ASTRO 101 Principles of Astronomy

Instructor: Jerome A. Orosz (rhymes with “boris”) Contact: Telephone: WWW: Office: Physics 241, hours T TH 3:30-5:00

Homework/Announcements Homework due Tuesday, March 12: Question 4, Chapter 5 (Why is Earth’s surface not riddled with craters as is that of the Moon?).

Homework/Announcements Homework due Tuesday, March 19: Question 6, Chapter 7 (What role did Charon play in enabling astronomers to determine Pluto’s mass?).

Comets! Comet PANSTARRS should be viewable in the western skies starting March 7. It will be close to the crescent Moon on March Comet ISON might be very spectacular in December, 2013, provided it survives its close encounter with the Sun.

Comets!

Next: Chapter 5: Other Planets and Moons.

Mercury Mercury is the closest planet to the Sun. It is never seen against a dark sky, and it is never far above the horizon.

Mercury as Seen From the Earth Here is the best ground-based image of Mercury.

Mercury as Seen From Earth Mercury is hard to study from the ground since it is close to the Sun. We can measure its average density. We find the density is 5.4 grams/cc, much like the Earth. We can measure the albedo, and we find it is about 10%, much like the Moon. Mercury mass is 5.5% of the Earth’s mass, and its gravity is 38% of the Earth’s. We expect Mercury to be similar to the Moon.

Mercury Seen up Close In 1974 NASA sent a probe to Mercury. It really does look like the Moon.

Mercury Seen up Close. Mercury is covered with craters.

Mercury Seen up Close In many cases you can see rays of material ejected by the impacts.

Mercury’s Interior Mercury has a large iron core. This core is relatively cold. There is very little evidence of present- day geological activity.

Mercury Mercury has a very thin atmosphere. There is no water. There is essentially no erosion. It is relatively hot on the day side (up to 800 o F) since it is near the Sun. However, on the night side it can be as low as -280 o F It looks a lot like the moon on the surface, but it is different in its interior.

Venus Venus has a mass and radius similar to that of the Earth. Its gravity is strong enough to retain a substantial atmosphere. The albedo is very high, more than 75%. We do not see the surface, but rather the tops of the clouds.

Venus Venus is the second closest planet to the Sun. It is never seen against a very dark sky, and it is never far above the horizon.

Venus No surface features are seen from Earth.

Venus The cloud patterns are changing over several hours.

Venus The surface temperature is about 475 o C, compared to about 25 o C for Earth.

Venus The temperature at the surface of Venus is high.

Venus The surface temperature is about 475 o C, compared to about 25 o C for Earth. The atmospheric pressure at the surface of Venus is 90 times that of the Earth.

Venus The surface temperature is about 475 o C, compared to about 25 o C for Earth. The atmospheric pressure at the surface of Venus is 90 times that of the Earth. The composition of the atmosphere is about 96% CO 2, compared to mostly N and O on the Earth.

Venus The surface temperature is about 475 o C, compared to about 25 o C for Earth. The atmospheric pressure at the surface of Venus is 90 times that of the Earth. The composition of the atmosphere is about 96% CO 2, compared to mostly N and O on the Earth. ??????

The Greenhouse Effect Venus has a “runaway” greenhouse effect that heats the planet an extra 375 o C.

The Greenhouse Effect

Venus has a “runaway” greenhouse effect that heats the planet an extra 375 o C. Some visible light from the Sun reaches the surface and heats it.

The Greenhouse Effect Venus has a “runaway” greenhouse effect that heats the planet an extra 375 o C. Some visible light from the Sun reaches the surface and heats it. The surface radiates the energy in the infrared, which the CO 2 in the atmosphere absorbs.

The Greenhouse Effect Some visible light from the Sun reaches the surface and heats it. The surface radiates the energy in the infrared, which the CO 2 in the atmosphere absorbs. The extra heat “bakes out” more CO 2 from the rocks.

The Greenhouse Effect The surface radiates the energy in the infrared, which the CO 2 in the atmosphere absorbs. The extra heat “bakes out” more CO 2 from the rocks. The extra CO 2 leads to more trapping of the surface infrared radiation.

The Greenhouse Effect The extra heat “bakes out” more CO 2 from the rocks. The extra CO 2 leads to more trapping of the surface infrared radiation. The extra trapped heat bakes out more CO 2, and so on…

The Surface of Venus Soviet spacecraft have landed on Venus and recorded close-up pictures. These images show basalt, which is quite similar to lava rock.

The Surface of Venus The Venusian surface has been mapped with radar by the Magellan spacecraft. These maps reveal gently rolling hills, two “continents”, and many volcanoes.

