Astronomy Unit 3

To discuss the Jovian Planets we much first talk about
the Voyage program.
The mission of Voyager 1 & 2 is to
visit the Outer Solar System and beyond.
The voyager 2 velocity profile shows
the velocity flips at each planet.
Our booster was able to reach
Jupiter without gravity assist.
With gravity assist we have
left the Solar System.
Jupiter can be imaged well from Earth, even with a
small telescope.
Mass of jupiter
more than twice as much as all other planets put together
Radius of jupiter
11.2 times earth’s radius
density of jupiter
only 1.3 x the density of water – cannot be rocky or metallic as terrestrial planets are
rotation rate of jupiter
problematic, as jupiter has no solid surface; different parts of atmosphere rotate at different rates. the solution came from magnetic field, whose rotation period is 9 hr 55 min.
early images of jupiter showed the
great red spot and stripes
as our instruments improved
many more details emerged.
the spot became a _______, and stripes became ______________.
giant storm, bands of rising and falling gases
great red spot has existed for at least
300 years, possibly much longer
it seems to be an inverted storm dipping
to the planet rather than rising above it
the colors have changed over the years from
brick red to light brown
the size has changed from
3x to the size of earth to just over 2x
the atmosphere of jupiter has
bright zones and dark belts
zones are rising
warmer gasses from the interior, and are higher than belts.
the belts are
cooler falling gasses returning to be re-warmed.
the many storms seen in the belts are due to
turbulence caused by differential rotation in the atmosphere
the composition of jupiter’s atmosphere is mostly
molecular hydrogen and helium with small amounts of methane, ammonia, and water vapor.
the impurities seem to account for the
colors, probably due to complex chemical interactions that we are still studying.
no solid surface;
take top of the troposphere to be 0 km
the lowest level of the atmosphere is
the stripes. telescopes can not see through it.
measurements by Galileo probe show
high wind speeds even at great depth – probably due to heating from planet, not from Sun.
great red spot has existed for at least
300 years, possibly much longer.
color and energy source still
not fully understood
lightning-like flashes have been seen; also
shorter-lived rotating storms
one example: brown oval
really a large gap in clouds
we find that jupiter radiates more energy than
it receives from the sun
core is still
cooling off from heating during gravitational compression
jupiter could not have been a star;
it is far too cool and too small for that. it would need to be about 80 more massive to be even a very faint star
no direct information is available about jupiter’s interior, but its main components
hydrogen and helium, are quite well understood. the central portion is a rocky core
jupiter is surrounded by
belts of charged particles, much like the van allen belts but vastly larger
magnetosphere is
30 million km across
intrinsic field strength is
20,000 times that of earth
magnetosphere can extend
beyond the orbit of saturn
more than 60 moons have now been found orbiting jupiter, but most are
very small
the four largest are the
galilean moons, so called because they were first observed by galileo
galilean moons are
io, europa, ganymede, callisto
galilean moons have similarities to terrestrial planets;
orbits have low eccentricity, largest is somewhat larger than mercury, and density decreases as distance from jupiter increases
the small moons move in
mostly eccentric orbits far from jupiter
io is the most
dense of jupiter’s moons, and the most geologically active object in the solar system
io has many
active volcanoes, some quite large. it can change surface features in a few weeks. there are no impact craters, they fill in too fast.
io has the youngest
surface of any solar system object
the vulcanism on io is due to
tidal forces.
io is very close to
jupiter in a rather eccentric object, and also experiences gravitational forces from europa and ganymede.
the tidal forces on io are
huge and provide the energy for the volcanoes.
volcanic eruptions also eject
charged particles; those interact with jupiter’s magnetosphere and form a plasma torus
the moon europa has no
impact craters. the surface is water ice, likely with liquid water below.
tidal forces stress and crack the ice allowing
liquid water to flow out keeping surface glass smooth
ganymede is the
largest moon in the solar system – larger than planet mercury
impact history similar to earth’s moon, but
water ice and dirt instead of lunar rock
surface areas of ganymede once thought to be
cratered and flat turn out to have structures. these may be due to a form of plate tectonics
calisto is similar to
ganymede except there is no evidence of plate activity
one of the big surprises of the voyager program was the discovery of
a ring around jupiter.
these four moonlets are associated with jupiter’s ring. the two tiniest, ________, are embedded in the rin and seem to be shattering to feed the ring. the other two, ________, are “shepherd” moons.
