1. 7,000 years
   One million years
2. 2.5 billion years
   4.6 billion years

Although it's not entirely clear how our solar system came to be, the most widely accepted theory is called core acceleration. Within a solar nebula (a rotating cloud of dust and gas), the sun was formed by gravity collapsing into the spinning nebula. Powerful solar winds pushed out the gases, leaving rockier materials closer to the sun and gases further away, giving us the planets and their compositions as we have them now.

1. One million miles
   12 million miles
2. 93 million miles
   One billion miles

From the center of the sun to the center of the earth is 93 million miles. This is also the unit of measure used to when measuring distances within the solar system.

1. 55
   122
2. 158
   275

So 122 AU may sound abstract—how big is that? Even knowing that 1 AU is 93 million miles may not help, so here's the math: that distance is 9 billion miles.

1. Four minutes
   Eight minutes
2. Twenty minutes
   One hour

Even though we're 93 million miles away from the sun, light travels pretty quickly. If you want to do the math, it's 93 million miles divided by the speed of light, which is 186,282 miles per second—it's a little over 8 minutes, 30 seconds.

1. 25 percent
   45 percent
2. 80 percent
   99 percent

The actual percentage is 99.86 percent of the known mass, which is 1.9891 × 10^30 kilograms. The bigger planets, Jupiter and Saturn, take up most of the rest of that percentage. To compare, Earth isn't a small little rock, with a mass of 5.972 × 10^24 kilograms—but it would take 1.3 million earths to fill the sun.

1. Heliosphere
   Sun shield
2. Radiation vesicle
   Cosmic cul-de-sac

Also known as the heliopause, the heliosphere's electrically conductive particles are in a plasma state, meaning the particles are highly responsive to electromagnetic forces. This plasmic bubble protects the planets from galactic cosmic radiation.

1. Radiosphere
   Magnetosphere
2. Heliosphere
   Junosphere

Earth's magnetosphere is essentially the planet's magnetic field, and between the four terrestrial planets, Earth's is the strongest. Created by the molten iron at Earth's core, the comet-shaped magnetosphere helps to protect us from solar winds as well as from solar and cosmic radiation.

1. Radial belts
   Telluric radiation shields
2. Photon polarizers
   Van Allen radiation belts

The charged particles in the Van Allen belts are considered to be trapped from solar winds as well as from cosmic radiation from other galaxies. There are two belts—an inner belt and an outer belt—which can change shape during solar storms. The belts have been studied by NASA for the past few years through probes, since radiation can affect astronauts, spacecraft and satellites.

1. Sirius
   Barnard's star
2. Proxima Centauri
   Tau Ceti

Sirius is a binary star and is a part of the constellation Canis Major. Historically, the rising of Sirius on the eastern horizon is where we get the phrase the "dog days of summer," because it was associated several phenomena including drought, flash thunderstorms and rabid dogs.

1. Seven
   Eight
2. Nine
   Ten

Until August 24, 2006, Pluto was considered to be one of the nine planets in our solar system. On that day, the International Astronomical Union (IAU) demoted Pluto from planet to dwarf planet. But it doesn't mean Pluto is no longer important, because earlier that year, NASA's New Horizons space probe project to Pluto and the Kuiper belt was launched, giving us new images and information about Pluto in 2015 and 2016.

1. One
   Two
2. Four
   Five

Currently, there are five recognized dwarf planets, meaning they're not a satellite or moon (orbiting a planet), but they're not a planet either (truly orbiting a sun). These are Ceres in the asteroid belt along with Pluto, Haumea, Makemake and Eris on the outer edge of the solar system. There are possibly hundreds to thousands more, but by IAU standards, these five are officially recognized as of 2008.

1. The Fab Four
   Warmer planets
2. Terrestrial planets
   Hot Rocks

Mercury, Venus, Earth and Mars are called terrestrial planets because of their composition. They're primarily made of rock and/or metal and have a solid surface. Other names for these four planets are telluric (Tellus is Latin for "earth") planets or rocky planets.

