Tell the children they will make a model of how objects — like planets — interact in space. Explain that space can act much like the surface of the trampoline.
The indentations made on the surface represent the "gravity wells" created by massive objects in space. Invite the children to experiment with the same effects on smaller—scale models. Separate the children into groups and give each group a prepared embroidery hoop, suspended in the air on bricks or books.
Explain that they will use marbles and Play-Doh balls to model the effects of gravity on objects in space. Facilitator's Note: Gravity is a universal force, like magnetism and electricity. However, it becomes important only at large scales. Gravity determines the interactions stars, planets, and moons. In the model, the balls are too small to exert a significant gravitational pull on each other. However, they are gravitationally pulled toward Earth! They move toward each other because the weights of heavier objects distort the sheet and lighter objects roll "downhill.
Invite the children to experiment with their models of space by placing and dropping the marbles together and separately onto the sheet. Ask the groups to each add a large, 2" round ball of Play-Doh to represent a large "planet" alone on the sheet.
Ask the children to hypothesize what will happen if the marbles are dropped onto the sheet, and have them record their thoughts in their journals before they test them. After they have dropped the marbles onto the sheet, share that this "pull" toward the "planets" is a model of gravity. Facilitator's Note: The Play-Doh and Styrofoam balls used in steps 5—7 serve to create test "wells" on the sheets. They should remain stationary while the children roll the marbles to see how they move at each step.
Encourage the children to only roll marbles, as the Play-Doh is sticky and will not model the motion accurately. Ask the groups to place a very small round ball of Play-Doh about half of the size of a marble , which represents a small asteroid, alone on the sheet.
Have them note their predictions in their journals and then test what will happen to marbles added to the sheet. Ask the groups to place the Styrofoam ball alone on the sheet and, keeping records in their journals, experiment with its gravitational pull. Remind the children that the gravitational pull of a planet depends on its mass and size. Saturn is large in size, but it does not have nearly as much mass packed into its volume as Jupiter does.
Facilitator's Note: Saturn does have plenty of mass, and as they explored in Heavyweight Champion: Jupiter! However, because it is not dense, a person standing in its cloud tops would only weigh about as much as they weigh on Earth. Saturn's cloud tops are far above the planet's bulky — and gravitationally strong — center.
Because the force of gravity depends on both mass and distance, planets that are puffy and less dense have less gravity at their cloud-tops or surfaces, which are far above the bulk of the mass in their interiors. When astronomers first located Pluto, the telescopes were not as good so Pluto and its moon, Charon, were seen as one much larger object Figure below.
With better telescopes, astronomers realized that Pluto was much smaller than they had thought. Better technology also allowed astronomers to discover many smaller objects like Pluto that orbit the Sun. One of them, Eris, discovered in , is even larger than Pluto Figure below. Even when it was considered a planet, Pluto was an oddball.
Unlike the other outer planets in the solar system, which are all gas giants, it is small, icy, and rocky. With more than million Kuiper belt objects, Pluto has failed the test of clearing other bodies out its orbit. In , the International Astronomical Union decided that there were too many questions surrounding what could be called a planet and so refined the definition of a planet. A dwarf planet is an object that meets items the first three items in the list above, but not but not the fourth.
Pluto is now called a dwarf planet, along with the objects Ceres, Makemake, and Eris. Pluto has three moons of its own. The largest, Charon, is big enough that the Pluto-Charon system is sometimes considered to be a double dwarf planet Figure below.
Two smaller moons, Nix and Hydra, were discovered in But having moons is not enough to make an object a planet. Ceres is the largest object in the asteroid belt Figure below. Before , Ceres was considered the largest of the asteroids, with only about 1. But unlike the asteroids, Ceres has enough mass that its gravity causes it to be shaped like a sphere. Like Pluto, Ceres is rocky. Is Ceres a planet? How does it match the criteria above?
Ceres orbits the Sun, is round, and is not a moon. As part of the asteroid belt, its orbit is full of other smaller bodies, so Ceres fails the fourth criterion for being a planet. Makemake is the third largest and second brightest dwarf planet we have discovered so far Figure below. With a diameter estimated to be between 1, and 1, km, it is about three-quarters the size of Pluto. Makemake orbits the Sun in years at a distance between It is thought to be made of methane, ethane, and nitrogen ices.
Largest Known Trans-Neptunian Objects. Makemake is named after the deity that created humanity in the mythology of the people of Easter Island.
The object was not discovered until because it is about three times farther from the Sun than Pluto, and almost times farther from the Sun than Earth is. Eris also has a small moon, Dysnomia that orbits it once about every 16 days. Astronomers know there may be other dwarf planets in the outer reaches of the solar system. Haumea was made a dwarf planet in and so now the total is five. Quaoar, Varuna and Orcus may be added to the list of dwarf planets in the future.
We still have a lot to discover and explore. Some planets orbit closer to the sun than others. And some are far away from the sun. The planets that are farthest from the sun are called the outer planets. The planets that are closer to the sun are called the inner planets. The inner planets are close to each other as well as close to the sun.
There are four inner planets:. The inner planets have a hard, rocky surface. It is possible to land a spacecraft on planets that have a hard surface. The five outer planets are not only farther from the sun, but they are also far apart from one another. The last planet discovered in our solar system is farthest away from the sun. It is Pluto. We don't know much about Pluto yet except that it is very, very cold.
Pluto is not like the other outer planets. And it is not like the inner planets, either. Pluto is a mystery. Create a List. List Name Save. Rename this List. Rename this list. List Name Delete from selected List. Save to. Save to:. Save Create a List. Create a list.
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