Europa is the fourth largest of Jupiter’s 95 moons. It’s the sixth-closest moon to the planet. Europa may be one of the most promising places in our solar system to find present-day environments suitable for some form of life beyond Earth. Scientists believe a saltwater ocean lies beneath its icy shell, holding twice as much water as Earth’s global ocean. It also may have the chemical elements that are key ingredients to life. NASA launched Europa Clipper on Oct. 14, 2024, to determine whether there are places below Europa’s surface that could support life.

In 1972, scientists using a telescope at Kitt Peak National Observatory in Tucson, Arizona, made spectroscopic observations that showed that Europa’s surface composition is mostly water ice. Thermal models dating back to 1971 also suggested that the interior of Europa could contain a layer of liquid water.

NASA’s Pioneer 10 and 11 spacecraft flew by Jupiter in the early 1970s, but the first spacecraft to image the surfaces of Jupiter’s moons in significant detail were the Voyager 1 and 2 spacecraft.

Voyager 1’s closest approach to Jupiter occurred on March 4, 1979. The spacecraft snapped a full global image of Europa from a distance of about 1.2 million miles (2 million kilometers).

A few months later, Voyager 2 had its closest encounter with Europa on July 9, 1979. Images from the two Voyagers revealed a surface brighter than that of Earth’s moon, crisscrossed with numerous bands and ridges, and with a surprising lack of large impact craters, tall cliffs, or mountains. In other words, Europa has a very smooth surface, relative to the other icy moons.

Scientists think Europa’s ice shell is 10 to 15 miles (15 to 25 kilometers) thick, floating on an ocean 40 to 100 miles (60 to 150 kilometers) deep. So while Europa is only one-fourth the diameter of Earth, its ocean may contain twice as much water as Earth’s global ocean. Europa’s ocean is considered one of the most promising places in the solar system to look for life beyond Earth.

Neptune is the eighth and farthest planet from the sun but it is not the coldest. Our solar system’s blue gas giant is far larger than Earth, at more than 17 times Earth’s mass and nearly 58 times Earth’s volume, according to NASA. Neptune’s rocky core is surrounded by a slushy fluid mix of water, ammonia and methane ice. Astronomer Galileo Galilei was one of the first people to identify Neptune as a space object, however, he assumed it was a star based on its slow movement.

At the same time Le Verrier was calculating the existence of Neptune, so was English astronomer John Couch Adams. The two scholars independently came up with nearly identical mathematical predictions about Neptune’s existence. Le Verrier then informed his colleague, German astronomer Johann Gottfried Galle, about his calculations, and Galle and his assistant Heinrich d’Arrest confirmed Le Verrier’s predictions by viewing and identifying Neptune through the telescope at his observatory in Berlin. In accordance with all the other planets seen in the sky, and as suggested by Le Verrier, this new world was given a name from Greek and Roman mythology — Neptune, the Roman god of the sea.

The planet’s cloud cover has an especially vivid blue tint that is partly due to an as-yet-unidentified compound and the result of the absorption of red light by methane in the planet’s mostly hydrogen-helium atmosphere. By studying the cloud formations on the gas giant, scientists were able to calculate that a day on Neptune lasts just under 16 hours long.

The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus. The common name comes from a drawing that somewhat resembled a crab with arms produced by William Parsons, 3rd Earl of Rosse, in 1842 or 1843 using a 36-inch (91 cm) telescope. The nebula was discovered by English astronomer John Bevis in 1731. It corresponds with a bright supernova recorded by Chinese astronomers in 1054 as a guest star. The nebula was the first astronomical object identified that corresponds with a historically-observed supernova explosion.

With an apparent magnitude of 8.4 and located 6,500 light-years from Earth in the constellation Taurus, the Crab Nebula can be spotted with a small telescope and is best observed in January. The nebula was discovered by English astronomer John Bevis in 1731, and later observed by Charles Messier who mistook it for Halley’s Comet. Messier’s observation of the nebula inspired him to create a catalog of celestial objects that might be mistaken for comets.

