jovian planets Flashcards
Jovian planets are radically different in size & copmposition from
terrestrial planets = “gas giants” because
e hydrogen (H
2) & helium (He)
are predominant or important components, though Uranus & Neptune
are also called “ice giants” as they mainly consist of ice-forming
molecules
Jupiter & Saturn are made almost entirely of
f hydrogen (H
2
)
& helium (He)
Jupiter & Saturn have
thick mantles
of metallic H
2.
Uranus & Neptune still have large amounts of
H2 & He
Uranus & Neptune still have large amounts of H2 & He but
less than 50% as they are made primarily of hydrogen compounds, e.g. H 2O, CH 4 & NH 3.
Saturn has a larger ice content than Jupiter, but
Uranus & Neptune have much-much more (>50%!) because of the ices’ increasing
abundance further and further away in the initial Solar nebula
Jovian planets formed in the outer Solar system beyond
the frost line, where it was
cold enough for the more
abundant hydrogen compounds to condense into ices.
All 4 Jovian planets have formed around ice-rich
planetesimals with a similar mass of
~10MEarth that
grew to great size subsequently drawing in H2, He, and
other compounds (self-reinforcing positive feedback).
…again, because of their increasing abundance further and further
away in the primordial Solar nebula
All planets stopped accreting at the same time when the
first solar winds blew remaining material in space
Jovian planets: Origin of their compositional differences—–> Timing
: Planets that start earlier will capture more material before the
first solar winds blow it away
Jovian planets: Origin of their compositional differences—–> Location
Planets formed easier & earlier in a denser part of the nebula (i.e. closer to the Sun) as their cores quickly gathered H2 & He first, and grew faster!
Hydrogen compounds not formed in icy particles if too “close” to the Sun
(i.e. Jupiter & Saturn orbits)
Uranus & Neptune are denser than Saturn! →
because they have
(much) less amounts of low density gases (H2 & He)
The more low density stuff there is, the less dense the overall (i.e. the more
low density material there is in the composition of a planet, the smaller its
final overall density)
Logical that Saturn is less dense than Uranus & Neptune — ;>
Hydrogen compounds, rock, metal are all denser than H2 & He gases
but Jupiter is more dense than Saturn → it doesn’t follow the
pattern… WHY?
Jupiter’s radius is close to the max. possible radius for a ”normal” Jovian planet
Smallest stars are even smaller than Jupiter!
…though some exoplanets can be larger!!
because are
made of much lighter elements, without large, rocky cores
inside.
Jupiter is 3
× more massive but only slightly larger than Saturn → extra mass strongly compresses its interior to much higher
density
Jupiter: Internal structure
No solid surface but fairly distinct interior layers.
Mostly H2 & He except the core.
H2 present in different phases.
Gaseous H2 in outer layer is ~10% of radius = Jupiter’s
atmosphere.
Liquid hydrogen occupies next 10% of Jupiter’s interior
In most of the rest of Jupiter, the extreme T & p force H2 into a compact metallic form! Its molecule & atoms break
into free protons (p+) & electrons (e–)= plasma!
conducts electricity
generates Jupiter’s MF.
At those extreme T & p metallic hydrogen exists as a LIQUID
rather than a solid! (not solid like a metal!).
Core = mix of H2 compounds, rock & metals.
Most probably all mixed together (non-differentiated)
Saturn’s 4 interior layers differ from Jupiter due to its
lower mass & weaker gravity Lower mass phase changes occur deeper in Saturn thicker gaseous layer & thinner & deeply buried metallic hydrogen. Weaker gravity but less dense & fast rotation centrifugal force stronger at equator (more) flattened shape
Because of their rapid rotation and low density,
the Jovian planets are not quite spherical. Saturn shows the biggest difference between its actual shape and a perfect sphere
Uranus & Neptune have almost identical interiors:
Both have rocky cores like Jupiter & Saturn, but this is where
the similarity ends.
p not high enough to form liquid or metallic H2 at all
H2& He layer surrounds odd “oceans” of liquid “ices” of H2 compounds.
All Jovian planets radiate amazing amounts of energy,
more than they receive from the Sun!
Jupiter:, TALK ABOUT ITS RADIATION
Jupiter radiates up to 2× as much energy as it receives
Most of the energy comes from slow contraction of interior
(i.e. Jupiter is still slowly contracting, releasing potential
energy).
This thermal energy heats up from below the atmosphere playing an
important role in its structure & weather.
