric CO2 absorbed–>More H2O vapors gradually disappear as UV
light breaks apart H2O molecules–>More CO2 in atmosphere–>↑↑↑↑
greenhouse effect–>Oceans completely evaporate & rocks release all CO2.
(Positive feedback cycle)
Venus is too close to the Sun to have liquid oceans for dissolving &
fixating CO
2 in rocks
why Venus does not have oceans
Gradual but relentless heating up–>↑ temperature–> More H2O vapors retained
in atmosphere–> ↑↑ greenhouse effect–> Even more H2O evaporated and, hence,
less atmospheric CO2 absorbed–>More H2O vapors gradually disappear as UV
light breaks apart H2O molecules–>More CO2 in atmosphere–>↑↑↑↑
greenhouse effect–>Oceans completely evaporate & rocks release all CO2.
(Positive feedback cycle)
Venus is too close to the Sun to have liquid oceans for dissolving &
fixating CO
2 in rocks
Mars is much larger than the Moon or Mercury but
much smaller than Earth or Venus——–>geology expected to be between these
worlds
is mars much larger than the moon or merc
yes
mars surface area size
Total surface area is 25% of Earth’s–> same land area as Earth’s!
mars distance to sun
It is 50% farther than Earth from the Sun
the martian year
the Martian year is almost twice as long, but the Martian day is only slightly longer
than an Earth day.
mars surface
Much of its present-day surface looks like
some deserts or volcanic plains on Earth.
Polar caps contain frozen CO2 in addition to water ice.
Superficial similarities with Earth made idea of life on Mars a staple of science fiction for more than a century.
mars rotation axis
s tilted similarly to Earth’s, but different orbi
mars seasons
Seasons much like Earth’s but also affected by its more elliptical orbit
—->closer to Sun during southern hemisphere summer
& farther away during
southern hemisphere winter
Mars’s axial tilt varies wildly
–from 0 to 60!– on timescales of hundreds of thousands (~10 ^ 5) y → due to 2 reasons:
Jupiter’s gravity has a greater effect on its axis than on Earth’s
Not stabilized by any big moon
Mars atmosphere
Atmosphere of CO
2 is so thin that it creates only a weak
greenhouse effect—>liquid H2O cannot exist on the surface!
talk about the mars o3 layer
No O3 layer—>strong UV radiation on surface
mars seasonal changes
Its extreme seasonal changes strongly affect the Martian winds.
Large atmospheric pressure differences between the N & S hemispheres drive strong pole-to-pole winds→ can initiate huge dust storms (can envelop the whole planet!)
Although there is no liquid H2O on mars
there is a large amount of water ice in the polar caps (and probably also underground)
talk about dramatic differences in terrain around different parts of Mars:
S hemisphere: relatively high elevation and many large impact craters.
N hemisphere: below the average surface level and with few impact
craters→ younger than S hemisphere and some more recent geological processes erased most of its impact craters
mars surface features
Volcanism was the most important process that erased ancient
craters.
Impact craters on slopes of volcanoes suggest they have been
inactive for at least 10s millions of years.
Recent compared to age of Solar system & likely to erupt again.
Recent observations also point to on-going underground volcanic activity,
indicating that there could still be some residual internal heat at least in
some regions (i.e. the interior of Mars is not totally cold and/or not all of
it).
Nevertheless, the Martian interior is cooling & its lithosphere is
thickening—> will become geologically dead within a few by
mars tectonics
Mars also has tectonic features, but none on a global scale like
the plate tectonics of Earth.
The most prominent tectonic feature is the long, deep system of
valleys called Valles Marineris.
Extends a fifth of the way along the equator, with a length corresponding
to the width of US, and 4× as deep as Grand Canyon!
Not exactly known how Valles Marineris was formed, since
neither lava nor water flows could have been responsible
Probably due to tectonic stresses from uplifting of material that created Tharsis Bulge, cracking the surface & leaving behind the tall cliff walls of the valley.
Mars (cont’d) – Ancient surface waterL
There are numerous erosional features on the surface of Mars.
Channels, river & lake beds on Mars appear to have been carved
by running water → the only substance that could have been
liquid under past Martian conditions & is sufficiently abundant
to create such extensive erosion.
Signs of erosion by rainfall were also found
No liquid water exists anywhere on the surface of Mars today
it would immediately turn into ice if T < 0oC, or would quickly evaporate even if temperature were above freezing.
Robotic rovers found minerals that form in water.——> Mars must have had rain
& surface water (and, therefore, a much thicker atmosphere) in the distant past.
