2014-Space, Time & Cosmos Lecture 2 Solar System - The Terrestrial (Inner) Planets Prof. Ken Tsang

The Plane of the Ecliptic is illustrated in this Clementine star tracker camera image which reveals (from right to left) the Moon lit by Earthshine, the Sun's corona rising over the Moon's dark limb, and the planets Saturn, Mars, and Mercury.

Inner planets: characteristics

Mercury obtained during MESSENGER’s second flyby (October 6, 2008) The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s. A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper.

Mercury is the smallest and closest to the Sun of the eight planets in the Solar System, with an orbital period of about 88 Earth days. Seen from the Earth, it appears to move around its orbit in about 116 days, which is much faster than any other planet. This rapid motion may have led to it being named after the Roman deity Mercury, the fast-flying messenger to the gods.

Because Mercury is so close to the Sun, it is hard to directly observe from Earth, except during twilight. Mercury never elongates more than 28 degrees from the Sun, which limits its visibility from the Earth to about one hour before sunrise or after sunset and then only when it is at its greatest elongation. Before the 4th century BC, Greek astronomers believed the planet to be two separate objects: one visible only at sunrise, which they called Apollo (morning star); the other visible only at sunset, which they called Hermes (evening star).

Visible in this mosaic are many lava-flooded craters and large expanses of smooth volcanic plains, which appear similar in texture to volcanically emplaced mare deposits on the Moon. These images are from MESSENGER, a NASA Discovery mission to conduct the first orbital study of the innermost planet, Mercury.

Caloris basin on Mercury, spanned about 1,500 km in yellowish hues in this enhanced color mosaic, is one of the solar system's largest impact basins. It was created during the early history of the solar system by the impact of a large asteroid-sized body, the basin. Orange splotches around the basin's perimeter are now thought to be volcanic vents.

Current and Past Missions to Venus Akatsuki/Planet-C - ISAS Venus Orbiter (2010) Venus Express - ESA Venus Orbiter (2005) MESSENGER - NASA Mercury Orbiter (2004) (Two Venus Flybys) Magellan - NASA Venus Radar Mapping Mission ( ) Pioneer Venus - NASA Orbiter/Probes to Venus ( ) Galileo - NASA Mission to Jupiter (Venus flyby ) Vega 1 - Soviet mission to Venus-Comet Halley (Venus flyby ) Vega 2 - Soviet mission to Venus-Comet Halley (Venus flyby ) Venera - Soviet Venus Missions ( ) Mariner 10 - NASA Mission to Venus and Mercury ( ) Mariner 5 - NASA Venus flyby (1967) Mariner 2 - NASA Venus flyby (1962)

Venus, named after the Roman goddess of beauty. In true color it is obscured by a thick blanket of clouds. Venus is sometimes called Earth's "sister planet" because of their similar size, gravity, and bulk composition (Venus is both the closest planet to Earth and the planet closest in size to Earth).

Venus ' brightness (second brightest object in the night sky after the Moon) compared to other stars and planets inspired visions of a beautiful goddess. The diameter of Venus is 12,092 km (only 650 km less than the Earth's) and its mass is 81.5% of the Earth's. Conditions on the Venusian surface differ radically from those on Earth, due to its dense carbon dioxide atmosphere. The mass of the atmosphere of Venus is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.

Venus Revealed : Radar images show what Venus would look like without its constant clouds. The composite image below was processed to improve contrast and to emphasize small features, and color-coded to represent elevation, result of more than a decade of radar investigations culminating in the Magellan mission.

What happened on Venus? The Earth and Venus are near each other in the Solar System, and are similar in size, density, and composition. Based on our understanding of the origin of the Solar System, we would expect that their initial atmospheres would have been rather similar. Yet the present atmospheres of the two planets could hardly be much more different than they are. How did this come to be? The reason is thought to lie in what is termed the "Runaway Greenhouse Effect".

Greenhouse effects

Venus: Death of a Planet Why did Earth thrive and our sister planet, Venus, died? From the fires of a sun's birth... twin planets emerged. Then their paths diverged. Nature draped one world in the greens and blues of life. While enveloping the other in acid clouds... high heat... and volcanic flows. Why did Venus take such a disastrous turn?

Mars: World That Never Was Did Mars long ago develop far enough for life to arise? If so, does anything still live within Mars' dusty plains, beneath its ice caps, or somewhere underground? In 1964 the Mariner Four spacecraft flew by Mars and got a good look. What it saw looked more like the Moon than the Earth. Then, in the mid-1970's, two lander-orbiter robot teams, named Viking, went in for an even closer look. The landers tested the soil for the chemical residues of life. All the evidence from Viking told us: Mars is dead. And extremely harsh.

Current and Past Missions to Mars NASA Mars Science Laboratory - NASA Mars Rover (2011) Phobos-Grunt - Attempted Russian Phobos Sample Return (2011) Yinghuo-1 - Attempted Chinese Mars Orbiter (2011) Phoenix - NASA Mars Scout Lander (2007) Mars Reconnaissance Orbiter - NASA Orbiter (2005) Mars Exploration Rovers - Two NASA Rovers to Mars (2003) Spirit Opportunity Mars Express - ESA Mars Orbiter and Lander (2003) 2001 Mars Odyssey - NASA Orbiter Mission to Mars (2001) Mars Polar Lander - NASA attempted lander to Mars (1999) Deep Space 2 - NASA attempted penetrator mission to Mars (1999) Mars Climate Orbiter - NASA attempted orbiter to Mars (1998) Nozomi (Planet-B) - ISAS (Japan) orbiter to Mars (1998) Mars Global Surveyor - NASA Mars orbiter (1996) Mars Pathfinder - NASA lander and rover to Mars (1996) Mars 96 - Russian attempted mission to Mars (1996) Mars Observer - NASA attempted mission to Mars (1992) Phobos - Soviet missions to Mars (1988) Viking - NASA orbiters/landers to Mars (1975) Mars 6 - Soviet Mars lander (1973) Mars 5 - Soviet Mars orbiter (1973) Mariner 9 - NASA Mars orbiter (1971) Mars 3 - Soviet Mars orbiter and lander (1971) Mars 2 - Soviet Mars orbiter and lander (1971) Mariner 7 - NASA Mars flyby (1969) Mariner 6 - NASA Mars flyby (1969) Mariner 4 - NASA Mars flyby (1964)

Color image of Phobos obtained by Mars Reconnaissance Orbiter on March 23, 2008.> < Image of Deimos taken by the Mars Reconnaissance Orbiter on February 21, 2009