Our Solar System

The details of our solar system

THE SUN:
The Sun looks 1600 times fainter from Pluto than it does from the Earth.
Comets' tails point away from the Sun at all times. Thus, when a comet is moving away from the Sun, its tail is actually leading. Comet tails are caused by dust and gas being lost from the comet and then pushed away from the Sun by the solar wind (charged particles moving out from the Sun) and by radiation pressure from the Sun.

The Sun is a fairly average star in terms of mass, temperature, and size.

The Earth orbits the Sun at an average velocity of approximately 30 kilometers per second (18 miles per second). Planets closer to the Sun travel faster in their orbits and planets further away travel slower.

Sunspots appear dark because they are cooler than the surrounding areas on the Sun, and therefore radiate less light and appear "dark" relative to the areas around them. Sunspot temperatures average about 3800 degrees versus 5800 degrees Celsius for the average surface of the Sun.

Due to frequent collisions with subatomic particles, it takes a typical gamma ray photon about one million years to travel from the core of the Sun to its surface, even though gamma rays travel at the speed of light (the gamma ray region of light has shorter wavelengths than X-rays). By the time the photon that started out as a gamma ray photon escapes the solar furnace, it has lost so much energy through collisions that it emerges from the Sun's surface as a photon of ordinary, visible light.

MERCURY:
The water ice may exist in the bottoms of craters at Mercury's poles, based upon radar data taken in recent years. Even though Mercury is the closest planet to the Sun, and extremely hot over most of its surface, ice may exist at the bottoms of some polar craters because the crater floors are permanently shadowed by the crater rims.

VENUS:
The surface of Venus is obscured by clouds at ultraviolet, visible, and infrared wavelengths, which is why the Pioneer and Magellan spacecraft used radar to penetrate the clouds and image the surface.

The atmospheric pressure you would experience on the surface of Venus is approximately equal to the pressure you would experience 3000 feet (approx. 1 km) down in the Earth's oceans, i.e., about 90 times the pressure at the Earth's surface.

Venus rotates very slowly. A Venus day, the time it takes Venus to rotate once, is approximately 243 Earth days long.

Venus is the brightest natural object in the sky besides the Sun and Moon. It can be as much as 15 times brighter than the brightest star (Sirius).

All of the major features on the planet Venus are named after famous women in history and mythology.

EARTH :
This is the only unique planet that has life in the known world.
Almost all of the Oxygen in the Earth's atmosphere has been produced by living organisms. Oxygen accounts for 21% of our atmosphere, with Nitrogen making up 78%, and a mixture of other gases composing the remaining 1%. Oxygen only occurs as a minor constituent in the atmospheres of other planets in our Solar System.

The Earth has the highest average density (5.52 g/cubic cm) of any planet in our Solar System. Saturn has the lowest (0.69 g/cubic cm). For reference, the density of liquid water is 1 g/cubic cm.

MARS:
The liquid water does not currently occur on Mars because of the cold temperatures and low atmospheric pressures. Only water ice and water gas (vapor) are stable. However, large channels on Mars appear to have been cut by outflows of liquid water during Mars' distant past which may have had warmer temperatures and a much thicker atmosphere.

The largest canyon system in the Solar System is Valles Marineris on Mars. It is more than 3000 miles long and so would stretch from California to New York. In some places it reaches 3 miles in depth and 200 miles in width.

Mars' surface area is approximately the same as the surface area of all the land (as opposed to water) on Earth. So, even though Mars is a smaller planet, studying its surface is just as large a task as studying all of Earth's land surfaces.

Mars has two large-scale geologic regions (in addition to many smaller geologic variations within both regions). The "Southern Highlands," which cover a little more than half of Mars' surface, are composed of old (at least 3.9 billion years) densely cratered terrain. The "Northern Plains" have lower and more variable crater densities, indicating that the plains are younger and formed over a much longer period of time. The cause of this Martian geologic dichotomy is not yet agreed upon.

The gravitational force at the surface of Mars is only about one-third as strong as the gravitational force at the surface of the Earth.

Many of the larger rocks at the Viking Lander sites on Mars were given names. These included Toad, Badger, and Guppy, all of which were named because of some resemblance to those creatures, as well as ones named for all seven dwarfs, and the largest of the rocks near the landers was named Big Joe.

At its closest approach to Earth, Mars appears about as big as a tennis ball viewed from a distance of one and a half miles (two and a quarter kilometers).

