Download Earth The Moon`s surface

Earth
The Moon’s surface
• The Moon: basic characteristics
– Size, Mass, Density, Gravity (near and far side)
– Atmosphere, water, magnetic field, surface temperature
– Structure:
• Crest
• Never see the far side: reasons; 59% of surface
• Dark spots
– Lunar seas
• Remains of lava flows
• Craters
– lithosphere
– 30 000 with d>1km
– Circular
– Age of the surface
• Mantle
• Core
• Light spots
– Highlands
Mars
Satellites of Mars discovered 1877
Phobos: 23 km, 7h 39 min, 9378 km
Deimos: 15 km, 1.26 days, 23460 km
Mass of Mars
Courtesy Calvin J. Hamilton
Credit & Copyright: Johannes Schedler
1
Jupiter’s satellites
Io
Europa
Callisto
Ganymede
• 52+ natural satellites: 20 of them are Discovered in 2003
• Rings discovered in 1979 by Voyager 1 spacecraft
Io
Two Sides of Io.
The orange colored deposits are sulfur snow;
the white color is sulfur dioxide.
2
Volcanic Plume on Io
An enormous volcanic feature that is
rising about 250 km above Io’s
surface.
Volcanic activity on Io and tidal heating
Giant Lava Flow on Io
The longest active lava flow yet discovered in
the solar system (500 x 200 km).
Fig 11-13, p.251
Europa
Europa - cracks on the surface
Europa is a strange looking moon of Jupiter
with a large number of intersecting features.
3
Europa – internal structure
Radius = 2631 km
Ganymede is the
largest moon of
Jupiter and is the
largest natural
satellite in our
solar system.
Surface – similar to Moon,
but icy.
Callisto
Callisto
Jupiter’s outermost
large satellite
shows a heavily
cratered surface
of dark ice.
4
What is interesting about
the Jovian Moons?
¾ Io has acting volcanoes due to tidal deformations
¾ Europa – covered with water ice.
Is there liquid water under the ice?
¾ Ganymede – the largest moon in the Solar system,
bigger than Mercury and Pluto. Surface similar
to the Moon, but icy. Weak magnetic field.
¾ Calisto –heavily cratered
Uranus
Saturn
31+ moons, 7 large
Icy surfaces, different
activity in the past.
Titan: heavy atmosphere
of mostly nitrogen,
argon and methane.
Surface T ~ -180oC
A near-infrared view of Uranus and
moons Miranda (top) and Ariel
• 5 moderate size satellites which masses and
densities are known
–
–
–
–
–
Low densities – mixture of rock and ice
Their surfaces are dark
Many impact craters
Some signs of geological activity in the past
Signs of tidal heating in the past: Miranda
• 16+ small moons
5
The surface of Miranda is covered
with craters, canyons, valleys, and
cliffs.
The surface of
Ariel is covered
with craters and
long rift valleys.
The surface of Umbriel is
heavily cratered and is
Uranus' darkest satellite.
The surface of Titania is
covered in craters and
interconnected valleys.
The surface of
Oberon is heavily
cratered and icy.
6
Neptune
Triton – Neptune’s largest satellite
• Neptune’s satellites - small ice bodies
• Triton – Neptune’s largest satellite
– Retrograde orbit
– High orbital inclination with respect to Neptune’s equator
– The only large satellite with retrograde orbit. Probably
captured ?
– Surface – icy (water ice on the surface), reflective, impact
craters and cracks
– Surface T ~ -236oC
– Thin nitrogen atmosphere
– Nitrogen geysers observed.
– Internal heat in the past but not now
– The radius of Triton’s orbit is decreasing – will be destroyed
by the tidal force (in ~ 100 mill yrs)
Pluto and Charon are tough to see even with the best telescopes
Triton
• There are very few craters visible; the
surface is relatively young.
• Almost the entire southern hemisphere is
covered with an "ice cap" of frozen nitrogen
and methane.
• There are extensive ridges and valleys in
complex patterns all over Triton's surface.
