Tour Around the Inner Planets

Shot from Mariner 10 probe, 1974. MERCURY Earth-based telescopic photo of Mercury taken from Catalina Observatory 1.5 meter (61 inch) telescope Shot from Mariner 10 probe, 1974.

The surface of Mercury

The surface of Mercury has landforms that indicate its crust may have contracted.

Messenger Probe shots, currently doing flyby—enters orbit in 2011 (click here)

Venus

Many discoveries about Venus have been made using Earth-based radio telescopes, which can transmit powerful radar signals and detect the weak echoes reflected from the planet's surface. At 300 meters (1,000 feet) across, Arecibo is the world's largest radio "dish."

This map was produced in 1988 by the Arecibo radio telescope This map was produced in 1988 by the Arecibo radio telescope. Features as small as 1 kilometer (0.6 mile) across are visible.

Magellan's large main antenna bounced radar signals off the surface of Venus and transmitted the resulting data back to Earth. A computer processed the data to form the images displayed below. The smaller "horn" antenna is a radar altimeter, which measured the heights of surface features. The solar panels provided electric power. Magellan orbited Venus from 1990 until 1995, when it burned up in the planet's atmosphere.

Smooth plains formed by fluid lava cover most of Venus Smooth plains formed by fluid lava cover most of Venus. A dense pattern of fractures covers the plains in this image. Narrow ridges and fractures such as these form when the crust is pulled and pushed by geologic forces.

Volcanoes of all sizes are found on Venus, from thousands of small domes that dot the plains to large mountains. This volcano, Sapas Mons, is 4 kilometers (2.5 miles) tall and surrounded by lava flows. Two steep volcanic domes occur at the summit. Both show evidence of massive landslides along their flanks. The image color is computer generated.

Large, steep-sided volcanic domes occur in clusters on Venus Large, steep-sided volcanic domes occur in clusters on Venus. They are often covered with complex fracture patterns.

The surface of Venus is dry and hot--475 °C (900 °F) day and night throughout the year-- and the atmospheric pressure is 90 times that of Earth's. Few probes have entered this harsh environment, and none has survived long. Only four, all Soviet Venera spacecraft, have returned images from the surface. The rocks on Venus are a dull gray, but sunlight filtered by the thick atmosphere gives them a yellow tint. This Venera 13 color photo shows plates of rock thought to be basalt, with dark soil between some of them. The lower photo has been corrected to show the color of the surface as it would appear under direct sunlight. This site is probably typical of the plains on Venus.

Earth

Compared to the size of the Earth , the atmosphere is a thin shell Compared to the size of the Earth , the atmosphere is a thin shell. The part of the atmosphere we know best - the troposphere - is an even thinner shell, only 12 kilometers (7.5 miles) thick. It is in the troposphere that all weather occurs; it is only here that life exists.

Clouds of ionized (electrically charged) gases from the solar wind become trapped in the magnetosphere to form the aurorae or northern lights (aurora borealis) and southern lights (aurora australis) . The aurorae generally occur at altitudes above 100 kilometers (60 miles) in rings about 17 degrees from the magnetic poles.  These images show spectacular views of Earth's aurorae taken by astronauts aboard the Space Shuttle.

Water is Key to Life!

Albedo=reflectivity We will talk more about this when we learn about the atmosphere of the Earth in detail

White clouds are visible in this view of Mars from the Hubble Space Telescope.

This picture of Mars was taken from a distance of 418,000 kilometers (260,000 miles) by the Viking 2 spacecraft. Near the center of the picture is the large volcano Ascraeus Mons. A bright band of clouds trails off to the northwest from the volcano's summit.

Spacecraft exploration of Mars began in 1964 with Mariner 4 Spacecraft exploration of Mars began in 1964 with Mariner 4. Previous attempts by both the USSR and United States to send a spacecraft to Mars had failed. Mariner 4 reached the red planet on July 15, 1964 and returned photographs and atmospheric measurements. Three more Mariner spacecraft, Mariner 6,7 and 9, successfully orbited Mars by the end of 1971. This is Mariner 4…..

The Mars Pathfinder spacecraft landed on the surface of Mars on July 4, 1997. The Lander camera and instruments returned data on the Mars atmosphere and surrounding terrain in an ancient floodplain in the Ares Vallis region. The rover Sojourner became the first micro-rover to operate on another planet, analyzing rocks and soils and testing new rover technology for use in future planetary exploration.

Panoramic view of the surface of Mars from the Viking 1 Lander Panoramic view of the surface of Mars from the Viking 1 Lander. This image is a mosaic constructed from individual Viking images.

Twenty-four images from the Mars Global Surveyor were combined to create each of these global views of Mars when it was winter in the planet's southern hemisphere. Note the large south polar cap. NASA/JPL/Malin Space Science Systems

Earth Comparisons Atmosphere Water Structure Solar Energy MERCURY Almost nothing! Ice at poles Molten core? Rocky crust Hot/Cold during Night/Day VENUS 97% CO2 Dried up! Liquid core? Hottest planet! 467 C EARTH 78% Nitrogen 21% Oxygen 71% of surface Solid/liquid core Rocky crust Average 15 C MARS < 1/100 of Earth 95% CO2 Ice discovered by Mars Lander Solid core? 2.5 times less than Earth Ave is -61 C