This large mosaic of the Crab Nebula was assembled from 24 individual exposures captured by Hubble over three months. The colors in this image do not match exactly what we would see with our eyes but yield insight into the composition of this spectacular stellar corpse. The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The blue in the filaments in the outer part of the nebula represents neutral oxygen. Green is singly ionized sulfur, and red indicates doubly ionized oxygen. These elements were expelled during the supernova explosion.

A rapidly spinning neutron star (the ultra-dense core of the exploded star) is embedded in the center of the Crab Nebula. Electrons whirling at nearly the speed of light around the star’s magnetic field lines produce the eerie blue light in the interior of the nebula. The neutron star, like a lighthouse, ejects twin beams of radiation that make it appear to pulse 30 times per second as it rotates.

1. Origin of the Universe: The Big Bang theory proposes that the universe began as an extremely hot and dense singularity about 13.8 billion years ago.
2. Expansion: According to the theory, the universe has been expanding and cooling ever since its inception. This expansion is supported by observational evidence such as the redshift of distant galaxies.
3. Cosmic Microwave Background Radiation (CMB): One of the key pieces of evidence for the Big Bang theory is the discovery of cosmic microwave background radiation, which is leftover radiation from the early universe. This radiation is nearly uniform in all directions and provides strong support for the idea of a hot, dense beginning.
4. Formation of Matter: As the universe expanded and cooled, subatomic particles began to form, eventually leading to the formation of atoms. These atoms later coalesced into stars, galaxies, and larger cosmic structures.
5. Nucleosynthesis: During the first few minutes after the Big Bang, the conditions were right for nucleosynthesis, the formation of light atomic nuclei such as hydrogen, helium, and lithium. This process played a crucial role in the early evolution of the universe.
6. Inflationary Epoch: Some versions of the Big Bang theory include a period of rapid expansion known as cosmic inflation, which occurred in the first fractions of a second after the Big Bang. Inflation helps to explain the large-scale structure of the universe and several other observed phenomena.
7. Formation of Galaxies and Clusters: Over billions of years, gravity caused matter to clump together, forming galaxies, galaxy clusters, and superclusters. These structures continue to evolve due to gravitational interactions.
8. Dark Matter and Dark Energy: The Big Bang theory suggests that most of the matter in the universe is in the form of dark matter, which interacts gravitationally but does not emit light. Additionally, dark energy, a mysterious force that is driving the accelerated expansion of the universe, is thought to constitute a significant portion of the universe’s energy density.
9. Observable Universe: The observable universe, the portion of the universe that we can see, is finite because the speed of light imposes a limit on how far we can observe. However, the entire universe may be much larger, possibly infinite.
10. Ongoing Research and Challenges: While the Big Bang theory has withstood decades of scrutiny and is the prevailing cosmological model, there are still unanswered questions and areas of active research, such as the nature of dark matter and dark energy, the initial conditions of the universe, and the possibility of a multiverse.

A solar eclipse occurs during the new moon phase, when the moon passes between Earth and the sun, casting a shadow on Earth and totally or partially blocking our view of the sun. A total solar eclipse swept across North America on Monday, April 8, offering a spectacle for tens of millions of people who live in its path and others who traveled to see it. Here are some facts about solar eclipses:

1. In ancient Greece, a solar eclipse was seen as a sign that the gods were angry and was thought to be an omen of bad things to come. The word eclipse comes from the Greek word ekleipsis which means “being abandoned”.

2. In ancient China, the solar and lunar eclipses were regarded as heavenly signs that foretell the future of the Emperor and so predicting eclipses was of high importance for the state. Over four millennia ago, legend has it that two astrologers, Hsi and Ho, were executed for failing to predict a solar eclipse.

3. Herodotus, the father of history, who lived in the 5th century BC, cited that the Greek philosopher Thales (ca. 624-547 BC) predicted the solar eclipse of 28 May 585 BC that put an end to the conflict between the Lydians and the Medes. Herodotus wrote: … day was all of sudden changed into night. This event had been foretold by Thales, the Milesian, who forewarned the Ionians of it, fixing for it the very year in which it took place. The Medes and the Lydians when they observed the change, ceased fighting, and were alike anxious to have terms of peace agreed on.

