NEW FOUND PLANET orbits backward

Planets orbit stars in the same direction that the stars rotate. They all do. Except one.

A newfound planet orbits the wrong way, backward compared to the rotation of its host star. Its discoverers think a near-collision may have created the retrograde orbit, as it is called.

The star and its planet, WASP-17, are about 1,000 light-years away. The setup was found by the UK's Wide Area Search for Planets (WASP) project in collaboration with Geneva Observatory. The discovery was announced today but has not yet been published in a journal.

"I would have to say this is one of the strangest planets we know about," said Sara Seager, an astrophysicist at MIT who was not involved in the discovery.

What's going on

A star forms when a cloud of gas and dust collapses. Whatever movement the cloud had becomes intensified as it condenses, determining the rotational direction of the star. How planets form is less certain. They are, however, known to develop out of the leftover, typically disk-shaped mass of gas and dust that swirls around a newborn star, so whatever direction that material is moving, which is the direction of the star's rotation, becomes the direction of the planet's orbit.

WASP-17 likely had a close encounter with a larger planet, and the gravitational interaction acted like a slingshot to put WASP-17 on its odd course, the astronomers figure.

"I think it's extremely exciting. It's fascinating that we can study orbits of planets so far away," Seager told SPACE.com. "There's always theory, but there's nothing like an observation to really prove it."

Cosmic collisions are not uncommon. Earth's moon was made when our planet collided with a Mars-sized object, astronomers think. And earlier this week NASA's Spitzer Space Telescope found evidence of two planets colliding around a distant, young star. Some moons in our solar system are on retrograde orbits, perhaps at least in some cases because they were flying through space alone and then captured; that's thought to be the case with Neptune's large moon Triton.

The find was made by graduate students David Anderson at Keele University and Amaury Triaud of the Geneva Observatory.

Bloated world

WASP-17 is about half the mass of Jupiter but bloated to twice its size. "This planet is only as dense as expanded polystyrene, 70 times less dense than the planet we're standing on," said professor Coel Hellier of Keele University.

The bloated planet can be explained by a highly elliptical orbit, which brings it close to the star and then far away. Like exaggerated tides on Earth, the tidal effects on WASP-17 heat and stretch the planet, the researchers suggest.

The tides are not a daily affair, however. "Instead it's creating a huge amount of friction on the inside of the planet and generating a lot of energy, which might be making the planet big and puffy," Seager said.

WASP-17 is the 17th extrasolar planet found by the WASP project, which monitors hundreds of thousands of stars, watching for small dips in their light when a planet transits in front of them. NASA's Kepler space observatory is using the same technique to search for Earth-like worlds.

Who lives in the eleventh dimension? - PARALLEL UNIVERSES

Five New Planets Found; Hotter Than Molten Lava

Most of the five new planets are much hotter and bigger than any planet in our solar system.

Illustration courtesy William Borucki, NASA

Victoria Jaggard in Washington, D.C.

National Geographic News

January 4, 2010

Five new planets have been found orbiting distant stars—the first confirmed new worlds from NASA's recently launched Kepler space telescope mission, astronomers announced today.

Like many of the more than 400 exoplanets—planets outside our solar system—found to date, the new planets are so-called hot Jupiters. They're about the same mass as Jupiter and orbit very close to their host stars, which makes the planets relatively easy to spot from Earth.

The smallest of the new planets is about the same size as Neptune, though much more massive. All of the planets are hotter than molten lava and could turn gold to goo, according to NASA temperature estimates.

Dubbed Kepler 4b, 5b, 6b, 7b, and 8b, the five new planets range in temperature from 2,000 to 3,000 degrees Fahrenheit (1,090 to 1,650 degrees Celsius), William Borucki, Kepler's principal investigator, said today during a press briefing at the American Astronomical Society's annual meeting in Washington, D.C.

One of the worlds, Kepler 7b, is among the lowest-density planets yet found, with about the same density as Styrofoam, he said. (Related: "'Backward' Planet Has Density of Foam Coffee Cups.")

