Another Thousand Circles 'Round the Sun Quiz

Answer: 241 years

Mercury is the closest planet to the Sun and has an elliptical orbit of 88 days meaning it travels around the Sun almost four times in the one year it takes the Earth to revolve around the Sun. The planet gets as close as 29 million miles (47 million km) to the Sun, and as far away as 43 million miles (70 million km) from the Sun. However it takes 59 Earth-days for Mercury to make one rotation. It is the smallest planet in the solar system and its diameter of 3,030 miles (4,876 kilometres) makes it only slightly bigger than Earth's moon. It is smaller than both Saturn's moon Titan and Jupiter's moon Ganymede.

Mercury, counter-intuitively, can be very cold. The temperature can reach 840 degrees Fahrenheit (450 degrees Celsius), during the day but, at night, temperatures can drop to minus 275 F (minus 170 C). The range of more than 1,100 F (600 C), is the largest of any planet in the solar system. The craters at the poles never receive sunlight and it is postulated they contain water ice.

The atmosphere around Mercury is so thin it is actually an exosphere, which is atoms blown off the surface by solar wind. The exosphere is composed mostly of oxygen, sodium, hydrogen, helium, and potassium.

Answer: Both options are true

It takes Venus longer to rotate once on its axis (i.e. one day) than to orbit the Sun (i.e. one year). It takes 243 Earth days to make a single rotation on its axis - the longest rotation of any planet in the Solar System - and yet only 225 Earth days to complete an orbit of the Sun.

There are several theories regarding why Venus spins clockwise. (The only other planet to do this is Neptune). These include:

1. The planet was struck by a very large meteor early in its formation
2. The spin axis flipped like a gyroscope can do
3. The spin slowed to zero then, as a result of the combination of the sun's gravity, a dense atmosphere and friction between core and mantle, started spinning the other way
4. The theory that Mercury was a moon of Venus still persists. In this model, the effect of the "Mercury moon" caused tides on Venus causing retrograde motion. This would explain why nearly all the iron in Venus would have been driven up into the crust by the high spin rate, with Mercury getting most of the iron during the fission process. This would explain why Mercury has a stronger magnetic field than Venus, and why Mercury has a really deep dense iron core but Venus only has thin iron deposits in its mantle

None of the theories is totally accepted - each has its faults.

The atmosphere, most of it at least, is made up of carbon dioxide, causing a greenhouse effect warming Venus' surface. Temperatures there exceed 870 degrees Fahrenheit (470 degrees Celsius). Venus' clouds are mostly made of toxic sulfuric acid. In 2020, astronomers found phosphine (PH3) in Venus' clouds. This compound on Earth is usually produced by microbes. so this suggested that the planet might host life. Other scientists have refuted this theory and offered other, more credible, inorganic explanations.

Answer: No

Earth days are getting longer.

When Earth formed 4.5 billion years ago, a day was about six hours long. In more modern (geologically speaking) times, about 620 million years ago, a day had increased to 21 hours 55 minutes. Today we think of a day as 24 hours but a day is increasing at the rate of 1.7 milliseconds every century. This is because the Moon is slowing down the Earth's rotation due to the Earth's tides, which are caused by the moon's gravitational attraction. According to NASA, Earth's spin causes the "position of its tidal ocean bulges to be pulled slightly ahead of the axis" between Earth and the Moon. This causes a twisting force (torque) that decelerates Earth's rotation.

So if you live to be a centenarian, your 100th birthday will be longer than the day you were born by 1.7 milliseconds

Answer: An object the size of Mars collided with Earth and was caught in Earth's gravitational attraction

The giant impact hypothesis states that 4.5 billion years ago, when the solar system was forming but still chaotic, an object called Theia, the size of Mars, collided with Earth. The impact scattered matter from Earth's crust, and the debris attached to the remnants of Theia through the force of gravity and became the Moon. This explains why the Moon is made up of lighter elements typical of those found in Earth's outer layer.

Earth's moon is the fifth largest moon behind Ganymede, Titan, Callisto and Io respectively. Titan revolves around Saturn with the other three revolving around Jupiter. Ganymede is larger than Mercury, the smallest planet. The Moon is the biggest satellite in relation to the planet it orbits with a diameter of 2159 miles (3300 km). It is a little more than one-quarter the size of Earth.

