|Seven Wonders of the Solar System
Extraordinary Phenomena are Happening Right in our own Cosmic Backyard
We are in the midst of the greatest era of space discovery. Twenty first-century spacecraft and sophisticated imaging technology are venturing into uncharted territory every day, and much of the extraordinary phenomena are happening right in our own cosmic backyard.
For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System.
People believed the Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky.
Take an exhilarating, unprecedented 3D tour of the seven most amazing wonders of our solar system, beginning with a trip to Enceladus, one of Saturn s outer moons, where icy geysers spout from its surface.
Then venture to Saturns famous rings, which contain mountain ranges that rival the Alps; dive into Jupiters Great Red Spot, the eye of the biggest storm in the solar system; soar through the Asteroid Belt, made of millions of rocks left over from the formation of the solar system.
Trek up Mount Olympus, the largest volcano located on Mars; have a close encounter with the searing surface of the sun; and finish the journey by exploring our very own home planet Earth.
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago.
Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane.
The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, the gas giants, are substantially more massive than the terrestrials.
The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".
The Solar System is also home to a number of regions populated by smaller objects.
The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc; linked populations of trans-Neptunian objects composed mostly of ices such as water, ammonia and methane.
Within these populations, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.
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.
The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.
The Rings of Saturn
Enceladus is the sixth-largest of the moons of Saturn. It was discovered in 1789 by William Herschel.
In late 2008, scientists observed water vapor spewing from Enceladus's surface. This could indicate the presence of liquid water, which might also make it possible for Enceladus to support life.
Until the two Voyager spacecraft passed near it in the early 1980s, very little was known about this small moon besides the identification of water ice on its surface.
The Voyagers showed that the diameter of Enceladus is only 500 kilometers (310 mi), about a tenth of that of Saturn's largest moon, Titan, and that it reflects almost all of the sunlight that strikes it.
Voyager 1 found that Enceladus orbited in the densest part of Saturn's diffuse E ring, indicating a possible association between the two, while Voyager 2 revealed that despite the moon's small size, it had a wide range of terrains ranging from old, heavily cratered surfaces to young, tectonically deformed terrain, with some regions with surface ages as young as 100 million years old.
In 2005, the Cassini spacecraft performed several close flybys of Enceladus, revealing the moon's surface and environment in greater detail. In particular, the probe discovered a water-rich plume venting from the moon's south polar region.
This discovery, along with the presence of escaping internal heat and very few (if any) impact craters in the south polar region, shows that Enceladus is geologically active today.
Moons in the extensive satellite systems of gas giants often become trapped in orbital resonances that lead to forced libration or orbital eccentricity; proximity to the planet can then lead to tidal heating of the satellite's interior, offering a possible explanation for the activity.
Conversely the geologic activity could be caused by the remnant heat of a massive impact. Enceladus is one of only three outer solar system bodies (along with Jupiter's moon Io and Neptune's moon Triton) where active eruptions have been observed.
Analysis of the outgassing suggests that it originates from a body of sub-surface liquid water, which along with the unique chemistry found in the plume, has fueled speculations that Enceladus may be important in the study of astrobiology. The discovery of the plume has added further weight to the argument that material released from Enceladus is the source of the E ring.
In May 2011, NASA scientists at an Encedalus Focus Group Conference reported that Enceladus "is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it".
Jupiters Great Red Spot
The rings of Saturn are the most extensive planetary ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometres to metres, that form clumps that in turn orbit about Saturn.
Saturn's rings may be very old, dating to the formation of Saturn itself. There are two main theories regarding the origin of Saturn's rings.
One theory, originally proposed by Édouard Roche in the 19th century, is that the rings were once a moon of Saturn whose orbit decayed until it came close enough to be ripped apart by tidal forces.
A variation of this theory is that the moon disintegrated after being struck by a large comet or asteroid.
The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material from which Saturn formed.
The ring particles are made almost entirely of water ice, with some contamination from dust and other chemicals.
Although reflection from the rings increases Saturn's brightness, they are not visible from Earth with unaided vision.
In 1610, the year after Galileo Galilei first turned a telescope to the sky, he became the very first person to observe Saturn's rings, though he could not see them well enough to discern their true nature.
In 1655, Christiaan Huygens was the first person to describe them as a disk surrounding Saturn.
Although many people think of Saturn's rings as being made up of a series of tiny ringlets (a concept that goes back to Laplace), true gaps are few.
It is more correct to think of the rings as an annular disk with concentric local maxima and minima in density and brightness. On the scale of the clumps within the rings there is much empty space.
There are several gaps within the rings: two opened by known moons embedded within them, and many others at locations of known destabilizing orbital resonances with Saturn's moons. Other gaps remain unexplained. Stabilizing resonances, on the other hand, are responsible for the longevity of several rings, such as the Titan Ringlet and the G Ring.
Well beyond the main rings is the Phoebe ring, which is tilted at an angle of 27 degrees to the other rings and, like Phoebe, orbits in retrograde fashion. In December 2010, National Geographic suggested that the rings of Saturn could be the remains of a giant lost moon that was stripped of its icy shell before it crashed into the planet.
The Great Red Spot (GRS) is a persistent anticyclonic storm, 22° south of Jupiter's equator, which has lasted for at least 181 years and possibly longer than 346 years. The storm is large enough to be visible through Earth-based telescopes.
An anticyclonic storm is a weather storm where winds around the storm flow contrary to the direction dictated by the Coriolis effect about a region of low pressure.
Jupiter's Great Red Spot is a well-known extraterrestrial example of an anticyclonic system.
The GRS rotates counterclockwise, with a period of about six Earth days or 14 Jovian days. Its dimensions are 24–40,000 km west–to–east and 12–14,000 km south–to–north. The spot is large enough to contain two or three planets the size of Earth.
At the start of 2004, the Great Red Spot had approximately half the longitudinal extent it had a century ago, when it was 40,000 km in diameter.
At the present rate of reduction it could potentially become circular by 2040, although this is unlikely because of the distortion effect of the neighboring jet streams. It is not known how long the spot will last, or whether the change is a result of normal fluctuations.
The Great Red Spot's latitude has been stable for the duration of good observational records, typically varying by about a degree. Its longitude, however, is subject to constant variation.
Because Jupiter does not rotate uniformly at all latitudes, astronomers have defined three different systems for defining the longitude.
System II is used for latitudes of more than 10°, and was originally based on the average rotation rate of the Great Red Spot of 9h 55m 42s. Despite this, the spot has "lapped" the planet in System II at least 10 times since the early 19th century.
Its drift rate has changed dramatically over the years and has been linked to the brightness of the South Equatorial Belt, and the presence or absence of a South Tropical Disturbance.
It is not known exactly what causes the Great Red Spot's reddish color. Theories supported by laboratory experiments suppose that the color may be caused by complex organic molecules, red phosphorus, or yet another sulfur compound. The GRS varies greatly in hue, from almost brick-red to pale salmon, or even white.
The reddest central region is slightly warmer than the surroundings, which is the first evidence that the Spot's color is affected by environmental factors. The spot occasionally disappears from the visible spectrum, becoming evident only through the Red Spot Hollow, which is its niche in the South Equatorial Belt.
The visibility of GRS is apparently coupled to the appearance of the SEB; when the belt is bright white, the spot tends to be dark, and when it is dark, the spot is usually light. The periods when the spot is dark or light occur at irregular intervals; as of 1997, during the preceding 50 years, the spot was darkest in the periods 1961–66, 1968–75, 1989–90, and 1992–93.
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter.
Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that it would be improbable to reach an asteroid without aiming carefully.
Nonetheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more, depending on the lower size cutoff.
Over 200 asteroids are known to be larger than 100 km, while a survey in the infrared wavelengths shows that the main belt has 700,000 to 1.7 million asteroids with a diameter of 1 km or more.
It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt is also termed the main asteroid belt or main belt because there are other asteroids in the Solar System such as near-Earth asteroids and trojan asteroids.
More than half the mass of the asteroid belt is contained in the four largest objects: Ceres, 4 Vesta, 2 Pallas, and 10 Hygiea.
These have mean diameters of more than 400 km, while Ceres, the asteroid belt's only identified dwarf planet, is about 950 km in diameter.
The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that multiple unmanned spacecraft have traversed it without incident.
Nonetheless, collisions between large asteroids do occur, and these can form an asteroid family whose members have similar orbital characteristics and compositions.
Collisions also produce a fine dust that forms a major component of the zodiacal light. Individual asteroids within the main belt are categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).
The asteroid belt formed from the primordial solar nebula as a group of planetesimals, the smaller precursors of the planets, which in turn formed protoplanets. Between Mars and Jupiter, however, gravitational perturbations from the giant planet imbued the protoplanets with too much orbital energy for them to accrete into a planet.
Collisions became too violent, and instead of sticking together, the planetesimals and most of the protoplanets shattered. As a result, most of the asteroid belt's mass has been lost since the formation of the Solar System. Some fragments can eventually find their way into the inner Solar System, leading to meteorite impacts with the inner planets.
Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits.
Olympus Mons (Latin for Mount Olympus) is a large volcanic mountain on the planet Mars. At an estimated height of between 21 and 29 km (69,000-95,000 ft), it is roughly three times as tall as Mount Everest and is the tallest known mountain in the Solar System.
Olympus Mons is the result of many thousands of highly fluid, basaltic lava flows that poured from volcanic vents over a long period of time.
The extraordinary size of Olympus Mons is likely because Mars lacks mobile tectonic plates. Unlike on Earth, the crust of Mars remains fixed over a stationary hotspot, and a volcano can continue to discharge lava until it reaches an enormous height.
Olympus Mons is the youngest of the large volcanoes on Mars, having formed during Mars' Amazonian Period.