These planets are "certainly no place to look for life—that will be coming later," with discoveries of Earth-like planets, Borucki said.

Kepler "Working So Well"

Kepler's main goal is to find rocky, Earthlike planets orbiting in stars' habitable zones—the regions in which planets receive enough heat from their stars for liquid water to exist.

While the new finds don't meet those criteria, they do show that the instrument is working as expected—offering "a tantalizing hint at what we can expect in a few years' time," noted Greg Laughlin, an astronomer at the University of California, Santa Cruz.

"It's wonderful to see Kepler working so well."

How to Find New Planets

Kepler looks for extrasolar planets by spying the decrease in starlight as a planet transits, or crosses in front of, its host star, as seen from Earth.

The orbiting telescope, which launched last March, spotted the five new worlds in its first six weeks of operation.

Each planet's existence was later confirmed using a method called radial velocity, which looks for the wobble in a star's orbit caused by the gravitational pull of an orbiting planet.

The radial velocity observations were "a beautiful match" for Kepler's data, Borucki said. "It completely confirms that we really have planets here."

Having both sets of data creates a "truly valuable situation" in planet hunting, UCSC's Laughlin added.

That's because each method does more than just help confirm the other. Each technique provides different types of information, which help build a more complete picture of the alien world.

Radial velocity, for example, gives details about a planet's mass and orbit, while transits can reveal a planet's size relative to its star. This in turn tells astronomers about the planet's density.

Planet-hunting missions such as Kepler have shown us that the densities of exoplanets are all over the map, Laughlin said.

Some of the biggest worlds, for instance, have been found to be unexpectedly "puffed up" by an as-yet unexplained heat source.

Kelper 5b, for instance, is much more massive than Jupiter but is much less dense then water, said mission co-investigator Dimitar Sasselov.

"It's like looking at a football team," Laughlin said. "You might guess that they're all 250 to 300 pounds. But then you find out that some of them are 25 pounds—that would come as a surprise."

Hundreds of Candidates for New Planets

Although Kepler's five new planets are the only ones confirmed by the mission so far, the telescope's first few months of data actually contain hundreds of candidates.

The Kepler mission, expected to last at least three and a half years, will likely announce many more new worlds in coming years as astronomers are able to confirm the planets' existence.

But it will take several Earth years before Kepler scientists can be sure they've seen an Earth-size world in its star's habitable zone, Laughlin said.

That's because a planet orbiting at the right distance from its star will be farther out than a hot Jupiter and so will take much longer to complete an orbit of its star—making transits much rarer.

To be sure you've seen a planet, "you have to watch long enough to see three to four transits," Laughlin said.

Overall, though, the new finds help make it clear that planets with otherwise similar traits can have very different personalities, Laughlin noted.

"It's not a situation of, You've seen one, you've seen them all."

NASA Astronomers Discover Two New Planet

NASA announced that Kepler spacecraft has discovered the first confirmed planetary system with more than one planet "transiting," or crossing in front of, a central star.

The findings, published in Thursday's issue of the journal Science, came from observing about 156,000 stars for seven months as part of a pioneering search for Earth-size planets outside our solar system.

Kepler's ultra-precise camera measures tiny decreases in a star's brightness caused by the orbiting of the planet as it crosses in front of its sun. The size of the planets can be determined by measuring these temporary dips.

Two planets in the newly discovered system, 2,000 light-years away, are the size of Saturn, and a third possible planet is a "super-Earth," 11/2 times the size of our planet. That planet is the size thought to be potentially habitable, but it orbits too close to its star to support life, Washington Post reports.

The planets, now named named Kepler-9b and 9c, were seen transiting the sun-like star called Kepler-9. The announcement comes just days after ESO released data on a planetary system believed to have five orbiting planets, discovered with the HARP ground-based telescope.

Kepler found more than 700 possible planets in its first 43 days, and has discovered five more systems that appear to have more than one transiting planet, TG Daily informs.

Earth-Like Planet Discovered in Libra

Scientists have discovered a new planet in the constellation Libra. The small, rocky planet is special because it appears to have mild temperatures, like Earth. Researchers believe it looks like the first planet outside of our solar system that could be home to liquid water, and maybe even life.