4. In Viking fables the sun god Sol is chased by the wolf Skoll. When the Skoll catches Sol, a solar eclipse happens. When this occurs, the people were instructed to bang pots and pans together to frighten off the wolf and return the sun.

5. On 2 August 1133 a solar eclipse occurred and King Henry I died shortly afterwards, prompting the spread of the superstition that eclipses are bad omens for rulers.

6. The Pomo, an indigenous group of people who live in the northwestern United States, tell a story of a bear who started a fight with the Sun and took a bite out of it. The Pomo name for a solar eclipse is “Sun got bit by a bear.”

7. According to the Batammaliba people from Benin and Togo in West Africa during an eclipse the Sun and Moon are fighting. The only way to stop the conflict, they believe, is for people on Earth to settle their differences.

8. In Italy, it is believed that flowers planted during a solar eclipse are brighter and more colorful than flowers planted any other time of the year.

9. Solar eclipses will come to an end. In about 600 million years, due to tides on Earth and the slowing down of the Earth’s rotation, the moon will be too far away from the Earth to cover the sun, thus bringing an end to solar eclipses.

Jupiter’s moon Ganymede is the largest moon in our solar system, bigger than the planet Mercury and dwarf planet Pluto. NASA’s Hubble Space Telescope has found the best evidence yet for an underground saltwater ocean on Ganymede. The ocean is thought to have more water than all the water on Earth’s surface. Ganymede’s ocean is estimated to be 60 miles (100 kilometers) thick – 10 times deeper than Earth’s ocean – and is thought to be buried under a 95-mile- (150-kilometer-) thick crust of mostly ice. Identifying liquid water is crucial in the search for habitable worlds beyond Earth, and in the search for life as we know it.

Ganymede is the only moon known to have its own magnetic field – a discovery made by NASA’s Galileo spacecraft in 1996. The magnetic field causes auroras, which are ribbons of glowing, hot, electrified gas, in regions circling the north and south poles of the moon. Because Ganymede is close to Jupiter, its magnetic field is embedded in, or lies within, Jupiter’s magnetic field.

When Jupiter’s magnetic field changes, the auroras on Ganymede also change, “rocking” back and forth. It was by watching the rocking motion of the two auroras, that a team of scientists led by Joachim Saur of the University of Cologne in Germany came up with the idea of using the Hubble space telescope to learn more about the inside of the moon.

Discovery and Name

Ganymede was discovered by Italian astronomer Galileo Galilei on Jan. 7, 1610. The discovery, along with his discovery of three other large moons around Jupiter, was the first time a moon was discovered orbiting a planet other than Earth. The discovery eventually led to the understanding that planets in our solar system orbit the Sun, instead of our solar system revolving around Earth. (Jupiter now has 53 named moons and 26 provisional moons awaiting confirmation of discovery).

In mythology, Ganymede (“GAN uh meed”) was a beautiful young boy who was carried to Olympus by Zeus (the Greek equivalent of the Roman god Jupiter) disguised as an eagle. Ganymede became the cupbearer of the Olympian gods.

Potential for Life

A computer model of Ganymede’s interior created in 2014 supported the idea that the development of primitive life might be possible there. The model indicated the icy moon’s rocky sea bottom might be in contact with salt water. Scientists think water and rock interacting are key for the development of life.

Size and Distance

Ganymede has a radius of 1,635 miles (2,631 kilometers) and is the largest moon in our solar system. It’s bigger than Mercury and Pluto. Ganymede is about 665,000 miles (1.07 million kilometers) from Jupiter, which orbits about 484 million miles (778 million kilometers) from the Sun. Jupiter is 5.2 astronomical units away from the Sun. One astronomical unit (abbreviated as AU) is the distance from the Sun to Earth. From this distance, it takes sunlight 43 minutes to travel from the Sun to the Jovian system.

Orbit and Rotation

Ganymede orbits Jupiter at a distance of 665,000 miles (1,070,000 kilometers), making it third in distance from Jupiter among the Galilean satellites. Ganymede completes an orbit around Jupiter about every seven Earth days (7.155). Ganymede orbits the Sun along with Jupiter and its other satellites every 12 Earth years.

Formation

Ganymede and Jupiter’s other large moons (Io, Europa, and Callisto) likely formed from leftover material after Jupiter condensed out of the initial cloud of gas and dust surrounding the Sun, early in the history of our solar system. Ganymede is likely about the same age as the rest of the solar system – about 4.5 billion years old.

Atmosphere

Astronomers using the Hubble Space Telescope have found evidence of a thin oxygen atmosphere on Ganymede. The researchers think the oxygen is coming from Ganymede’s icy surface. Ganymede is much colder than Earth, with daytime surface temperatures ranging from -297 to -171 degrees Fahrenheit (90 to 160 Kelvin). Jupiter and its moons receive less than 1/30th the amount of sunlight that the Earth does, and Ganymede doesn’t have a dense atmosphere to trap heat.

Saturn is the sixth planet from the Sun and the second-largest planet in our solar system. Like fellow gas giant Jupiter, Saturn is a massive ball made mostly of hydrogen and helium. Saturn is not the only planet to have rings, but none are as spectacular or as complex as Saturn’s. Saturn also has dozens of moons. From the jets of water that spray from Saturn’s moon Enceladus to the methane lakes on smoggy Titan, the Saturn system is a rich source of scientific discovery and still holds many mysteries. The farthest planet from Earth discovered by the unaided human eye, Saturn has been known since ancient times.

The planet is named for the Roman god of agriculture and wealth, who was also the father of Jupiter. Saturn’s environment is not conducive to life as we know it. The temperatures, pressures, and materials that characterize this planet are most likely too extreme and volatile for organisms to adapt to. While planet Saturn is an unlikely place for living things to take hold, the same is not true of some of its many moons. Satellites like Enceladus and Titan, home to internal oceans, could possibly support life. With a radius of 36,183.7 miles (58,232 kilometers), Saturn is 9 times wider than Earth. If Earth were the size of a nickel, Saturn would be about as big as a volleyball.

From an average distance of 886 million miles (1.4 billion kilometers), Saturn is 9.5 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight 80 minutes to travel from the Sun to Saturn.Saturn has the second-shortest day in the solar system. One day on Saturn takes only 10.7 hours (the time it takes for Saturn to rotate or spin around once), and Saturn makes a complete orbit around the Sun (a year in Saturnian time) in about 29.4 Earth years (10,756 Earth days).

Saturn is home to a vast array of intriguing and unique worlds. From the haze-shrouded surface of Titan to crater-riddled Phoebe, each of Saturn’s moons tells another piece of the story surrounding the Saturn system. As of June 8, 2023, Saturn has 146 moons in its orbit, with others continually awaiting confirmation of their discovery and official naming by the International Astronomical Union (IAU). Saturn’s rings are thought to be pieces of comets, asteroids, or shattered moons that broke up before they reached the planet, torn apart by Saturn’s powerful gravity.

They are made of billions of small chunks of ice and rock coated with other materials such as dust. The ring particles mostly range from tiny, dust-sized icy grains to chunks as big as a house. A few particles are as large as mountains. The rings would look mostly white if you looked at them from the cloud tops of Saturn, and interestingly, each ring orbits at a different speed around the planet.

Saturn took shape when the rest of the solar system formed about 4.5 billion years ago when gravity pulled swirling gas and dust in to become this gas giant. About 4 billion years ago, Saturn settled into its current position in the outer solar system, where it is the sixth planet from the Sun. Like Jupiter, Saturn is mostly made of hydrogen and helium, the same two main components that make up the Sun.

1. Pluto was first discovered by a young research assistant in 1930

Photographic evidence of the former ninth planet was first sighted by 24-year-old research assistant Clyde Tombaugh at the Lowell Observatory in Flagstaff, Ariz. Tombaugh’s ashes are aboard the New Horizons spacecraft that passed by Pluto on Tuesday. Astronomer Percival Lowell predicted Pluto’s existence 15 years prior to Tombaugh’s discovery–even charting its approximate location based on the irregularity of Neptune’s orbit.

2. An 11-year-old girl gave Pluto its name

When Venetia Burney’s grandfather told her the news of the newly discovered planet, she proposed the name Pluto, after the Roman god of the Underworld. It seemed fitting, for after all, Pluto the planet, like the God, sat at the far reaches of the solar system. Her grandfather was taken by the name and suggested it to a friend–conveniently an astronomy professor at Oxford University. Astronomers were particularly keen on Pluto because the first two letters of the word are Percival Lowell’s initials.

3. Pluto is smaller than Earth’s moon but larger than previously thought

Pluto is 1,473 miles in diameter, according to recent measurements obtained from New Horizons, while Earth’s moon has a diameter of 2,160 miles. Pluto is 18.5% the size of Earth.

4. Disney’s Pluto the dog was named after the former planet

Disney’s Pluto the dog debuted in the same year the former planet was discovered, but contrary to popular belief, the dog was named after Pluto the (ex)-planet, not vice versa. Disney animators speculated that Walt Disney chose the name to capitalize on the hubbub surrounding the new planet.

5. New Horizons, the first vessel devoted to studying Pluto’s environment, is the size of a grand piano

The New Horizons probe cost $700 million yet, weighing in at 1,000 pounds, is only the size of a grand piano. It completed the nine-year, 3-billion mile journey to Pluto on Tuesday morning, whizzing about 6,000 ft. from the dwarf planet at 31,000 mph, and snapping the closest pictures of Pluto to date as it passed.

6. Pluto has a heart shape on its surface

Images released on Tuesday by NASA show a heart shape that measures approximately 1,000 miles across. As NASA reports, “much of the heart’s interior appears remarkably featureless–possibly a sign of ongoing geologic processes.”

7. Pluto was demoted to dwarf planet status in 2006–but not for the commonly believed reason

The news of Pluto’s larger than expected size on Monday was particularly exciting to Pluto partisans because many believe the outsider was stripped of its planetary status because it was too small. However, Pluto was actually downgraded to dwarf planet because it’s simply not unique. Pluto is merely the brightest member of the Kuiper Belt, a mass of objects that orbit the sun beyond Neptune.

8. Scientists discovered the Solar System’s third zone because of Pluto

While Pluto’s frigid neighbors are responsible for its solar system downfall, they are also what make the New Horizons vision so compelling. As Jeff Moore said, “Pluto may be the star witness to the whole third zone of the solar system.” Before the discovery of the Kuiper Belt, the solar system was believed to be comprised of two zones: the inner zone, containing the rocky planets from Mercury to Mars, and the outer zone, containing the gas giants from Jupiter to Neptune. However, Pluto exposed astronomers to our solar system’s third zone, which Moore referred to as a “vast realm of ice worlds.”

Io is the fifth moon of Jupiter and the fourth largest moon in the solar system. It is the innermost of the Galilean moons that orbit Jupiter. Io is the most volcanically active body in the solar system, spewing out sulphur as high as 300 km (190 miles) in the air. Like Europa, Ganymede and Callisto, Io was discovered in 1610 by the Italian scientist Galileo.

Io was the first discovered moon after Earth’s moon.

Galileo Galilei discovered Io on January 8th, 1610 and the discovery, along with the three other Jovian moons Europa, Ganymede and Callisto, were the first moons discovered that were orbiting a planet other than Earth. Technically, Galileo discovered Io the night before, but he wasn’t able to distinguish between Io and Europa until the following night. The discovery of Io and the Galilean moons led to the understanding that planets orbit around the Sun – and that Earth was not the centre of our solar system.

The moon is named after a nymph seduced by Zeus in Greek mythology.

