Jul 17, 2008

The science of our Solar System

All images appear courtesy of NASA

Our Solar System

The Solar System consists of the Sun and the other celestial objects gravitationally bound to it: eight planets, 166 known moons, three dwarf planets (Ceres, Pluto, and Eris and their four known moons), and billions of small bodies.

This last category includes asteroids, Kuiper belt objects, comets, meteoroids, and interplanetary dust.

The Sun

A handle-shaped cloud of plasma erupts from the Sun.

The Sun is the closest star to Earth, at a distance from our planet of 92.96 million miles.

The Sun, a huge sphere of mostly ionized gas, supports life on Earth. It powers photosynthesis in green plants, and is ultimately the source of all food and fossil fuel. The connection and interactions between the Sun and Earth drive the seasons, ocean currents, weather, and climate.


Mercury's heavily-cratered south pole.

The small and rocky planet Mercury is the closest planet to the Sun and speeds around it in an elliptical orbit that takes it as close as 47 million km and as far as 70 million km.

Mercury orbits the Sun every 88 days at nearly 50 km/second. Temperatures reach a scorching 467 degrees Celsius.

The length of one Mercury day is equal to 58.646 Earth days.


Pictures show Venera 9, a Soviet space probe designed especially to explore Venus, and the Surface of Venus from the Venera 10 Lander.

Venus is similar in size, mass, composition, and distance from the Sun as our Earth, however Venus is covered by thick, rapidly spinning clouds that trap surface heat. This creates a scorched greenhouse-like world with temperatures hot enough to melt lead.

The clouds reflect sunlight in addition to trapping heat and because of this Venus reflects so much sunlight and is usually the brightest planet in the sky.

The pressure is so intense that standing on the surace would feel the same as the pressure 900m down in the Earth's oceans.


Earth is the only planet in our solar system known to harbour life. It is made up of complex, interactive systems that are often unpredictable.

Air, water, land, and life - including humans - combine forces to create a constantly changing world that we are striving to understand.

The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees.

Picture shows the Aurora Australis photographed from the Space Shuttle Discovery in May 1991 at the peak of the last geomagnetic maximum.

The payload bay and tail of the Shuttle can be seen on the left hand side of the picture.

Auroras are caused when high-energy electrons pour down from the Earth's magnetosphere and collide with atoms.

Red aurora occurs from 200 km to as high as 500 km altitude and is caused by the emission of 6300 Angstrom wavelength light from oxygen atoms.

Green aurora occurs from about 100 km to 250 km altitude and is caused by the emission of 5577 Angstrom wavelength light from oxygen atoms. The light is emitted when the atoms return to their original unexcited state.

Earth's Moon

Picture: Man and Machine: 11.20.1969 .Charles Conrad Jr., Apollo 12 Commander, examines the unmanned Surveyor III spacecraft. The Lunar Module (LM) "Intrepid" is in the right background.

More than 70 spacecraft have been sent to the Moon; 12 astronauts have walked upon its surface and 382 kg of lunar rock and soil have been brought back.

The Moon stabilizes Earth's wobble and has influence on Earth's cycles notably its tides.

Scientists believe the Moon was formed when a Mars-sized body hit Earth, and the resulting debris accumulated to form the Moon.

It may have formed approx 4.5 billion years ago and when it formed, its outer layers melted under very high temperatures, forming the lunar crust probably from a global "magma ocean."


Hubble Snaps Mars when it was just 34,648,840 miles away, and a recent "color enhanced" version of the 360-degree "Gallery Pan", the first contiguous, uniform panorama taken by the Imager for Mars (IMP).

Mars is a small rocky body whose surface has been changed by volcanism, impacts from other bodies, movements of its crust, and atmospheric effects such as dust storms.

Where Earth tectonics involve sliding plates that grind against each other or spread apart in the sea floors, Martian tectonics seem to be vertical, with hot lava pushing upwards through the crust to the surface.

Periodically, great dust storms engulf the entire planet. The effects of these storms are dramatic, including giant dunes, wind streaks, and wind-carved features

It has polar ice caps that grow and recede with the change of seasons


Asteroids Eros and Gaspra.

Asteroids are rocky fragments left over from the formation of the solar system about 4.6 billion years ago and a region exists in a belt between Mars and Jupiter.

There are more than 90,000 numbered asteroids ranging in size from Ceres, 940 km in diameter, to bodies less than 1 km across.

Stray asteroids have slammed into Earth in the past, playing a major role in the planet's history.

The extinction of the dinosaurs 65 million years ago has been linked to a devastating impact near the Yucatan peninsula in Mexico.


"Shooting stars" or meteors are bits of material falling through Earth's atmosphere which are heated to incandescence by the friction of the air.

The bright trails as they are coming through the Earth's atmosphere are termed meteors, and large chunks hurtling through space are called meteoroids.

Pieces that do not vaporize completely and reach the surface of the Earth are termed meteorites.

Meteor Crater is one of the youngest and best-preserved impact craters on Earth.

The crater formed roughly 50,000 years ago when a 30-metre-wide, iron-rich meteor weighing 100,000 tons struck the Arizona desert at an estimated 20 km per second.

The resulting explosion exceeded the combined force of today's nuclear arsenals and created a 1.1-km-wide, 200-metre-deep crater.


Jupiter is the largest planet in our solar system, with four planet-sized moons and many other smaller ones.

It resembles a star in composition and if it had been eighty times bigger it would have become a star rather than a planet.

This is the original Voyager 'Blue Movie' (so named because it was built from Blue filter images).

It records Voyager 1's approach during a period of over 60 Jupiter days.

