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:
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.
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...
Solar SystemLast Updated on 2011-01-18 00:00:00
Stars often have a number of objects orbiting around them in an adjacent region of space known as a solar system. Our solar system formed about five billion years ago and consists of the Sun, eight planets, at least thee dwarf planets, about 130 satellites, and a large number of comets and asteroids. A planet can be defined according to the following criteria: 1) It is a celestial body that orbits a star, 2) it has cleared the space along its orbital path of objects, 3) self-gravitational force has shaped its surface to be nearly spherical, and 4) it does not have the ability to generate its own light. The definition of a dwarf planet meets all the criteria of a planet, except that it has not cleared the space along its orbital path of objects. Satellites are bodies that orbit around planets and dwarf planets. The Earth’s moon is considered to be a satellite. An asteroid is a... More »
DawnLast Updated on 2009-09-30 15:17:18On 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) MissionLast Updated on 2009-08-28 16:05:10Nation: U.S. (71)
Objective(s): L1 Libration Point
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
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 »
Sun - Detail, ExpandedLast Updated on 2009-04-15 00:00:00
The Sun is a huge, glowing ball at the center of our solar system. The sun provides light, heat, and other energy to Earth. The sun is made up entirely of gas. Most of it is a type of gas that is sensitive to magnetism. This sensitivity makes this type of gas so special that scientists sometimes give it a special name: plasma. Nine planets and their moons, tens of thousands of asteroids, and trillions of comets revolve around the sun. The sun and all these objects are in the solar system. Earth travels around the sun at an average distance of about 92,960,000 miles (149,600,000 kilometers) from it.
The sun is one of over 100 billion stars in the Milky Way Galaxy. It is about 25,000 light-years from the center of the galaxy, and it revolves around the galactic center once about every 250 million years. One light-year, the distance that light travels in a vacuum in a year, equals about... More »
Sun - DetailLast Updated on 2009-03-26 00:00:00The Sun is the star around which the Earth revolves and the gravitational center of the Solar System; it lies about 270,000 times closer to us than the next nearest star. The Sun is a solitary, yellow dwarf star of spectral type G2 that has been on the main sequence for about 4.6 billion years.
The Sun consists largely of hydrogen (71% by mass) and helium (27%), with much smaller amounts of heavier elements. It puts out 400 trillion trillion watts of energy, produced by the fusion of hydrogen to helium by the carbon-nitrogen cycle in its core. The Sun is 109 times wider than the Earth. It spins on its axis with a period that varies from 25 days at the equator to 33.5 days near the poles.
The visible surface, or photosphere, is surrounded by the chromosphere and, beyond this, the corona. Important features of the chromosphere include the chromospheric network, plages, prominences,... More »
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