Introduction to Astronomy ! AST0111-3 (Astronomía) ! ! ! ! ! ! ! ! ! ! ! ! Semester 2014B Prof. Thomas H. Puzia

Venus

The is very dense and an opaque layer of clouds covers the planet, such that we cannot see the surface directly and it can only be mapped by radar. ! For this reason, it was very difficult to determine the duration of rotation of the planet. The 243 d rotation period was measured by radar from . ! This rotation is retrograde, however, probably due to a collision when the planet was forming.

The atmospheric clouds are not composed of water vapor, but sulfuric acid. Due to its atmosphere, the surface conditions are extreme: the temperature (735K) and pressure (93 bar vs 1 bar on Earth’s surface) are quite high. Venus

Venus is the planet closest to the Earth, orbiting at about 0.7 AU from the . ! Many properties of the planet are quite similar to our own. For example, its size and interior structure are very similar to that of the Earth. ! However, there are some important differences: Venus has no magnetic field like Earth because its rotation is so slow, and its atmosphere is about 100 times denser than ours.

The high atmospheric density has led Venus to undergo a runaway greenhouse effect. All of the greenhouse gases like CO2 and H2O have ended up in the atmosphere, causing extreme greenhouse conditions. What does the lack of a strong magnetic field mean for planets like Venus?

A. They have no north and south. B. They have no aurorae. C. They can be more directly affected by the solar wind. D. They can be more directly affected by high-energy particles called cosmic rays, which travel large distances throughout our Galaxy. E. More than one of the above. Probe

In the 1990s, the Magellan spacecraft took detailed images of the surface of Venus using radar that can pass easily through the clouds. ! The Magellan radar images revealed a complex terrain, including volcanoes, volcanic domes, valleys, canyons, and many pristine impact craters. The latter implies the volcanoes are largely inactive now and there is little large scale erosion. ! There are two elevated regions or “continents”, in the north and the landmass of Aphrodite in the equatorial zone. The highest mountains are the , which are higher than Mount Everest. Probes

The only spacecraft to land on the surface successfully were the Russian spacecraft Venera 9 and 10 in 1975 and then , 14, 17 and 18. ! The Venera photos show a rocky soil that is eroded, with sharp-edged flat rocks. Some rocks are basalt, volcanic, and others appear to be granite, probably from the old planetary crust. Venera Probes

The Venera probes landed in some highland regions called . ! These ships only survived for an hour before succumbing to the pressures and extremely high temperatures of the corrosive atmosphere. That was enough to make and broadcast some images of the surface. The real color of the surface and the air would be ochre, with lighting that looks like a very cloudy day on Earth. Venera Probes

Earth

Internal Structure Geologically active planet Surface: oceans and continents Atmosphere Greenhouse effect Life Magnetic Field Earth and Moon images taken from Mars!

Earth and Moon as seen from Mars (at a distance of 139 million km) from the MGS spacecraft in 2003. Earth and Moon as seen from Mars (at a distance of 139 million km) from the MGS spacecraft in 2003.

Earth

The Earth has 6 principle regions, from inner to outer:

1. The core 2. The mantle 3. The crust 4. The hydrosphere 5. The atmosphere 6. The magnetosphere Geological Activity

The Earth is a geologically active planet, its land is always being renewed, although on time scales very slow compared to human life. ! We find abundant evidence of geologic activity, volcanism, earthquakes, plate tectonics. Earthquakes, Volcanoes, and Plates

The interior of the Earth is a furnace. Pressure builds and needs to be released from time to time. Earthquakes, Volcanoes, and Plates

Earthquakes as probes of the interior structure! The Surface

The surface of the Earth has extreme variety. With the view from orbit, we lose the magnificent scenery. ! Life, including humans, are adapted to different ground conditions. Antarctica and Atacama desert are two of the most extreme places in the world. ! The Hydrosphere

More than 70% of the Earth's surface is covered with water. ! The highest concentration of water is in the southern hemisphere. The Hydrosphere The largest reserve of fresh water on the planet is in Antarctica. • Superficial Temperature • Superficial Temperature