Answer: Atmosphere

Mars is Earth's neighbour. It is smaller than Earth with a diameter of 6800km / 4200 mi compared with 12700 km / 7900 mi. It averages 228 million km (141 million mi) distance from the sun compared with 150 million km (93 million mi for Earth). This means a year on Mars is 687 days long but a day is similar at 24 hours 37 minutes. Similarly, Mars experiences seasons as the tilt on the axis is 24 degrees. Gravity is 37% of Earth's.

Earth's atmosphere is 78% nitrogen, 21% oxygen and several minor gases with carbon dioxide comprising less than 1% of its atmosphere, By comparison, Mars has a very thin atmosphere comprising 96% carbon dioxide and 3% nitrogen. The thin atmosphere cannot trap heat from the sun so the temperature varies from -100C in winter to 20C in summer.

Mars has two moons: Phobos and Deimos. These may be captured asteroids, though this has never been proven.

There is an asteroid belt between Mars and Jupiter containing hundreds of thousands of asteroids. Almost half of this entire mass is made up of four dwarf planets: Ceres, and three other asteroids called Vesta, Pallas and Hygiea. Ceres is 950km in diameter. The diameters of Vesta, Pallas and Hygiea are between 400-500km.

Answer: No

A star must be massive:

While Jupiter is known as the second biggest object in the solar system besides the Sun, its size is truly big - Jupiter is twice more massive than all of the other planets in the solar system combined and their moons. Its volume is equivalent to 1321 Earths. Its diameter is 11 times that of Earth . It is also the fastest spinning planet with a day of just under 10 hours and a year of 11.8 Earth-Years. If Jupiter got any bigger in mass, it would actually get smaller. Extra mass would make the planet more dense, which would cause it to start contracting it in on itself as it has a massive gravitational force. It is estimated that Jupiter could absorb four times its current mass, and yet remain about the same size.

A star must be able to fuse hydrogen:

Jupiter is composed primarily of gas and liquid. Like the other gas giants, the planet is divided between a gaseous outer atmosphere and an interior that is much denser. Its upper atmosphere is composed of about 75% hydrogen and 24% helium by mass, with the remaining one percent consisting of other elements like ammonia and methane. As you go deeper, the hydrogen concentration decreases and helium increases with 5% being other elements like metallic gases. The core is unknown but is thought to be liquid and rocky though, as yet, unproven. While Jupiter is abundant in hydrogen and helium, ironically Jupiter does not have enough mass to initiate fusion reactions in its core which is how stars generate energy: by fusing hydrogen atoms together under the most extreme conditions of heat and pressure to create helium, causing energy release manifested as light and heat in the process.

Answer: Less than 3km / 2 mi thick

If you had a model of Saturn, like a globe, that was one meter (3 feet) wide, its rings would be over 10,000 times thinner than a razor blade.

All four gas giant planets in our solar system have rings. Saturn, however, has the most extensive and most distinctive.. They were discovered by Galileo Galilei, in 1610, who observed them with the telescope he invented. On September 1, 1971, a very close view of the rings was observed by Pioneer 11 spacecraft when it flew past Saturn .

Saturn's rings are comprised of millions and millions of particles that range in size from dust grains to objects the same size as small mountains. These are made up of chunks of ice and rock. These came from asteroids, comets or, possibly, moons that broke apart before they reached Saturn.

Saturn's rings are divided into seven groups, named in the order of their discovery (outwards from Saturn: D, C, B, A, F, G and E). Prometheus and Pandora, ('shepherd moons') keep the F ring in place. Other moons create divisions in the rings and also have a role in shepherding them.

Saturn is the second largest planet in the solar solar system. Its equatorial diameter is 120,536 km (making is 10 times longer than Earth's) but its polar diameter is 108 728 km making it the flattest planet. Despite this huge size, its mass is only 100 times that of Earth - if it was the same density as Earth it would be over 1000 times heavier. You can't walk on Saturn as it is composed of gases (besides you would be snap frozen at -129C).

Saturn's upper atmosphere is divided into bands of clouds. The top layers are
mostly ammonia ice while the clouds below are largely water ice. Under that are layers of hydrogen, getting denser farther into the planet. Eventually, the hydrogen becomes metallic, becoming liquid metal .

In 2019, 20 more moons of Saturn were discovered, bringing the total to 82.

Answer: Summer or winter lasts 42 years at the poles

A year on Uranus is 84 Earth years - the time it takes to rotate around the sun.

