Post on 11-May-2015
Planetesimal Ejection
Larger “debris” leftover from creating the planets are either captured as moons of the larger planets, or the gravity of the planets guides the debris into the asteroid belt, Kuiper belt, or Oort cloud.
Asteroids and meteoroids are small objects made of mainly rock and metal. They are found primarily in and around the Inner Solar System.
The only difference between the two is size. Asteroids are all larger than 100 meters in diameter, or have a mass more than 10,000 tons - meteoroids are smaller.
Inner Solar System
Asteroids and meteoroids are usually found near the plane of the solar system.
Those orbiting between Mars and Jupiter are in the asteroid belt, while those in Jupiter’s orbit are in the Trojan regions.
Some of these asteroids and meteoroids come closer to the Sun. Those that cross the orbit of Earth are called Apollo asteroids.
A meteor is seen when any comet, asteroid, or meteoroid enters the Earth’s atmosphere. The “shooting star” you see is a meteor.
A meteorite is the chunk of rock or metal that has reached the surface of the Earth from space.
A meteoroid is a small chuck of rock or metal that orbits the Sun
Why does this asteroid look “weathered”? Like a rock you might find on a beach?
Everything gets hit by meteoroids!
Meteor Trail
Barringer Crater
Meteoroids are constantly hitting the Earth. Most of these meteoroids are the size of grains of sand or so. They make short quick meteor trails visible only at night. Usually you can see about 1 or 2 an hour. Larger meteors are very rare.
Big meteoroid strikes like the one that produced Barringer Crater (the meteoroid was about 50 meters across and hit with an energy of few megatons of TNT) occur once every few thousand years.
The most recent event was in 1908 in Tunguska, Siberia.
We are not sure if the object was a meteoroid or a comet, but it exploded in midair with an energy of about 20 to 40 megatons of TNT!
Tunguska Debris
We think that asteroid impacts are even more rare. We guess that they occur once every 600,000 years or so. Such impacts would be large enough to cause global climate changes - a “nuclear winter”.
The leading theory about the extinction of the dinosaurs of course involves an asteroid impact. All over the world you can see evidence for this in the K-T boundary in geologic strata (layers).
Comets
Unlike asteroids and meteoroids, comets are made up of ices - frozen water, CO2, and possibly other lighter gasses - and also rock and dust. As the ices evaporate off the comet, a cloud called the coma is formed around the nucleus. The solar wind and radiation pushes the gas and dust away from the nucleus to form the tail.
Halley’s Comet Closeup
Comet Tails
There are usually two tails for a comet, and ion tail and a dust tail. The ion tail is made of ionized comet material and is pointing directly away from the Sun. The dust tail is curved as the dust particles orbit around the Sun after getting released by the comet.
Meteor Showers
As Earth passes through the debris path of a comet, observers on Earth can see many many meteors coming from the same general area of the sky. These meteor showers or storms are often named for the constellation that they seem to “come from”.
Comet Reservoirs
Long period comets are thought to mainly come from the Oort cloud.
Short period comets (like Halley’s) are thought to come from the Kuiper belt.
We believe that most objects in the Kuiper Belt and Oort cloud are made of ices and rock.
Since they are so far form the Sun, even oxygen and nitrogen will turn to ice!
The Discovery of Pluto
After the discovery of Neptune, astronomers still thought another planet might (but they were wrong) be influencing the orbits of Uranus and Neptune. In 1930 Clyde Tombaugh discovered Pluto while looking for this new planet. Pluto is the only planet we have not explored with a spacecraft. The New Horizons craft should get there in 2015!
Pluto and Charon
Pluto and its moon are both probably Kuiper Belt objects. By measuring their size and mass we can calculate their density. From this we believe are mainly made up of rock and ice, very similar to Europa, Ganymede, Callisto and Triton.
Pluto
A fuzzy map of Pluto made from Hubble Telescope images.
The Hubble telescope has just recently discovered two new moons around Pluto. In 2006 they were given the names of Nix and Hydra. The appear to be in the same plane as Charon, so their formation should be related.
KBOs Compared
In the last few years several Kuiper Belt objects have been found. And several even have their own moons.
There are at least 11 KBOs with diameters of 1000 km or more. M. Brown/Keck Observatory
Pluto’s Demotion
RESOLUTION 5AThe IAU therefore resolves that planets and other bodies in our Solar System, except satellites,be defined into three distinct categories in the following way:
(1) A "planet"1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects3, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
IAU - INTERNATIONAL ASTRONOMICAL UNION web site - http://www.iau2006.org/mirror/www.iau.org/iau0602/index.html
Planet X
Astronomers once thought that another large planet (Earth size or bigger) might exist far out in the Kuiper belt or Oort cloud. In fact Pluto was found searching for planet X. Such a planet could disrupt the orbits of objects out there, and send them in toward the inner Solar System, where we see them as comets.
