Karen Hill

The planet Neptune has eight moons. The two largest moons, Nereid and Triton, were discovered soon after the planet itself, and the other six were identified by Voyager 2. Of all the satellites, Triton has the most interesting detail. It is the only known moon in the solar system that orbits its host in an … Read more

The moons Titania and Oberon, the largest and most distant satellites of the planet Uranus, show different signs of cratering. On Titania, the craters are small, which probably means that the original large craters were eroded by some kind of geological force. Astronomers believe that large surface cracks, over 600 miles (960 km) long and … Read more

Miranda, the closest of Uranus’s large moons, has a varied surface of craters, valleys, faults, ridges, and canyons. Three large regions have ridges and valleys reminiscent of a plowed field. One of the regions displays a large V-shape called a chevron. A system of canyons, some as deep as 12 miles (19 km), can be … Read more

Neptune, the eighth planet from the sun, is the smallest of the gas giants, and the farthest from the Sun. Its discovery, in 1846, came about through mathematical calculation, rather than simple observation. We knew little about Neptune before 1989, when the spacecraft Voyager 2 began photographing it. Voyager could observe only the southern hemisphere, … Read more

The planet Neptune has an atmosphere of hydrogen, helium, and methane, just as Uranus does. The methane, which lies in a haze over the planet’s thick cloud cover, absorbs the red end of the spectrum, reflecting the blues. Neptune’s vivid deep azure, however, is a little different from Uranus’s milder aquamarine. Neptune’s atmospheric methane content … Read more

Galileo first observed Neptune on December 28, 1612, but he mistook Neptune for a fixed star when it appeared very close to Jupiter in the night sky. The search for Neptune began when astronomers noticed that Uranus’s movements, particularly its orbit, didn’t correspond to their expectations. One explanation was that another planet existed beyond Uranus, … Read more

The planet Uranus has a mass that is about 14.5 times of the planet Earth, and it is the least massive of the giant planets in our solar system. Uranus lacks a distinct equatorial bulge and an interior source of heat, which means that it probably does not have a molten or liquid interior. Its … Read more

The eleven rings around Uranus are thin bands some 0.6 to 7.0 miles (1 to 11 km) thick. The exception is the farthest edge of the farthest ring, which ranges up to 60 miles (96 km). The rings are composed of extremely dark particles, which vary in size from micrometers to a fraction of a … Read more

Sir Frederick William Herschel, born in 1738, led a varied and distinctive life. As a young man, he witnessed the Seven Years’ War in Europe while playing oboe in a military band. His music skills, and his winning personality, earned him an organist position in Bath, England. While there, his studies in musical harmony led … Read more

How Many Moons Does the Planet Uranus Have and How Did the Moons Orbiting Uranus Get Their Names? Before the space age, we knew of five satellites orbiting Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon. The names came from the works of Shakespeare and the poet Alexander Pope. Ten more moons, discovered by the spacecraft … Read more

Uranus is the third gas giant and the seventh planet from the Sun. The planet Uranus has a diameter of about 30,000 miles (50,000 Km), and is the size of 63 earths. Uranus is roughly 2 billion miles, or 3 billion Km (about 20 AU) from the Sun. The planet’s equator rotates about where we … Read more

To get a sense of Uranus’s unique rotation and revolution, you may want to create a model of it. This is easy enough to do. Find a ball, or other spherical object, and mark an equator and a north and south pole on it. Hold the ball with the north pole at the top and … Read more

Uranus has an axial tilt of 97.77 degrees, and its axis of rotation is close to parallel with the plane of the Solar System. Near the time of Uranian solstices, one pole faces the Sun continuously while the other pole faces away. During the equinoxes, the Sun faces the equator of Uranus giving day and … Read more

A sidereal day equals one planetary rotation. A single rotation takes the planet Uranus 17 hours and 54 minutes to complete. If we think in terms of a solar day, how long it takes the Sun to go from high noon to high noon, we get a different picture. The combined effect of Uranus’s tilted … Read more

As Uranus orbits the Sun, first the north pole faces the solar surface, then the equator, then the south pole, and then the equator again. This gives Uranus seasons that are unique and are completely unlike those of the other major planets in our solar system. Each pole gets around 42 years of continuous sunlight, … Read more

Voyager 2 registered a nearly consistent temperature of –155°F (-221°C) on Uranus. Strong winds, up to 180 miles (288 km) per hour, that blow in the same direction as Uranus rotates keep the temperature steady all around the planet. The cold is responsible for our inability to see any surface detail on this pale blue … Read more

