SOLAR SYSTEM SIZE-UP
How big is our solar system? In this activity, students will see the relative sizes of the planets and how far apart they really are. This activity will especially emphasize how large and empty of a place our solar system really is.
To introduce young Earthlings to the rest of their solar neighborhood.
Students will be able to:
- List the planets and at least two attributes about each planet.
- Describe the planets in terms of their comparative size
Set up: 30 min.
Activity: 30 min.
- 100 meter (or longer) measuring tape
- Objects to represent the sun and planets at 1/10 billionth scale as indicated by the blue text in parentheses near the planet names and listed next
- 2 sesame seeds
- 2 un-popped popcorn kernels
- 1 grain of salt
- 1 cantaloupe or volley ball
- 1 cherry or large marble
- 1 raspberry or small marble
- 1 grain of sugar
- 1 poppy seed
- Long open area 600 meters in length (a full city block works well or a sports field)
- 10 large pieces of poster board
- Markers or paint
- Scotch tape
Our Solar System began about 5 billion years ago as a cloud of gas and stellar debris called a nebula. It contracted under gravity and began to spin, eventually spawning a central star we call the sun. It is thought that planet formation is only possible in nebulas with heavy minerals because heavy minerals have more concentrated mass and therefore more gravity, so it becomes possible for multiple gravitational centers to form in addition to a proto-star at the center. The local gravitational pull of these proto-planets is stronger than the larger but much more distance influenced by the central star. The more matter these early planets absorbed, the stronger their gravitational attraction became. Increasing mass also causes planets to accelerate along orbital paths and better resist the pull of a growing star. As these maturing planets raced through the nebula the larger ones captured smaller ones, which became their moons. For about a billion years the young planets endured countless impacts from smaller asteroids and comets. At last, the free floating material that once made the nebula was either all absorbed into the star and planets, or blasted away into deep space by the diverse mix of energy, called solar wind, emitted by the young star. It is in this manner that our solar system formed.
The following is a list of information about the planets and star of our solar system that will help you in the following activity.
Mass = 332,946 Earths (cantaloupe or volleyball)
Density = 1.41
Gravity = 27.9 times Earth's
The sun is our closest star. It is composed of 92% Hydrogen and 8% Helium. Through nuclear fusion this ball of burning gas converts hydrogen to helium. As far as stars go it is average in every respect: size, temperature, age, composition, etc. The one thing that makes it unique is that our sun is accompanied by planets.
Mercury (The Little Bullet)
Distance from the Sun = 57.91 million km (5.79 m)
Mass = .0553 Earths (grain of salt)
Density = 5.43
Gravity = .284 of Earth's
Mercury is so small and speeds so close to the sun that it can't maintain an atmosphere; therefore it has no defense against incoming meteorites. As a result the entire planet's surface is pock-marked by craters. Furthermore, without an atmosphere, Mercury can't redistribute heat, so whichever side faces the sun is searing hot and the other horrifically cold. Mercury only rotates 1 ½ times per revolution. Mercury has no moons.
Venus (The Searing Gas Chamber)
Distance from the Sun = 108.2 million km (10.82 m)
Mass = .8149 Earths (sesame seed)
Density = 5.25
Gravity = .878 of Earth's
Because of its similar mass, gravity, and proximity to Earth, Venus has been called our sister planet. In actuality Venus is so different than Earth that these planets should not even be consider the same species, let alone siblings. The atmospheric pressure of Venus is 90 times that of Earth or the same amount of pressure you would feel if you were 900 meters deep in one of Earth's oceans. Venus is even hotter than the sunny side of Mercury. Its thick clouds of hydrochloric and hydrofluoric acid create a planetary greenhouse effect so that Venus's surface temperature averages 900° F (500° C). Venus makes barely more than one rotation per revolution, therefore a year and a day are almost exactly the same length of time on Venus. Venus has no moons.
Earth (The Blue Marble of Life)
Distance from the Sun = 149.597 million km (14.96 m)
Mass = 5.974 X 1024 kg (sesame seed)
Density = 5.52
Gravity = 9.8 meters/sec2
Earth is our home. It is the only planet in the solar system confirmed to have water (in the liquid state) and living life. Earth also has the highest density of all the planets. Earth has only 1 moon.
Mars (The Fixer-upper?)