Grand Canyon, Arizona Vegetation ! Impact cratering, volcanism, tectonics, erosion, life all modify surface! Emisiones Humanas

We also have some direct impacts on Earth’s appearance South America at night Emisiones Humanas

We also have some direct impacts on Earth’s appearance South America at night The Atmosphere

100 km

RT=6300 km The Atmosphere

The Earth has a fairly dense atmosphere. ! Atmosphere contains water vapor clouds and sometimes rain, snow or ice. ! Winds are generally moderate, although giant storms form in the equatorial sea with winds of over 150km / h. The Atmosphere The atmosphere is divided into layers, with the densest being lowest.

NOTE: logarithmic scale! The Atmosphere (Earth’s Energy Budget)

What happens to sunlight? ! Greenhouse effect... ! How do these processes affect our “appearance” from space? ! Now imagine this process on other planets, with different surface and air compositions... ! ! we can learn a lot! Evolution of the terrestrial atmosphere The original atmosphere of Earth was lost early on in its history. ! The current “second” atmosphere is due largely to volcanism and comets. The oceans also ...

J. Kasting 2004 Evolution of the terrestrial atmosphere • The atmosphere changes as a consequence of life on Earth original today

J. Kasting 2004 Evolution of the terrestrial atmosphere

This begs a few questions: ! Will the chemical composition of our atmosphere continue to evolve? On what timescales? ! How can we differentiate changes in the atmosphere due to human activity and those due to evolution? Magnetosphere

Earth acts a crude/chaotic dynamo ! The magnetosphere protects the Earth's surface (including atmosphere) from solar wind particles. Magnetosphere

auroras Magnetosphere

auroras The Moon The mass of the moon is so small that it lacks an atmosphere. ! It also does NOT have a magnetic field like Earth. ! It is a geologically dead planet, with no volcanism, although occasionally it has “moonquakes”. ! It is covered with impact craters and "seas" (darker regions caused by ancient lava flows).

The Moon Formation of Craters

Cratering process. The morphologies of the craters depend on: ! 1. Meteor mass 2. Meteor velocity 3. Impact angle 4. Terrain features ! We can learn about the Moon’s (and by extension the solar system’s) history via careful crater counting and studying the size distribution of craters. History of Craters

a) Period of intense bombardment (“craterization”) b) Period of intense volcanism c) Cooling and formation of more craters Moon

Effects of the Moon on the Earth – Eclipses – Tides (mareas) Formation of the Moon

The formation of the Moon is currently thought to be due to a collision with an object the size of Mars From its formation, the Moon does not possess a large nucleus with heavy fundamental elements (Fe, Ni) like the Earth or Mercury. ! ! !

Moon

Before landing for the first time, many orbiting spacecraft photographed the Moon in detail. As the rotation period of the Moon is equal to the period of travel around the Earth, the Moon always shows the same face to Earth. Rest assured, the dark side of the Moon is morphologically similar to the visible face.

• Various spacecrafts have allowed us now to image the entire surface of the Moon in fine detail. Moon

Due to its relative proximity, the moon is the most studied extraterrestrial body by humans. Different spacecraft have explored the planet. ! It is rather uninteresting, however, in terms of sustaining life or mining. Moon

The Moon is the only object outside the Earth where we have set foot. Astronaut Aldrin "walking" on the moon.

AstronautsAstronauts on the Moonon the MoonThere is no atmosphere, yet the sky is black due to contrast. The force of gravity is very low, equivalent to 1 / 6 that of Earth. North Pole of the Moon

Although the Moon would be very useful for space development and exploration of the solar system because of its low gravity, the main difficulty of having a moon base is the lack of water. Various probes have found evidence of water ice in craters at the lunar poles. However, direct evidence has yet to be confirmed. ! It will be important to establish permanent lunar bases as a “relay” station if we ever seriously consider future plans for colonizing the Solar System. What do we conclude if a planet has few impact craters of any size?

A. The planet was never bombarded by or comets B. Its atmosphere stopped impactors of all sizes. C. Other geological processes have erased evidence of craters. D. Bruce Willis saved it from all the impactors.