The main constituent of the Martian atmosphere, carbon dioxide, actually freezes n the surface during the winter, particularly in the polar regions. This can cause global atmoshperic pressure changes. On Earth, water freezes out, but is a minor constituent in the atmosphere.

JUPITER:
The most volcanically active body in the solar system besides the Earth is Jupiter's moon Io. Erupting volcanoes were discovered on Io by the Voyager spacecraft.

Jupiter's magnetosphere is the largest single structure inside the Solar System. If you could see it with your eyes, it would appear larger than our full Moon.

Jupiter's moon Europa may have a liquid water "ocean" far beneath its water ice covered surface.

The Great Red Spot on Jupiter is a hurricane-like storm system. It is large enough that two Earths could fit across it. The Red Spot has been around since at least the early 1600's when it was first detected shortly after the invention of the telescope.

From the Jupiter-facing side of the moon Amalthea, Jupiter would fill up a huge chunk of sky: equivalent to going from the horizon to half way above the horizon.

Jupiter's moon Io, less than 1/3 the size of Earth, puts out twice as much heat as the Earth. This is primarily due to tidal forces from Jupiter's enormous gravitational field causing a constant squeezing and stretching of Io. Heat generated by that squeezing and stretching accounts for Io being the most volcanically active body in the Solar System.

Jupiter's moon Ganymede is the largest moon in the Solar System, and is larger than the planets Mercury and Pluto.

A Jupiter day, the time required for the planet to rotate once, is only about 10 hours long. Jupiter has the shortest day (rotation period) of any planet in the Solar System.

Europa, covered with mostly water ice, has the smoothest surface of any large object in the solar system. This satellite of Jupiter has a mostly flat surface, with no discovered topographic relief larger than 1 km (0.6 mi) in height, even though Europa has an intricate set of cracks criss-crossing its icy surface.

Jupiter's moon Ganymede, the largest moon in the Solar System, has a surface area that is approximately half that of Earth's land surface area (not including Earth's oceans).

Jupiter's core is thought to consist primarily of metallic hydrogen.

SATURN:
All four giant planets (Jupiter, Saturn, Uranus, and Neptune) have ring systems. As of 20 years ago, only Saturn was known to have rings. Saturn's ring system is by far the largest and most developed of the four.

URANUS:
Methane gas, which absorbs red light, is what causes Uranus and Neptune to look bluish in color. Methane is a relatively minor constituent of their atmospheres, however. Like Jupiter and Saturn, Uranus and Neptune have atmospheres made mostly of hydrogen and helium.

The planet Uranus was discovered by the eminent English astronomer William Herschel in 1781. He briefly considered naming the planet George in honor of England's King George III.

PLUTO:
Pluto's elliptical orbit sometimes brings it inside of the orbit of Neptune for a few years. We are currently in one of those periods, so right now Neptune is the farthest planet from the Sun.

On average, the distance from Pluto to the Sun is approximately 40 times the distance from the Earth to the Sun. Put a different way, if a scale model were constructed with the Sun on the California coast and the Earth about 75 miles inland, then on the same scale Pluto would be in New York.

MOONS:
Did you know that some of the moons in our Solar System are larger than some of the planets? Jupiter's moon Ganymede, the largest moon in the Solar System, and Saturn's moon Titan are both larger than the planets Mercury and Pluto. The Earth's Moon, Jupiter's moons Callisto, Io, and Europa, and Neptune's moon Triton are all larger than Pluto, but smaller than Mercury.
If you added up the mass of all of the thousands of known asteroids in the asteroid belt, the total would be less than ten percent the mass of the Earth's moon.

Our moon has only one eightieth the mass of the Earth.

A Blue Moon is the second of two full Moons that fall in the same month. This can occur because full Moon's occur roughly every 29.5 days. A Blue Moon occurs roughly every two and three-quarter years. So, now you know how long once in a Blue Moon really is.

The Moon actually appears much brighter than the Sun at gamma ray wavelengths (as seen from the Earth-orbiting Compton Gamma Ray Observatory).

COMETS:
As comets approach the Sun, their tails can become long enough that they stretch from one planet's orbit across the orbit of another planet.

Comet Hale-Bopp is putting out approximately 250 tons of gas and dust per second. This is about 50 times more than most comets produce.

For the first 100 million years or so after the formation of the solar system, a bright, naked-eye comet was visible in the skies of Earth roughly once a week.