So far we have no evidence that “planet X” exists. However we have searched only a small fraction of the Kuiper Belt, and know even less about the Oort cloud.
Stellar Balance
Our Sun lives in a state of balance....
between the force of gravity pushing in....
and the pressure from fusion pushing out.
Solar Composition Change
As stars burn Hydrogen into Helium the amount of Heliumin the star’s core builds up.
At this point in the star’s life the temperature in its core is not high enough to fuse Helium into other elements, so the Helium just sits there inert.
Solar Composition Change
When the amount of Helium builds up to a certain level, fusion at the center of the corestops, with fusion only occurring in a shell surrounding the non-burning Helium.
Since the temperature of the core is much higher than before, the core is producing a lot more energy. This extra energy “pushes out” the rest of the star and the star gets bigger!
So as the core gets smaller the rest of the star gets larger!
The center of the core is now no longer beingpushed out by the energy produced from fusion. As the amount of Helium “ash” grows, gravity starts to compress it.
As the core is compressed the temperature goes up until Helium can be fused.
We see many different stars in our galaxy. Some stars are enormous Red Giants that are hundreds of times larger than our Sun.
Will our Sun ever become a Red Giant?
YES!
How? When?
Red Giant
When this happens to our Sun in about 4 billion years our Sun will expand to possibly engulf the Earth!
Now Helium is being fused into Carbon, and the process repeats, the core shrinks and gets hotter, but our Sun is not large enough for Carbon fusion to start…
G-Type Star Evolution
Throughout the stars life, as the star uses up its fuel, the core continues to shrink, the core temperature continues to rise, and more and more energy is being emitted by the core, and the star gets larger and larger until…
Planetary Nebulae
White Dwarf on H–R Diagram
After all the fuel is gone, and the star has made a nebula, all that is left is a White Dwarf
This is the leftover core of the old star, itis very small (Earth sized) and very hot
White dwarfs shine only due to stored heat, as they cool they grow fainter and fainter.
Eventually (trillions of years from now) they will be cold enough to stop emitting lightaltogether,
If the star is massive enough the temperature in the core of the star can get high enough (1 billion K) to start the fusion of Carbon into heavier elements like Aluminum, Neon, and Sodium. When this happens, the core shrinks again and the star expands again.
Stars that are massive enough to produce temperatures up to 4 billion K can burn all the elements up to Iron in their cores.These stars can grow up to 1000 times the size of our Sun - Supergiants!
Heavy Element Fusion
Iron is the stopping point for any star, fusing Iron into heavier elements does not release energy. Fusion still continues around the iron core, which keeps growing.
In the iron core, there is no fusion to create an outward pressure to counteract the force of gravity.
Core collapse supernova
The iron core of the star that is about the size of the Earth. The iron in the core is made up of ...
protons (+)neutrons (0)electrons (-)
Most of the space inside an atom is taken up by the electrons. When the Iron core of a star reaches critical mass called the Chandrasekhar mass (1.4 times the mass of our Sun) the force of gravity is too great and the protons and electrons get “squeezed” together to make neutrons.
Core collapse supernova
Now the core of the star is made up of just
neutrons (0) !!!
Without electrons around to take up space, gravity can cause the core to collapse.
In about 1 minute or so the core (that was supporting the weight of the entire star) collapses from the size of the Earth to the size of Chicago (~10 miles across). The rest of the star collapses onto the core and then “bounces”.
Supernova 1987A
The core becomes a Neutron star and we see a Supernova!
This core-collapse supernova is also called a type II supernova.
Over the time period of just a few days, a supernova can emit as much energy as our Sun will in its 10 billion year lifetime.
Supernova Light Curves
Astronomers can tell the two types of supernovae apart by looking at how bright the supernova is over a period of time.
Also astronomers can distinguish the two types by looking at a spectrum and seeing how much hydrogen was present in the explosion. A type I (carbon-detonation) supernova has very little hydrogen present, unlike a type II (core-collapse) supernova.
Supernova Remnants
In our galaxy we estimate there is a type I and a type II supernova about once every 100 years. The last one that we saw in our galaxy was in 1604....so we are due!
We do see supernovae quite often in other galaxies.
Supernova 1987A
This supernova was the closest in recent history, and the only one where we were able study it accurately.
Neutron Stars
Neutron stars are extreme objects
Density: 1015 g/cm3
Temperature: 1012 K when born
Magnetic Field: 1012 times stronger than Earth’s
Spin: from 60 rpm to 38,000 rpm
Curved Space
Newton’s Law of Gravity:The force between mass m1 and mass m2 is....