Similar to Jupiter’s Great Red Spot, a white spot on Saturn reveals the presence of a huge atmospheric storm. Unlike Jupiter’s ever-present spot, Saturn’s white spot appears only periodically, approximately every 30 years. First identified in 1876, the spot has appeared more or less on schedule ever since. It is located near the equator and … Read more

Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens. The moon’s name came from John Herschel, son of William Herschel, discoverer of Mimas and Enceladus, in 1847, and was inspired by the names of the mythological Titans, sisters and brothers of Cronos, the Greek Saturn. Saturn’s largest and brightest moon, Titan, seems to … Read more

Saturn not only has its many rings, it is also endowed with more known moons than any other planet. Some eighteen moons have been named and astronomers suspect, are even sure, that several more exist. The closest named moon to the planet is Pan, a body some 12 miles (19.2 km) in diameter. Pan moves … Read more

William Herschel (1738-1822) was a musician who began to study the mathematical foundation of harmony. Mathematics led him to astronomy, and, with the help of his sister, Caroline, Herschel set out to map every star in the northern hemisphere with a magnitude of 4 or greater. Through his detailed and methodical observations, Herschel found and … Read more

The planet Uranus’s axis is tilted in a peculiar way. Earth’s axis tilts at 23.5°; Uranus’s axis tilts at 97.9°, which is at more than a right (90°) angle. Imagine Earth’s poles being located near the equator. The planet, however, still rotates around its north-south axis. Because it is tilted more than 90°, Uranus’s rotation … Read more

The two most prominent divisions in Saturn’s ring system are the Cassini division and the Encke division, named after their discoverers. The Cassini division extends for 2,100 miles (3,360 km) between rings A and B. The 200-mile (320-km) Encke division lies within ring A. These divisions appear to be gaps between rings, allowing us to … Read more

Idiosyncratic rings around the planet Saturn are rare and, for the most part, inexplicable. They do not conform to the laws of physics as we understand them. The primary rings, A through G, orbit Saturn in circles. According to physics, it should be impossible for a ring to do otherwise, to have an elliptical, or … Read more

Within the rings lies the second largest planet in the solar system, Saturn. Its composition is similar to that of its next-door neighbor, Jupiter, mostly hydrogen and helium gases. The planet’s ice-covered core of iron and silica is just a little bit bigger than Earth. Compressed hydrogen around the core resembles a metal, and is … Read more

The planet Saturn generates more heat than it receives from the Sun. It has lost the heat caused by its formation, but helium drops “rain” down from the atmosphere, mostly hydrogen, which creates heat. The droplets of helium releasing heat by friction as they fall down through the lighter hydrogen. The cloud-top temperature ranges around … Read more

Because Saturn is made mostly of gas, it has varying rotation speeds. Because Earth is solid, its rotation period is 24 hours at every latitude. Latitudes nearer the poles, however, have a shorter distance to travel in 24 hours, so they rotate more slowly. Since Saturn is not bound together in a solid form, the … Read more

The planet Saturn has a very strong magnetic field. Spacecraft sent to study the planet recorded regularly pulsing radio waves to determine the core’s rotational speed. The magnetic field on Saturn is at least 500 times, some say 1,000 times, stronger than Earth’s magnetic field. Saturn’s magnetic poles are almost exactly aligned with its geographic … Read more

The answer depends on how you count the rings around Saturn. Seven of Saturn’s ring systems have been identified and named by scientists, but some of those rings are made up of countless thin rings that parallel each other. There could be thousands of them. The seven major rings are named for the first seven … Read more

The whole system of rings, gaps and all, begins about 40,000 miles (64,000 km) out from Saturn’s equator and ends 290,000 miles (464,000 km) from the surface. That’s 250,000 miles (400,000 km) of rings and gaps. The particles are not spread out on a single plane, but the rings are very thin. Compared to the … Read more

Astronomers believe that Saturn’s rings are made of water, ice, and rock. This icy matter can range from the size of a tiny grain of sand to bigger than a boulder, over 30 feet (9 meters) across. The particles probably came from passing comets or moons that got too close to Saturn and were broken … Read more

Ring B is the largest and brightest ring around Saturn. It orbits the planet at a distance of 55,000 to 70,000 miles (88,000 to 112,000 km). The B ring is made up of thousands of smaller concentric rings that are so close to each other, they are indistinguishable from each other when viewed from Earth. … Read more