Based upon data from the International Ultraviolet Explorer (IUE) satellite, Comet Hyakutake was found to be ejecting ten tons of water every second as it passed near the Sun.

SPACE SHUTTLE:
It only takes the Space Shuttle about 8 minutes to accelerate to its orbital speed of more than 17,000 miles per hour.

The Space Shuttle main engine weighs 1/7th as much as a train engine, but delivers as much horsepower as 39 train engines.

Pioneer 11's speed going past Jupiter was over 107,000 mph, the fastest speed ever traveled by a human-made object.

At almost six billion miles away, Pioneer 10 is the most distant object built by humans.

A Space Shuttle and its boosters ready for launch are the same height as the Statue of Liberty but weigh almost three times as much.

Each of the Space Shuttle's solid rocket boosters burns 5 tons of propellant per second.

The Galileo probe, weighing in at 339 kilograms (750 pounds), will enter Jupiter's atmosphere at 170,000 kilometers per hour (106,000 mph), or more than 50 times faster than a bullet shot out of a rifle. The probe will experience deceleration forces as high as 230 times Earth's gravity. In about two minutes, the orbiter's speed will be slowed to about 1,600 kilometers per hour (1,000 mph).

The amount of power transmitted by the Galileo spacecraft's radio is about the same amount used by a refrigerator light bulb--about 20 watts. By the time they reach Earth, the radio signals from Galileo are incredibly weak (about a billion times fainter than the sound of a transistor radio in New York as heard from Los Angeles).

The average radiation dose per minute absorbed by the Galileo spacecraft during its orbital mission is equivalent to what the average person receives in a whole year on Earth. On December 7, as it made its closest approach to Jupiter, the radiation dose per minute to Galileo exceeded by several times what a person on Earth would receive in their entire lifetime and would have been quite lethal to a human.

The Voyager spacecraft delivery accuracy at Neptune (100 km or 60 mi.) (62 mi), divided by the trip distance of 7,128,603,456 km (4,429,508,700 mi), was the equivalent of sinking a 3630 km (2260 mi.) golf shot, although Voyager, as opposed to a golf shot, was allowed a few minor trajectory adjustments along the way.

It takes radio signals from Earth (traveling at the speed of light: 186,000 miles per second) approximately 9 hours to reach the Pioneer 10 spacecraft, which is the most distant object built by humans. It takes another 9 hours for the spacecraft's response to reach Earth.

NASA's Compton Gamma Ray Observatory, launched in 1991 aboard the Space Shuttle Atlantis, is the heaviest spacecraft ever deployed by a Space Shuttle.

The Space Shuttle flies about 200 miles (330 km) above the Earth's surface (equivalent to roughly half the distance between Los Angeles and San Francisco). In contrast, geostationary (stationary with respect to the Earth's surface) communications satellites have to be lofted approximately 21,500 miles (35,800 km) above the Earth's surface, and the Apollo spacecraft were approximately 227,000 miles (378,000 km) above the Earth's surface when they reached the Moon.

In its six years of operation, the Hubble Space Telescope has observed approximately 8000 objects, which is roughly equivalent to the number of stars that can be seen from the surface of Earth with the naked eye.

It currently takes radio signals approximately 35 minutes to get from the Galileo spacecraft to Earth. Galileo, in orbit around Jupiter, is over 635 million kilometers (about 395 million miles) from Earth.

The amount of power being transmitted by the Galileo spacecraft radio is about the same as that used to power a refrigerator light bulb--about 20 watts

The Solid Rocket Boosters (SRBs) used during Space Shuttle launches are the largest solid-propellant motors ever flown and the first designed for reuse. Each is 149.16 feet long and 12.17 feet in diameter.

The speed required for a spacecraft or other object to completely escape the gravitational pull of the Earth (escape velocity) is approximately 11 km/s (7 mi/s), or about 40,000 km/hr (25,000 mi/hr).

The Galileo spacecraft traveled 2.4 billion miles on its way to Jupiter and along the way used about 67 gallons of fuel to control the flight path and spacecraft attitude. This is the equivalent of about 36 million miles per gallon, although Galileo's usage of fuel was not at all continuous, but rather occurred in discrete bursts.

Each Space Shuttle Solid Rocket Booster (SRB) has a thrust of approximately 3,300,000 pounds at launch.

The propellant mixture in each Space Shuttle Solid Rocket Booster (SRB) consists of ammonium perchlorate (oxidizer, 69.9 percent by weight), aluminum (fuel, 16 percent), iron oxide (a catalyst, 0.4 percent), a polymer (a binder that holds the mixture together, 12.04 percent), and an epoxy curing agent (1.96 percent).