1. Jovian planets
   Giant planets
2. Gas planets
   All of the above

Jovian planets relates to the Roman name for Jupiter, Jove. They're called the gas planets because they're primarily comprised of helium and hydrogen, along with other gases, and have no solid surfaces; but Uranus and Neptune are also called the ice giants because they are comprised more of heavier elements in frozen states such as sulfur, oxygen and carbon. Jupiter and Saturn are primarily comprised of helium and hydrogen and are sometimes called gas giants.

1. Earth and Mars
   Mars and Jupiter
2. Jupiter and Saturn
   Neptune and Pluto

The asteroid belt, also called the main belt or the main asteroid belt, has minor planets and asteroids in between Mars and Jupiter. It forms a boundary between the inner and outer planets. The thickness of the belt is about 1 AU, but there's quite a bit of space between objects.

1. Milky Way
   Interstellar space
2. Kuiper belt
   Plutonian space

The Kuiper belt (sometimes called the Edgeworth-Kuiper belt or the Kuiper-Edgeworth belt) contains millions of these icy SSSBs—leftovers from the creation of the solar system. They're also calls Kuiper belt objects (KBOs). Dwarf planets Pluto, Eris, Makemake and Haumea reside here.

1. Kuiper's cloud
   Oort cloud
2. Solar cloud
   The Great Cloud of the Milky Way

The spherical Oort cloud, also known as the Öpik–Oort cloud, is theoretically where long-period comets (such as Halley's comet) originate. The Oort cloud looks to be part of the remnants of the solar system's formation. This can be seen as our solar system's outer boundary in relation to the rest of the Milky Way and the universe.

1. Neptune
   Saturn
2. Earth
   Pluto

Earth is the only planet without a mythological name. Earth comes from the Old English word "eorthe," meaning ground or soil.

1. Supergiant
   Red dwarf
2. Red giant
   Main sequence star

The sun is like most stars in the Milky Way and in the universe—a main sequence star. The central feature of main sequence stars is that at their cores, they convert hydrogen into helium, a nuclear fusion process which creates a massive amount of energy.

1. You weigh the same on Earth as you do on the moon.
   The moon has an atmosphere, similar to the one found on Earth.
2. Only two people have walked on the moon.
   The moon has quakes.

Due to the tidal forces from the Earth, the moon can actually have quakes—some shallow and some deep. Some of the quakes come from the impact of meteorites, and some quakes occur when the moon's crust is exposed to the sun again after two weeks in darkness, causing the crust to expand.

1. Mercury
   Pluto
2. Jupiter
   Saturn

Saturn lacks density is due to its outer layer, which is made of gas. And although the core is solid, comprised of rock, the planet's density makes it lighter than water, meaning it could float on water.

1. Mercury
   Venus
2. Earth
   Mars

Because Mercury has no atmosphere, it's actually the second-hottest planet in the solar system. And without an atmosphere to trap heat, the temperature fluctuations on Mercury can run about 1100 degrees Fahrenheit between day (800 degrees) and night (-280 degrees). Venus is slightly hotter due to its denser atmosphere, almost completely comprised of carbon dioxide, with temperatures reaching up over 860 degrees Fahrenheit.

1. Sulfuric acid
   Oxygen
2. Nitrous oxide
   Hydrochloric acid

Venus' clouds are so thick, 60 percent of sunlight is reflected back into the universe. It was once hoped that, because Earth and Venus are similar and size, that life could be sustained on Venus, but the composition and thickness of these clouds alone would make it a harsh environment for human life—or any life.

1. Mars has a magnetic field.
   Like Earth, Mars has seasons.
2. Mars has the tallest known mountain in the solar system.
   It takes Mars 687 days to orbit the sun.

Unlike Earth, Mars does not have a magnetic field because its core is solid—or, at the very least, partially solid. But it does have a magnetosphere; it's just not as substantial as Earth's is. That magnetosphere protect Mars' surface from solar winds.

1. Comet
   Meteor
2. Asteroid
   Meteorite

Comets are made of some rocks along with icy material, such as frozen water, ammonia or methane. Comets seem to come from the Kuiper belt and the Oort cloud. Another nickname for the "dirty snowball" is the "cosmic snowball."

