Our Solar System
Our galaxy – the Milky Way – is a spiral galaxy with arms extending from the center like a pinwheel. Our solar system is in the Orion arm of the Milky Way. Our Sun is one of about 100 billion stars in the Milky Way. And our galaxy is just one of roughly 100 billion in the visible universe.
Sun
Plasma erupts from the Sun in the shape of a massive handle.
The Sun is a star, a hot ball of glowing gases at the heart of our solar system. Its influence extends far beyond the orbits of distant Neptune and Pluto. Without the Sun’s intense energy and heat, there would be no life on Earth. And though it is special to us, there are billions of stars like our Sun scattered across the Milky Way galaxy.
Mercury:
MESSENGER spacecraft images have revealed portions of Mercury never seen by human eyes.
Sun-scorched Mercury is only slightly larger than Earth’s Moon. Like the Moon, Mercury has very little atmosphere to stop impacts, and it is covered with craters. Mercury’s dayside is super-heated by the Sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even exist in craters. Mercury’s egg-shaped orbit takes it around the Sun every 88 days.
Venus:
Magellan spacecraft radar data enabled scientists to penetrate Venus' thick clouds and create simulated views of the surface.
Venus is a dim world of intense heat and volcanic activity. Similar in structure and size to Earth, Venus’ thick, toxic atmosphere traps heat in a runaway ‘greenhouse effect.’ The scorched world has temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains. Venus spins slowly in the opposite direction of most planets.
Earth:
A true-color NASA satellite mosaic of Earth.
Earth is an ocean planet. Our home world’s abundance of water – and life – makes it unique in our solar system. Other planets, plus a few moons, have ice, atmospheres, seasons and even weather, but only on Earth does the whole complicated mix come together in a way that encourages life – and lots of it.
Earth’s Moon:
The Galileo spacecraft sent back this image of the Moon as it headed into the outer solar system. The distinct bright ray crater at the bottom of the image is the Tycho impact basin.
Our moon makes Earth a more livable planet by moderating our home planet’s wobble on its axis, leading to a relatively stable climate, and creating a rhythm that has guided humans for thousands of years. The Moon was likely formed after a Mars-sized body collided with Earth and the debris formed into the most prominent feature in our night sky.
Mars:
Water-ice clouds, polar ice, polar regions, and geological features can be seen in this full-disk image of Mars.
Mars is a cold desert world. It is half the diameter of Earth and has the same amount of dry land. Like Earth, Mars has seasons, polar ice caps, volcanoes, canyons and weather, but its atmosphere is too thin for liquid water to exist for long on the surface. There are signs of ancient floods on Mars, but evidence for water now exists mainly in icy soil and thin clouds.
Asteroids:
This picture of Eros, the first of an asteroid taken from an orbiting spacecraft, is a mosaic of four images obtained by NASA's NEAR mission immediately after the spacecraft's insertion into orbit.
Asteroids are rocky, airless worlds that orbit our Sun, but are too small to be called planets. Tens of thousands of these ‘minor planets’ are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called Near-Earth Objects (NEOs).
Meteors & Meteorites:
NASA's Opportunity rover found this meteorite on Mars. It is about the size of a basketball.
Little chunks of rock and debris in space are called meteoroids. They become meteors — or shooting stars — when they fall through a planet’s atmosphere; leaving a bright trail as they are heated to incandescence by the friction of the atmosphere. Pieces that survive the journey and hit the ground are called meteorites.
Jupiter:
A true-color image of Jupiter taken by the Cassini spacecraft. The Galilean moon Europa casts a shadow on the planet's cloud tops.
Jupiter, the most massive planet in our solar system — with dozens of moons and an enormous magnetic field — forms a kind of miniature solar system. Jupiter does resemble a star in composition, but it did not grow big enough to ignite. The planet’s swirling cloud stripes are punctuated by massive storms such as the Great Red Spot, which has raged for hundreds of years.
Saturn:
While cruising around Saturn in early October 2004, Cassini captured a series of images that have been composed into this large global natural color view of Saturn and its rings.
Adorned with thousands of beautiful ringlets, Saturn is unique among the planets. All four gas giant planets have rings – made of chunks of ice and rock – but none are as spectacular or as complicated as Saturn’s. Like the other gas giants, Saturn is mostly a massive ball of hydrogen and helium.
Uranus:
Uranus' moon Ariel (white dot) and its shadow (black dot) were caught crossing the face of Uranus in this Hubble Space Telescope image.