Our solar system has only eight planets — nine if you count Pluto. But outside of our solar system, around other stars, scientists have found dozens and dozens of planets.

"We have discovered more than 100 planets, here in Geneva," says Michel Mayor, a planet hunter at the University of Geneva.

Almost all of these known "extrasolar" planets are giant balls of gas, much like Jupiter or Saturn. Such massive planets are relatively easy to find. They have a gravitational pull that makes their stars wobble, and when scientists see that wobble, they know there is a planet. Small, rocky planets cause less of a wobble, making them harder to find.

Still, Mayor and his colleagues have had some luck using the European Southern Observatory's big telescope at La Silla, Chile. They recently pointed it at a nearby star called Gliese 581, in the constellation Libra.

"It's one of our closest neighbors in the galaxy," Mayor says.

His team has found three planets around this star, and one of them is particularly interesting. They think the planet is a little bigger than Earth, with about five times the Earth's mass. It orbits very close to its star, going all the way around in just 13 days. The planet isn't super hot though, because Gliese 581 is a red dwarf, which is much dimmer and cooler than our sun.

Scientists calculate that average temperatures on the surface of the planet should be around 32 to 104 degrees Fahrenheit. Mayor says that is a friendly environment for liquid water and maybe even life.

"We do not have any reason to believe that life exists on that planet," Mayor concedes. "We can only say that we have the temperature to permit the development of life. I would say it's one very interesting step in a long process going in the direction to having some major discovery related to life in the universe."

A report on the discovery has been submitted to the journal Astronomy and Astrophysics, and other experts agree that it is a significant find. Alan Boss is a planetary scientist at the Carnegie Institution of Washington.

"This seems to be the first discovery of an Earth-like planet," Boss says. "It's not exactly an Earth but it's close enough that I think it does deserve the title of perhaps the first Earth-like planet."

Other small planets discovered in the past have been very hot, or very cold. In many ways, though, this planet is a mystery.

"We do not know what the composition of the planet is," says Boss, explaining that scientists assume it is made of rock and metal like Earth. "We do not know how much water it may or may not have on it."

Boss says we could learn a lot more if scientists launched a space telescope that is specially designed to look at faraway planets. NASA has one in development called the Terrestrial Planet Finder, but it has been delayed indefinitely by budget woes.

"Things like Terrestrial Planet Finder are no longer really in the active NASA plan," Boss says.

Still, some scientists have a mental picture of the place. Todd Henry, an astronomer at Georgia State University, says that if you were standing on this planet and looked up, its sun would appear to be huge — five times bigger than our sun looks to us.

"It's going to look very different in this sort of alien situation that we're in than what we're used to here on Earth," Henry says. "The star itself is actually going to look sort of the color of Mars — sort of a red, ruddy color. But it would be much bigger in the sky than we're used to."

He says the star is also notable because the Geneva team found those two other planets circling it. They are also relatively small planets, which have been harder to find.

"This is starting to look like a solar system we're familiar with," Henry says. "If you were in a spaceship and you sort of flew into this system, this is one of the most interesting ones there is out there now."

But don't count on visiting anytime soon. Even though Gliese 581 is close, compared with other stars, it still would take over 20 years to get there — if we could travel at the speed of light, which we can't do.

6 new planets!

Six New Planets Discovered

ScienceDaily (June 22, 2010) — An international team, including Oxford University scientists, has discovered six diverse new planets, from 'shrunken-Saturns' to 'bloated hot Jupiters', as well a rare brown dwarf with 60 times the mass of Jupiter.

The CoRoT (Convection, Rotation and Transits) space telescope is operated by the French space agency CNES. It discovers planets outside our solar system -- exoplanets -- when they 'transit', that is pass, in front of their stars.

Once CoRoT detects a transit, additional observations are made from the ground, using a number of telescopes all over the world. Although astronomers cannot see the planets directly, they use the space- and ground-based data to measure the sizes, masses, and orbits of these new planets precisely. This is why, among all known exoplanets, those with transits yield the most complete information about planet formation and evolution.