F = Gm1m2/R2
So if an object has no mass, there should be no force on it due to gravity!
Einstein: Mass causes space itself to curve and warp, and objects travel on this surface....
Tests of General Relativity
The first test of Einstein’s theory of general relativity came when we measured how the gravity of our own Sun can bend light.
Gravitational Redshift
The gravity of a black hole is so strong, that light can not escape!
The region where this is true is inside the event horizon.
The event horizon is NOT the surface of the black hole. It is just the boundary between where light can escape, and where it can’t!
Black Holes
Black holes are formed when you compress an object to a size smaller than the Schwarzschild radius for that object.
For the Earth it is about 1 cm
For Jupiter it is about 3 m
For our Sun it is about 3 km.
The only force strong enough that we know of to produce a black hole is a type II (core-collapse) supernova. Even then only very massive stars will end up as black holes.
Black Holes
If you were far from the black hole, you would feel no unusual effects. In fact if our Sun suddenly became a black hole the Earth would simply keep orbiting it like usual.
As you approach a black hole the gravity gets stronger, and the tidal forces start to stretch you.
If you could survive to come close to the black hole, you would observe severe distortions in both space and time as predicted by Einstein!
Robot–Astronaut
What is IN a black hole?
We believe that all matter could be compressed to a singularity! A point of infinite density and zero size.
BUT....
There is no way to find out!
The Solar System
There are three kinds of objects in our SolarSystem (other than the Sun)
Terrestrial planets
Jovian planets
and other stuff.....
asteroids, comets, and meteoroids
Sun and Planets - Relative Sizes
This is the Eagle nebula as seen by the Hubble telescope.
Fusion creates elements heavier than hydrogen and helium, and supernovae disperse these elements out into the galaxy.
The dust and gas seen here is probably made up of gas from the Big Bang and also from many supernovae.
This gas and dust is the raw materials that stars and solar systems are made out of.
Right now, new stars and solar systems are being formed in this cloud of gas and dust.
As intense radiation from stars just outside the cloud “blow” the cloud away, we can see small clumps of denser regions of gas and dust being revealed.
In each of these clumps is a solar system that is forming, each with a sun that could someday be much like our own, and each perhaps with planets like Earth.
It all starts with a cloud of gas and dust. The gravitational attraction between the gas and dust particles slowly causes the cloud to collapse, to contract. This causes all of the matter in the cloud to become more concentrated.
Because the initial gas cloud had some rotation, as the collapse happens this rotation speeds up, and the cloud flattens out into a disk.
This is due to something called conservation of angular momentum.
In the center of the disk the gravity is the strongest, so most of the mass in the solar system accumulates there. This will become a protostar.
The rest of the material starts clumping together in orbit around this central mass. Larger clumps condense out of the gas and dust.
These clumps then start to join together in a snowball effect. This forms planetesimals.
During this time a protostar has formed. It is bigger than our Sun, but not as hot yet. The temperature in the core is not hot enough for fusion to start. Once fusion starts, it becomes a star!
Beta Pictoris
The Virial Theorem
How does the dust and gas in the cloud heat up as it collapses?
A small part of the cloud that is far away from the center of the cloud has a lot of gravitational potential energy. As this small part of the cloud “falls” closer to the center, it loses potential energy and gains kinetic energy. It starts moving faster.
However, the cloud is spinning, and the faster the small part of the cloud moves, the farther away from the center orbits.
So how does the cloud collapse? The small part of the cloud needs to lose both potential and kinetic energy. It does this by turning potential and kinetic energy into heat! Gas molecules and dust grains hit each other, and these collisions turn kinetic energy into heat and the temperature of the cloud goes up!
The Virial TheoremYou can derive an equation from Newton’s laws that shows how much energy the gas and dust will turn into heat as it slowly spirals in toward the center of the cloud.
This equation is called the virial theorem.
Basically what this means is that as matter collects to form a large object, like the Sun, Earth or even our Moon, the matter heats up to higher temperatures.
This is how the temperature in the center of our protostar got high enough (10 million Kelvin) for fusion to start.
This is one of the reasons why the center of the Earth is hot enough to melt metal.
The planetesimals in orbit around the protostar are still growing larger, accumulating more and more material.
Eventually the planetesimals all clump together and form protoplanets! These have roughly the right sizes as our planets do today, but they are not quite done growing yet.
Temperature in the Early Solar Nebula
Because of the higher temperatures in the inner solar system the protoplanets near the protostar were very different than those farther away. The near protoplanets were made of mostly rock and metal, with very little hydrogen, helium, oxygen, water, nitrogen, or other lighter chemicals
The protoplanets that were farther out were made more out of the lighter chemicals.
Since there were more of these lighter materials than anything else in the early solar system the outer planets became much larger.
http://sohowww.nascom.nasa.gov/
When fusion starts and our Sun is born, it starts emitting huge amounts of energy.
The enormous amounts of radiation and solar wind that the new star produces “blows” or “pushes” away all of the dust and gas that is leftover from the production of the planets.
The new planets in the solar system looked nothing like what we see today. Planets were all very hot, the inner planets were all completely molten.
The atmospheres of all the planets were mainly made of hydrogen and helium. The smaller planets like Earth didn’t have a strong enough gravity to hold on to this atmosphere for very long.
The planets were undifferentiated - meaning they did not have different regions made of different materials.
Planetesimal Ejection
Larger “debris” leftover from creating the planets are either captured as moons of the larger planets, or the gravity of the planets guides the debris into the asteroid belt, Kuiper belt, or Oort cloud.
Comet Reservoirs
By learning about the Earth we can make comparisons to the other planets and understand them better.
The Earth
Earth has a ....
magnetosphere
atmosphere
hydrosphere
crust
mantle
and an outer and inner core
Planetary ScienceAll the different parts of the Earth ....
- magnetosphere- atmosphere- hydrosphere- crust- mantle- core
... affect each other. The dynamics of how processes in these regions affect the planet is called Planetary Science.
Earth’s Interior
The interior of the Earth is differentiated because the Earth was completely molten at some point in its history.
Both radioactivity and asteroid impacts supplied the heat to melt the Earth.
Seismology
Seismology is the study of how shock waves from earthquakes travel through the Earth.
We can learn about the density of the interior of the Earth this way much like an ultrasound test can see inside people
Sudden changes in density can cause these waves to be reflected or refracted. Seismic waves also can show if the material is solid or liquid.
Earth’s Interior
From seismology we know that the Earth’s core is much more dense than the silicate based mantle and crust, and the core is made of a solid center, and a liquid outer region.
From the density measurements made using seismology we believe that the core is mostly made of iron, with some nickel
Plate Drift
Earth is a very geologically active place with volcanoes and plate tectonics. The mantle is semi-molten, with convection slowly causing hotter material to rise and cooler material to fall in the mantle. The tectonic plates of the Earth “float” on these convection currents.
Global Plates
Seismology
Here you see the seismic waves from the 2004 Sumatra earthquake. You can see how the seismic waves could still be detected even after going around the world almost two times
Earth’s Magnetosphere
Magnetohydrodynamics is the study of how electrically conductive fluids behave.
Because the Earth’s core is a rotating and convecting system of a metallic liquid, strong electrical currents are produced in the Earth’s core.
This produces the Earth’s magnetic field!
Earth’s Magnetosphere
Computer calculations using magnetohydrodynamics have shown that if a planet does not have
• a conducting liquid• convection• and rotation
The planet will not have a strong magnetic field like the Earth’s.
Van Allen Belts
The Earth’s magnetic field deflects and traps particles from the Solar Wind. The trapped particles are located in two regions called the Van Allen belts.
Aurora Borealis
Some of the Solar Wind makes it through the Earth’s magnetic field and hits our atmosphere making it glow. This usually happens at the North and South poles – the Aurora Borealisand the Aurora Australis
Earth’s Atmosphere
Convection
Most of Earth’s weather occurs in the troposphere. Weather on Earth is driven by convection, warm air rising and colder air falling.
The Greenhouse Effect and Global Warming
Over the last two decades evidence has been growing that the Earth’s atmosphere is getting warmer.
Most likely this is due to human activity. It is possible that this rise in temperature is linked to the increase in “greenhouse gases” like CO2 in the atmosphere.
Greenhouse Effect
The Greenhouse effect refers to the “blanket like” effect that certain gases have. These gases absorb and re-emit infrared radiation, which prevents this radiation from escaping to space so easily.
Ocean currents – like the thermohaline current shown here – can have a profound effect on the climate by the transportation of energy (heat) and matter (dissolved gasses).
Hydrosphere
Lunar Tides
Lunar Tides
The force of gravitydecreases with increasing distance. This is responsible for the tidal force effect.
This effect causes the Earthto very slightly deform or bestretched by the moon’s gravity.
Since water is more free to move than solid ground, we seethis effect mostly in the Earth’s oceans – the tides. In the open ocean this effect is quite small only about a 1 meter high bulge.
Solar and Lunar Tides
The Sun also produces a tidal effect on the Earth but it is much smaller than the moon’s effect.
The largest tides are the Spring tides when the Sun, Moon, and Earth are all roughly in a line.
The smallest tides are the Neap tides when the Moon and Sun are at right angles to the Earth.
Tidal Bulge
The Tides on Earth are not directly in line with the Moon. Since the tidal bulge is offset, the Moon can affect the Earths rotation, and the Earths rotation can affect the Moon’s orbit! This is causing the Earth’s rotation to slow down, and the Moon to mover farther away from the Earth.
Tidal Bulge
Just like the moon produces a tidal bulge on Earth, the Earthmakes a tidal bulge on the moon. Over time the effect of Earth’s gravity on the moon’s tidal bulge changed the rotation of the moon. This is why the same side of the moon always faces the Earth. This is called tidal locking. The Moon’s orbit and rotation are tidally locked or synchronized.
Tidally locked means that the time it takes for the Moon to rotate is the same as the time it takes to orbit the Earth. So we can only see one side of the Moon from Earth.
Tidal Bulge
The Earth’s rotation is not yet synchronized with the Moon’s orbit. The Earth’s rotation will keep slowing down, and the Moon will keep moving away until they become tidally locked, and only one side of the Earth will face the Moon.... many billions of years from now.
The Earth’s rotation is slowing at a rate of 0.002 seconds per century and the Moon is moving away 3.8 cm per year.
Full Moon, Near Side
There are two different kindsof surfaces on the near sideof the moon.
Maria – flat, darker regions that are made of younger material. Produced by lava flows.
Highlands – older, lighter colored regions with manymountains and craters
Full Moon, Far Side
On the far sidewe find mainly justhighlands and very few maria.
The Moon
Since the moon is differentiated, it too was molten at some time in its history.
However not a lot is known about the interior of the moon.
We believe that the core of the Moon is no longer molten.
Moon, Close Up
When the Moon was younger and its crust was thinner and its interior still molten, we believe that the crust cracked and lava flowed up through these cracks and formed the maria.
Meteoroid Impact
Lunar Surface
A layer of dust covers the surface of the Moon. This dust is caused by the many, many impacts of meteoroids that continually occur on the Moon.
Lunar Formation
The dominant theory of how our Moon formed is the Impact Theory – which says a protoplanet about the size of Mars hit the Earth shortly after the Earth formed
Lunar Formation
A fraction of the debris from this impact collected together to form our Moon.
The Terrestrial Planets
The Messenger spacecraft
We were not able to learn much about Mercury from Mariner 10 (the only spacecraft to visit Mercury). The Messenger spacecraft is on its way to Mercury right now, it will do 3 flybys of Mercury in 2008 and 2009, and then go into orbit in 2011. Since Messenger is more modern and advanced than Mariner 10, we will learn much much more.
Mercury’s Rotation
Mercury’s rotation (59 days) is tidally locked to 2/3 of an orbital period (88 days). Its orbit and rotation is not synchronized like our Moon’s because Mercury’s orbit is eccentric (more elliptical than the orbits of most planets). This means that one “day” (from noon to noon) on Mercury lasts 176 Earth days!
108
Because it is so small the core of Mercury is probably mostly solid, meaning that scientists did not expect to find a magnetosphere!
One the scale shown the Earth’s field would register at around 50,000nT, so we think that something very different is causing Mercury’s magnetic field.
Mercury’s Surface
Mercury’s surface has a large number of these scarps or cliffs like giant cracks in its surface.
Mercury never had plate tectonics like the Earth. When the crust of Mercury cooled it shrank causing the crust to crack.
Venus, Up Close
Because of Venus’s dense cloud cover most of what we know about Venus’s surface and rotation comes from using radar.
There has been only a few spacecraft to land on Venus,but each survived for only a short time.
The atmosphere of Venus is made up of carbon dioxide, with clouds of sulfuric acid. The atmosphere is some 90 times denser than Earth’s. The Greenhouse effect causes the surface temperature of Venus to be close to 730K day or night.
The Atmosphere of Venus
This is warmer than even Mercury which is a lot closer to the Sun! Venus is far too hot for gases lighter than CO2 to stay in its atmosphere. Venus has almost no water, O2, or N2.
Venus Magellan Map
In 1995 the Magellan spacecraft was ableto make a much moredetailed radar map of Venus.
Possibly active shield volcanoes, craters, and volcanic structures called coronae were seen by Magellan.
Venus’s Surface Features
pictures from Magellan spacecraft NASA/JPL
Venus Corona and Volcanoes
pictures from Magellan spacecraft NASA/JPL
We can not tell from these radar images if Venus is geologically active right now, but we believe it could be active. We believe that Venus is much like a “young” Earth was just before Earth’s oceans formed.
Venus has several times more volcanoes as Earth does, however Venus does not have plate tectonics like Earth. This could be why the surface of Venus appears older than Earth’s surface (~500 million years vs. ~100 million).
