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!