Olympus Mons had been known to astronomers since the late 19th century as the albedo feature Nix Olympica (Latin for "Snows of Olympus"). Its mountainous nature was suspected well before space probes confirmed its identity as a mountain.
Olympus Mons is a shield volcano, similar in morphology to the large volcanoes making up the Hawaiian Islands.
The edifice is about 600 km (373 miles) wide and stands nearly 22 km (14 miles) above the surrounding plains (a little over twice the height of Mauna Kea as measured from its base on the ocean floor).
The summit of the mountain has six nested calderas (collapse craters) forming an irregular depression 60 × 80 km (37 × 50 miles) across and up to 3.2 km (2 miles) deep.
The volcano's outer edge consists of an escarpment, or cliff, up to 8 km (5 miles) tall, a feature unique among the shield volcanoes of Mars. Olympus Mons covers an area approximately the size of Arizona.
Being a shield volcano, Olympus Mons has a very low profile. The average slope on the volcano's flanks is only 5°. Slopes are highest near the middle part of the flanks and grow shallower toward the base, giving the flanks a concave upward profile. The shape of Olympus Mons is distinctly asymmetrical.
Its flanks are shallower and extend out further from the summit in the northwestern direction than they do to the southeast. The volcano's shape and profile have been likened to a "circus tent" held up by a single pole that is shifted off center.
Because of the size of Olympus Mons and its shallow slopes, an observer standing on the Martian surface would be unable to view the entire profile of the volcano, even from a great distance. The curvature of the planet and the volcano itself would obscure such a synoptic view.
Similarly, an observer near the summit would be unaware of standing on a high mountain, as the slope of the volcano would extend beyond the horizon, a mere 3 kilometers away.
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields.
The Sun was formed about 4.57 billion years ago when a hydrogen molecular cloud collapsed. The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. The Sun does not have enough mass to explode as a supernova.
Instead, in about 5 billion years, it will enter a red giant phase, its outer layers expanding as the hydrogen fuel in the core is consumed and the core contracts and heats up.
It has a diameter of about 1,392,000 km, about 109 times that of Earth, and its mass (about 2×1030 kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System.
Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. Less than 2% consists of heavier elements, including oxygen, carbon, neon, iron, and others.
The Sun's stellar classification, based on spectral class, is G2V, and is informally designated as a yellow dwarf, because its visible radiation is most intense in the yellow-green portion of the spectrum and although its color is white, from the surface of the Earth it may appear yellow because of atmospheric scattering of blue light.
In the spectral class label, G2 indicates its surface temperature of approximately 5778 K (5505 °C), and V indicates that the Sun, like most stars, is a main sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium.
In its core, the Sun fuses 620 million metric tons of hydrogen each second.
Once regarded by astronomers as a small and relatively insignificant star, the Sun is now thought to be brighter than about 85% of the stars in the Milky Way galaxy, most of which are red dwarfs.
The absolute magnitude of the Sun is +4.83; however, as the star closest to Earth, the Sun is the brightest object in the sky. The Sun's hot corona continuously expands in space creating the solar wind, a stream of charged particles that extends to the heliopause at roughly 100 astronomical units. The bubble in the interstellar medium formed by the solar wind, the heliosphere, is the largest continuous structure in the Solar System.
The Sun is currently traveling through the Local Interstellar Cloud in the Local Bubble zone, within the inner rim of the Orion Arm of the Milky Way galaxy. Of the 50 nearest stellar systems within 17 light-years from Earth (the closest being a red dwarf named Proxima Centauri at approximately 4.2 light years away), the Sun ranks fourth in mass.
Attack of the Sun
The Sun orbits the center of the Milky Way at a distance of approximately 24,000–26,000 light years from the galactic center, completing one clockwise orbit, as viewed from the galactic north pole, in about 225–250 million years.
Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of constellation Hydra with a speed of 550 km/s, the sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.
The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though the distance varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds.
The energy of this sunlight supports almost all life on Earth by photosynthesis, and drives Earth's climate and weather. The enormous effect of the Sun on the Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity.
An accurate scientific understanding of the Sun developed slowly, and as recently as the 19th century prominent scientists had little knowledge of the Sun's physical composition and source of energy. This understanding is still developing; there are a number of present-day anomalies in the Sun's behavior that remain unexplained.
along with the Solar System, is situated in the Milky Way galaxy,
orbiting about 28,000 light years from the center of the galaxy. It is
currently about 20 light years above the galaxy's equatorial plane in
the Orion spiral arm.
Earth (or the Earth) is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System.
It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet, or by its Latin name, Terra.
Earth formed 4.54 billion years ago, and life appeared on its surface within one billion years. The planet is home to millions of species, including humans.
Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land.
The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period.
The planet is expected to continue supporting life for at least another 500 million years. Earth's outer surface is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years.
About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap).
The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core. Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 solar days, or one sidereal year.
The Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation.
Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment. Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population.
These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth or in the Earth as the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship.