INSIDE ƒ Essential Questions ƒ Synopsis ƒ Missions ƒ Come Prepared Checklist ƒ Correlation to Standards ƒ Connections to Other Halls ƒ Glossary

ONLINE ƒ Student Activities ƒ Additional Resources EssentialEssential Questions Questions

What is the solar ? In the , began leaving . NASA’s Our consists of our —the —and all the program was the first to humans on billions of objects that it. These objects, which are bound another , carrying 12 to the ’s to the Sun by , include the eight , . Since then we’ve sent our proxies—robots—on , Earth, , , , , and ; missions near and far across our solar system. several dwarf planets, including and ; hundreds missions allow limited glimpses; orbiters survey ; of orbiting the planets and other bodies, including landers get a close-up understanding of their landing Jupiter’s four major moons and Saturn’s seven, and, of course, location; and rovers, like human explorers, set off across the Earth’s own moon, the Moon; thousands of ; millions surface to see what they can find and analyze. of ; and billions of icy objects beyond Neptune. The solar system is shaped like a gigantic disk with the Sun at The results of these are often surprising. With its center. Everywhere we look throughout the we the Moon as our only reference, we expected other see similar disk-shaped bound together by gravity. to be , dry, dead places, but has revealed Examples include faraway , planetary systems astonishing variety in our solar system. Mars, for example, has orbiting nearby , and the system of moons orbiting a long history of , with dry lakebeds and gullies showing Jupiter, which resembles the solar system itself. Disks are that liquid water once flowed abundantly on its surface; a common because when a of material (such as gas or of water lies beneath its southern polar cap today. dust) surrounds a massive rotating object (such as a star, Gravitational from Jupiter’s enormous the , or black hole), it will flatten out like a spinning ball interior of the planet’s moon , where saw of pizza dough. erupting from active volcanoes onto its frosty surface. And the spacecraft discovered evidence that liquid water lies Uranus beneath the frozen surface of Jupiter’s moon . Jupiter belt What makes Earth habitable? Mercury Venus Sun Earth Along with Mars and Venus, Earth lies in what is often referred Saturn Mars to as the Goldilocks Zone: near enough to the Sun to be warm enough for liquid water, but not so close that it’s too hot to sustain . But isn’t the only consideration. Earth has many factors that allowed life to evolve and flourish. The Neptune , a gas blanket of mostly and , protects Earth’s surface from harmful solar while The solar system. The , a ring of irregularly shaped objects, lies letting through enough of the Sun’s warmth. dioxide, sparsely distributed between the of Mars and Jupiter. Four hot, rocky planets a small, important component of the atmosphere, helps with geological processes similar to those of Earth—including Earth itself—orbit trap that warmth, but human activity over the past 200 between the Sun and the asteroid belt. Four cold planets orbit beyond the asteroid has pumped more and more of this into belt: first the gas Jupiter and Saturn, and then two ice giants, Uranus and the atmosphere, with dangerous consequences. Earth’s Neptune. (Graphic is not to scale.) churning, molten outer core produces a magnetic that surrounds the planet; this protects us How do scientists study the by deflecting the bulk of the charged streaming worlds within our solar system? from the Sun, known as the solar . Mars and Venus lack protective ; on Mars the Throughout history people have observed the , first stripped away most of the atmosphere, and on Venus it with our naked eyes and then with the help of land-based stripped away the water necessary for life. The Moon, too, instruments like . Early philosophers believed helps by stabilizing Earth’s and causing , which Earth was the center of the universe, but as early as the transfer heat around the and churn their water along fourth century BCE, evidence such as the curve of the coastlines. Those in-between, intertidal areas had favorable and the motion of the planets convinced some observers that conditions for the evolution of life. If conditions on Earth had Earth was a ball revolving around the Sun. been just a little bit different, perhaps we would not be here. Synopsis

1 The Moon was the perfect choice 3 The solar system started out as for our first to another world a cloud of gas, ice, and dust Our closest neighbor, it’s only a few days’ journey away by Just over four and a half ago, gravity caused spacecraft. Dark patches of ancient lava tell us that long this cloud to collapse in on itself, forging a central star, ago the Moon was volcanically active, just like Earth, but our Sun, surrounded by a swirling disk of . The the gray scars of ancient, giant craters planets formed within this disk, along with diverse objects made by comets and asteroids like moons, comets, and asteroids. Scientists think each crashing into the Moon’s surface planet carved out its own orbit, growing as it incorporated tell us that its dynamic days ended the material in its path. billions of years ago. Although the Moon is the only alien world we’ve been to in person, we’ve launched our proxies—robots—to visit it and other worlds in our solar system. Earth’s Moon