Besides this blackbody radiation component, part of Jupiter’s emitted
energy does NOT obey Planck’s law → due to synchrotron radiation from the particles trapped in Jupiter’s strong MF
what is synchotron radiation
occurs when a charged particle encounters a strong magnetic field - the particle is accelerated along a spiral path following the magnetic field and emitting radio waves in the process - the result is a distinct radio signature that reveals the strength of the magnetic field
Internal heat – Saturn
Saturn also radiates more energy than it absorbs from the
Sun: it emits 2.3× more energy than it receives (more than
Jupiter!).
Saturn is less massive than Jupiter
should have less leftover
accretion heat and also cannot generate it by (still) contracting!
Potential energy of falling He rain converts into
kinetic energy and its interior heats up (the precipitation of helium inside its metallic hydrogen mantle).
This gradual He rain represents a sort of ongoing differentiation: higher density material (liquid He) is still slowly sinking inside the planet.
Jovian planets: Internal heat - Uranus & Neptune
Uranus lacks a strong internal energy source like Jupiter &
Saturn: radiates only 1.1 × the energy received from the Sun.
Neptune emits 2.7 × more energy as it receives from the Sun; most possibly because of an intense greenhouse effect due to the abundance of CH4 in its composition.
Other possible sources of internal heat:
EITHER resulted from some mysterious still on-going contraction,
OR is accretion heat that should have been radiated b.y.a., like Uranus
(but all or most of it still retained due to extreme greenhouse effect
mentioned above).
Another possible heating mechanism is atmospheric interaction with
ions trapped in its MF.
The internal heat of ALL Jovian planets is the
crucial factor driving atmospheres & in the generation of MFs.
Jovian planets’ atmospheres & weather
- Jupiter
Much thicker (than Earth’s), also much more dynamic (very
strong winds of hundreds of km/h) & turbulent on large
scales (many storms, some larger than Earth!)…
… due to:
its fast rotation (causing a stronger Coriolis force)
splits the large
equator-to-pole circulation cells into many (>3) smaller cells,
the much larger amounts of energy injected in it,
From the bottom = internal heat.
From the top = very energetic particles trapped in its strong MF (besides
solar radiation).
The absence of any solid surface to slow down Jupiter’s storm
systems/spots
can persist for many years (sometimes decades,
even centuries!).
Made up of mainly H2 & some He but many other
components are also present in small amounts, of which H2 compounds are the most important.
Jovian planets’ atmospheres & weather - Jupiter (cont’d)
Structure & temperature variation are very similar to Earth’s.
H2 compounds in Jupiter’s atmosphere form clouds
Cloud
layers correspond to the condensation points of different H2 compounds at various corresponding altitudes.
Each makes clouds of a different color.
Just as for Earth, the atmospheres of Jovian planets are governed
by interactions between sunlight and gases, with Jupiter’s the
best example:
Thermosphere: absorbs solar X-rays AND energetic particles trapped in
the intense Jovian magnetosphere.
Stratosphere: absorbs solar UV
drives chemical reactions that create a
smog-like haze that masks the color & sharpness of clouds & layers below.
Troposphere: greenhouse gases trap heat from BOTH Jupiter & the Sun
Strong convection in the troposphere causes Jovian winds and
weather (strongest near equator).
Jovian planets’ atmospheres & weather
- Saturn
The temperature profile of each Jovian planet determines the color of its appearance→ Various cloud layers form
where a particular gas condenses.
Saturn has the same cloud layers as Jupiter, but they form
deeper (since Saturn is colder on the overall because it’s
farther away from the Sun, despite its larger amount of
internal heat) and spread farther apart (due to its reduced
overall density and lower gravity).
Large tilt & long orbit period should cause long extreme seasons, but
strong internal heat greatly reduces seasonal temperature differences.
Its features are hazy and washed-out because its atmosphere is
thicker: lower mass means lighter gravity
its atmosphere is
less compressed & less dense than Jupiter’s.
Winds at high(er) velocities on Saturn due to more energy
emitted from its core as compared to Jupiter
r
Jovian planets’ atmospheres & weather - Uranus
The atmosphere of Uranus is also mainly composed of H2 with some He but in different proportions (it has more He),
and with much more hydrogen compounds, of which CH4 is
predominant (which gives its pale blue color) and small
amounts of hydrocarbons.
Lacks a strong internal energy source
much less active
atmosphere, with fewer features (storms, eddies, etc.),
however…
Its extremely tilted axis ultimately produces very uneven
warming of its hemispheres
long term N-S flows
across the latitude zones that can drive very fast winds.
The combination of these effects
washed out atmospheric
features, like Saturn’s
Jovian planets’ atmospheres & weather
- Neptune
The atmosphere of Neptune although still mainly made of H2
has even more He than Uranus, also with CH4 and traces of other compounds
Yet something else must contribute to Neptune’s vivid blue color, but
scientists aren’t certain what.