3.6 b y.a. the Martian atmosphere must have had a pressure of
0.9 bar —> at this pressure liquid H2O could have existed for extended
periods of time on the surface!
Not everything on Mars conforms with
the picture of a warmer, wetter planet in the past
why does not everything on Mars conforms with the picture of a warmer, wetter planet in the past
Mars is located 50% further away from the Sun than Earth is
the
amount of solar energy it receives is far too low to keep any water on its
surface in a liquid state
Additionally, the Sun at that time was radiating even less energy
NO proof (yet?) of minerals normally produced by weathering of rocks
under warm, wet conditions
The greenhouse effects of a CO2 atmosphere could not have created a wet
climate: no matter how thick it was, it could not have trapped enough
heat to stabilize liquid water.
Other possible positive contributing factors to mars not having water
Periods of intense volcanic activity may have released vast quantities of
greenhouse gases.
Perhaps Mars water is heavily laced in salts that lower the freezing point
of water, allowing water to flow at temperatures that would have
otherwise caused it to freeze.
The Martian regolith is packed with perchlorates, a highly toxic
oxidizing agent that could create briny pockets of liquid water
Cyclical changes in Mars’ tilt created “transient intervals” with
atmospheric conditions favorable for a thicker atmosphere. Every
120,000 years, Mars’ tilt undergoes precession, which would have
influenced the quantity of sunlight hitting the poles. This cycle may have
caused episodic freezing and thawing of the Martian surface water.
Not everything on mars conforms with
the picture of a warmer, wetter planet in the past
mars is located 50% further
away from the Sun than Earth
talk about the amount of solar energy mars receives
too low to keep any water on its surface in a liquid state
what is there no proof of yet on mars
minerals normally produced by weathering of rocks
under warm, wet conditions
talk about greenhouse effects of a CO2 atmosphere on mars
e could not have created a wet
climate: no matter how thick it was, it could not have trapped enough
heat to stabilize liquid water.
why must mars have had rain and surface water and a much thicker atmosphere in the distant past
There are numerous erosional features on the surface of Mars.
Channels, river & lake beds on Mars appear to have been carved
by running water → the only substance that could have been
liquid under past Martian conditions & is sufficiently abundant
to create such extensive erosion.
Signs of erosion by rainfall were also found
No liquid water exists anywhere on the surface of Mars today
it would immediately turn into ice if
T < 0
oC, or would quickly
evaporate even if temperature were above freezing.
Robotic rovers found minerals that form in water.
robotic rovers have form what on mars
Robotic rovers found minerals that form in water.
why does No liquid water exists anywhere on the surface of Mars today
it would immediately turn into ice if T < 0oC, or would quickly evaporate even if temperature were above freezing.
what appears to have been carved by running water on mars
Channels, river & lake beds
what is running water to mars
→ the only substance that could have been
liquid under past Martian conditions & is sufficiently abundant
to create such extensive erosion.
how did venus retain c02 in it’s atmosphere
due to a lack of
oceans to dissolve & lock it away in rocks —> runaway
greenhouse effect!
what did venus retain in it’s atmosphere
c02
earth has as much co2 as venus, but why aren’t we fucked up
it is locked away in
rocks
what happened to outgassed water on VENUS
On Venus outgassed water was decomposed by UV radiation and the molecules stripped away by the solar wind due to the lack of
a MF!
Why doesnt present-day Venus shows no evidence of Earth-like plate
tectonics
because either mantle convection is weak OR it has a thicker & stronger lithosphere that is resisting fracture
Its high surface temperature baked out
the crust & mantle → evaporated H2O in
rocks that can soften & lubricate them
No direct evidence (yet) but most strongly
supported hypothesis.
Why is there a lack of erosion on venus
due to the hot environment & slow rotation. Hot rain & snow not possible Slow rotation no wind or weather yet very strong high-altitude winds → nobody knows why they blow
how do you determine the age of venus
Counting of uniformly-distributed craters suggest a surface age of 750m years everywhere on Venus.
Entire surface must have been “re-paved” at that time, erasing previously
formed features
Probably due to tectonic & esp. volcanic processes.
venus is too close to the Sun so?
s too close to the Sun to have liquid oceans for dissolving & fixating CO2 in rocks
what is s the most important process that erased ancient
craters on mars
volcanism
Impact craters on slopes of volcanoes on mars
suggest they have been
inactive for at least 10s millions of years.
Recent compared to age of Solar system & likely to erupt again.
Recent observations also point to on-going underground volcanic activity,
indicating that there could still be some residual internal heat at least in
some regions (i.e. the interior of Mars is not totally cold and/or not all of
it).