metis and adastria, amalthea and thebe
the extremely faint gossamer rings, extending out beyond the main ring, are made up of
the very fine particles that escape the shepherd moons.
jupiter’s nickname
lord of the planets
saturn’s mass
5.7 x 10^26 kg
saturn’s radius
60,000 km
saturn’s density
700 kg/m^3 – less than water
saturn’s rotation
rapid and differential, enough to flatten saturn considerably
saturn’s rings
very prominent; wide but extremely thin
saturn’s atmosphere is similar to ______, except
jupiter’s, the pressure is lower
saturn’s atmosphere has
three cloud layers
cloud layers and the haze layer are
deeper than jupiter’s and more dense
like jupiter, saturn has
stripes and differential rotation
they are much more ______ and are rarely seen through saturn’s ________ and ________ ___________.
subdued, haze, cloud cover
jupiter-style “spots” are
rare on saturn. they don’t form as often and quickly dissipate if they do
saturn also has a strong __________, but only about ___ as strong as ________.
magnetic field, 5%, jupiter’s
it has van allen belts where charged particles form the
solar wind are trapped and they produce aurorae
saturn’s ring system – only ____ ring was seen
one
as our instruments got better we were able to
distinguish more detail
the rings are labeled by
letter in the order of their discovery
ring particles range in size from
fractions of a millimeter to tens of meters
they are made of
dust and rock covered with water ice
why rings? they are too close to planet for
moon to form – tidal forced would tear it apart
closest distance that a moon could survive by saturn is called the
roche limit; planetary ring systems are all inside this limit
the cassini division turns out
not to be completely empty.
the gap seems to be caused by an
orbital resonance with other ring particles and saturn’s innermost moon
voyager also found _________ that _____ and then __________.
radial “spokes”, formed, dissipated; this probably happens frequently
it was expected that sharp edges and divisions in the rings would be caused by
shepherd moons.
the other edges and divisions in the rings now seem to be the result of
resonance
however, a shepherd moon does define the
outer edge of the A ring through gravitational interactions
strangest ring is the
F ring. it appears to have braids and kinks
F ring’s oddities are probably caused by
two shepherd moons
details of ring formation are
unknown
it is thought that rings are
too active to have lasted since the birth of the solar system
either they must be _________ ____________ or they are the result of a
continually replenished, catastrophic events
saturn’s many moons appear to be made of
water ice or carbon based rocks covered with ice
besides the small moons, saturn has:
six medium-sized moons and one large moon
names of saturn’s six medium-sized moons
mimas, enceladus, tethys, dione, rhea, and iapetus
saturn’s one large moon is called _____ and it’s almost as large as _______
titan, ganymede
titan has an atmosphere ______ and ______ than ___________.
thicker, denser, earth’s
titan’s atmosphere is made mostly of _____ and _____ but it also has some very interesting chemistry in its upper atmosphere
nitrogen, argon
the surface of titan
can not be seen through the haze
after votage there was much desire to learn about
titan and the saturn system
the cassini orbiter and the huygens probe were sent
to make that study
the huygens probe analyzed the
atmosphere of titan as it descended
many trace chemicals mostly derived from
methane make the atmosphere chemically complex
on 9/16/05 huygens landed on a
slushy area dotted with boulders composed of water ice, under orange clouds composed of complex hydrocarbons
mimas, enceladus, tethys, dione, and rhea all orbit between
3 and 9 planetary radii from saturn, and all are tidally locked
tidally locked means
they have “leading” and “trailing” surfaces.
iapetus orbits
59 radii away, and is also tidally locked
rhea, the largest, has a
highly reflective, heavily cratered surface
the wispy features on rhea are on the
trailing side but not the leading
dione and tethys are
similar, having icy, heavily cratered surfaces
mimas is the
closest to saturn and has a crater covering one-third of its surface, the result of an impact that must have almost destroyed the moon
iapetus is
two-faced; its leading side is very dark (reflects 3% of incoming light) while its trailing side is bright (reflects 50% of incoming light)
enceladus orbits close to
mimas, but is very shiny, indicating a surface covered with ice crystals
enceladus possesses a
region of terrain near its south pole that is dramatically devoid of impact sites. scientists suspected its geologically active. the discovery in 2009 of material jetting from the pole and creating a great plume of icy particles confirmed these suspicions. the cassini continues to study it because it seems to have liquid water inside
hyperion, orbiting between ______ and ______, is so affected by their ____________ __________ that is orbital speed and the orientation of its axis are constantly __________ in a never-repeating pattern
titan, iapetus, gravitational fields, changing
uranus was discovered in _____ by _____; _____ planet to be discovered in recorded history.
