Wednesday 13 April 2011
3rd exam-==-=-=- 22 April 2011
Reading for exam 3 (solar system)- sections as in HORIZONS ed. 12e
Chapter 15 read 15-1 and 15-2 and 15-4 skip 15-3
Chapter 16 read it all , Sooner Fans
Chapter 17 skip 17-1 , read 17-2 and 17-3
Chapter 18 read intro, section 18-1, 18-2, 18-3, 18-6
you can skip sections 18-4, 18-5 (about Neptune and Uranus)
Chapter 19 read it all, Sports Fans
Telescope viewing of Saturn Monday nite. There was a pretty good turnout, given the last-minute announcement (I never know what the weather will do, so I usually wait til day of viewing to announce). If you were unable to make it to the observatory Monday nite, there will be at least one more chance to see Saturn though the OU telescope in the next month.
Jupiter from ground Jupiter is one of the favorite objects of the backyard astronomer who watch the cloud bands and Great Red Spot which grace the planet. The 4 Galilean moons (and sometimes their shadows on the planet) provide endless amusement.
Jupiter vs Earth size
Its HUGE , Sooner Fans! About 11 times diameter of Earth.
Voyager movie This movie was derived from images over a period of about 40 days from one of the Voyager spacecraft as it appoached Jupiter. The movie shows one image each Jupiter rotation period. (Jupiter rotates every 10 hours). The different cloud bands show differential rotation, proving that the disk we see cannot be a solid surface.
Giant planet interiors Jupiter and Saturn are composed mostly of hydrogen and helium, with a smattering of heavier elements. This is COMPLETELY opposite of the terrestrial (or inner) planets like the Earth- Earth has very little hydrogen and hardly any helium. The interior of Jupiter can loosely be described as a liquid, as the hydrogen and helium gases are compressed by the great gravity of Jupiter into a liquid-like substance. Actually, it is hard to imagine what this stuff would actually look like- we simply cannot acheive these pressures in any lab on Earth, so we don't have a sample of the material in the interior of Jupiter to play with. In the diagram, this strange material is labeled "metallic hydrogen".
Jupiter atmospheric probe Jupiter was visited briefly by the Voyager spacecraft in the late 1970s, as part of the outer solar system "Grand Tour" of the 4 outer planets from the 1970s thru the 1980s.
A spacecraft called Galileo was sent to Jupiter, arriving in 1995. Galileo orbited Jupiter, studying the planet and its moons for 7 years. In 2002, part of the Galileo spacecraft detached from the main spacecraft and went on a suicide mission into Jupiter. The probe radioed back info for about an hour before being crushed by the pressure. In 2003, the main spacecraft, by then hardly working due to radiation damage, was crashed into Jupiter on purpose to avoid any possibility of it crashing into Europa and bringing any Earth bacteria to Europa.
Juno at Jupiter (artists conception) A new NASA spacecraft, called Juno, will (we hope) blast off this August and arrive at Jupiter in 2016 for an extended orbital mission. (Juno was Jupiter's wife, as you all remember from Mythology 101, right? Here is what the NASA web site says: In Greek and Roman mythology, Jupiter drew a veil of clouds around himself to hide his mischief. It was Jupiter's wife, the goddess Juno, who was able to peer through the clouds and reveal Jupiterís true nature. The Juno spacecraft will also look beneath the clouds to see what the planet is up to, not seeking signs of misbehavior, but helping us to understand the planetís structure and history. )
Moons of the Solar System Shown to scale are all the large and medium sized moons of the solar system, along with some of the smaller ones. Top row is our Moon, then 2 moons of Mars (very small compared to Moon). Next row is Jupiter moons. Next is Saturns, then Uranus and Neptune. Finally, Charon, moon of Pluto. Since this slide was made, two additional moons of Pluto have been discovered.
Jupiter's 4 big moons Io, Europa, Ganymede and Callisto (read from top down). (I eat green cheese)
Jupiter and Io
Io Io , the pizza moon. Io is the most volcanically active place in the solar system (per square kilometer). The surface is covered with sulfur and sulfur dioxide frost from the volcanoes. (The average surface temperature is cold- about 130 K).
Why is Io so volcanically active? Io is the closest moon to massive Jupiter and the tidal forces caused by Jupiter and pulls from the other moons cause Io to be twisted and "kneaded" like a lump of dough. This causes internal friction and heat inside Io that keeps its interior molten. Cracks the the surface layer allow some of this molten material to escape, creating the volcanic vents we observe.
The following images show some of the volcanic features on Io.
Io volcano Because Io has only a tenuous atmosphere, volcanic eruptions spray out like a symmetric lawn sprinkler (but one that can be 10s to 100s of km high!). On Earth, volcanic eruptions are disrupted by winds.
Io lava flow
Io's changing face Images taken some time apart show extensive changes in surface of one region of Io due to volcanic eruptions.