The Surface of Venus The Venusian surface has been mapped with radar by the Magellan spacecraft. There are relatively few impact craters. Perhaps melting of the surface has erased earlier craters.

Venus Summary Although Venus has a similar mass and radius as the Earth, it is a very different place owing to the runaway greenhouse effect: –The temperature at the surface is about 475 o C. –The atmospheric pressure is about 90 times that on the Earth. –The atmosphere is mostly CO 2.

NEXT:

Mars Named for the Roman god of war, owing to its red color. Its mass is 10% of the Earth’s mass, its radius is 50% of Earth’s radius, and its gravity is 38% of Earth’s gravity. Mars has usually been considered to be the place to look for extraterrestrial life.

Mars In some ways, Mars is a bit like Earth:  Its rotation rate is 24 hours and 37 minutes.  The inclination of the axis is 25.2 o.  The seasonal variations of the solar heating are similar to that on Earth.

Mars Mars is different from the Earth in some important ways:  The surface temperature ranges from about -125 o C to 25 o C, with typical temperatures below 0 o C.  The atmospheric pressure is about 1% of that on the Earth, which is too thin to maintain a significant greenhouse effect.

Why the Interest in Mars? Every few years Mars passes relatively close to Earth. During these close passages, it is possible to see surface features through a good telescope.

Early Observations of Mars Early observations were by eye (through a telescope). The observer had to draw what he saw. Here is drawing from 1800 (image from William Sheehan,

Early Observations of Mars Here is drawing from (image from William Sheehan,

Early Observations of Mars  The Italian astronomer Schiaparelli made detailed observations in the 1870s.  He noted the presence of “canali.” (image from William Sheehan,

Early Observations of Mars Schiaparelli meant “channels.” English translations used “canals,” implying that they are of intelligent design. Note, however, that beavers dig canals too.

Early Observations of Mars Schiaparelli meant “channels.” English translations used “canals,” implying that they are of intelligent design. Note, however, that beavers dig canals too. Near the turn of the 20 th century, many people were convinced that there was life on Mars.

Life on Mars This famous movie made in 1953 was based on H.G. Well’s classic novel of On Oct 30, 1930, Orson Wells broadcast a fake news report of invading Martians, causing widespread panic.

Modern Views of Mars We know now that the early observations of “canals” were in error. There are no cities or civilizations.

Modern Views of Mars The surface of Mars has been mapped extensively by orbiting spacecraft. One sees plains, deep canyons, numerous craters, and volcanoes, which are extinct.

Modern Views of Mars The surface of Mars has been mapped extensively by orbiting spacecraft. One sees plains, deep canyons, numerous craters, and volcanoes, which are extinct.

Modern Views of Mars The surface of Mars has been mapped extensively by orbiting spacecraft. One sees plains, deep canyons, numerous craters, and volcanoes, which are extinct.

Searching for Life How do you detect primitive life remotely?

Searching for Life How do you detect primitive life remotely?  Organisms on Earth breathe and have certain metabolisms, so look for signs of respiration and other biological processes.

Searching for Life How do you detect primitive life remotely?  Organisms on Earth breathe and have certain metabolisms, so look for signs of respiration and other biological processes. What if life on Mars is different than that on Earth?

Searching for Life How do you detect primitive life remotely?  Organisms on Earth breathe and have certain metabolisms, so look for signs of respiration and other biological processes. What if life on Mars is different than that on Earth?  Life on Earth is carbon-based, so look for organic compounds.

Searching for Life How do you detect primitive life remotely?  Organisms on Earth breathe and have certain metabolisms, so look for signs of respiration and other biological processes. What if life on Mars is different than that on Earth?  Life on Earth is carbon-based, so look for organic compounds. What if life on Mars is different than that on Earth? Also, organic compounds can be made by other means.

Searching for Life In 1976 the Viking spacecraft landed on Mars. Soil was analyzed by three experiments, but no signs of life were found.

Searching for Life In 1984 a meteorite from Mars was discovered in Antarctica. Evidence for microscopic fossils in the meteorite was announced in Most scientists today remain unconvinced.

Recent Events: Mars Rover Recently, NASA landed twin rovers on Mars. These probes are vastly more superior than the Viking landers.

Recent Events: Mars Rover The cameras deliver extremely high quality images.

Recent Events: Mars Rover The cameras deliver extremely high quality images.

Recent Events: Mars Rover The cameras deliver extremely high quality images.

Recent Events: Mars Rover rover-sees-life-friendly-conditions-in-ancient-mars-rock?litehttp://cosmiclog.nbcnews.com/_news/2013/03/12/ curiosity- rover-sees-life-friendly-conditions-in-ancient-mars-rock?lite

Evidence for Water on Mars These images and others suggest the presence of liquid water on Mars, at least in the past.