1. Falling star
   Comet
2. Asteroid
   Meteor

Meteors typically come from asteroids, but they can come from other places, such as the moon or Mars. There are three general composition types: metallic (i.e., they contain iron), stony or a mixture of stone and iron. If it lands on the surface of a planet, it becomes a meteorite, but if it burns up in the atmosphere, then it's a meteor.

1. Jupiter's largest moon, Ganymede, is the largest moon in our solar system.
   Jupiter does not have rings.
2. Jupiter's Great Red spot is a large storm.
   Jupiter has at least 67 moons orbiting around it

Jupiter indeed does have rings (albeit faint ones)—in fact, all the outer planets do. Mainly comprised of dust, the rings of Jupiter were first seen via the Voyager 1 probe in 1979 and have been observed and researched since then.

1. Uranus
   Neptune
2. Mercury
   Venus

Uranus was discovered by astronomer William Herschel in 1781. He then realized that the path this "comet" was taking was more circular and less elliptical than a comet's path. Uranus' rings weren't discovered until almost two centuries later, in 1977.

1. Uranus
   Neptune
2. Pluto
   Jupiter

Neptune may be the smallest planet of the outer planets, but it's the windiest of our solar system, with wind speeds of up to 1,200 mph. Neptune is also the densest of the gas planets with possibly extremely hot oceans kept in place by exceedingly high pressure.

1. Eris
   Makemake
2. Ceres
   Pluto

What caused scientist to demote the planet was its location in the Kuiper belt, surrounded by bodies called plutoids. Because of those bodies, astronomers believed that Pluto didn't fully own its transit. Months before that decision, the New Horizons space mission began, and in 2015 and 2016, we've received updated data and pictures on this now dwarf planet.

1. Pluto
   Ceres
2. Eris
   Uranus

Ceres is the largest body located in the asteroid belt and was first seen as a comet by Italian astronomer Giuseppe Piazzi. And then it was thought to be a planet but then was later classified as an asteroid in 19th century. In 2006, when Pluto was considered to be reclassified, Ceres was also considered to be reclassified—but both planets didn't meet the full criteria for a planet and received a dwarf-planet classification.

1. Makemake
   Eris
2. Pluto
   Mars

Named after the Rapa Nui goddess of fertility, Makemake was discovered in 2005 and classified as a dwarf planet in 2008. Not much is known about Makemake yet, but in 2016, the Hubble Space Telescope found a small moon with a radius of 50 miles, nicknamed MK2.

1. Ceres
   Pluto
2. Eris
   Haumea

Named after the Hawaiian goddess of fertility, Haumea was discovered in either 2003 or 2004—and it depends on who you ask, because two teams are claiming the discovery. Because Haumea spins so quickly, it has more of an oblong or oval shape and it has a very short day—only four hours. It was classified as a dwarf planet and officially named in 2008.

1. Neptune
   Eris
2. Haumea
   Ceres

Aptly named after Eris, the Greek goddess of strife and discord, this celestial body is what sparked the fierce debate about the definition of a planet (which, by the way, the debate has not been completely resolved). Eris was discovered in 2003 by the same Palomar Observatory team that discovered Makemake in 2005. This dwarf planet and its moon Dysnomia are the furthest from the sun, as it is beyond the Kuiper belt.

1. Planet Whip
   Planet X
2. Dimension X
   Dune

In 2015, researchers at Caltech announced that, based on mathematical modeling (not by observation), there is evidence of a large planet which is in a quite long orbit in our outer solar system, which would explain the orbits of five objects in the Kuiper belt. As astronomers search for this planet via powerful telescope, they've dubbed it "Planet Nine," but the typical placeholder name for a planet beyond Neptune is Planet X.

1. Andromeda Galaxy
   Large Magellanic Cloud Galaxy
2. Messier 83 (M83) Galaxy
   Bode's Galaxy

Appearing in the constellation Andromeda, the Andromeda Galaxy (Messier 31 or M31) is our closest galactic neighbor, about 2.5 million light-years away from Earth. And four billion years from now, the Milky Way and the Andromeda Galaxy will combine and become the Milkomeda Galaxy. Also our largest neighbor, the Andromeda Galaxy has approximately one trillion stars with the span of 220,000 light-years.