It has the fastest winds in the Solar system, up to ~2,200
km/h!
must be due to a significant internal energy (heat?)
source since its outer atmosphere is one of the coldest places
in the Solar System, with cloud tops at ~55 K.
Possible sources of the impressive internal heat mentioned earlier.
Its internal source of energy powers the atmosphere to produce cyclone-like storms that are not seen on its twin – Uranus- but which, very surprisingly, are short lived.
talk again about the galilean moons
Io is the most volcanically active body in the Solar system.
Europa has one of the smoothest surfaces in the Solar system.
Ganymede is the only satellite in the Solar system known to
possess an magnetosphere (due to a hot core-generated MF).
Callisto is a heavily cratered undifferentiated ice ball.
what about the volcanoes on io surface man
Io’s entire surface is covered with large active volcanoes with so
frequent eruptions that they constantly refresh the surface and
cover any other features (e.g. asteroid craters)
What do the active volcanoes on IO surface mean
Io must be quite hot inside but it should be geologically dead
talk to me about IO tidal forces
Io’s slightly elliptical orbit causes tidal heating due to huge tidal forces
exerted by Jupiter.
Why does Io have an elliptical
orbit?
caused by orbital resonances
the phenomenon of orbital periods falling
into a simple mathematical relation (a
certain ratio) between the 3 inner
Galilean moons, that resulted in periodic
alignments
→ not a coincidence but a direct consequence of (mutual) feedback
from the tides these moons exert on each
other and on Jupiter.
what;s the ice/water world
europa
briefly tell me part 1 europa
Europa is another big moon (similar to Luna’s size), also tidally
locked with Jupiter and with a surface totally made up of water ice
(covered in many places with a reddish layer believed to be the
result of a reaction between salts deposited from water brought to
the surface with the sulphur ejected from Io)
briefly tell me part 2 europa
Lacks large-scale features but has a a fractured, frozen surface,
with patches of different types of areas
All these indicate ongoing cryogeological activity due to tidal stresses
briefly tell me part 3 europa
It must have an interior made hot by tidal heating, but weaker than on Io due to farther distance from Jupiter
Measurements by Galileo spacecraft suggest it has:
A metallic core with a rocky mantle;
A magnetosphere, due to an induced magnetic field (MF) – i.e. it is NOT generated in a hot core but induced in its underlying ocean by interaction with Jupiter’s MF
briefly tell me part 43 europa
All these indicate most possibly that a (very?) salty ocean
of global extent must be present (very deep, most probably
next to the solid core)
Could be at least as salty as Earth’s oceans
However, we do not have enough evidence that Europa’s
subsurface convecting material is water rather than ice
Still, Europa remains a prime contender for Life in the Solar system!
which moon has a salty ocean, of jupiter’s
europa
tell me about the largest and most massive moon of jupiters
ganymede
part 1 gany
Ganymede: the largest & most massive moon, also tidally locked with Jupiter and also with a surface covered by (mostly
water) ice
Ganymede’s surface is a mix of 2 types of terrain
Dark highly cratered regions
Very old (~b y.)
Lighter, somewhat younger (but still ancient), regions with an
extensive array of grooves and ridges
Must have been
refreshed by occasional upswellings of liquid H2O or slushy ice
Measurements by Galileo spacecraft confirmed it has, for ganymede I mean
An ocean deep under the surface, probably extending to depths
of hundreds of km, which is salty;
A magnetosphere
→ The only moon in the Solar System
known to possess a core-convection caused MF
hence it has a source of internal heat (hot liquid Fe core)
Callisto:
The 3rd-largest moon after Ganymede & Titan
The largest object in the Solar System that may not be
differentiated
a ~50%-50% mix of rock & H2O ice
Tidally locked to Jupiter but NOT in orbital resonances with the other 3 Galilean moons
has NO tidal heating
Callisto has a heavily cratered surface that:
Has 2 types of terrain:
Bright white patches on ridges → pure water ice
A dark powdery substance covering low-lying areas (most
of surface)
Lacks tectonic features → expected for an undifferentiated object without a source of internal heat
Callisto MF
It has an induced MF!
most possibly a deep ocean
150…200 km deep is present under its undifferentiated
surface
Callisto could be partly differentiated. WHY?
Because water ice can have various phases, whose melting temperatures ↓ with ↑ p
TITANNNNNNNN
saturn’s largest moooooon (and the second largest in the solar system) AND IT IS LARGER THAN MERCURY
tell me about the subsurface ocean of tITANNNNNNN
An NH3-rich subsurface ocean (~240 km thick?) may
exist under a crust of CH4-rich ice (~35 km thick?)
does titan have a differentiated interior
yes
only moon known to have a dense atmosphere
Titan —> e (2 × as thick as Earth’s!) of 95% N2, 4.9% CH4 (in the lower troposphere!
