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How did the solar system evolve to its current diverse state?

Many of the other solar systems have massive Jupiter like planets close to their Sun, closer even than Mercury.  Many scientists now believe that these gas giants could not have formed there.  Rather, they must have began out where our Jupiter is, and moved inwards, scattering the smaller planets with their powerful gravity as they went.  Why is it that our Jupiter and Saturn did not migrate inward?  We are trying to learn more about our outer solar system by sending probes there.   We sent Galileo to Jupiter, Cassini is at Saturn right now, and New Horizons is on its way to Pluto even as you read this.

Planets also change even if they don't move closer to the Sun.  For example, Mars once had water on the surface. We know that thanks to our two rovers on Mars and a spacecraft in orbit.  We recently launched Phoenix to explore near the pole and sniff the dirt for organic molecules.  By studying Mars we will learn more about how rocky planets can change.  If other planets change, then ours can change too.

Related missions:

*Sort missions by clicking the column headers.

DivisionNameLaunch DatePhase
Planets Cassini
The Cassini Mission is in the midst of a detailed study of Saturn, its rings, its magnetosphere, its icy satellites, and its moon Titan. Cassini also delivered a probe (called Huygens, provided by the European Space Agency) to Titan, and ...
19971015 October 15, 1997 3Operating
Planets Dawn
The Dawn mission intends to orbit Vesta and Ceres, two of the largest asteroids in the solar system. According to current theories, the very different properties of Vesta and Ceres are the result of the asteroids being formed and evolving ...
20070927 September 27, 2007 3Operating
Planets Deep Impact
The Deep Impact mission was selected as a Discovery mission in 1999. The spacecraft was launched aboard a Delta II rocket on January 12, 2005 and left Earth’s orbit toward Comet Tempel 1. The spacecraft consists of two main sections, ...
20050112 January 12, 2005 4Past
Planets LADEE
Lunar Atmosphere and Dust Environment Explorer (LADEE) is a NASA mission that will orbit the Moon and its main objective is to characterize the atmosphere and lunar dust environment. This mission is part of SMD's Robotic Lunar Exploration program.
20130906 September 2013 2Development
Planets Mars Science Laboratory
NASA proposes to develop and to launch a roving long-range, long-duration science laboratory that will be a major leap in surface measurements and pave the way for a future sample return mission. The mission will also demonstrate the technology for ...
20111126 November 26, 2011 3Operating
Planets New Horizons
The New Horizons Pluto-Kuiper Belt Mission will help us understand worlds at the edge of our solar system, by making the first reconnaissance of Pluto and Charon. The mission will then visit one or more Kuiper Belt Objects, in the ...
20060119 January 19, 2006 3Operating
Planets Stardust
Stardust is the first U.S. space mission dedicated solely to the exploration of a comet, and the first robotic mission designed to return extraterrestrial material from outside the orbit of the Moon. This mission is part of SMD's Discovery Program. ...
19990207 February 07, 1999 4Past