These are probably the result of
freezing/thawing cycles.
• The most interesting (and totally
unexpected) features are the ice
volcanoes.
7
The largest satellites in the Solar System
Orbit on its side. Charon is in a prograde orbit – probably born with Pluto
The Kuiper
Belt
Trans-Neptunian Objects (TNO)
Any object in the solar system that orbits the Sun at a greater
distance on average than Neptune
The Kuiper belt,
Scattered disk, and
Oort cloud are
names for three
divisions of this
volume of space.
Courtesy of Windows to the
Universe,
http://www.windows.ucar.edu
Courtesy of
Windows to the
Universe,
http://www.wind
ows.ucar.edu
8
Comparing the small distant ‘planets’
to the Earth
About 800 objects (diameter > 50 km) are currently known in the Kuiper belt
beyond Neptune. Cold icy worlds at 40-50 A.U. from the Sun.
Kuiper belt objects: Planet
candidates in the Solar System
The largest: Pluto, Charon, 2003 UB313
Gerard Kuiper (1951)
The
scattered
disk objects
and the
Oort Cloud
50,000 to 100,000 AU from the Sun
Courtesy of Windows
to the Universe,
http://www.windows.uc
ar.edu
9
COMETS AND THE OORT CLOUD
•
Comets are "dirty snowballs," few km across, largely ice, small rocky cores
•
Orbit around the Sun on elongated elliptical orbits.
•
As comet approaches Sun, ice evaporates, dust escapes, comet becomes much
brighter
•
Pressure of Sun's light and "solar wind" (particles streaming from Sun) stretch
evaporating gas and dust into long, reflective tail.
•
Long orbital periods (millions of years), semi-major axis of ~ 1000-50,000 AU.
•
Come from distant, spherical reservoir surrounding Sun, called the Oort Cloud.
•
Deflected into inner solar system by gravity of passing stars (nearest star today is
200,000 AU from Sun).
•
Asteroids and comets are debris left over from early solar system. Oort cloud is
material kicked out of the inner solar system by gravitational interactions with Jupiter.
COMETS AND THE OORT CLOUD
Comet Halley
Parts of a Comet.
This composite of three images
(one in red, one in green, one in
blue) shows Comet Halley as
seen with a large telescope in
Australia in 1985.
This schematic
illustration shows
the main parts of a
comet.
Nucleus
Coma – spherical
cloud of gas and
dust
Invisible cloud of
hydrogen
Plasma Tail
Dust Tail
Edmund Halley (1656–1742).
Fig 12-13, p.277
10
Comet Hale–Bopp was one of the
most attractive and easiest to see
comets of the 20th century. It is
shown here as it appeared in the sky
on March 8, 1997. You can see the
comet’s long blue ion tail and the
shorter white dust tail.
Comet Tail Points Away from the
Sun.
The orientation of a typical comet tail
changes as the comet passes
perihelion.
Comet Tails. The smoother tail of dust curving to the right as individual dust
particles spread out along the comet’s orbit, and the straight ion tail pushed outward
from the Sun by its wind of charged particles.
A particle that is believed to be a tiny fragment of cometary dust,
collected in the upper atmosphere of the Earth.
Fig 12-19, p.280
11
Close-ups of Comets Halley and Borrelly
This historic photograph of the black, irregularly shaped nucleus of Comet Halley was
obtained by the Giotto spacecraft from a distance of about 1000 km. The bright areas
are jets of material escaping from the surface. The length of the nucleus is 10 km, and
details as small as 1 km can be made out.
Close-ups of Comets Halley and Borrelly
Even more detail is visible in this photo of Comet Borrelly taken at a range of 3000
km. The nucleus is 8 km long and very dark, with an average reflectivity less than 2
percent.
Head of Comet Halley
Here we see the cloud of gas and dust that make up the head or coma of Comet Halley
on January 20, 1986. On this scale, the nucleus (hidden inside the cloud) would be a
Fig 12-17, p.279
dot too small to see.
12