Venus
Venus has no detectable magnetosphere, probably due in part to Venus’s very slow rotation rate and a lack of convection in the core.
We expect Venus to have a crust, mantle and a core like Earth
Venus in Situ
This is one of the few pictures of the surface of Venus that we have. There have only been 6 Russian landers (no US) each lasting only an hour or two before running out of power.
Terrestrial Planets’ Spin
While Venus is the planet that is closest in size to the Earth, Mars has a rotation rate (24.6 hours) and a tilted axis (24 degrees) that are very similar to Earth.
Mars, Up CloseThe rovers have made many rock and soil measurements. The main components of this sample were silicon, iron, and calcium. The Martian soil is rich in iron, which is why is is red.
Mars Atmosphere
Mars has a very thin atmosphere (less than 1% of Earth’s) of mainly carbon dioxide. The surface temperature is around 50K lower than Earth’s, but would be colder without the greenhouse effect.These temperatures were taken by a combination of the Mars Global Surveyor and the rover Opportunity.
Picture taken by Spirit of a sunset on Mars.
Water on Mars
Because of orbiter pictures and geologic studies done by the rovers we are now fairly confident that large amounts of liquid water was present at some time on Mars.
Water on Mars
NASA/JPL
Martian Outflow
Where is all of this water now? Most of it was probably lost when Mars lost it’s atmosphere, but some of it might still be there, frozen under the surface.
Scientists believe that because Mars is so small and so far from the Sun, that the planet cooled off much faster than the Earth did. When the core of the planet started to solidify it started to lose its magnetosphere. Mars lost almost all of its atmosphere due to a combination of being exposed to the Solar wind, and having much weaker gravity than Earth.
Martian Outflow
We have seen evidence for liquid water maybe existing on the surface of Mars recently.
NASA/JPL/Malin Space Science Systems
Life on Mars?
We still do not have absolute proof that life existed on Mars. But we think it is possible that it did long ago.
Planetesimal Ejection
Larger “debris” leftover from creating the planets are either captured as moons of the larger planets, or the gravity of the planets guides the debris into the asteroid belt, Kuiper belt, or Oort cloud.
Inner Solar System
Most asteroids and meteoroids are usually found orbiting between Mars and Jupiter are in the asteroid belt.
Some of these asteroids come closer to the Sun. Those that cross the orbit of Earth are called Apollo asteroids.
Why does this asteroid look “weathered”? Like a rock you might find on a beach?
Everything gets hit by meteoroids!
Barringer Crater
Meteoroids are constantly hitting the Earth. Most of these meteoroids are the size of grains of sand or so. They make short quick meteor trails visible only at night. Usually you can see about 1 or 2 an hour. Larger meteors are very rare.
Big meteoroid strikes like the one that produced Barringer Crater (the meteoroid was about 50 meters across and hit with an energy of few megatons of TNT) occur once every few thousand years.
The most recent event was in 1908 in Tunguska, Siberia.
We are not sure if the object was a meteoroid or a comet, but it exploded in midair with an energy of about 20 to 40 megatons of TNT!
Tunguska Debris
We think that asteroid impacts are even more rare. We guess that they occur once every 600,000 years or so. Such impacts would be large enough to cause global climate changes - a “nuclear winter”.
The leading theory about the extinction of the dinosaurs of course involves an asteroid impact. All over the world you can see evidence for this in the K-T boundary in geologic strata (layers).
Jupiter’s Interior
The interiors of the Jovian planets are very different from the Terrestrial planets.
What we call the “surface” of Jupiter is really the top of the the atmosphere.
Just like the Sun, Jupiter is made up of mostly hydrogen and helium. The colorful clouds in Jupiter’s atmosphere are made of ammonia, methane, water, and phosphorous and other chemicals.
Jupiter’s Convection
Jupiter radiates about twice as much heat than it absorbs from the Sun. All this energy drives Jupiter’s weather system.
The lighter colored zones are regions where warmer material is rising, and the darker colored belts are regions where material is sinking. All of this convection activity causes many swirling “storm” systems to be present at any one time in Jupiter’s atmosphere
The weather on Jupiter is very dynamic and chaotic. There are many storms or “vortices” like these pictured by the Galileo probe.
All Jovian planets have differential rotation - meaning that different regions of the planet rotate at different rates.
Galileo mission Nasa/JPL
Jupiter
Most of what we have learned about the Jovian planets has come from spacecraft.
Voyager I and II
Galileo and probe
Cassini and Huygens
Jupiter’s Storms
The largest of these storms is the Great Red Spot, first seen by astronomers over 300 years ago. It is so large the Earth could easily fit inside of it. What causes it and why it is red are still mysteries.
Galileo mission Nasa/JPL Here you see two pictures taken about 75 min. apart on the dark side of Jupiter, the white specks are lightning in Jupiter’s atmosphere, some 100 to 1000 times brighter than on Earth.
Jupiter’s Interior
The “atmosphere” ends about 20,000 km below the surface. The pressure is so great here that hydrogen is forced to become a liquid, and acts like a metal.
The very core of Jupiter is probably rocky and metallic, like Earth, but probably larger and much more dense.
Pioneer 10 Mission
All the Jovian planets have extensive magnetic fields
Jupiter’s extends well past the orbit of Saturn!
Jupiter’s magnetic field is so strong because of the large sea metallic hydrogen that is under the atmosphere.
If you could “see” Jupiter’s magnetosphere, from Earth it would look 5 times larger than the full Moon!
Auroras on Jupiter and Saturn
Aurorae have been seen on both Jupiter and Saturn.
Saturn
Cassini is currently in orbit around Saturn and is continually sending back more data about Saturn and its moons.
Saturn is very similar to Jupiter in many ways. Their atmospheres are similar, with Saturn having thicker upper level clouds, so less of the more colorful lower clouds can be seen.
Both Jupiter and Saturn rotate in less then 10 hours. This fast rotation rate gives them a squashed look.
Saturn’s Atmosphere
Saturn radiates three times as much as it receives from the Sun (unlike Jupiter that radiates only twice as much).
We think that this extra heat is coming from the helium in Saturn’s atmosphere condensing and forming “rain”. As this rain falls its energy is turned into heat.
This also explains why there is less helium in Saturn’s upper atmosphere compared to Jupiter.
Jovian Interiors
Since Saturn is not quite as large as Jupiter, its internal pressures and temperatures are not as high as those in Jupiter, and so its region of metallic hydrogen is not as thick.
Saturn’s Weather
The weather on Saturn is similar to Jupiter, however there is no “Great Red Spot” like storm on Saturn.
NASA/JPL/Space Science Institute
NASA/JPL/Space Science Institute
Some storms on Saturn have been seen to rotate “backward” compared to storms on Earth. This has also been seen on Jupiter.
Saturn’s Cloud Structure
We have discovered a strange hexagon structure around Saturn’s north pole…. And a “hurricane” with a central “eye” at Saturn’s south pole.
Uranus and Neptune
Just one spacecraft (Voyager II) has visited Uranus and Neptune
Both planets get their bluish color from methane in their atmospheres.
Jovian Interiors
We believe both Uranus and Neptune are just smaller versions of Jupiter and Saturn on the inside. Neptune emits more heat than it absorbs (just like Jupiter and Saturn), but Uranus does not!
Uranus’s Seasons
Jovian Magnetic Fields
Uranus’ and Neptune’s magnetic fields have strange orientations, and are not at all aligned with the rotation of the planet.
Other than the Earth’s Moon, there are only 6 other “major” satellites in the Solar system: Io, Europa, Ganymede, Callisto, Titan, and Triton. There are many many more satellites, but all of them are smaller than these. Each of these moons are special and unique in its own way.
The four moons of Jupiter discovered by Galileo are called the Galilean moons. Io orbits the closest to Jupiter, followed by Europa, Ganymede, and last Callisto.
Galilean Moon Interiors
Io is the most geologically active moon or planet in the Solar System. Tidal forces from Jupiter are constantly deforming the planet. All of the friction deep within the moon causes numerous volcanoes to be active on the surface.
We believe that Europa might contain a thick liquid water ocean beneath a crust of solid ice. The tidal forces on Europa are not as strong as they are of Io, but they are enough to keep its oceans from freezing solid. Because there is liquid water on the moon, scientists believe Europa is our best bet of finding life on a world other than our own!
Io
Europa
Galilean Moon Interiors Ganymede is the largest moon in the Solar System, even larger than Mercury or Pluto. Ganymede and Europa both have a magnetic field. We believe Ganymede has a thick water/ice layer around a rocky mantle and an iron core.
While we think Callisto is made up of similar material as Ganymede, Callisto is undifferentiated. Basically no geological activity has occured there since it was created some 4.5 billion years ago. This makes it the most heavily cratered object in the Solar System.
Ganymede
Callisto
Titan
Titan’s Atmosphere
Titan is the only moon to have a thick atmosphere. The atmosphere is made up of mostly nitrogen and methane. The methane on Titan acts very much like water does in the weather here on Earth.
Huygens ProbeThe Huygens probe appears to have seen an ocean and rivers as it descended to the surface of Titan. The surface temperature on Titan is only 94 K (-350 F)! So there is no chance that the ocean and rivers have liquid water, instead they probably have liquid methane.
