NASA's planetary playbook

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With the end of what was arguably NASA's marquee mission, the space shuttle program, the space agency is keen to maintain public interest in its remaining missions, especially those doing planetary exploration within our own solar system.

All eight planets within our system, plus recently "demoted" dwarf planet Pluto, are or have been targets for NASA spacecraft, with the space agency eager to release data and images to keep the public involved in its efforts as it faces an uncertain budgetary future.

The current "star" of NASA missions is of course the Curiosity rover now on Mars, with the space agency releasing images of every rock examined and giving daily updates as to just how far the rover has traveled in its scientific sojourns.

But other planets have had their visitors or are in the sights of new spacecraft making the long journey to their distant destinations.

Starting from the sun and moving outwards, these are some of NASA's exploratory activities:

Mercury

Mission: Messenger

Intended to study our system's smallest planet and its surface composition, magnetic field and interior structure, Messenger went into orbit around the innermost planet March 17, 2011.

Messenger discovered Mercury has a complex internal structure, with a core unexpectedly large for the planet's size, about 85 percent of the planetary radius.

Venus

Mission: Venus Express

Launched in cooperation with the European Space Agency and designed to study the planet's surface and atmosphere, the Venus Express reached Venus in April 2006.

Its most significant discovery is that Venus has shown volcanic activity within the last 3 million years, suggesting the planet is still geologically active.

Asteroids

Mission: Dawn

Launched in September 2007, the Dawn spacecraft's task is to study the asteroid Vesta and dwarf planet Ceres to gain clues to the solar system's earliest days when both bodies were formed.

Dawn went into orbit around Vesta June 16, 2011, and studied the asteroid until Sept. 5 of this year.

It is now on its way to Ceres, scheduled to arrive in July 2015.

Jupiter

Mission: Juno

Currently on its way to the solar system's largest planet, Juno will enter a unique polar orbit around Jupiter to map its gravity field, magnetic field and atmospheric structure.

The spacecraft will spend a year orbiting Jupiter, coming to within 3,100 miles of the planet's cloud tops as the first spacecraft to see below the planet's dense cloud cover.

Saturn

Mission: Cassini

Named in honor of Giovanni Cassini, the 17th century astronomer who discovered gaps in Saturn's rings, the Saturn mission is an international effort with three space agencies and 17 countries involved.

Cassini is the first spacecraft to orbit Saturn and has been circling the ringed planet since 2004, studying its atmosphere, rings and magnetosphere and its moons, particularly Titan, a study of which has given scientists clues to what Earth might have been like before life evolved.

Pluto

Mission: New Horizons

Launched in 2006, the New Horizons spacecraft will need nearly 10 years to reach the distant dwarf planet, making its closest approach in July 2015.

Pluto, its moons and other frozen worlds in the distant Kuiper Belt will be studied by the spacecraft's seven scientific instruments.