Saturn’s rings have circular orbits, but they revolve at various speeds. Parts of a single ring even orbit Saturn at different rates. For instance, the outer edge of ring E, furthest from the planet, has an orbital period of 4 hours, but the inner edge, some 180,000 miles (288,000 km closer) takes 22 hours to … Read more

Saturn’s planetary rings D, E, and G are not visible from Earth at all. We only discovered E and G by sending up spacecraft. The system as a whole circles the planet Saturn at its equator. Saturn’s axis, around which the planet rotates, is tilted 26.7° in relation to its equator, so that sometimes the … Read more

Astronomers frequently use orbital period, or how long one revolution takes, to measure speed instead of miles, or kilometers per hour. The three families of satellites are clustered by period as well as distance. Of the four closest moons, none takes more than 1 day to orbit Jupiter. The four Galilean moons, also in the … Read more

Galileo Galilei was the first astronomer to observe Jupiter’s moon Ganymede on January 7, 1610. Ganymede, made mostly of ice and rock, is the third farthest Galilean moon from Jupiter and is the planet’s largest satellite. Ganymede is also the biggest moon, or satellite in our solar system. Its surface is cratered, like Jupiter’s farthest … Read more

Jupiter’s sixth moon Europa was discovered in 1610 by Galileo Galilei, and is named after a mythical Phoenician noblewoman, Europa, who was courted by Zeus and became the queen of Crete. The Galilean moon Europa orbits Jupiter between Io and Ganymede. Europa is about the same size as Earth’s moon. It has a surface of … Read more

The third-largest moon in the Solar System Callisto was discovered in 1610 by Galileo Galilei. The farthest Galilean moon from Jupiter, Callisto is mostly made of ice and rock. Its surface shows many craters, but unlike our Moon craters, these are rather shallow with low walls encircling them. Callisto’s craters were probably partially filled in … Read more

Rocky Io is the closest Galilean moon to Jupiter. The craters that mark its surface are volcanic craters, not the result of meteorite bombardment. The tallest volcanoes are about 5.5 miles (8.8 km) high. Instead of molten rock, sulfur compounds spew out of Io’s volcanoes, covering evidence of any impact craters and giving the moon … Read more

Saturn is known as the planet with the rings around it, although Jupiter, Uranus, and Neptune also have rings. These rings, which encircle the sixth planet at its equator, have distinct characteristics. The planet itself is a gas giant quite light in density and bright in luminosity. Its surface sometimes reveals a Great White Spot, … Read more

Since the seventeenth century, observers have seen a huge, oval red spot south of Jupiter’s equator. The Great Red Spot has a greater surface area than Earth: 8,400 miles (13,440 km) wide by 24,000 miles (38,400 km) long. Scientists have determined that the spot is a huge atmospheric storm. It appears as a hollow, or … Read more

The moons all revolve around their host planet, Jupiter, but their orbits are different in distance, speed, and inclination of orbital plane. This all makes for quite a bit of activity. Jupiter’s moons act something like a microcosm, or a miniature version of the solar system, and astronomers have learned a lot about the whole … Read more

One of the best known features of the planet Jupiter is the Great Red Spot. The Great Red Spot is a permanent anticyclonic storm, and is significantly larger than the Earth. The spot on Jupiter usually can be found 22° south of the equator, in or near the South Equatorial Belt. It rotates counterclockwise, with … Read more

Jupiter’s sixteen known moons travel in three distinct groups. The first, including the four Galilean moons, ranges from 77,000 miles (124,000 km) to over 600,000 miles (960,000 km). The next group orbits from 6.6 million miles (10.56 million km) to almost 7.2 million miles (11.52 million km) away. The third family of satellites is almost … Read more

If Jupiter had just eighty times more mass, it could be a star. However, if it were a star, Earth would not exist. Jupiter and the Sun would be a binary star system and the solar system would be completely different. The largest planet in the solar system, Jupiter measures near 88,700 miles (141,920 km) … Read more

Although Jupiter is a great distance from the Sun, it is a relatively hot planet. Scientists have discovered that almost twice as much heat radiates from the planet’s rocky core than is received from the Sun. The core’s exact temperature is unknown, but it is probably around 30,000°K (53,500°F/30,000°C). Jupiter continues, from the time of … Read more