Uranus is the only giant planet whose equator is nearly at right angles to its orbit. A collision with an Earth-sized object may explain Uranus’ unique tilt. Nearly a twin in size to Neptune, Uranus has more methane in its mainly hydrogen and helium atmosphere than Jupiter or Saturn. Methane gives Uranus its blue tint.
Neptune:
Voyager 2 captured this image of Neptune in 1989.
Dark, cold and whipped by supersonic winds, Neptune is the last of the hydrogen and helium gas giants in our solar system. More than 30 times as far from the Sun as Earth, the planet takes almost 165 Earth years to orbit our Sun. In 2011 it will complete its first orbit since its discovery in 1846.
Pluto:
A Hubble Space Telescope image of Pluto and its Moons, Charon, Hydra and Nix. Charon is the largest moon close to Pluto. Hydra is the higher of the two dots to the right of Pluto. Nix is the lowest dot.
Discovered in 1930, Pluto was long considered our solar system’s ninth planet. But after the discovery of similar intriguing worlds deeper in the distant Kuiper Belt, icy Pluto was reclassified as a dwarf planet. This new class of worlds may offer some of the best evidence about the origins our solar system.
Comets:
This image of Comet C/2001 Q4 (NEAT) was taken at Kitt Peak National Observatory near Tucson, Ariz. in 2004.
Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. When a comet’s orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the Sun for millions of kilometers.
Kuiper Belt & Oort Cloud:
Artist's concept of Eris and its moon. The Sun is in the distance. Image credit: Robert Hurt (IPAC)
In 1950, Dutch astronomer Jan Oort proposed that certain comets come from a vast, extremely distant, spherical shell of icy bodies surrounding the Solar System. This giant swarm of objects is now named the Oort Cloud, occupying space at a distance between 5,000 and 100,000astronomical units. (One astronomical unit, or AU, is the mean distance of Earth from the Sun: about 150 million kilometers or 93 million miles.) The outer extent of the Oort Cloud is considered to be the “edge” of our solar system, where the Sun’s physical and gravitational influence ends.
The Oort Cloud probably contains 0.1 to 2 trillion icy bodies in solar orbit. Occasionally, giant molecular clouds, stars passing nearby, or tidal interactions with the Milky Way’s disc disturb the orbit of one of these bodies in the outer region of the Oort Cloud, causing the object to streak into the inner solar system as a so-called long-period comet. These comets have very large, eccentric orbits and have been observed in the inner solar system only once.
Dwarf Planets:
This artist's concept shows dwarf planets Eris, Pluto and Ceres in comparison to Earth. Pluto's moon Charon also is shown.
What is a planet? We’ve been asking that question at least since Greek astronomers came up with the word to describe the bright points of light that seemed to wander among fixed stars. Our solar system’s planet count has soared as high as 15 before it was decided that some discoveries were different and should be called asteroids.
Many disagreed in 1930 when Pluto was added as our solar system’s ninth planet. The debate flared again in 2005 when Eris – bigger than Pluto – was found deep in a zone beyond Neptune called the Kuiper Belt. Was it the 10th planet? Or are Eris and Pluto examples of an intriguing, new kind of world?
The International Astronomical Union decided in 2006 that a new system of classification was needed to describe these new worlds, which are more developed than asteroids, but different than the known planets. Pluto, Eris and the asteroid Ceres became the first dwarf planets. Unlike planets, dwarf planets lack the gravitational muscle to sweep up or scatter objects near their orbits. They end up orbiting the Sun in zones of similar objects such as the asteroid and Kuiper belts.
Our solar system’s planet count now stands at eight. But the lively debate continues as we enter another exciting decade of exploration and discoveries.
Beyond Our Solar System:
There are billions of stars and countless solar systems in our galaxy. So far we know almost 400 of them have planets in their orbits.
Before 1991, the worlds of our own solar system were the only known planets. Astronomers did not believe that our sun’s environment was the only planet producer in the universe. But they had no evidence of planets outside our solar system.
How quickly things change.
In 1991 radio astronomers detected the first extrasolar planets orbiting a dying pulsar star. Although the deadly radiation from the pulsar would not sustain life, it was the first example of a star other than our Sun producing planets.
Since then more than 450 planets have been found orbiting other stars. Some of them are orbiting extremely close to their parent star like the 51 Peg planetary system, while others are found to be at distances comparable to where Mars and Jupiter orbit in our solar system.
from rahinur.com
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