... Spacecraft . ... To space by cannon? Finally, the deep space explorers --spacecraft which break away from the Earth's gravity . ... The "Luna" series of the USSR conducted 7 soft landing of unmanned probes, two of them with wheeled robotic "Lunokhods," and two of those missions returned samples to Earth. Others spacecraft have visited the major planets of the Solar system. ... The Mariner series have explored Venus and Mars--and Mariner 10 even reached Mercury, for three separate encounters! ...

Jupiter is the largest of the nine planets, more than 10 times the diameter of Earth and more than 300 times its mass. ... The mean density of Earth is 5.245 times that of water. The pull of gravity on Jupiter at the top of the clouds at the equator is 2.4 times as great as gravity's pull at the surface of Earth at the equator. ... It is tipped about 11њ to Jupiter's axis of rotation, similar to Earth's, but it is also offset from the center of Jupiter by about 10,000 kilometers (6,200 miles). ...

... The motion of a planet around the Sun or of a scientific satellite around Earth follows different equations (though a connection exists), but in many respect it resembles that of the stone. ... Kepler's law states: . ... Illustrating Kepler's 2nd law: . ... As an example, let the drawing on the right represent the orbit of an Earth satellite, and let AB and CD be the portions of the orbit covered in 3 hours near apogee and near perigee, respectively. ... Gravity can also provide energy. ...