"Each of these planets is interesting in its own right, but what is really fascinating is how diverse they are," said co-investigator Dr. Suzanne Aigrain from Oxford University's Department of Physics. "Planets are intrinsically complex objects, and we have much to learn about them yet."

"Every discovery of an extrasolar planetary system is a new piece in the puzzle of how these systems do form and evolve. The more systems we uncover, the better we can hope to understand the processes at play," said Magali Deleuil, researcher at the Laboratoire d'Astrophysique de Marseille (LAM) and head of the CoRoT exoplanet program.

The six new planets are:

CoRoT-8b: the smallest in this batch: At about 70% of the size and mass of Saturn, CoRoT-8b is moderately small among the previously known transiting exoplanets. Its internal structure should be similar to that of ice giants, like Uranus and Neptune, in the Solar System. It is the smallest planet discovered by the CoRoT team so far after CoRoT-7b, the first transiting Super-Earth.

CoRoT-10b: the eccentric giant: The orbit of CoRoT-10b is so elongated that the planet passes both very close to and very far away from its star. The amount of radiation it receives from the star varies tenfold in intensity, and scientists estimate that its surface temperature may increase from 250 to 600°C, all in the space of 13 Earth-days (the length of the year on CoRoT-10b).

CoRoT-11b: the planet whose star does the twist: CoRoT-11, the host star of CoRoT-11b, rotates around its axis in 40 hours. For comparison, the Sun's rotation period is 26 days. It is particularly difficult to confirm planets around rapidly rotating stars, so this detection is a significant achievement for the CoRoT team.

CoRoT-12b, 13b and 14b: a trio of giants: These three planets all orbit close to their host star but have very different properties. Although CoRoT-13b is smaller than Jupiter, it is twice as dense. This suggests the presence of a massive rocky core inside the planet. With a radius 50% large than Jupiter's (or 16 times larger than the Earth's), CoRoT-12b belongs to the family of `bloated hot Jupiters', whose anomalously large sizes are due to the intense stellar radiation they receive. On the other hand, CoRoT-14b, which is even closer to its parent star, has a size similar to Jupiter's. It is also massive, 7.5 times the mass of Jupiter, which may explain why it is less puffed up. Such very massive and very hot planets are rare, CoRoT-14b is only the second one discovered so far.

CoRoT-15b: the brown dwarf: CoRoT-15b's mass is about 60 times that of Jupiter. This makes it incredibly dense, about 40 times more so than Jupiter. For that reason, it is classified as a brown dwarf, intermediate in nature between planets and stars. Brown dwarfs are much rarer than planets, which makes this discovery all the more exciting.

Dr. Suzanne Aigrain leads a team of UK researchers at the Universities of Oxford, Exeter and St Andrews who participate in the CoRoT exoplanet program. Their research is supported by the Science and Technology Facilities Research Council.

Earth 100 Million Years From Now

Voyage to Pandora: The First Interstellar Space Flight

Life on Mars

Couple of photos captured and sent by the Nasa’s Mars explorer vehicle, Earth by Spirit on Mars’ surface, might indicate there are life forms on the red planet.

Look at the picture attached above, looks like a female figure is sitting on a rock with her arm outstretched – she could be waiting for a bus. More pictures attached below!

The Mars explorer vehicle had landed Mars four years ago and been going around to capture images and send back to Earth. The pictures have created some buzz over the Internet.

Some say that it could be naked aliens running around, but some believe that is simply an optical illusion caused by a landscape, which I also believe so.

Initial inspection shows nothing unusual, but after having a zoom to have a closer examination by amateur astronomers has thrown up these intriguing pictures.

Eris

Eris, formal designation 136199 Eris, is the largest known dwarf planet in the Solar System and the ninth-largest body known to orbit the Sun directly. It is approximately 2,500 kilometres (1,600 mi) in diameter and 27% more massive than Pluto.