Europa Europa's surface is the smoothest of any major body in the solar system. It is composed mainly of ice. Europa has a very thin atmosphere composed primarily of oxygen (O2). This is presumably derived from solar UV photons breaking apart H2O molecules on the surface and near-surface of the moon. There are few impact craters on Europa, indicating a "young" surface.
Europa ice rafts This image (showing a region about 45 km across) show what is interpreted as a region of recent ice flow, resulting in chaotic ice rafts (now frozen in place).
Ocean or ice? What is below Europas outer ice shell? Some clues (magnetic field, surface cracks in ice) suggest a salty subsurface H20 ocean!
Perhaps that ocean contains creatures?? We would love to go to Europa and drill down through the ice and see if anything looks back at us! How thick is the ice on Europa? That, my friend, is the big question. Estimates range from 1 km to 100's of km. Sending a robot spacecraft half a billion miles to drill through what may be miles of ice is not something we can even think about doing today.
Saturn Move aside Sauron, this is the real Lord of the Rings! (All the giant planets have rings, but the others pale to insignificance compared to Saturn's). The rings are composed of particles of almost pure H20, ranging in size up to meters across. The rings may have been formed by the tidal disruption of an icy moon about 300 km across (a "medium sized" moon). The age of the rings are hotly debated. The brightness of the ice argues for a recent origin (so that there has not been time for dust to darken the ice) but the particles have frequent collisions, which would break off "fresh" surfaces even in ancient ice.
The rings are a truly amazing physical system. They are extremely thin for their huge size. There are ring gaps which have moons in them, and ring gaps that don't. Although gravity is the dominant physics, there are some aspects that cannot be explained with gravity (like the spokes).
Saturn's rings at opposition As Saturn orbits the Sun every 29 years, we see the rings from a continuously changing orientation. Every 15 years or so there is a "ring plane crossing" when we see the rings exactly edgeon. The rings are so thin they literally disappear.
Saturn and Earth
Saturn as seen from Voyager Voyagers 1 and 2 provided spectacular images of the outer planets, but were only flyby missions, so could not provide continuing coverage. Later missions were dedicated to individual planets and provided much more detailed information- Galileo to Jupiter and Cassini- Huygens to Saturn.
Saturn as seen from Voyager Spacecraft can of course see planets and moons from angles impossible to see from Earth. At Saturn, the interplay of shadows of the rings on the planet and shadow of the planet on the rings provide for many visually stunning images.
Saturn from Cassini Wow! One of my favorite images of Saturn. Its on a poster outside my office. (Or, rather, it USED to be. Somebody stole my Saturn poster!)
Another awesome Saturn image
Backlit Rings (and Earth!) Wow! An image of the rings seen backlit by Sun, which is behind Saturn in this picture taken by Cassini. Very faint tenuous rings and clouds of dust are seen. The little dot outside the main rings just inside one of the fuzzy rings (on left side of Saturn- at about 9:30 position) is- us!
Cassini-Huygens spacecraft (artists conception) Cassini-Huygens is an ambitious, school bus sized NASA/ESA (European Space Agency) spacecraft that has been orbiting around Saturn since 2004. In 2005 a probe, called Huygens, separated from the mother ship and landed on Titan! A far cry from the Voyager days, when the spacecraft got one brief encounter as it whizzed by the planet on its way to the next ( If this is Tuesday, it must be Saturn)
Titan in visible light Titan is the only moon with a substantial atmosphere. The atmosphere, mostly made of nitrogen (N2) has a surface pressure 1.5 sea level pressure here on Earth. The coloring is perhaps from chemicals more complex than hydrocarbons, perhaps molecules called tholins. The atmosphere is almost opaque in visible light, and is sometimes referred to as "smoggy" (presumably not from SUVs). Titan has a bit of a "reverse greenhouse effect", as the atmosphere is more transmissive in the IR than in the visible, unlike the atmospheres of Earth, Venus, and Mars.
Earth and Titan Titan is larger in volume than Mercury (but less massive). Here it is shown with clouds digitally removed. Some of the dark areas on Titan may be lakes of liquid hydrocarbons!
Surface of Titan The Huygens Titan lander dropped from Cassini took these awesome pictures of the surface of Titan. The "rocks" are probably frozen methane or ethane. The lander sent back data for about an hour from the surface of Titan. This is by far the most distant object from Earth that we have landed spacecraft on.
Neptune Earth Uranus to scale Neptune and Uranus are sometimes called the "ice giants". The word "ice" here is used in a compositional, rather than a physical state, context. "Ice" is most everything between H and He (the gases) and silicon and iron.
Neptune The blue color is due to methane absorbing most of red light and perhaps an unknown coloring agent.
Uranus A milder blue than Neptune, but still colored by methane. Looks like not much is going on in its atmosphere.