All planets rotate on an axis which is usually tilted. Mars and Earth tilt 23-24 degrees. This tilt is what causes the seasons on all planets. Uranus has a tilt of 99 degrees making it look as if it is rotating on its side. Other planets look like spinning tops as they orbit the sun, Uranus looks like a ball rolling in a circular pattern. So, while a day lasts a very Earth-like 17 1/4 hours, a season lasts 42 years because of this tilt. If (theoretically) you could stand at the North (or South) Pole on Uranus, the sun would rise and circle (yes circle) for 42 years. This is summer, then the sun would set below the horizon causing 42 years of a very dark winter.

Uranus is the seventh planet from the Sun, orbiting at a distance of 2.88 billion km. Neptune, averages a distance of 4.5 billion km from the Sun. However, Uranus is colder than Neptune. On Uranus, the average temperature is -201 °C/-330 °F), but can reach as low as -218 °C/-360 °F. At the top of its cloud cover (it is after all a gas giant) which is categorised as its 'surface" temperature, it, unlike other planets, is colder at this level. This is due to Uranus actually giving off less heat than it absorbs from the Sun (which isn't much anyway). While the other large planets have very hot cores, radiating infrared radiation, Uranus' core has cooled down such a degree that it no longer radiates any significant thermal energy. The atmosphere (i.e. "surface") comprises hydrogen, helium and methane; its mantle is water, ammonia and methane ices whereas its core is iron and nickel silicate rock.

Uranus has thirteen discernible rings but they are very dark and comprise very small particles in the range of 10^-6- 10^-3 metres. The composition of the rings may at one time have been part of a moon (or moons) that was shattered by high-speed collisions.

Answer: Gravity is non-existent

A year on Neptune takes 165 years with a day taking 16 Earth hours. Because it has an axial tilt of 28 degrees (Earth = 23.5 degrees), it has seasons but each season is forty years long! Even when Pluto was considered a planet, Pluto's orbit was so elliptical that Neptune was often still the most distant planet from the sun. This was the case between 1979 and 1999.

While Neptune is the smallest of the gas giants, it is actually more massive than Uranus by 18% which is because it has the highest density of the gas giants at 1.638 /cm3. The gravity of Neptune is only 17% stronger than Earth's but, of course, it would do you no good standing on Neptune. It has no rocky surface, and is just a ball of gas and ice (though it may have a rocky core). Even if you could stand on the planet, at minus 220 degrees Celsius, you would not be able to stand still as the winds on Neptune are a fierce 2100 km/hr or 1200 mph.

Neptune also has rings but they are not as prominent as Saturn's. Neptune has five rings, named after astronomers connected to discoveries about Neptune - Galle, Le Verrier, Lassell, Arago, and Adams. These rings are least 20% dust (up to 70%) The rest of the ring materials consist of small rocks.

The rings of Neptune are not old compared with the Solar System. There is a theory that Triton, the largest of Neptune's many moons, was a Kuiper belt object that was caught by Neptune's gravity as it spins in the opposite direction to the other Neptune satellites. Triton at some point will crash into Neptune and form another ring (but not in our lifetime or anytime soon in the next several hundred million years)

The Kuiper belt is a belt of icy/rocky bodies within the plane of the Solar System that extends beyond the orbit of Neptune. Named in 1992 after Dutch astronomer Gerard Kuiper, the belt was believed to be the reservoir of the short period comets. It contains over 100 000 KBOs (Kuiper Belt Objects) with Pluto, the largest KBO, considered one of these. The belt is 50 Astronomical Units wide (1AU = Distance from Sun to Earth). Its abrupt outer edge, at 50AU, lends weight to the theory that the belt pushed out to its present position as Neptune migrated outwards.

Beyond the Kuiper belt are scattered disc objects which have eccentric orbits and the dwarf planet Eris which is the size of Pluto and has at least one moon. Beyond that is the Oort Cloud which is a spherical shell of icy bodies surrounding the Solar System.

Answer: 230 million years

For the solar system to make one complete orbit around the Milky Way in 230 million years, it is travelling at an average velocity of 828,000 km/hr. This is one cosmic year.

The Milky Way is a spiral galaxy. It comprises a central swelling or bulge, four major arms, and a few shorter arms. The Sun and solar system are located on the Orion arm, between two major arms called Perseus and Sagittarius. The diameter of the Milky Way is about 100,000 light-years and the Sun is located about 28,000 light-years from the galactic centre. Theoretically, if light left the outer reaches of the Milky Way at the speed of light (which is 1,080,000,000km/hr or 670,000,000 mph) it would take 100,000 years to reach the other side.