Io was a nymph loved by the Greek god of the skies, Zeus, and the planet which was formerly known as Jupiter I was named for this nymph in the mid-1800s. In the mythological story, Zeus turned Io into a heifer (a cow) to hide his infidelity from his wife Hera.

Everything we know about Io comes from the Voyager and Galileo spacecraft missions.

A number of spacecraft have flown past the planet Jupiter and its moons – sending back images and a lot of information about the Jovian worlds. Pioneer 10 was the first spacecraft to visit in 1973, and was followed shortly after by Pioneer 11 in 1974. The Voyager 1 and Voyager 2 missions were the first to return photos of Io and the Jovian worlds during their flybys. The Galileo spaceprobe arrived at Jupiter in 1995 after a six year flight and passed as low as 162 miles (261 km) over the surfaces of the Galilean moons, producing the detailed images of the objects we have today.

NASA describes Io as “a giant pizza covered with melted cheese and splotches of tomato and ripe olives”.

The interior of Io is made of an iron or iron sulfide core but its brown silicate outer layer which gives the planet its distinctive splotchy orange, yellow, red, black and white appear is the most interesting and noticeable. The colorful appearance is down to the silicates (such as orthopyroxene), sulfur, and sulfur dioxide which frosts the surface and forms the yellow to yellow-green regions.

Radiation on Io is 1000x stronger than is needed to kill a human being.

Io lies in the doughnut-shaped plasma cloud around Jupiter, known as the “Io plasma torus” which is the result of Jupiter’s very strong magnetic field. As Io rotates, this torus strips ions from Io as it rotates, effectively making it an electrical reactor which produces radiation levels so strong that a human being could not survive. Io receives about 3,600 rem (36 Sv) of radiation per day. Doses greater than 100 rem received over a short time period would result in death in just a few weeks.

Io has over 400 active volcanoes.

Io is the only world other than Earth that is observed to have active volcanoes and is the most geologically and volcanically active object in the solar system. Volcanic plumes can rise 300 km (190 miles) above the surface. This was originally discovered by NASA’s Voyager 1 mission in 1979. The reason for this volcanic activity is the tidal heating which happens as Io is stretched and squeezed while it orbits Jupiter. This tidal bulge also shifts Io’s surface up by as much as 100 m throughout it’s orbit. The irregular orbit of the moon around Jupiter increases the tidal activity which is what makes the moon so volcanic.

Io has mountains larger than Mount Everest.

The surface of Io is dotted with more than 100 mountains – a result of the compression at the base of its crust that uplifted the surface. Some of these peaks are taller than Mount Everest. These mountains have an average height of 6 km (4 miles) and a large average length of 157 km (98 miles) long.

Io is composed of silicate rock surrounding a molten iron or iron sulfide core.

While most moons in the outer solar system, like Callisto for example, are made up of mostly water ice and rock, Io is composed of silicate rock which surrounds either a molten iron or iron sulfide core. This makes Io closer to the terrestrial planets in bulk composition than the satellites of the outer solar system. Io has a density of 3.5275 g/cm³, which is higher than any moon in the solar system and significantly higher than the other Galilean moons of Jupiter. It is denser than Earth’s Moon as well.

Mercury, the closest planet to the sun, is only slightly larger than Earth’s moon and is pockmarked with craters. The planet is visible to the unaided eye and as such as has long been known to humans. The planet was first observed through the newly invented telescope in 1631 by astronomers Galileo Galilei and Thomas Harriot, according to NASA Science(opens in new tab).

According to Universe Today(opens in new tab), the Sumerians mentioned the planet as early as the 2nd millennium BC (a period spanning 2000 BC to 1001 BC), and the Babylonians called it the planet Nabu. We know it by the name given by the Romans, after their swift-footed messenger god Mercury.

Even though Mercury is the closest planet to the sun, its surface can still be extremely cold, thanks to its lack of a heat-trapping atmosphere. The temperature during the day can reach a scorching 800 degrees Fahrenheit (430 degrees Celsius), but at night, temperatures can plummet as low as minus 290 F (minus 180 C), according to NASA(opens in new tab). That fluctuation equals a temperature swing of about 1,100 F (600 C), the largest of any planet in the solar system.