Jupiter’s primary gases, hydrogen and helium, are colorless. Trace chemicals within the planet’s gas layers, such as methane, ammonia, and phosphine, are responsible for the colors of the belts and zones. The colors range from cream and yellow through pink, orange, and brown to brick red. Brighter areas suggest hotter temperatures, and darker areas, cooler … Read more

The Great Red Spot on Jupiter is a persistent anticyclonic storm that is about 24–40,000 km × 12–14,000 km, and is large enough to contain two or three planets the size of Earth. We don’t know whether or not the Great Red Spot will disappear for good one day. Storms on Earth sooner or later … Read more

Jupiter has sixteen known satellites, but astronomers believe there could be more. The discovery of the four largest, Ganymede, Callisto, Io, and Europa, is credited to Galileo, who recorded them in 1610. The average diameter of the Galilean moons measures 2,540 miles (4,230 km), whereas the average diameter of the other Jovian moons is a … Read more

Size and composition are the two major characteristics shared by Jupiter, Saturn, Uranus, and Neptune. The smallest outer planet, with the exception of Pluto, which is in a category by itself, is Neptune, and Neptune is almost four times larger than Earth. The outer planets have small cores and huge gaseous outer surfaces. When the … Read more

Jupiter is a big planet. The planet Jupiter is the largest planet in our Solar System, with a diameter of 142,984 km at its equator. It’s larger than all the other planets and their moons combined, almost big enough to be a star. 1321 earths could fit inside Jupiter. Most of its bulk comes from … Read more

The planet Jupiter’s rotation is the fastest of all the Solar System’s planets. Jupiter does not rotate as a solid body does, all at the same speed, because it is made out of hydrogen and helium. Around the equator, the gas layer of Jupiter has a rotation period of 5 hours, 50 minutes, and 30 … Read more

According to current speculation, Jupiter probably has a small, solid core of silica. Above that lies a shell of a different form of liquid hydrogen. Jupiter’s core is surrounded by dense metallic hydrogen, which extends outward to about 78 percent of the radius of the planet. Droplets of helium and neon precipitate downward through this … Read more

Some eighteen zones and belts can be identified by their different colors, brightness, spots, and rotation periods. Zones are dark bands; belts are bright bands. The main two are the North Equatorial Belt, at approximately 7° to 20° latitude, and the South Equatorial Belt, at approximately –7° to –21° latitude. Both change in width, with … Read more

The planet Mars seems to have a rocky crust approximately 30 miles (50 km) deep. Its mantle is rich in the element silica, like Earth, but it is solid, unlike Earth’s partially molten mantle. There is no magnetic field on Mars, so presumably its core is solid. It is likely to be solid iron. While … Read more

The surface of Mars is covered in a fine dust that is rich in iron oxide, also known as rust. There are massive winds on the planet that create dust storms, and so a red-pink smog always hangs over it. Consequently, Mars’s general appearance is red, but powerful telescopes reveal that the surface is multicolored. … Read more

Experiments on Earth have concluded that certain cells can survive a simulated Martian environment. In 1996, a meteorite that originated on Mars was discovered. The announcement that this rock contained possible evidence of life on Mars or evidence that life once existed on Mars, has sped up plans to send missions back there. Remember, however, … Read more

One of the most intriguing, and fanciful, photographs taken of Mars by Voyager 1 showed what appeared to be a mask-like face of a human being buried just under the surface. Imagine the uproar in the scientific and science fiction communities. The “face on Mars” turned out to be a purely natural surface formation that, … Read more

The planets that orbit the Sun beyond the asteroid belt in our solar system are known as the outer planets. Besides their location, they share many other similarities, except for Pluto, which is a highly unusual planet. Jupiter, Saturn, Uranus, and Neptune are all much larger than Earth and are made mostly of gas. This … Read more

The atmosphere on Mars is relatively weak. It is so thin that damaging ultraviolet solar radiation makes its way unimpeded to the planet’s surface. Carbon dioxide makes up 95 percent of the atmosphere, followed by nitrogen (2.7 percent) and argon (1.6 percent). Oxygen, water vapor, neon, krypton, xenon, and ozone comprise less than 1 percent … Read more

Mons Olympus, the tallest known volcano, and mountain, in the solar system, is one of many large volcanoes on Mars. Mons Olympus is about 27 km tall, and can be found in the vast upland region Tharsis, which contains several other large volcanoes. Mons Olympus is Latin for “Mount Olympus”, and is believed to have … Read more

