Planetary Motion By Carol Greco

Why do planets move the around the sun the way they do? First you need to understand that scientists have discovered an invisible force that exists between two objects that pulls these two objects towards each other. They call this force gravity. Click to see attraction.

Centripetal Motion Next, the gravitational force the Sun pulls on a planet is perpendicular to the direction of the planet's movement. This gravitational force constantly changes the direction of the planet's forward motion so that it revolves in a nearly circular orbit around the Sun. This force is described as centripetal motion. Click to see this motion.

Kepler’s First Law In the early 1600’s a scientist named Johannes Kepler observed that planets moved in ellipses, or ovals, with the Sun at one focus. Click to see this law. When the planet gets closer to the sun the gravitational pull between them increases.

Kepler’s Second Law He also observed that the radius vector describes equal areas in equal times. Or you could say it this way, that if you drew an imaginary line connecting the planet to the Sun it would sweep out equal areas in equal times. Click to see an example of this law.

NASA’s current missions exploring our neighboring planets MESSENGER Venus Express LRO Lunar Reconnaissance Orbiter Missions to Mars Dawn Cassini New Horizons Click on each picture to learn about that mission!

MESSENGER MErcury Surface, Space Environment, GEochemistry and Ranging MESSENGER was designed to map the surface composition, study the magnetic field and interior structure of our solar system's smallest and innermost planet -- Mercury. It carries eight instruments to study Mercury's polar deposits, core and magnetic dynamo, crust and mantle, magnetosphere, crustal composition, geologic evolution and exosphere. For more information on this mission click the link below Click Back to Missions Slide

Venus Express Click Back to Missions Slide The European Space Agency's Venus Express is designed to study the atmosphere of Venus, from the surface to the ionosphere. The mission is reusing the same design as ESA's Mars Express and spare parts from other deep space missions. For more information on this mission click the link below

LRO Lunar Reconnaissance Orbiter Click Back to Missions Slide NASA's Lunar Reconnaissance Orbiter (LRO) was sent to the Moon to make high-resolution maps of the composition of the lunar surface and seek out potential sources of water-ice that may exist in the bottom of dark polar craters. The spacecraft is seeking potential landing sites and resources for future human exploration of the Moon. LRO was launched with the LCROSS lunar impact mission.LCROSS For more information on this mission click the link below

Missions to Mars Click on each picture to learn more about each mission Click Back to Missions Slide Mars 2001 Odyssey Mars Express MRO Spirit Opportunity Mars Odyssey is an orbiter carrying science experiments designed to make global observations of Mars to improve our understanding of the planet's climate and geologic history, including the search for water and evidence of life-sustaining environments. The European Space Agency's Mars Express was designed to study the geology, atmosphere, surface environment, history of water and potential for life on Mars. It also carried Great Britain's Beagle 2 lander to Mars. The fast- track mission borrowed technology from the failed Mars 96 mission and the Rosetta comet-chaser mission..Beagle 2Mars 96Rosetta Mars Reconnaissance Orbiter is designed to track changes in the water and dust in Mars' atmosphere, look for more evidence of ancient seas and hot springs and peer into past Martian climate changes by studying surface minerals and layering. The orbiter carries a powerful camera capable of taking sharp images of surface features the size of a beach ball. The orbiter also serves as a data relay station for other Mars missions. Spirit and its twin Opportunity were designed to study the history of climate and water at sites on Mars where conditions may once have been favorable to life. Each rover is equipped with a suite of science instruments to read the geologic record at each site, to investigate what role water played there, and to determine how suitable the conditions would have been for life.

Dawn Click Back to Missions Slide For more information on this mission click the link below Dawn is designed to study the conditions and processes of the solar system's earliest epoch by investigating in detail two of the largest protoplanets remaining intact since their formations. The orbiter will visit both the asteroid Vesta and dwarf planet Ceres, two main asteroid belt worlds that followed very differently evolutionary paths.

Cassini Click Back to Missions Slide Cassini was designed to explore the Saturnian system from orbit: the planet and its atmosphere, rings and magnetosphere and its moons, particularly Titan and the icy satellites. Cassini also carried Europe's Huygens probe to its rendezvous with Titan. Huygens For more information on this mission click the link below

New Horizons Click Back to Missions Slide For more information on this mission click the link below NASA's New Horizons spacecraft is designed to make the first close-up study of Pluto and its moons and other icy worlds in the distant Kuiper Belt. The spacecraft has seven scientific instruments to study the atmospheres, surfaces, interiors and intriguing environments of Pluto and its distant neighbors.

Resources The Solar System (slide 1) NASA Kepler Mission (slide 4 picture and information) Keplar’s Laws (slides 4 and 5 animations) Solar System Explorations: Missions (slide 6-13)