In the stratosphere there is only 1.4% CH4) and a small percentage
of many hydrocarbon compounds, with ethane (C2H6), propane (C3H8) & acetylene (C2H2) the most important ones (although even PAHs were discovered) → caused by the CH4 breakup by UV light in smaller reactive molecules that subsequently bond with one another.
what are the key features of titan
Surface pressure: about 1.45 × that of Earth’s!
It receives only ~1% of Earth’s sunlight but its atmospheric CH4 causes a strong greenhouse effect, without which its surface would be
far COLDER!
titan is a moon of?
saturn
Ethane and methane are liquid on which surface
titan
talk about the surface of titan
Ethane and methane are liquid on Titan’s surface and form a network
of seas, lakes and rivers
Titan’s CH4 cycle is a distant cousin to
Earth’s water cycle but it similarly carves the surface of Titan
The only other body in the Solar system with liquids on its surface, including
complex hydrocarbons (but at 94 K)!
talk about the ch4 on titan
UV light-based break-up should have used up all CH4 in Titan’s
atmosphere within 50m y.
CH4 must be somehow replenished from a reservoir on or within Titan itself, e.g. probably from cryovolcanoes
The continued presence of CH4 in atmosphere is a major enigma.
titan c’est un prime contender for life>?
The presence of many, including complex, hydrocarbon
compounds make it an intriguing but prime contender for (the
possibility of a very different type of) Life in the Solar system!
Weird fuckin name, sounds like a head pain elephant
Enceladus
, Saturn’s 6th largest moon
talk about the surface and body of encie
Its surface (like Europa’s) is totally covered by water ice
one of the most reflective bodies of the Solar system.
It may have a massive rocky core.
Its surface is craterless in many places and also criss-crossed by
crevasses (“tiger stripes”) which are much warmer than the rest of the surface
Seems to have strong tidal heating
Cryovolcanoes shoot km-high water-rich plumes venting from the S polar region (most of which later disperse into space to feed Saturn’s E ring) indicating that under the ice surface a large ocean of liquid water could be present
A very strong candidate for Life in the Solar system!
triton
The 7th & largest of Neptune’s 14 moons, and the only one massive enough to be spheroidal.
which is the only other body in the solar system with liquids on its surface, including complex hydrocarbons at 94K
titan
Triton part 1
Properties similar to Pluto but ~40% more massive!
The only large moon that has an unusual retrograde orbit around its
planet, AND at a high inclination relative to Neptune’s equator —–»> it probably is an icy dwarf planet captured from the Kuiper Belt before many of the moons now seen orbiting the planet formed.
Triton part 2
Moreover, Triton is tidally locked.
Triton’s icy surface has one of the highest albedo in the Solar system —–> it reflects so much of what little sunlight reaches it that the moon is one of the coldest objects in the Solar system.
The sublimation of surface ices creates a thin, hazy atmosphere
(pressure = 1/100,000…1/70,000 of Earth’s)
Regions on its surface show evidence of cryovolcanic and cryotectonic activity. The internal heat source for Triton’s geologic activity is not known, but it may involve tidal heating.
Why do Jovian planets have rings?
All Jovian planets have rings: we can no longer think that rings
are rare!
An explanation is needed for the formation of rings, that doesn’t require rare events, to have happened for ALL 4
Jovian planets
Rings formed from dust that was and is constantly being created by
many small impacts on moons orbiting those planets.
Cannot be leftover from planet formation: particles too small to have survived this long.
Also cannot be remnants of a broken up moon (moons don’t just “wander” away and this is a very rare occurrence).
There must be a constant replenishment of these tiny particles.
All Jovian planets have rings because they possess many small moons
close-in
Tiny impacts gradually grind away these small moons, but they are large enough to
still exist after 4.5b years of such sandblasting.
In some cases it is also due to (cryo)volcanic eruptions.
Why do Jovian planets have rings? (cont’d)
Jupiter’s ring system may be formed by dust kicked up as interplanetary
meteoroids smash(ed) into the giant planet’s small innermost moons.
Additionally, Io & Europa constantly eject new material
Saturn’s incredible rings may be an accident of our time
Very wide: ~4× larger than the planet radius!
Although very large and wide, they’re also very thin: (a few tens of meters)
the thinnest known astronomical structure!
