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The Solar System

The Solar System consists of the Sun and those celestial objects bound to it by gravity. These objects are the eight planets, their 166 known moons, five dwarf planets, and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust.

The charted regions of the Solar System are the Sun, four terrestrial inner planets, the asteroid belt, four gas giant outer planets, the Kuiper belt and the scattered disc. The hypothetical Oort cloud may also exist at a distance roughly a thousand times beyond the charted regions.

A flow of plasma from the Sun (the solar wind) permeates the Solar System. This creates a bubble in the interstellar medium known as the heliosphere, which extends out to the middle of the scattered disc.

In order of their distances from the Sun, the eight planets are:

  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune

As of mid-2008, five smaller objects are classified as dwarf planets. Ceres is in the asteroid belt, and four orbit the Sun beyond Neptune: Pluto (formerly classified as the ninth planet), Haumea, Makemake, and Eris.

Six of the planets and three of the dwarf planets are orbited by natural satellites, usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.


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Dawn Last Updated on 2009-09-30 15:17:18 On an eight-year, 4.9 billion-kilometer (3-billion-mile) mission to answer basic questions about the formation of planets in our solar system, NASA's unmanned Dawn spacecraft will be the first to orbit two planetary bodies on a single voyage. Beginning in August 2011, Dawn will make the first of two rendezvous with the asteroid Vesta and dwarf planet Ceres (in 2015), two of the largest objects that lie within the asteroid belt between Mars and Jupiter. Scientists theorize that objects like Vesta and Ceres may be the "seeds" of planets that never formed. Dawn's scientific instruments will measure shape, surface topography, tectonic history, elemental and mineral composition, and search for water-bearing minerals. Dawn spacecraft itself will also be used to measure the masses and gravity fields of Vesta and Ceres. A Delta II-Heavy rocket propelled the 1,217.7 kilograms (2,684.6 pounds)... More »
ACE (Advanced Composition Explorer) Mission Last Updated on 2009-08-28 16:05:10 Nation: U.S. (71) Objective(s): L1 Libration Point Spacecraft: ACE Spacecraft Mass: 752 kg Mission Design and Management: NASA GSFC Launch Vehicle: Delta 7920-8 (no. D247) Launch Date and Time: 25 August 1997 / 14:39 UT Launch Site: ESMC / launch complex 17A Scientific Instruments: 1) SWIMS solar wind ion mass spectrometer 2) SWICS solar wind ion composition spectrometer 3) ULEIS ultra-low-energy isotope spectrometer 4) SEPICA solar energetic-particle ionic charge analyzer 5) SIS solar isotope spectrometer 6) CRIS cosmic-ray isotope spectrometer 7) SWEPAM solar wind electron, proton, and alpha monitor 8) EPAM electron, proton, and alphaparticle monitor 9) MAG magnetometer 10) RTSW real-time solar wind experiment Results: The Advanced Composition Explorer (ACE) spacecraft was designed to study spaceborne energetic particles from the L1 Libration Point, about 1.4 million kilometers... More »
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