Eris was first identified in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity verified later that year. It is a trans-Neptunian object (TNO) native to a region of space beyond the Kuiper belt known as the scattered disc. Eris has one moon, Dysnomia; recent observations have found no evidence of further satellites. As of 2009, its distance from the Sun is 96.7 AU, roughly three times that of Pluto. With the exception of some comets the pair are the most distant known natural objects in the Solar System.

Because Eris is larger than Pluto, its discoverers and NASA initially described it as the Solar System’s tenth planet. This, along with the prospect of other similarly sized objects being discovered in the future, motivated the International Astronomical Union (IAU) to define the term planet for the first time. Under a then-new IAU definition approved on August 24, 2006, Eris is a "dwarf planet" along with Pluto, Ceres, Haumea and Makemake.

Makemake

Makemake, formally designated (136472) Makemake, is the third-largest known dwarf planet in the Solar System and one of the two largest Kuiper belt objects (KBO) in the classical KBO population.^[b] Its diameter is roughly three-quarters that of Pluto. Makemake has no known satellites, which makes it unique among the largest KBOs. Its extremely low average temperature, about 30 K (−243.2 °C), means its surface is covered with methane, ethane, and possibly nitrogen ices.

Initially known as 2005 FY₉ and later given the minor planet number 136472, it was discovered on March 31, 2005, by a team led by Michael Brown, and announced on July 29, 2005. Its name derives from the Rapanui god Makemake. On June 11, 2008, the International Astronomical Union (IAU) included Makemake in its list of potential candidates to be given "plutoid" status, a term for dwarf planets beyond the orbit of Neptune that would place the object alongside Pluto, Haumea and Eris. Makemake was formally classified as a plutoid in July 2008.

Haumea

Haumea, formal designation 136108 Haumea, is a dwarf planet in the Kuiper belt. Its mass is one-third the mass of Pluto. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and, in 2005, by a team headed by J. L. Ortiz at the Sierra Nevada Observatory in Spain, though the latter claim has been contested. On September 17, 2008, it was designated a dwarf planet by the International Astronomical Union (IAU) and named after Haumea, the Hawaiian goddess of childbirth.

Haumea's extreme elongation makes it unique among known dwarf planets. Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its greatest axis twice as long as its shortest. Nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, thereby meeting the definition of a dwarf planet. This elongation, along with its unusually rapid rotation, high density, and high albedo (from a surface of crystalline water ice), are thought to be the results of a giant collision, which left Haumea the largest member of a collisional family that includes several large TNOs and its two known moons.

Pluto

Pluto, formal designation 134340 Pluto, is the second-largest known dwarf planet in the Solar System (after Eris) and the tenth-largest body observed directly orbiting the Sun. Originally classified as a planet, Pluto is now considered the largest member of a distinct population known as the Kuiper belt.

Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small: approximately a fifth the mass of the Earth's Moon and a third its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the Sun. This causes Pluto to periodically come closer to the Sun than Neptune.

From its discovery in 1930 until 2006, Pluto was considered the Solar System's ninth planet. In the late 1970s, following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto's very low mass, its status as a major planet began to be questioned. In the late 20th and early 21st century, many objects similar to Pluto were discovered in the outer Solar System, notably the scattered disc object Eris in 2005, which is 27% more massive than Pluto. On August 24, 2006, the International Astronomical Union (IAU) defined what it means to be a "planet" within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category "dwarf planet" along with Eris and Ceres. After the reclassification, Pluto was added to the list of minor planets and given the number 134340. A number of scientists continue to hold that Pluto should be classified as a planet.

Pluto and its largest moon, Charon, are sometimes treated together as a binary system because the barycentre of their orbits does not lie within either body. The IAU has yet to formalise a definition for binary dwarf planets, and until it passes such a ruling, they classify Charon as a moon of Pluto. Pluto has two known smaller moons, Nix and Hydra, discovered in 2005.

DWARF PLANETS : CERES

Ceres, formally designated 1 Ceres, is the smallest identified dwarf planet in the Solar System and the only one in the asteroid belt. It was discovered on 1 January 1801, by Giuseppe Piazzi, and for half a century it was classified as the eighth planet. It is named after Ceres, the Roman goddess of growing plants, the harvest, and motherly love.