Distance from the Sun = 227.94 million km (22.79 m)
Mass = .1074 Earths (poppy seed)
Density = 3.95
Gravity = .379 of Earth's
Mars has captured the imagination of scientists as well as science-fiction writers and readers. While we are virtually certain life doesn't exist on Mars now, recent evidence gleaned from Martian meteorites that have fallen to Earth suggest that at least simple organisms like bacteria might have once thrived on Mars. Even more intriguing is that like Earth, Mars is still an active planet. It has enormous volcanoes, rift valleys, and mountain ranges which all suggest an active system of plate tectonics. Other geologic features like canyons and alluvial fans suggest that Mars once had flowing water. Perhaps Mars once had complex life-forms and maybe their fossils are still there?! However the most compelling question is "Can we colonize Mars?" It is agreed that Mars would be our best candidate for a second home. Fortunately Mars does have some water mixed in with the dry-ice ice caps at its poles. Mars is cold but not too cold, especially at its equator. It has enough gravity to maintain a thin but potentially breathable atmosphere, but its current atmosphere needs a lot of work - there's no oxygen. Mars also has the right tilt to its axis to generate seasons - important for restoring a water cycle. Unfortunately Mars also has catastrophic dust storms that make even the largest of Earth's hurricanes look tame. Still, the optimists say that colonization is not a question of "if" but of "how much will it cost" and when? Maybe your grandchildren will be Martian terraformers? Maybe you will?
Jupiter (The Great One)
Distance from the Sun = 778.33 million km (77.83 m)
Mass = 318 Earths (cherry or a big marble)
Density = 1.33
Gravity = 2.4 times Earth's
Jupiter is huge! But if Jupiter were a few times larger it might have become a solar system all to itself, or at least a sister star to our sun. Jupiter has at least 63 moons, the largest of which (Ganymede) has more mass than Pluto and Mercury. Yet Jupiter never became large enough to have the phenomenal internal pressure needed to fuse hydrogen into helium. So instead of burning like the sun, Jupiter's atmosphere remains a swirling torrent of gases. The Great Red Spot, visible to most telescopes, is a storm larger than three Earths that has been raging for over 300 years. Part of the reason why Jupiter's atmosphere is so volatile is that the entire planet rotates every 10 hours (fastest in the solar system), which would translate to 14,300 km per hour at the equator! Jupiter's moons are equally inhospitable. Io is covered in volcanoes that spew molten sulfur into outer space. Io also plunges into Jupiter's magnetic field for part of its orbit creating so much static electricity that lightning arcs from Io to Jupiter's atmosphere! Callisto has the highest density of meteorite impact craters of any object in the solar system. Initially, Europa also appeared to be a nasty place. Its surface is completely frozen and 5 km thick. Yet closer observations have found huge cracks in this icy crust that open and close like those of Earth's arctic ice caps, suggesting there must be something moving underneath. Perhaps its true water - H20? Perhaps it's saltwater? Maybe the entire moon is one enormous ocean? If so, maybe there's something swimming underneath all that ice? Europa's atmosphere also has oxygen. Some astronomers feel that Europa is the mostly likely in our solar system to find extraterrestrial life!
Saturn (The Planet with a Necklace)
Distance from the Sun = 1426.98 million km (142.70 m)
Mass = 95.181 Earths (raspberry or small marble)
Density = .69
Gravity = .923 of Earth's
Saturn isn't the only planet in our solar system with rings: Jupiter, Uranus, and Neptune also have them. Saturn's rings are the largest and most visible from earth. Planetary rings are made up of particles of ice ranging in size from microscopic to house size boulders. All this debris concentrates along a planet's equator because that's where centripetal force, created by a planets high speed rotation, is maximized. This is why Saturn's rings are several hundred thousand kilometers across and only 100 meters thick. Saturn's rings are also maintained by the gravitational pull of some of its smaller moons. Saturn has at least 31 moons. Another fun fact is that if a big enough body of water could be found Saturn could float in it. The majority of the planet is gas so that its average density is less than 0.69. The density of water is 1.0.
Uranus (The Sideways Planet)
Distance from the Sun = 2870.99 million km (287.10 m)
Mass = 14.531 Earths (un-popped popcorn kernel)
Density = 1.29
Gravity = .793 of Earth's
Uranus is also a gas giant - large but with low density. Uranus wasn't discovered until 1781. Even though Uranus is the third largest of all the planets in the solar system, it's not usually visible to the naked eye because it's twice as far away from the sun as Saturn! Uranus's axis is 98° which means its equator and its rings are nearly vertical instead of horizontal, giving the entire planet a sideways appearance. Uranus has 21 moons one of which, Miranda, appears to have been shattered after colliding with an asteroid but then subsequently glued back together by the force of gravity.
Neptune (The Predicted Planet)
Distance from the Sun = 4,497.07 million km (449.71 m)
Mass = 17.135 Earths (un-popped popcorn kernel)
Density = 1.64
Gravity = 1.122 time Earth's
When Neptune was discovered in 1846 its orbit doubled the size of the known solar system. It had been observed for several years that Uranus's orbital path had some irregularities as if it were being acted upon by another large object. Once the math was complete astronomers knew where to point their telescopes and they found Neptune. Neptune, like Venus, is unusual in that it follows a nearly perfect circular orbit and travels at a consistent speed. Most planets orbit the sun in off-centered elliptical paths, causing the planets to speed up as they approach and pass by the sun and slowing down as they head back out into deep space. Neptune has the highest density of the four gas giant planets, the faintest rings, and the least amount of moons -- numbering eight.