During launch, the main engines of the Space Shuttle use liquid hydrogen and liquid oxygen, which are stored in the large, expendable central fuel tank.

During landing of a space shuttle, it takes approximately one minute between touchdown of the wheels and wheelstop, the point at which the shuttle comes to a complete stop.

Viking Lander 1 was originally scheduled to land on July 4, 1976, just as Mars Pathfinder will land on July 4. However, the landing was delayed and the site adjusted because the original site appeared too hazardous in Viking Orbiter photographs. Landing occurred July 20, 1976, seven years after Apollo 11 landed on the Moon.

Mariner 10 was the first spacecraft to encounter two planets (besides Earth) on one mission. It flew past both Venus and Mercury in the early 1970's.

ASTRONAUTS:
Who is the only astronaut to have flown into space on board all five Space Shuttles (including Challenger)? The answer is Story Musgrave.

The first American to eat food in space was Scott Carpenter aboard the Mercury spacecraft Aurora 7 in 1962.

Stump your friends: who was the last astronaut to fly in space alone in a spacecraft? For you space buffs who immediately thought of Mercury astronaut Gordon Cooper, think again. It was Apollo 17 command module pilot Ron Evans, who circled the Moon alone while astronauts Gene Cernan and Harrison Schmitt went to the surface.

Only 12 humans have ever visited another world--all of them walking on the Moon during brief stays between July 20, 1969 and Dec. 13, 1972 as part of the Apollo program.

MARS PATHFINDER:
The Mars Pathfinder rover, named Sojourner, is 63 cm (25 in) long and 48 cm (19 in) wide, and weighs approximately 12 kg (25 lb).

Large channels and valleys on Mars are named after the name for Mars in various languages. For example, Pathfinder landed at the end of Ares Vallis. Ares is the Greek word for Mars.

SIZES & DISTANCE:
Size comparisons: About 1000 Earths would fit inside Jupiter, and about 1000 Jupiters would fit inside the Sun.

Our Solar System, by virtue of its proper motion through our galaxy (the Milky Way) is moving at a speed of 43,000 miles per hour toward the globular cluster of stars known as M13 in the constellation Hercules.

Some of the objects visible in Hubble Space Telescope images are nearly four billion times fainter than the limits of human vision.

Comet Hyakutake's orbit will carry it over 1000 astronomical units from the Sun before it once again heads back towards the Sun in another 7,000 years (1 astronomical unit = the average distance from the Earth to the Sun = 93 million miles = 150 million km). Such large orbits are not unusual for long-period comets. For comparison Pluto is on average 40 astronomical units from the Sun and orbits the Sun once every 248 years.

The largest mountain in the Solar System is Olympus Mons on Mars. At a height of over 26 km (16 mi.), it is nearly 3 times taller than Mt. Everest. Olympus Mons is also enormous in its width: 600 km (360 mi.) across.

If you suspend three grains of sand in a large sports arena, such as Madison Square Garden in New York, the arena will be more closely packed with sand than our galaxy is with stars.

A beam of light travels just over twelve inches in one nano-second (a billionth of a second). Some have suggested naming this unit of distance the phoot.

The elements Carbon, Hydrogen, Oxygen, and Nitrogen - all crucial to life - are found in roughly the same proportions in comets and human beings.

At Voyager 1's present distance, sunlight is only one five-thousandth as intense as it is on Earth. Radio signals from Voyager 1, traveling at the speed of light (300,000 kilometers per second) take 9 hours and 36 minutes to reach Earth.

The first experimental confirmation of Einstein's General Theory of Relativity was made during the total solar eclipse of May 29, 1919. During an eclipse, bright stars become visible. Einstein had predicted that gravity from the Sun would slightly bend the path of starlight passing close to the Sun. Astronomers tested this assertion by measuring the positions of several stars that appeared close to the Sun during the 1919 eclipse. The deviations in the observed positions of these stars due to the Sun's gravity matched Einstein's predictions.

If all of the particles that make up Saturn's rings were gathered together, they would form a sphere about 120 miles in diameter, roughly the size of Saturn's seventh largest moon, Mimas.

The average distance between stars in the spiral arms of the Milky Way galaxy is currently estimated to be seven light years, or sixty-six trillion kilometers. This distance is equal to roughly 443,000 times the distance between the Earth and Sun.