With a diameter of about 950 km (590 mi), Ceres is by far the largest and most massive body in the asteroid belt, and contains almost a third (32%) of the belt's total mass. Recent observations have revealed that it is spherical, unlike the irregular shapes of smaller bodies with lower gravity. The Cererian surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clays. Ceres appears to be differentiated into a rocky core and ice mantle, and may harbour an ocean of liquid water underneath its surface.

From the Earth, Ceres' apparent magnitude ranges from 6.7 to 9.3, and hence at its brightest it is still too dim to be seen with the naked eye. On 27 September 2007, NASA launched the Dawn space probe to explore Vesta (2011–2012) and Ceres (2015).

Neptune

Neptune is the eighth and farthest planet from the Sun in our Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third-largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 Earth masses and not as dense. On average, Neptune orbits the Sun at a distance of 30.1 AU, approximately 30 times the Earth-Sun distance. Its astronomical symbol is , a stylized version of the god Neptune's trident.

Discovered on September 23, 1846, Neptune was the first planet found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently observed by Johann Galle within a degree of the position predicted by Urbain Le Verrier, and its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining 12 moons were located telescopically until the 20th century. Neptune has been visited by only one spacecraft, Voyager 2, which flew by the planet on August 25, 1989.

Neptune is similar in composition to Uranus, and both have compositions which differ from those of the larger gas giants Jupiter and Saturn. Neptune's atmosphere, while similar to Jupiter's and Saturn's in that it is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, contains a higher proportion of "ices" such as water, ammonia and methane. Astronomers sometimes categorize Uranus and Neptune as "ice giants" in order to emphasize these distinctions. The interior of Neptune, like that of Uranus, is primarily composed of ices and rock. Traces of methane in the outermost regions in part account for the planet's blue appearance.

In contrast to the relatively featureless atmosphere of Uranus, Neptune's atmosphere is notable for its active and visible weather patterns. At the time of the 1989 Voyager 2 flyby, for example, the planet's southern hemisphere possessed a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h. Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching −218 °C (55 K). Temperatures at the planet's centre, however, are approximately 5,400 K (5,000 °C).^[17][18] Neptune has a faint and fragmented ring system, which may have been detected during the 1960s but was only indisputably confirmed in 1989 by Voyager 2.

Uranus

Uranus is the seventh planet from the Sun, and the third-largest and fourth most massive planet in the Solar System. It is named after the ancient Greek deity of the sky Uranus (Ancient Greek: Οὐρανός) the father of Cronus (Saturn) and grandfather of Zeus (Jupiter). Though it is visible to the naked eye like the five classical planets, it was never recognized as a planet by ancient observers because of its dimness and slow orbit. Sir William Herschel announced its discovery on March 13, 1781, expanding the known boundaries of the Solar System for the first time in modern history. Uranus was also the first planet discovered with a telescope.

Uranus is similar in composition to Neptune, and both are of different chemical composition than the larger gas giants Jupiter and Saturn. As such, astronomers sometimes place them in a separate category, the "ice giants". Uranus's atmosphere, while similar to Jupiter and Saturn's in its primary composition of hydrogen and helium, contains more "ices" such as water, ammonia and methane, along with traces of hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (–224 °C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clouds. In contrast the interior of Uranus is mainly composed of ices and rock.

Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun. As such, its north and south poles lie where most other planets have their equators. Seen from Earth, Uranus's rings can sometimes appear to circle the planet like an archery target and its moons revolve around it like the hands of a clock, though in 2007 and 2008 the rings appeared edge-on. In 1986, images from Voyager 2 showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants. However, terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per second (900 km/h, 560 mph)

Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus (the Titan father of Zeus), the Babylonian Ninurta, and the Hindu Shani. Saturn's symbol represents the Roman god's sickle (Unicode: ♄).