Pluto (Not Really a Planet?)
Distance from the Sun = 5,913.52 million km (591.35 m)
Mass = .0022 Earths (grain of sugar)
Density = 2.03
Gravity = .041 of Earth's
Pluto was discovered in 1930. Pluto is perhaps the strangest object in the solar system. Everything about Pluto suggest that is doesn't belong. Its orbit is extremely elliptical and on a different plane than all the other planets. Pluto's orbit also crosses inside Neptune's orbits meaning that some day in the future they might collide and that some time in the past they might have traveled together. Many years later in 1978 Pluto's single moon Charon was found. Pluto and Charon behave more like double planets than a planet and a moon. Pluto and Charon are very close together. Charon revolves around Pluto at the same rate Pluto rotates on its axis, therefore one side of Pluto never sees Charon. This behavior has led some astronomers to speculate that Pluto and Charon might actually be two escaped moons that once belonged to Neptune, rather than a true planet and its moon.
Comets are dirty balls of ice and rock that come from deep space in a hypothetical region called the Oort Cloud - a place halfway to the closest stars. The Oort Cloud is thought to be a small nebula that never had enough mass to become a star or a solar system. Instead it condensed forming thousands of tiny gravitational centers we know as comets. With no local strong source of gravity these comets are attracted over billions of kilometers by the pull of our sun, passing by the sun in enormous highly elliptical orbits. As a comet approaches the sun, the sun's energy, called solar wind, causes the comet to melt, sending a tail of gas and vapor into space in the opposite direction of the sun. Once the comet rounds the sun, its tail shoots out in front of it as it returns to deep space. A few comets like Haley return at a predictable interval. Haley's return interval is 76 years. However, most comets are either just passing through or have such enormous orbits that they are not predictable and may only visit us once every million years or more. Several new comets are discovered every year; however its only a couple of times a decade that comets pass close enough to the earth that they are visible to the naked eye.
Asteroids and Meteorites are rocks floating in space that range in size from a grain of rice to mountain-sized pieces. Meteorites are asteroids that enter Earth's atmosphere and impact the planet's surface. Many asteroids come from a region known as the asteroid belt which is halfway between Mars and Jupiter. The asteroid belt consists of thousands of rocks floating in a single orbit around the sun. Its not known whether the asteroid belt is a planet that was ruptured by a collision or a proto-planet that never properly formed.
Collisions between asteroids cause some to tumble out of their orbit and wreck havoc and destruction on anything in their path. Some tumble toward the sun, others end up headed towards Neptune and Pluto. 65 million years ago a 5-mile wide asteroid hit Earth's Yucatan peninsula at 100,000 km per hour causing , along with other factors, the extinction of the dinosaurs and all other animals that weighed more than 25 kg that were not crocodiles. Sometimes, collisions with planets cause pieces of that planet to be blasted into outer space creating more asteroids. This is how rocks from Mars reach Earth.
Meteor showers are predictable rains of rice grain sized debris from comets still lingering in the comet's orbital paths. As Earth moves through the orbital path of these long-gone comets, the night sky fills with streaks of light as these tiny pieces of rock or ice burn up in Earth's atmosphere. Every year Earth passes through 10 comet orbits, creating meteor showers.
- Present the background information to the students.
- Organize class into 10 groups and assign each group one of the 9 planets and the sun.
- Pass a sheet of poster board to each group and have them write their solar system object's name and to draw/paint a picture of it.
- Pass out the corresponding 1/10 billionth scaled objects, for example Earth = sesame seed, and have the students tape the object to their sheet of poster board.
- Using a 100 meter tape, have the students help you create 1/10 billionth scale version of the solar system by measuring out distances according to the blue numbers above. Place each poster board representing the planets and the sun in the correct places.
Once the 1/10 billionth scale solar system is complete, take the kids on tour through the solar system inviting them to comment on each of the planets comparative sizes and the huge vastness between them. Ask the students to speculate as to why living on planets other than earth would be difficult or even impossible.
Increase the scale to make the planets larger but realize that doing so dramatically increase the distances between planets and the overall size of the solar system: instead of walking to Pluto you might need to drive! Decrease the scale to make the distances between planets much smaller but realize that doing so would require you to use planets disproportionately large. Change the distance scale from a linear one to a logarithmic one then you can double or triple the size of the sun and planets: sun=beach ball, Jupiter = softball, Earth = BB.
Encourage the students to do further research into the planets. Assign them research papers and or presentation on individual planets. See the activity also in the Earth Systems Unit.
Included National Parks and other sites:
Bryce Canyon NP Night Sky Programs
Chaco Culture NHP Night Sky Programs
White Sands NM Public Astronomy Programs
Utah Science Core:
6th grade Standard 1 Objective 2
6th Grade Standard 3 Objective 2
6th Grade Standard 4 Objective 1
(top of page)