Similar to Jupiter’s Io, Enceladus also constantly supplies material to one of its
rings (ring E)
Asteroids are
rocky leftover planetesimals orbiting the Sun that never became part of a planet
Asteroids 1
Wide size ranges (up to 1/3 of the moon: Ceres = dwarf planet) but most are
small —–> non-spherical.
Made mostly of rock & metal but also large proportions of C-rich material
(because they condensed within the frost line in the Solar nebula) and some
even have small amounts of water.
Some are made ONLY of metal: possible core fragments of shattered planetoids
A meteorite is a
rock from space that falls through Earth’s
atmosphere and impacts the ground
Meteor refers to the
left by a particle/object plunging
through Earth’s atmosphere (many do not even touch the ground to leave a crater/meteorite, but burn completely in the atmosphere)
Most meteorites are pieces of asteroids falling on Earth.
Objects smaller than 10 m are called meteoroids
talk about the higher metal content of meteorites
Some have higher metal content, and often contain elements rare on Earth (e.g. Ir) & different ratios among their isotopes than in terrestrial rocks.
Two types of meteorites:
1) Primitive
2) Processed
Primitive meteorites
– unchanged in composition since they first formed 4.6 b years ago in the Solar nebula. Have 2 subtypes: Stony and C-Rich
Primitive meteorites Stony
made of (several) rocky materials mixed with some metallic flakes
Primitive meteorites C-Rich
Similar to stony but also contain large amounts of carbon compounds, and sometimes small amounts of water
Processed meteorites
– younger, and are pieces from core, mantle or crust of shattered early planetoids — > Some experienced processes like volcanism or differentiation. Also have 2 subtypes: Metal and Rocky
Metal Processed meteorites
high density; mainly made of Fe & Ni
Rocky Processed meteorites
lower density; made of rock with compositions resembling those of
terrestrial mantles and crust. Very similar to volcanic rocks on Earth.
The origin of primitive meteorites:
Why are some primitive meteorites
stony while others are C-rich? —> Depends where they formed/accreted
in the initial Solar nebula: beyond ~3 AUs carbon (C) compounds
could condense —> C-rich primitive meteorites formed in the more
distant/outer regions of the asteroid belt, and beyond
Yet a few other meteorites originated from other terrestrial planets, most often the Moon or Mars.
Blasted in space by a large impact of
that planet with another early
asteroid.
Comets
Comets are any leftover ice-rich planetesimals formed beyond
the frost line.
Comets 2
Regardless of size or whether it has a tail, or where it resides or came from
It is basically a chunk of ices (H2O, and various frozen gases) mixed with rocky dust together with some other complex chemicals
Comets 3, fuzzy ball
A comet appears in our sky as a fuzzy ball with a long tail
Comets 3, blind tails
Vast majority of comets do not have tails & are never visible in the
sky
Comets 3, bright tails
Only a few enter the inner Solar system to grow tails.
Most will not return, but a few end up in elliptical orbits & periodically
return close to the Sun
Comets are heated by????????
by the Sun when they enter the inner Solar system
“dirty snowball”
The nucleus is a “dirty snowball” (the chunk of ices & dust!) & the source for comet’s tail.
Coma
is the dusty atmosphere emanated by the heated nucleus.
How do they get their tails? PLASMA
The plasma tail is ionized gas (by
solar UV) swept from the coma &
pushed in a straight narrow tail by
the solar wind.
How do they get their tails? DUST
The dust tail is made of microscopic particles that are unaffected by the solar wind but are pushed by the much weaker radiation pressure (momentum exerted by photons in the sunlight). The coma & tail start appearing at a distance of ~3…5 AUs (typ. around Mars orbit)
We have never witnessed a m
a major impact on a solid world in
modern time.
However, a major impact by the Shoemaker-Levy 9 (SL9) comet
on Jupiter occurred in 1994.
Comet SL9 broke apart & caused a string of violent impacts with Jupiter
Stark reminder that such catastrophic collisions still happen
Did an impact kill the dinosaurs?
Many major impacts have occurred on Earth in the past.
Fossil records show occasional large dips in the diversity of species mass extinctions.
The most recent was 65m years ago, ending the reign of the
dinosaurs
Carancas, Peru
15 Sep 2007
Impact crater made by a 1.2 m stony meteorite filled with groundwater soon after impact.
Tunguska, Siberia
30 Jun 1908
A 40 m object (argued by some to
have been a comet) disintegrated &
exploded in the atmosphere.
Tunguska, Siberia/Carancas, Peru
Small impacts can be expected more frequently.
Major impacts are very rare, but the effects could be devastating
if it happens—> need for permanent observation of larg(er) objects
Very small impacts happen
almost daily.
Impacts large enough to cause mass extinctions are very rare
many m of years apart