1781, herschel, first
william herschel
born in germany, he anglicized his name when he came to england with hanover kings. he was a musician from a musical family. as an amateur astronomer, he looked at the sky with telescopes he built himself. among other things in the sky, he found what he thought was a comet. after future study, he realized he had found a planet, the first in recorded history. because of the fame of that discovery he became the court astronomer to king george 3rd
most of the planet have their axes slightly tipped with
respect to the plane of their orbits
uranus is unusual in that is is
tipped more than 90 degrees.
as a result of the tip, the rotation of uranus is
retrograde
during the voyager encounter in ____ we only saw a ________ as the sun shone on the _____ ____ ______ ________
1985, featureless face, pole of the planet
several years later, when the HST looked at it we could see
stripes and storms
as the uranus axis of rotation lies almost in the
plane of its orbit, the seasonal variations are extreme
rings around uranus were discovered from _______ and we saw ____ narrow rings and ______ broad rings
earth, 3, 2
the moon miranda has
large chunks of rock and large fields of ice. it looks like it has been shattered in the near past and is now pulling itself back together.
neptune was discovered in 1846, after
analysis of uranus’ orbit indicated its presence.
any new planet could not fit the
titus bode rule, hence the english and french astronomical societies ruled out another planet.
however, an englishman, _____ and a frenchman, __ _______, gave their calculations to a german, ______ ______, who found neptune immediately
adams, le verrier, john gottfried
voyager found a
great dark spot. it was determined to be a large storm.
of special interest were the
fast moving white clouds, demonstrating that the winds were the fastest in the solar system
the rings of neptune were discovered from the earth bu they looked like
arcs. voyager found complete rings but some of them were ‘lumpy’
neptune has _____ rings, ____ narrow and _____ broad. our ring theories have been badly stretched by these rings. they ______ seem to obey any rules
five, three, two, don’t.
two moons, ______ and ______, were discovered from the earth. _______ more were found by the voyager.
titan and nerid, eleven
the moon of most interest is _______. it is unique in many ways. it’s temperature is the ________ of any body in the solar system that we have visited, 32 degree k. it has an ___________, ______ _______, ____ ________, and ______ ___ ______ _____, ________ ______, and ______ ________.
triton, lowest, atmosphere, high winds, active geysers, evidence of plate tectonics, frozen lakes, water volcanoes
triton revolves around ________ retrograde and it rotates on its ______ retrograde
neptune, axis
the tidal forces and the retrograde motion will one day cause triton to
crash into the planet
nitrogen geysers have been observed on triton, contributing to
the surface features
also, there appear to be _____ _____ _____ and _____ ______ on triton
frozen water lakes, ice volcanoes
uranus and neptune are
very similar
mass of uranus
14.5 x E
mass of neptune
17.1 x E
radius of uranus
4.0 x E
radius of neptune
3.9 x E
density of uranus
1.3 x H2O
density of neptune
1.6 x H2O
uranus and neptune both have
substantial magnetic fields, but at a large angle to their rotation axes
the rectangle within each planet shows a bar magnet that would
produce a similar field.
magnetic fields of uranus and neptune must not be produced by
dynamos, as the other planets’ fields seem to be.
inferior structure of uranus and neptune, compared to that of
jupiter and saturn
rocks are
asteroids.
dirty snowballs are
comet nuclei
asteroids are quite ______, and most have ______ ______ in the asteroid belt between ______ and ________.
small, eccentric orbits, mars, jupiter
two other families _____ asteroids and _____ asteroids
apollo, trojan
the titus-bode rule predicted that there was
a planet at 2.8 AU from the sun. it was tentatively named the aster. when the field of rocks instead of a planet was discovered at that distance the tiny objects were called asteroids. now all rocks in space are called asteroids.
there are several motions of the asteroids in the solar system that have been identified:
– each in own elliptical orbit
– crossing orbits
– dissipation of belt
– captures by jupiter
– captures by mars
– captures by earth
– most finally fall into the sun
belt asteroids are ____, about ______ have been identified so far
rocky, 200,000.
belt asteroids are classified in types:
C-type, S-type, M-type
C-type
carbonaceous
S-type
silicate
M-type
metallic; iron and nickel
the three largest belt asteroids are
ceres, pallas, and vesta
vesta is the _____ largest asteroid, but _____ stop of the mission of the spacecraft dawn.
