The Moon and Mercury: Airless Worlds
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The Moon and Mercury: Airless Worlds Please take your assigned transmitter And swipe your student ID for attendance tracking.
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0. The Moon and Mercury: Airless Worlds. Please take your assigned transmitter And swipe your student ID for attendance tracking. :10. 0 of 5. The moon’s orbit around the Earth is tidally locked. This means that …. - PowerPoint PPT Presentation
Transcript of The Moon and Mercury: Airless Worlds
The Moon and Mercury:Airless Worlds
Please take your assigned transmitter
And swipe your student ID for attendance tracking.
The moon’s orbit around the Earth is tidally locked. This means that …
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1. the moon is rotating is rotating about its axis once per tidal period on Earth.
2. the moon is orbiting around the Earth once per tidal period on Earth.
3. the moon is rotating about its axis once per synodic orbital period.
4. the moon is rotating about its axis once per siderial orbital period.
5. the moon is not rotating at all.
The Moon:The View from Earth
From Earth, we always see the same
side of the moon.
Moon rotates around its axis in the same time that it takes to orbit around Earth:
Tidal coupling:
Earth’s gravitation has produced tidal bulges on the Moon;Tidal forces have slowed rotation down to
same period as orbital period
Lunar Surface FeaturesTwo dramatically different
kinds of terrain:
• Highlands: Mountainous terrain, scarred by craters
• Lowlands: ~ 3 km lower than highlands; smooth
surfaces:
Maria (pl. of mare):
Basins flooded by lava flows
Highlands and Lowlands
Sinous rilles = remains of ancient
lava flows.
May have been lava tubes which later collapsed due to
meteoride bombardment.
Apollo 15 landing site
Which are the older surface features on the moon?
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1. The highlands (cratered areas).
2. The lowlands (maria).
The HighlandsSaturated with craters
Older craters partially obliterated by more
recent impacts
… or flooded by lava flows
Impact CrateringImpact craters on the moon
can be seen easily even with small telescopes.
Ejecta from the impact can be seen as bright rays originating
from young craters
How long after the origin of the solar system did it take to clear away the remaining debris
from the inner solar system?
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1. 100,000 years2. 5 million years3. 100 million years4. ½ billion years5. 2 billion years
History of Impact Cratering
Rate of impacts due to interplanetary bombardment
decreased rapidly after the formation
of the solar system.
Most craters seen on the Moon’s (and Mercury’s) surface were formed within the first ~ ½ billion
years.
Formation of Maria
Impacts of heavy
meteorites broke the crust and produced large basins
that were flooded with
lava
Formation of Maria (II)Major impacts forming maria might have
ejected material over large distances.
Large rock probably ejected during the formation of Mare Imbrium (beyond the horizon!)
Apollo 14
The Apollo Missions
Apollo Landing SitesFirst Apollo missions landed on safe, smooth terrain.
Apollo 11: Mare Tranquilitatis; lunar lowlands
Later missions explored more varied terrains.
Apollo 17: Taurus-Littrow; lunar highlands
Apollo Landing Sites (II)
Selected to sample as
wide a variety as possible of
different lowland and
highland terrains.
Lowlands (maria)
Highlands
Modern Theory of Formation of the Moon
The Large-Impact Hypothesis
• Impact heated material enough to melt it
→ consistent with “sea of magma”
• Collision after differentiation of Earth’s interior
→ Different chemical compositions of Earth and moon
(in particular: The moon does not have a large iron core.)
The History of the Moon
Alan Shepard (Apollo 14) analyzing a moon rock, probably
ejected from a distant crater.
Moon is small; low mass → rapidly cooling off; small
escape velocity → no atmosphere → unprotected against meteorite impacts.
Moon must have formed in a molten state (“sea of lava”);
Heavy rocks sink to bottom; lighter rocks at the surface
No magnetic field → small core with little metallic iron.
Surface solidified ~ 4.6 – 4.1 billion years ago.
Heavy meteorite bombardment for the next
~ ½ billion years.
Where is this terrain?1. On the lunar highlands.2. On the lunar lowlands.3. On Mercury.4. On Venus.5. On Mars.
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MercuryVery similar to Earth’s moon in several ways:
• Small; no atmosphere
• lowlands flooded by ancient lava flows
• heavily cratered surfaces
Most of our knowledge based on
measurements by Mariner 10 spacecraft
(1974 - 1975)
View from Earth
Rotation and Revolution
Like Earth’s moon (tidally locked to revolution around Earth), Mercury’s rotation has been
altered by the sun’s tidal forces,but not completely tidally locked:
Revolution period = 3/2 times rotation period
Revolution: ≈ 88 days
Rotation: ≈ 59 days
The Orbit and Rotation of Mercury
How long is the Mercurian day?
(Rotation period: 58 days; orbital period: 88 days)
1. 44 Earth-days
2. 58 Earth-days
3. 88 Earth-days
4. 120 Earth-days
5. 170 Earth-days
Rotation and Revolution
Like Earth’s moon (tidally locked to revolution around Earth), Mercury’s rotation has been
altered by the sun’s tidal forces,but not completely tidally locked:
Revolution period = 3/2 times rotation period
Revolution: ≈ 88 daysRotation: ≈ 59 days
→ Extreme day-night temperature contrast: 100 K (-173 oC) – 600 K (330 oC)
The Surface of Mercury
Very similar to Earth’s moon:
Heavily battered with craters, including some large basins.
Largest basin: Caloris Basin Terrain on the opposite side jumbled by seismic waves
from the impact.
Lobate Scarps
Curved cliffs, probably formed when Mercury shrunk while cooling down
The Interior of MercuryLarge, metallic core.
Over 60 % denser than Earth’s moon
Mercury has a very large, iron-rich metallic core. Thus, would you expect
that it has a strong magnetic field?
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1. Yes.2. No.
The Interior of MercuryLarge, metallic core.
Over 60 % denser than Earth’s moon
Magnetic field only ~ 0.5 % of Earth’s
magnetic field.
Difficult to explain at present:
Liquid metallic core should produce
larger magnetic field.
Solid core should produce weaker field.