The interaction of the atmospheric clouds and storms shows how dynamic Jupiter's atmosphere is.


Like Jupiter, Saturn is made mostly of hydrogen and helium with its volume being 755 times greater than that of Earth.

Winds in the upper atmosphere reach 500 metres/second in the equatorial region.

These super-fast winds combined with heat rising from within the planet's interior cause the yellow and gold bands visible in the atmosphere.

Picture shows the Dragon Storm, a large, bright and complex convective storm that appeared in Saturn's southern hemisphere in mid-September 2004, and a neon Saturn, taken by Cassini spacecraft flying over the unlit side of Saturn's rings.

The first planet found with the aid of a telescope, Uranus was discovered in 1781 by astronomer William Herschel.

It is so distant that it takes 84 years to complete one orbit of the Sun.

Picture shows an infrared composite image of the two hemispheres of Uranus obtained with Keck adaptive optics. The North pole is at 4 o'clock.

Image Credit: Lawrence Sromovsky, University of Wisconsin-Madison/ W. M. Keck Observatory


Nearly 2.8 billion miles from the Sun, Neptune orbits the Sun once every 165 years and is invisible to the naked eye.

Neptune is actually the farthest planet from the Sun for a 20-year period out of every 248 Earth years.

The atmosphere of Neptune consists of mainly hydrogen, methane, and helium. Below is a liquid hydrogen layer including helium and methane. The lower layer is liquid hydrogen compounds, oxygen, and nitrogen.

It is believed that the planet core comprises rock and ice.

Average density, as well as the greatest proportion of core per planet size, is the greatest among the gaseous planets.

Image Credit: Lunar and Planetary Institute.


Once known as the smallest, coldest, and most distant planet from the Sun, Pluto has a dual identity, not to mention being enshrouded in controversy since its discovery in 1930.

On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet.

According to the new rules a planet meets three criteria:
1. It must orbit the Sun
2. It must be big enough for gravity to squash it into a round ball
3. It must have cleared other things out of the way in its orbital neighborhood.

The latter measure knocks out Pluto and 2003UB313 (Eris) which orbit among the icy wrecks of the Kuiper Belt, and Ceres which is in the asteroid belt.

No spacecraft have yet visited Pluto, however NASA has launched a mission called New Horizons that will explore both Pluto and the Kuiper Belt region.

Pluto is covered with methane ice and surface temperature is -230 degrees C.

Picture shows Pluto's Surface from 3 Billion Miles.

Images of Pluto taken by the NASA Hubble Space Telescope with the ESA Faint Object Camera.


Comets are dirty-ice leftovers from the formation of our solar system around 4.6 billion years ago and, as such, contain important clues about the formation of our solar system.

Around a dozen "new" comets are discovered each year and each can take as long as 30 million years to complete one trip around the Sun.

As many as a trillion comets may reside in the Oort cloud, orbiting the Sun near the edge of the Sun's gravitational influence

Picture shows a composite of images from NASA's Deep Space 1 spacecraft showing features of comet Borrelly's nucleus, dust jets escaping the nucleus and the cloud-like "coma" of dust and gases surrounding the nucleus.

False colour is used to reveal details of the jets and coma.

Kuiper Belt

The Kuiper Belt is often called our Solar System's 'final frontier.' This disk-shaped region of icy debris is about 2.8 billion - 4.6 billion miles from our Sun.

Its existence confirmed only a decade ago, the Kuiper Belt and its collection of icy objects - KBOs - are an emerging area of research in planetary science.

No spacecraft has ever traveled to the Kuiper Belt, but NASA's New Horizons mission, planned to arrive at Pluto in 2015, might be able to penetrate further into the Kuiper Belt.

Picture shows known objects in the Kuiper belt, derived from data from the Minor Planet Centre.

Objects in the main belt are coloured green, while scattered objects are coloured orange. The four outer planets are blue.

Neptune's few Trojan asteroids are yellow, while Jupiter's are pink.

The scattered objects between the Sun and the Kuiper belt are known as centaurs. The scale is in astronomical units.

Dwarf Planets

A "dwarf planet" is a celestial body that:
1. Is in orbit around the Sun
2. Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape
3. Has not cleared the neighborhood around its orbit
4. Is not a satellite.

This is the clearest view yet of the distant planet Pluto and its moon, Charon, as revealed by NASA's Hubble Space Telescope (HST).

The image was taken by the European Space Agency's Faint Object Camera on February 21, 1994 when the planet was 2.6 billion miles from Earth, nearly 30 times the separation between Earth and the Sun.

Oort Cloud

The Oort Cloud is an immense spherical cloud surrounding our Solar System.

Extending about 18 trillion miles from the Sun, it was first proposed in 1950 by Dutch astronomer Jan Oort.

The vast distance of the Oort cloud is considered to be the outer edge of the Solar System where the Sun's orb of physical and gravitational influence ends.

Beyond Our Solar System

Since 1991 more than 100 planets have been found orbiting other stars.

Some of them are orbiting extremely close to their parent star like the 51 Pegasi planetary system, while others are found to be at distances comparable to where Mars and Jupiter orbit in our solar system.

Stellar Quakes

On December 27, 2004, a neutron star flared up so brightly, it temporarily blinded all the X-ray satellites in space for an instant, and lit up the Earth's upper atmosphere.

This tremendous blast of energy was from a giant flare created by the neutron star's twisting magnetic field.

Objects like this are called magnetars, and they produce magnetic fields trillions of time more powerful than those here on Earth.

These fields are so strong they can actually buckle the surface of the neutron star causing these powerful star quakes.


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