Evidence for Water on Mars These images and others suggest the presence of liquid water on Mars, at least in the past.

Life on Mars There is no evidence that there is currently life on Mars. The recent Mars rovers will perform additional experiments along these lines. It is possible that there was primitive life in the early history of Mars, but the only way to be sure would be to go there.

Comparing the Inner Planets

Next: The Giant Planets

The Giant Planets The giant planets are Jupiter, Saturn, Uranus, and Neptune.

The Giant Planets The radii are between about 4 and 11 times that of Earth. The masses are between 14 and 318 times that of Earth.

The Giant Planets The radii are between about 4 and 11 times that of Earth. The masses are between 14 and 318 times that of Earth. However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high.

The Giant Planets The radii are between about 4 and 11 times that of Earth. The masses are between 14 and 318 times that of Earth. However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high. The planets are composed of light elements, mostly hydrogen and helium.

The Gas Giants The composition of the giant planets, especially Jupiter, is close to that of the Sun.

The Gas Giants The composition of the giant planets, especially Jupiter, is close to that of the Sun. The internal structures of these planets is completely different from that of the Earth.

The Gas Giants The composition of the giant planets, especially Jupiter, is close to that of the Sun. The internal structures of these planets is completely different from that of the Earth. In particular, there is no hard surface.

The Gas Giants These planets are relatively far from the Sun (more than 5 times the Earth-Sun distance), so heating by the Sun is not a big factor.

Jupiter Jupiter is by far the most massive planet in the solar system (it contains about 2/3 of the solar system mass outside the Sun). It has the largest radius of any solar system planet, and it rotates the fastest (once every 10 hours). It has at least 63 moons. In many categories, Jupiter is the most extreme case.

Jupiter’s Weather Owing to its rapid rotation, Jupiter has a very turbulent atmosphere, which is composed mostly of methane and ammonia (both hydrogen rich).

Jupiter’s Weather Owing to its rapid rotation, Jupiter has a very turbulent atmosphere, which is composed mostly of methane and ammonia (both hydrogen rich).

Jupiter’s Weather Owing to its rapid rotation, Jupiter has a very turbulent atmosphere, which is composed mostly of methane and ammonia (both hydrogen rich).

Jupiter’s Weather The most famous feature on Jupiter is the Great Red Spot.

The Great Red Spot The Spot is at least 150 years old. It is basically a giant hurricane, roughly three times the size of Earth. Smaller features are also evident.

The Great Red Spot

Similar storm systems have been observed to form recently.

Jupiter’s Interior There is no way to directly study the deep interior parts, we rely on computer models. The interior should be hot (35,000 K), with a solid core, possibly surrounded by liquid. The gaseous outer atmosphere surrounds molecular and liquid metallic hydrogen and helium.

Jupiter’s Atmosphere The atmosphere of Jupiter (and Saturn) consists of poisonous gas (ammonia and ammonium hydrosulfide) covering a layer of water vapor.

Jupiter’s Moons Jupiter has 4 fairly large moons, discovered by Galileo in 1610, and at least 59 other moons, all significantly smaller.

Jupiter’s Moons The largest moon is larger than Mercury. Image from Nick Strobel (

Jupiter’s Moons The 4 Galilean moons have small rocky or iron cores. They have similar densities to our Moon, indicating that each contains a thick layer of water and ice.

Io The surface of Io is unlike that of any other solar system body. There are no impact craters, so its surface must be young.

Io There are active volcanoes on Io, the only place in the solar system outside of Earth where this is the case.

Io There are active volcanoes on Io, the only place in the solar system outside of Earth where this is the case.

Volcanoes on Io Io’s surface is constantly altered by volcanoes.

Volcanoes on Io Io’s surface is constantly altered by volcanoes. On Earth, the energy for geological activity comes from radioactivity.

Volcanoes on Io Io’s surface is constantly altered by volcanoes. On Earth, the energy for geological activity comes from radioactivity. However, Io’s mass is relatively small, so it should have no radioactivity left.

Volcanoes on Io Io’s surface is constantly altered by volcanoes. On Earth, the energy for geological activity comes from radioactivity. However, Io’s mass is relatively small, so it should have no radioactivity left. The heating source turns out to be Jupiter’s gravity, which compresses Io as its orbits.

Europa Europa has a very smooth surface, and it may have an ocean of liquid water underneath the surface.

Europa Europa has a very smooth surface, and it may have an ocean of liquid water underneath the surface. Could there be primitive life?

Other Jovian Satellites The rest of Jupiter’s moons are small and have an irregular shape. These may be fragments of a once larger body or captured asteroids.

Jupiter’s Rings Jupiter also has dark rings, discovered by Voyager in the late 1970s.

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