Mars is a pretty cold planet. The average air temperature is –22°F (-30°C) in the day and –148°F (-100°C) at night. Surface temperatures on Mars vary from lows of about -87 °C during the polar winters to highs of up to -5 °C during the summers. The highest temperatures occur during the summer at the … Read more

The northern ice cap is permanently frozen water covered by frozen carbon dioxide (dry ice), which solidifies from the atmosphere at cold temperatures. During summer in the north, the ice cap shrinks, as some of the carbon dioxide reverts to gas in the atmosphere. In the winter, it grows much larger again. The ice cap … Read more

Evidence of water has fed scientific debates on the possibility of life on Mars for centuries. A well-known twentieth-century astronomer, Percival Lowell, spent his career mapping what he believed were irrigation canals built by Martians. His findings have been proven false, but there are dry channels on Mars that look like they were created by … Read more

More craters are found in the southern hemisphere on Mars. This makes astronomers think that the surface there is older than in the northern hemisphere. Something happened in the north, perhaps volcanic activity or water erosion, to cause craters to disappear. There is further evidence supporting the astronomers’ theory: the surface of the northern hemisphere … Read more

Mars has the deepest canyon in the solar system, the Vallis Marinaris, measuring 4.2 miles (6.7 km) deep, 300 miles (500 km) wide, and 2,800 miles (4,500 km) long. The nearby canyons average about 1.8 miles (3 km) deep. The deepest crater on Mars is the Hellas Planitia, some 3.6 miles (6 km) deep. Mars’s … Read more

Mars is home to the tallest and largest known volcano in the solar system: Mons Olympus. This extinct shield volcano has a base of about 420 miles (700 km) and reaches 15 miles (25 km) into the atmosphere. Its caldera (large opening) measures 53 miles (85 km) in diameter. By comparison, Mt. Everest, the tallest … Read more

How Do We Know So Much About the Planet Venus and How Much of Venus Has been Mapped By Astronomers? A number of unmanned spacecraft have flown by and even landed on the planet to take photographs. The views aren’t terribly appealing, dry broken rocks, small mounds, flat terrain, but they are informative. The probes … Read more

Mars, the closest superior planet to Earth, and the fourth planet from the Sun, frequently looks red, so it is sometimes called the red planet. We know a lot about Mars because it comes closer to Earth than any other planet in favorable opposition, in the best position for viewing, and because we have sent … Read more

No planet has a truly circular orbit around the Sun. Mars’s orbit is particularly elongated, which affects the planet’s seasons. Mars takes 788 Earth days to orbit the Sun. At its farthest (aphelion), it is about 155 million miles (250 million km) from the Sun. At its closest (perihelion), Mars is some 130 million miles … Read more

Summer in the southern hemisphere causes the most weather activity on Mars. The temperature increase shrinks the southern polar ice cap, at the same time, the northern ice cap, experiencing winter, grows larger, which increases the air pressure. Increased air pressure causes severe winds to blow toward the equator. The winds can reach up to … Read more

Mars’s axis is tilted 25.2°, compared to Earth’s 23.5°, and Mars is tilted in the same direction. This causes the planet Mars to have summer and winter, like Earth. Martian seasons are longer because it takes Mars longer to orbit the Sun. The seasonal temperatures on Mars stay much colder than on Earth because Mars … Read more

During winter in the southern hemisphere on Mars, the polar ice cap grows to cover almost one-quarter of the planet. At the same time, during summer in the northern hemisphere, the northern ice cap is shrinking. Temperatures on Mars can reach as low as –190°F (-123°C). Sometimes a frost consisting of water and dust covers … Read more

If all those planetesimals and asteroids were flying around some 4 billion years ago, colliding, accreting, and taking chunks out of planets, why don’t we see much evidence of them on Venus? Asteroids probably did hit Venus as much as any other planet; they just didn’t leave behind much visible evidence. Venus’s atmosphere would have … Read more

Because both Venus and Mercury are inferior planets, lying between Earth and the Sun, they exhibit phases, just like the Moon does, as they orbit the Sun. Venus is full during superior conjunction, on the other side of the Sun from Earth, and new during inferior conjunction, between the Sun and Earth. As it cycles … Read more

Venus transits the Sun, but not with every revolution. The reason for this is that its orbital plane is at a 3 percent incline to the ecliptic, the Sun’s apparent path around Earth. Only when Venus crosses the ecliptic at the time of its inferior conjunction will it transit the Sun. It usually passes above … Read more