Saturn, along with Jupiter, Uranus, and Neptune, is classified as a gas giant. Together, these four planets are sometimes referred to as the Jovian, meaning "Jupiter-like", planets. Saturn has an average radius about nine times larger than the Earth's. While only one-eighth the average density of Earth, due to its larger volume, Saturn's mass is just over ninety-five times greater than Earth's.

Because of Saturn's large mass and resulting gravitation, the conditions produced on Saturn are extreme. The interior pressures and temperatures are beyond what can be reproduced experimentally on Earth. The interior of Saturn is probably composed of a core of iron, nickel, silicon and oxygen compounds, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and an outer gaseous layer. Electrical current within the metallic-hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is slightly weaker than Earth's magnetic field and approximately one-twentieth the strength of the field around Jupiter. The outer atmosphere is generally bland in appearance, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h, significantly faster than those on Jupiter.

Saturn has nine rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two known moons orbit the planet, fifty-three are officially named. This is not counting hundreds of "moonlets" within the rings. Titan, Saturn's largest and the Solar System's second largest moon (after Jupiter's Ganymede), is larger than the planet Mercury and is the only moon in the Solar System to possess a significant atmosphere.

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune. Together, these four planets are sometimes referred to as the Jovian planets.

The planet was known by astronomers of ancient times and was associated with the mythology and religious beliefs of many cultures. The Romans named the planet after the Roman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of −2.95, making it on average the third-brightest object in the night sky after the Moon and Venus. (Mars can briefly match Jupiter's brightness at certain points in its orbit.)

Jupiter is primarily composed of hydrogen with a quarter of its mass being helium; it may also have a rocky core of heavier elements. Because of its rapid rotation, Jupiter's shape is that of an oblate spheroid (it possesses a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding the planet is a faint planetary ring system and a powerful magnetosphere. There are also at least 63 moons, including the four large moons called the Galilean moons that were first discovered by Galileo Galilei in 1610. Ganymede, the largest of these moons, has a diameter greater than that of the planet Mercury.

Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. The most recent probe to visit Jupiter was the Pluto-bound New Horizons spacecraft in late February 2007. The probe used the gravity from Jupiter to increase its speed. Future targets for exploration in the Jovian system include the possible ice-covered liquid ocean on the moon Europa.

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth. Mars is the site of Olympus Mons, the highest known mountain within the Solar System, and of Valles Marineris, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Unlike Earth, Mars is now geologically and tectonically inactive.

Until the first flyby of Mars occurred in 1965, by Mariner 4, many speculated about the presence of liquid water on the planet's surface. This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents; long, dark striations were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusions, yet of all the planets in the Solar System other than Earth, Mars is the most likely to harbor liquid water, and thus to harbor life. Geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface, while small geyser-like water flows may have occurred during the past decade. In 2005, radar data revealed the presence of large quantities of water ice at the poles, and at mid-latitudes. The Phoenix lander directly sampled water ice in shallow martian soil on July 31, 2008.

Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Martian Trojan asteroid. Mars is currently host to three functional orbiting spacecraft: Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. On the surface are the two Mars Exploration Rovers (Spirit and Opportunity) and several inert landers and rovers, both successful and unsuccessful. The Phoenix lander completed its mission on the surface in 2008. Observations by NASA's now-defunct Mars Global Surveyor show evidence that parts of the southern polar ice cap have been receding.

Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches −2.91, a brightness surpassed only by Jupiter, Venus, the Moon, and the Sun.

Earth

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,^{[note 6]} or by its Latin name, Terra.^{[note 7]} Home to millions of species including humans, Earth is currently the only place in the universe where life is known to exist. However, as of 2010, almost 500 extrasolar planets have been found, and some of them are thought to be potentially habitable. It is not yet known if Earth-like planets are common or rare.

The planet Earth formed 4.54 billion years ago, and life appeared on its surface within a billion years. 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 with salt water oceans, the remainder consisting of continents and islands which together have many lakes and other sources of water contributing to the hydrosphere. Liquid water, necessary for all known life, is not known to exist on any other planet's surface.^{[note 8][note 9]} 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 for every roughly 366.26 times it rotates about its 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 to 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 Earth as the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship.