Lec 18 and 19 Flashcards
(34 cards)
how would you determine an object’s true size?
we need to
know both angular size and distance to calculate an
object’s true size
are jovian planets all alike?
-all have much lower avg. densities than terr. planets
-dominated by hydrogen, helium and H
-share rotation rates that are rapid (measure by observing clouds)
what does the large radii of jovian planets indicate?
means their surface rotation speeds are much greater compared to Earth’s
how does fast rotation affect the shape of the jovian planets?
-gravity alone would make these planets perfect spheres, but rotation makes materials bulge outward
-material bulges the most near equator, where speeds around the rotation axis are highest
-size of equatorial bulge depends on balance between inward pull of gravity and outward push of rotation
-eq. bulge also helps keep moons and rings aligned with the equator
why is Jupiter sometimes referred to as a “failed star”
because it has a starlike composition but lacks the nuclear fusion needed to make it shine
–this is a consequence of its size:
Although Jupiter is large for a planet, it is about 1/80 as massive as the lowest-mass stars
As a result, its gravity is too weak to compress its interior to the extreme temperatures and densities needed for nuclear fusion.
how can the differences between the jovian planets be traced to their origins?
-according to the nebular theory, the jovian planets formed in the outer solar system, where it was cold enough for H compounds to condense into ices
-because H compounds were so much more abundant than metal and rock, some of the ice-rich planetesimals of the outer solar system grew big
-once planetesimals became massive, their gravity allowed them to draw in the hydrogen and helium gas that surrounded them
Models suggest that all four jovian
planets grew from ice-rich planetesimals of about the same mass but they captured different amounts of hydrogen and helium gas from the surrounding solar nebula.
Why did the different planets capture different amounts of gas?
Because of their distances from the sun as they formed
The solid particles that condensed farther from the Sun should have been more widely spread out than those that condensed nearer to the Sun, which means it would have taken longer for them to accrete into large, icy planetesimals
As the nearest Jovian planet to the Sun, Jupiter would have been the first to get a planetesimal large enough for its gravity to start drawing in gas, followed by Saturn, Uranus, and Neptune.
Because all the planets stopped accreting gas at the same time—when the solar wind blew all the remaining gas into interstellar space—the more distant planets had less time to capture gas and ended up smaller in size
What are jovian planets like on the inside?
-their large masses create strong gravity that most of their internal “gas” is compressed into other phases
Jupiter:
-extreme high temp and pressure (forces H into compact, metallic form
–conducts electricity
hypothesis for formation of Jupiter’s core
1) The formation of Jupiter’s core from icy planetesimals proceeded more slowly than scientists had predicted, so that Jupiter began to accrete hydrogen and helium gas
from the solar nebular while the core was still accreting.
2) Jupiter’s core formed quickly as expected, but a truly giant impact later disrupted
the core, dispersing its dense materials throughout the inner half of the planet.
internal heat
internal heat drives surface geology on the terrestrial worlds
-jovian planets do NOT have surface geo bc they don’t have solid surfaces
-most lost heat to space by emitting thermal radiation
Why does Saturn experience differentiation?
Emits twice as much energy as it receives from the sun, suggesting it has an ongoing source of heat
However, it’s mass is too small to be generating heat by contracting like Jupiter
Instead, its pressure and lower interior temp may allow helium to condense into liquid form at high levels within interior
The helium droplets slowly rain down to deeper interior
This gradual helium rain represents an ongoing differentiation
Means that higher-density material is still sinking into planet
what is the weather like on jovian planets?
Jovian atmospheres have dynamic winds and weather, with colorful clouds and enormous storms.
These atmospheres are made mostly of hydrogen and helium gas, mixed with
small amounts of various hydrogen compounds. The most
common compounds are water, methane
and ammonia
Some of these compounds condense to form the clouds
jupiter’s atmosphere
-Has a troposphere, a stratosphere, and
a thermosphere
Jupiter’s thermosphere consists of very low density gas heated to about 1000 K by solar x-rays and by energetic particles from Jupiter’s magnetosphere.
Below the thermosphere (still above clouds), is Jupiter’s stratosphere
–recall that a planet can have a stratosphere only if it has a gas that can absorb ultraviolet light from the Sun
–ozone plays this role on Earth
Jupiter lacks molecular oxygen and ozone, but
has a few minor atmospheric ingredients that absorb solar ultraviolet photons
Below the stratosphere lies Jupiter’s troposphere,
where the temperature rises with depth because greenhouse
gases trap both solar heat and Jupiter’s own internal heat.
what’s the condition for a planet having a stratosphere?
a planet can have a stratosphere only if it has a gas that can absorb ultraviolet light from the Sun
Jupiter and the coriolis effect
The same basic process occurs on Jupiter, but Jupiter’s greater size and faster rotation make its Coriolis effect much stronger.
As a result, instead of being split into just three smaller cells, each of
Jupiter’s circulation cells splits into many alternating bands of rising and falling air.
why do ammonia clouds form only in rising air and not falling air?
Jupiter’s lower atmosphere has
ammonia throughout, so there’s always ammonia in the air rising upward.
However, once the ammonia condenses to
form clouds of ammonia ice, these ice flakes fall back down as ammonia “snow,” so the air that continues to rise above the clouds has very little ammonia left in it.
When this ammonia-depleted air spills to the north and south and returns downward in the bands of falling air, there is not enough ammonia to form clouds
great red spot
Jupiter’s most famous feature—the Great
Red Spot—is a giant storm more than twice as wide as all of planet Earth.
It is somewhat like a hurricane, except that
its winds circulate around a high-pressure region rather than a low-pressure region
The color may be the result of chemicals formed by interactions between the storm’s high-altitude gas and solar ultraviolet light
A planet can have a global magnetic field if it has:
(1) an interior region of electrically conducting fluid
(2) convection in that layer of fluid
(3) at least moderately rapid rotation
how does jupiter’s moon, I0 contribute particles?
in Jupiter’s case its volcanically active moon, Io, contributes many additional particles
–these particles help create auroras on
Jupiter
They also create belts of intense radiation around Jupiter, which can cause damage to orbiting spacecraft.
Jupiter’s magnetosphere, in turn, has important effects on Io and the other moons of Jupiter.
The charged particles bombard the surfaces of Jupiter’s icy moons, with each particle blasting away a few atoms or molecules
–this process alters the surface materials and can even generate thin atmospheres
what does the strength of each planets magnetic field depend on?
The strength of each planet’s magnetic field depends primarily on the size of the electrically
conducting layer buried in its interior
why are almost all moons almost circular and close to equatorial plane?
Most of the medium-size and large moons probably formed by accretion within the disks of gas surrounding individual jovian planets
–that explains why their orbits are almost circular and lie close to the equatorial plane of their parent planet, and also why these moons
orbit in the same direction in which their planet rotates
how can the moon, Io be so hot inside?
Scientists have identified a process called tidal heating, which arises from effects of tidal forces exerted by Jupiter.
Just as Earth exerts a tidal force that causes the Moon to keep the same face toward us at all times, a tidal force from Jupiter makes Io keep the same face toward Jupiter as it orbits.
But Jupiter’s mass makes this tidal force far larger than the tidal force that Earth exerts on the Moon.
Moreover, Io’s orbit is slightly elliptical, so its orbital speed and distance from Jupiter vary.
This variation means that the strength and direction of the tidal force change slightly as Io moves through each orbit, which in turn changes the size and orientation of Io’s tidal bulges
The result is that Io is continuously being flexed in different directions, which generates friction inside it
The flexing then heats the interior
Why is I0’s orbit slightly elliptical, when all other large satellites have circular orbits?
This is due to orbital resonance, which can be explained by a relationship between the orbital periods of 2 or more objects
The three moons therefore line up periodically, and with each alignment they exert gravitational tugs on one another that are in the same direction and therefore add up over time.
This tends to stretch out their orbits, making them slightly elliptical
why is Europa one of only a few moons in the
solar system to have a magnetic field, and why does its magnetic field changes as Jupiter rotates?
The simplest way to explain this change is to hypothesize that Europa’s magnetic field is created (or induced) in response to the rotation of Jupiter’s strong magnetic field.
This type of response is possible only if
Europa has a liquid layer of electrically conducting material.
A salty ocean would fit the bill, but convecting ice would not. The data also suggest that Europa’s liquid ocean must be global in extent, and that it is about as salty as Earth’s
oceans