The planet Venus makes one rotation on its axis in 243 Earth days. Its solar day, the time it takes the Sun to reappear in the same place in the sky, is 118 Earth days. On Earth, the two are almost identical, 24 hours, so the Sun rises at approximately the same place every morning. … Read more

Why Does the Planet Venus Shine So Brightly In the Sky and How Much Sunlight Does Venus Reflect? Oddly enough, Venus is so brilliant because it is covered in clouds. These clouds are about 10 miles (16.5 km) thick and begin about 50 miles (83 km) above the ground. From the surface of a planet, … Read more

The clouds on Venus move, but not like clouds on Earth. Venus’s atmosphere is very thick and heavy. There are no major temperature or air pressure changes to cause air currents, as on Earth, but Venus’s atmosphere rotates around the planet at a fairly steady rate of 225 miles (360 km) per hour. The cloud … Read more

On Earth, clouds are created through water evaporation and condensation. The clouds are water-based. Venus’s clouds are made by a process called photochemistry, whereby the Sun’s ultraviolet rays react with chemicals in Venus’s atmosphere. The clouds around Venus have an acid base, sulfur dioxide. On Earth, sulfur dioxide is released during volcanic activity. It’s what … Read more

The Planet Venus is very hot indeed. The surface temperature averages almost 900°F (480°C) around the whole planet. This extreme heat results from the greenhouse effect, which occurs when infrared, or heat-producing rays from the Sun enter an atmosphere and cannot get back out. Carbon dioxide, which makes up 96.5 percent of Venus’s atmosphere, lets … Read more

The first few things you would notice if you could stand on Venus would probably be the heat, the relatively constant calm weather, and the orange-colored rocks and dry dirt at your feet. In general, it might feel like you were in one of the Great Plains states in the middle of a billion-year-long drought. … Read more

The transit of Venus was first observed in 1032 by the Persian astronomer Avicenna, but Venus has long been known to ancient civilizations as the “morning star” or “evening star”. He concluded that Venus is closer to the Earth than the Sun. Venus, the second planet from the Sun, is sometimes called the twin of … Read more

All of the other planets besides Venus, and Pluto, rotate on their axes from west to east, causing the Sun to rise in the east and set in the west. Venus’s rotation is called retrograde, moving from east to west. All eight planets in our solar system orbit the sun in the direction that the … Read more

The planet Venus has an extremely dense atmosphere. The atmosphere on Venus, the second planet from the Sun, consists primarily of carbon dioxide (96.5 precent). Nitrogen makes up 3.5 percent of the atmosphere. Traces of gases such as sulfur dioxide, carbon monoxide, hydrochloric acid, and oxygen (0.00003 percent) have also been detected. The atmospheric mass … Read more

The Romans who derived their religious pantheon from the Greek tradition, named the planet Venus after their goddess of love. On Venus, all topographical features except one are named for women, Venus being a goddess of womanhood. For instance, the main craters include Anna Pavlova (1881-1931), the prima ballerina of her lifetime; Sacajewea (c. 1789-1812), … Read more

Like Mercury, Venus is relatively close to the Sun. It is often called the evening or morning star because it is so bright at sunset and sunrise. Venus is the brightest planet in the sky, even brighter than the stars; therefore, it is a pretty easy object to find in the night sky. As a … Read more

The two major results of Venus’s atmosphere are the amount of pressure it exerts on the planet’s surface and the heat it traps. Carbon dioxide is a heavier gas than nitrogen. Because the atmosphere is more than 96 percent carbon dioxide, the pressure is ninety times greater on Venus than on Earth. Without state-of-the-art, space-age … Read more

Mercury is thought to be the densest of all the planets, which makes sense when you consider the theory that during the early phases of the solar system’s formation, the lightest materials were sent farthest into space. For a planet so small to be so dense, it may be mostly solid metal. Scientists believe that … Read more

We look at the way land, terra in Latin, was formed on Earth to understand how the surfaces of other terrestrial planets evolved. Volcanoes created most of Earth’s terrain. Molten material from Earth’s mantle bubbled up 4 billion years ago to form the first continents. On Mercury, land ridges provide evidence of extreme volcanic activity … Read more

An inferior planet, closer to the Sun, will appear in phases, like the Moon. As Mercury orbits, we generally only see it as a waxing or waning crescent. At a superior conjunction, lined up Earth-Sun-planet, Mercury is full, but it usually can’t be seen from Earth because it’s behind the Sun. We also cannot see … Read more