Mercury is the smallest planet in the solar system. The dinky planet is approximately 3,030 miles (4,876 kilometers) in diameter, making it about as wide as the continental United States and only slightly bigger than Earth’s moon.

Saturn’s moon Titan and Jupiter’s moon Ganymede are both larger than Mercury. Pluto was long considered to be the smallest planet in the solar system, but after it was reclassified as a dwarf planet in 2006, the award of the smallest planet has been bestowed upon Mercury.

Mercury speeds around the sun every 88 Earth days, hurtling along at nearly 29 miles (47 kilometers) per second — faster than any other planet in the solar system, according to NASA. Mercury’s orbit is not only very fast but also highly elliptical. The planet gets as close as 29 million miles (47 million km) to the sun and as far as 42 million miles (70 million km) from the sun.

In 2012, NASA’s MESSENGER spacecraft discovered water ice inside some of Mercury’s craters. In 2017, it was confirmed that Mercury has much more ice strewn across its north polar region than previously thought. The existence of ice had first been suggested in the 1990s when Earth-based telescopes detected highly reflective spots in the polar regions.

Mercury has the thinnest atmosphere of any planet in the solar system. The atmosphere is so thin that scientists have another name for it — an exosphere. Mercury’s exosphere is composed mostly of oxygen, sodium, hydrogen, helium and potassium, according to NASA.

Neptune is more than 30 times as far from the Sun as Earth and is the only planet in our solar system not visible to the naked eye and the first predicted by mathematics before its discovery. In 2011 Neptune completed its first 165-year orbit since its discovery in 1846. NASA’s Voyager 2 is the only spacecraft to have visited Neptune up close. It flew past in 1989 on its way out of the solar system.

• Neptune is about four times wider than Earth. If Earth were a large apple, Neptune would be the size of a basketball.
• Neptune orbits our Sun, a star, and is the eighth planet from the Sun at a distance of about 2.8 billion miles (4.5 billion kilometers).
• Neptune takes about 16 hours to rotate once (a Neptunian day), and about 165 Earth years to orbit the sun (a Neptunian year).
• Neptune is an ice giant. Most of its mass is a hot, dense fluid of “icy” materials – water, methane and ammonia – above a small rocky core.
• Neptune’s atmosphere is made up mostly of molecular hydrogen, atomic helium and methane.
• Neptune has 14 known moons which are named after sea gods and nymphs in Greek mythology.
• Neptune has at least five main rings and four more ring arcs, which are clumps of dust and debris likely formed by the gravity of a nearby moon.
• Voyager 2 is the only spacecraft to have visited Neptune. No spacecraft has orbited this distant planet to study it at length and up close.
• Neptune cannot support life as we know it.
• Because of dwarf planet Pluto’s elliptical orbit, Pluto is sometimes closer to the Sun (and us) than Neptune is.
• Even though Neptune is the farthest planet from our Sun, it’s a frequent stop in pop culture and fiction. The planet served as the backdrop for the 1997 science fiction horror film “Event Horizon,” while in the cartoon series “Futurama,” the character Robot Santa Claus has his home base on Neptune’s north pole. “Dr. Who” fans will remember that an episode entitled “Sleep No More” is set on a space station orbiting Neptune. And in the “Star Trek: Enterprise” pilot episode, “Broken Bow,” viewers learn that at warp 4.5 speed, it is possible to fly to Neptune and back to Earth in six minutes.

One popular myth that I was only made aware of a few years ago is that of Nibiru, a supposed planet that some claimed would collide with Earth at the end of the year 2012. But despite the buzz, there’s no scientific evidence supporting the alleged planet’s existence and, of course, our planet survived 2012 without absorbing a massive impact.