3rd, l1st
two small S-type asteroids, ____ and ___, were visited by the gallileo probe
gaspra, ida
ida has a small moon caleld
dactyl
a 2nd family of asteroids have orbits so eccentric that they _____________. they are called ________ ________, or near earth asteroids, and raise the concern of possible collision
cross earth’s orbital plane, apollo asteroids
over 26000 such asteroids have been discovered so far, of which about 600 have been
designated as potentially hazardous, due to their size, over one mile.
the NEAR-shoemaker spacecraft visited the _______ asteroid _____ on its way to its main target, ___.
C-type, mathilde, eros
mathilde, like many other asteroids, has a very low ____, and is probably not ____, but rather like a compact gravel pile
density, solid
eros does seem to be _____. it is covered with ____, as expected, but it also has free rocks sitting on it, not expected
solid, craters
the NEAR program presented an interesting challenge. not only did we need to go to a ____ ______ but we had to go to a new _____ ______. the maneuver was successful and we also landed on the asteroid.
new orbit, orbital plane
the ______ _______ _______ is located at the LaGrangian points for jupiter at L4 and L5
trojan asteroid family
comet nuclei are described as ______ ________. they reside in the _____ _____ which is a spherical cloud surrounding the sun. it came from the ____ caused when the sun went nuclear. the nuclei are ______ shaped objects of ice laced with dust and rock.
dirty snowballs, oort cloud, tsunami, irregular
the spherical oort cloud of comet nuclei is very _____ but not ________ populated. the trajectories go in every _______.
large, densely, direction
the ____ ____ ______ are more in the plane of the planets and are closer to the orbit of ______. they are roughly the same composition as the _______ _______ but many are much larger.
kuiper belt objects, neptune, comet nuclei
the kuiper belt begins around ___ AU from the sun, but continues out until it finally blends in with the _____ _____. the KBO orbits are irregular but move roughly in the ______ direction.
40, oort cloud, prograde
comets have:
a very small nucleus, a coma of gas and dust that is the most visible part that can be very large, a hydrogen envelope, a dust tail, and an ion tail.
the nucelus and the hydrogen envelope of comets are
not normally seen
comets have very eccentric
orbits
the comet’s tail always
points away from the sun, due to the sunshine and the solar wind.
the ion tail is
straighter than the dust tail.
long-period comets
over 2,000 years
short-period comets
less common and have period of less than 200 years
the theory of jupiter adjusting the orbit of an incoming comet would be
much less viable if we had not seen jupiter capture an incoming comet
halley’s comet is
on of the most famous.
halley’s comet has a period of
76 years and it has been observed since antiquity
halley’s comet’s orbit is not
in the plane of the solar system, so as it revolves around the sun, it passes through the plane of the earth’s orbit at a spot closer to the sun than the earth.
occasionally the earth passes through a
debris cloud left behind in the path of comets
the interaction of the atmosphere with these tiny particles looks like a
shower of meteors
meteor showers repeat
every year as the earth passes through that part of the sky
meteorites are defines as
any particle from space hat survives to reach the surface
most matter from space falls in
slowly and does not make a crater. these come mostly from the asteroid belt.
meteorites are mostly
very old. 4.4 to 4.6 billion years – and carry valuable information about the early stages of the solar system
rarely does a meteorite strike
near humans.
most meteorites are
rocky and often have a polished look from passing through the atmosphere.
they are distinguishable from earth rock by
their internal structure
a few are made of
iron and can be identified by their grain structure.
some large objects impact the earth when
their orbits intersect the earth’s orbit.
these are often larger from the apollo asteroids and their impact velocity can be
very large and their impact craters also large.
cretaceous-tertiary extinction likely resulted from
a giant meteorite impact near mexico 65 million years ago.
it caused a
10 year old “nuclear winter” that probably killed the dinosaurs along with 90% of the living things on earth and from which only 25% of the species recovered.
the event was likely due to an
impact of a near earth asteroid
Categories: Astronomy