jovian planets Flashcards
(96 cards)
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.