The story began in 1976, when Zecharia Sitchin wrote “The Twelfth Planet,” a book which used Stitchin’s own unique translation of Sumerian cuneiform to identify a planet, Nibiru, orbiting the sun every 3,600 years. Several years later, Nancy Lieder, a self-described psychic, announced that the aliens she claimed to channel had warned her this planet would collide with Earth in 2003. After a collision-free year, the date was moved back to 2012, where it was linked to the close of the Mayan long-count period. A planet with an orbit so eccentric that it took 3,600 years to orbit the sun would create instabilities inside our 4.5-billion-year-old solar system.

After only a few trips, its gravity would have significantly disrupted the other planets, whose own gravitational pushes would have changed the hypothetical world’s orbit significantly. According to the information available, a planet with a 3,600-year-long orbit that was due to impact Earth in 2012 should be available to the naked eye. Easily performed calculations show that, by April 2012, it would have been brighter than the faintest stars viewed from a city, and almost as bright as Mars at its dimmest. This would have made it visible to astronomers everywhere.

However; a planet called Nibiru, although not associated with Earth’s doomsday, featured briefly in the 2013 Star Trek film installment Star Trek Into Darkness. The planet appears in the opening scenes as a home of savage tribesmen and a supervolcano about to erupt. The planet, covered by a red jungle and an ocean deep enough to comfortably hide the Enterprise spaceship, is a target of exploration by the crew led by Captain James Kirk. However, things quickly go awry after Spock gets stranded on the super volcano while trying to stop the eruption, prompting the Captain to break the Prime Directive, which prohibits Star Trek explorers from interacting with alien civilizations.

Here are five fascinating facts about our neighbours in the solar system – Mars.

1. Mars Had Water In The Ancient Past: We’ve been debating for centuries about whether Mars had life or not. In fact, the astronomer Percival Lowell misinterpreted observations of “canali” — the Italian word for channels — on the planet as evidence of alien-made canals. It turned out Lowell’s observations were hampered by poor telescope optics of his day, and the canals he saw were optical illusions. That said, several spacecraft have spotted other signs of ancient water — channels grooved in the terrain and rocks that only could have formed in the presence of water, for example.

2. Mars Has Frozen Water Today: We’re very interested in the question of water because it implies habitability; simply put, life as we know it is more likely to exist with water there. In fact, the Curiosity rover’s mandate on Mars right now is to search for habitable environments (in the past or present). Mars has a thin atmosphere that does not allow water to flow or remain in large quantities on the surface, but we know for sure that there is ice at the poles — and possibly frosty locations elsewhere on the planet. The question is if the ice is capable of melting enough water in the summer long enough to support any microbes.

3. Mars Used To Have A Thicker Atmosphere: For water to flow in the past, the Red Planet needs more atmosphere. So something must have changed in the past few billion years. What? It is thought that the Sun’s energy striking the atmosphere must have “stripped” the lighter forms of hydrogen from the top, scattering the molecules into space. Over long periods of time, this would lessen the amount of atmosphere near Mars. This question is being investigated in more detail with NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft.

4. Mars Has Two Moons – And One Of Them Is Doomed: The planet has two asteroid-like moons called Phobos and Deimos. Because they have compositions that are similar to asteroids found elsewhere in the Solar System, according to NASA, most scientists believe the Red Planet’s gravity snatched the moons long ago and forced them into orbit. But in the life of the Solar System, Phobos has a pretty short lifetime. In about 30 million to 50 million years, Phobos is going to crash into Mars’ surface or rip apart because the tidal force of the planet will prove too much to resist.

5. We Have Pieces Of Mars On Earth: Remember the low gravity on Mars that we talked about? In the past, the planet has been hit by large asteroids — just like Earth. Most of the debris fell back on the planet, but some of it was ejected into space. That sparked an incredible journey where the debris moved around the Solar System and in some cases, landed on Earth. The technical name for these meteorites is called SNC (Shergottites, Nakhlites, Chassignites — types of geologic composition). Gases trapped in some of these meteorites has been practically identical to what NASA’s Viking landers sampled on the Red Planet in the 1970s and 1980s.