Nevertheless, the Martian interior is cooling & its lithosphere is
thickening —> will become geologically dead within a few by
Mars also has tectonic features, but ______
, but none on a global scale like the plate tectonics of Earth.
What is the most prominent tectonic feature on mars
The most prominent tectonic feature is the long, deep system of valleys called Valles Marineris.
how big is the valles marineris
Extends a fifth of the way along the equator, with a length corresponding
to the width of US, and 4× as deep as Grand Canyon!
talk about the valles marineris formation
Not exactly known how Valles Marineris was formed, since
neither lava nor water flows could have been responsible —> Probably due to tectonic stresses from uplifting of material that created Tharsis Bulge, cracking the surface & leaving behind
the tall cliff walls of the valley.
what are other contributing factors to the idea of water on mars
Other possible positive contributing factors:
Periods of intense volcanic activity may have released vast quantities of
greenhouse gases.
Perhaps Mars water is heavily laced in salts that lower the freezing point
of water, allowing water to flow at temperatures that would have
otherwise caused it to freeze.
The Martian regolith is packed with perchlorates, a highly toxic
oxidizing agent that could create briny pockets of liquid water
Cyclical changes in Mars’ tilt created “transient intervals” with
atmospheric conditions favorable for a thicker atmosphere. Every
120,000 years, Mars’ tilt undergoes precession, which would have
influenced the quantity of sunlight hitting the poles. This cycle may have
caused episodic freezing and thawing of the Martian surface water.
The Martian regolith is packed
with perchlorates, a highly toxic oxidizing agent that could create briny pockets of liquid water
perchlorates
a highly toxic oxidizing agent that could create briny pockets of liquid water
Cyclical changes in Mars’ tilt created
“transient intervals” with
atmospheric conditions favorable for a thicker atmosphere. Every
120,000 years, Mars’ tilt undergoes precession, which would have
influenced the quantity of sunlight hitting the poles. This cycle may have
caused episodic freezing and thawing of the Martian surface water
Mars’ tilt undergoes precession, which would have influenced ___________
the quantity of sunlight hitting the poles. This cycle may have caused episodic freezing and thawing of the Martian surface water.
Perhaps Mars water is heavily laced in salts _________
that lower the freezing point of water, allowing water to flow at temperatures that would have otherwise caused it to freeze.
Periods of intense volcanic activity may have released _______ on mars
Periods of intense volcanic activity may have released vast quantities of
greenhouse gases.
Almost all scientists that Mars had
wetter & possibly (much?)
warmer periods before ~3.6
b y.a. (billion years ago)
Though a few argue that the greenhouse effect & solar radiation (30%
weaker!) were not enough for liquid surface water and that most was ice
Very early in its history, Mars probably had
a dense atmosphere
from volcanic outgassing (mainly H2O vapors & CO2)—->a much
stronger greenhouse effect.
Clearly Mars must have somehow lost most of its atmosphere and WHAT DID THIS DO
increasingly weakened greenhouse effect until Mars froze over
Some condensed to make polar caps & chemically bound to rocks.
Bulk of CO2 & H2O probably lost to space
Early Mars most probably had
convecting metals in its core,
producing a protective magnetosphere—>Its MF weakened as
Mars rapidly cooled until core ceased to convect—>Solar wind
stripped away gases & the H2O in atmosphere
UV light also broke apart H2O into H2 & O2: H2 was quickly lost to space,
some O2 reacted & rusted Martian rocks—>distinctive red tint
Mars was shaped primarily by its
relatively small size.
Mars was shaped primarily by its relatively small size, elaborate on this
Big enough for volcanism
& outgassing to build atmosphere
Too small to maintain internal heat & MF
Its larger distance from Sun finally sealed its fate
talk about the role of planetary size in terrestrial planet formation for small terrestrial planets
interior cools rapidly, so that tectonic and volcanic activity cease after a billion years or so. Many ancient craters therefore remain.
Lack of volcanism means little outgasisng and low gravity allows has to escape more easily, no atmosphere means no erosion
talk about the role of planetary size in terrestrial planet formation for large terrestrial planets
warm interior causes mantle convection
leading to ongoing tectonic and volcanic activity, most ancient craters have been erased.
outgassing produced an atmosphere and strong gravity holds it, so that erosion is possible
core may be molten, producing a magnetic field if rotation is fast enough and a magnetosphere that can shield an atmosphere from the solar wind
more wind and weather means
more erosion
what does higher rotation speeds cause
more wind and weather
if the surface is too hot for rain snow or ice
little erosion occurs
high atmospheric temperature
allows has to escape more easily