From data on how the probe landed, it is believed that the probe landed in “mud” or soft sand.
Nasa/JPL/ESA
Enceladus
Enceladus
One of the “minor” moons of the Solar System, Enceladus is the 6th largest moon of Saturn. Cassini has observed a water “plume”. We believe this is a “geyser” formed from a pocket of liquid water under the surface of the moon.
Enceladus
Nasa/JPL/ESA
Triton
Not a lot is known about Triton. It is the only major moon to orbit its planet backwards. Because of this its orbit is slowly decaying, and someday might form a ring around Neptune! Triton does have a thin nitrogen atmosphere, in part due to cryovolcanism. Triton was probably was a Kuiper Belt object that was captured by Neptune.
Saturn’s Rings
Of course the most amazing thing about Saturn is its rings.
These rings are made up millions and millions of small clumps of ice, most about the size of a golf ball.
NASA/JPL/Space Science Institute
This is the Encke gap seen by Cassini right after orbital insertion around Saturn. Cassini was probably less than 1000 miles from the rings when this was taken.
NASA/JPL/Space Science Institute
Cassini actually went “through” a gap in the rings during orbital insertion around Saturn. So we were able to get some very close pictures of the rings.
The Rings of Saturn
Courtesy NASA/JPL-Caltech
NASA/JPL/Space Science Institute
The rings are made up of many many small bands. Several structures can be seen in the rings, gaps, waves, spokes
The Rings of SaturnHere “shepherd moons” make rings and gaps.
Here different colors represent different sizes of ice particles. The blue regions have smaller ice particles
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Distortions in the F ring due the gravity of the moon Prometheus
Roche Limit
When a moon comes within a planet’s Roche limit the tidal forces pull the moon apart, making rings!
Just recently Cassini has found larger moonlets in the rings (about 100m by 5000m in size). These could be larger fragments of the larger moon that broke up to form the rings.
NASA/JPL/Space Science Institute
Here Cassini is looking directly at the night side of Saturn. You can see the formation of new rings outside the Roche limit. The outer most ring (the E ring) is formed by the water plumes from Enceladus.
NASA/JPL/Space Science Institute
Miller-Urey Experiment
This showed that to create the building blocks of life you just need liquid water, basic chemicals, and a source of energy.
Hydrothermal Vents
Proof that life can exist and flourish without solar energy.
Life on Earth
We think it only took about 50 million years for life to develop once there was a solid surface and oceans on Earth, but for 2.5 billion years all life was single celled.
Life changed Earth’s early atmosphere, from one with CO2, N2, methane, and other gasses, to the atmosphere of O2 and N2 that we have today.
Only about half a billion years ago did complex multi-celled life (plants and animals) evolve.
Life Elsewhere in the Solar System
Possibly: Europa, Mars
Longshot:Ganymede, Enceladus
The Drake Equation
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The Drake Equation gives an estimate of the number of other intelligent civilizations that we can “talk to”.
R is the rate of star formation (~7 per year)fp is the fraction of stars with planets ne is the number of planets that are habitable fL is the fraction of habitable planets with life fi is the fraction of planets with life that is intelligent ft is the fraction of intelligent life to develop technology L is the lifetime of the technological civilization
The Drake Equation
LfffnfRN tilep
The Drake Equation gives an estimate of the number of other intelligent civilizations that we can “talk to”.
R is the rate of star formation (~7 per year)fp is the fraction of stars with planets (~1??)ne is the number of planets that are habitable (~0.1?)fL is the fraction of habitable planets with life (~1?)fi is the fraction of planets with life that is intelligent (~0.1?)ft is the fraction of intelligent life to develop technology (~0.5?)L is the lifetime of the technological civilization (100,000 years?)
These numbers are my guesses.... you can choose your own!
1000005.01.011.0173500
Drake Equation
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If there are 3500 intelligent civilizations in our galaxy then the average distance to the nearest alien civilization is about 160 light years!!
This means we will probably never have a “conversation” with aliens!
Our radio signals have only traveled some 70 light years.
1000005.01.011.0173500
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Gliese 581Gliese 581 is a red dwarf about 20 light years from Earth.
Planet “c” around Gliese 581 has a mass of about 5 times greater than Earth’s, and has a radius that could be around 1.5 times larger than Earth’s.
This is the first “Earth sized” planet that we have discovered around another star!
Gliese 581Just this year astronomers announced finding Gliese 581 e with a mass of 1.9 Earth masses. However it orbits very close to the star – it has an orbital period of just over 3 days!
Planet “c” has an orbital period of only 13 days and “d” has a period of 83 days! It has been calculated that “d” is in the star’s habitable zone where liquid water could exist on the planet!
Stellar Habitable Zones