2 The solar system is a giant disk containing billions of objects circling our Sun Closest to the Sun are the four rocky planets: hot little Mercury, then Venus, Earth, and Mars. Next, the asteroid belt, with its millions of rocky worlds, marks the boundary computer simulation of a solar system forming between the inner and outer solar system. Despite their high numbers, if you squeezed all the asteroids together into one object, it would have a mass less than that of our 4 Planets grow up as part of Moon. On the cold side of the asteroid belt sit the largest planets: the gas giants Jupiter and Saturn. Next are the a family coldest: Uranus and Neptune. Still farther out lies the Take Saturn, our solar system’s second largest planet. Belt, home to millions of smaller frozen worlds. And It’s surrounded by more than 80 moons. Moons can be farthest of all is the mysterious , with trillions of just as fascinating as the planets they orbit. For example, icy objects, some of which become comets. Saturn’s largest one, , has a thick atmosphere and just as Earth does—only it’s too cold for liquid water, so its is made of frozen water (ice), and its raindrops are made of liquid , or Jupiter (CH ). Saturn 4

asteroid belt spacecraft capturing images of Saturn’s rings. White lines represent the orbit paths of Saturn’s moons. 5 Goldilocks Zone. But Venus is missing one vital ingredient: Jupiter’s a a . Without it, Venus has had no protection family is hotter from the solar wind, which stripped away Venus’s water than you’d think and turned the planet into a carbon-dioxide greenhouse too hot for life. The planet’s surface is hot enough to melt At 800 million kilometers lead! Going to Venus deepened our understanding of global from the Sun, giant Jupiter and warming; pumping into our atmosphere is Jupiter’s moon Io its dozens of moons seem like raising and threatening life on Earth. they’d be pretty frigid. But as Voyager 1 saw, its fourth largest moon, Io, has active volcanoes! Io is caught in an intricate gravitational dance 8 Mars was once more like Earth— with one of its sister moons, Europa, along with Jupiter itself. Gravitational forces squash and stretch Io’s rocky but only briefly insides until they melt and erupt. The Galileo spacecraft Liquid water once ran over confirmed that Jupiter too is a dynamic world, with hot, the surface of Mars; flash liquid, metallic churning around its rocky core carved out the . and generating a magnetic field. And hidden beneath The dynamic planet’s active Europa’s icy is a liquid of salty water. volcanoes included , the highest peak in the solar system. And its molten 6 Comets carry chemical riches core generated a magnetic a deep, water-carved on field that protected the planet Mars, evidence that liquid water across the solar system once flowed on the planet’s surface from much of the solar wind. When the spacecraft But at about half the of Earth, Mars cooled too fast to visited 67P, it detected maintain its magnetic field and hang onto its water. It lost not just frozen water and most of its atmosphere, leaving behind a dry, frozen . dust, but also amino acids—the basic building blocks of life! Little objects like this (67P is 9 Earth is just right for life just a few kilometers across) Comet 67P Not only does Earth orbit the Sun in the Goldilocks Zone, can collide with planets and it’s just the right size to maintain a hot, dynamic interior moons, delivering their bounty of water and potentially where churning liquid iron generates a magnetic field. lifegiving organic ingredients. As a comet gets closer to Shielding Earth’s atmosphere from harmful solar radiation, the Sun, its ice transforms into gas that streams off into the magnetic field plays a vital space, carrying dust grains that could become shooting role in creating a biologically stars when they cross Earth’s orbit. safe space where, over the course of billions of years, 7 Venus is Earth’s toxic twin complex life was able to evolve. Earth is the only world Venus, our nearest neighbor planet, is similar in size we know of with sparkling blue to Earth, made of the same materials, and like Earth Earth’s magnetosphere deflects oceans and lush forests: harmful solar radiation, protecting and Mars it inhabits the same just-right planetary not only delicate and a perfect home. Now it’s up to neighborhood, not too hot and not too cold, called the electronic equipment, but also the us to sustain it. atmosphere necessary for life itself. Missions ROSETTA DESTINATION: Comet 67P Unlike the distant stars, the solar system is our cosmic neigh- WHEN: 2004–2016 borhood, so when we want to know more about its worlds, we PURPOSE: can go take a look. If a world is inconveniently far to visit in To follow, orbit, and land on a comet person, we can still send robots as extensions of ourselves. ACCOMPLISHMENTS: After a 10- journey through the solar system, Rosetta arrived at comet 67P, which it orbited, studying the comet’s environment and nucleus. It sent a to the surface, which tested for organic compounds, before Rosetta crashed into the comet itself two years later. Around the comet the mission found large amounts DESTINATION: The Moon of oxygen gas that was the product of ice from the comet interacting WHEN: 1971 with solar radiation. It measured the isotopic composition of the water WHO: , Alfred Worden, there, which turns out to be quite different from that of water on Earth, suggesting that our planet’s water did not arrive here on comets from the Kuiper Belt like 67P. PURPOSE: To explore the surface of the Moon and to bring back samples GALILEO ACCOMPLISHMENTS: The astronauts sampled three different kinds of DESTINATION: Asteroid Gaspra, Comet Shoemaker-Levy 9, lunar structure: the Apennine Front, and Jupiter produced by a collision between the Moon and a large object; horizontal WHEN: lava flows in an impact basin; and a ray of ejecta from a geologically 1989–2003 recent crater. One sample, later named “ Rock,” turned out to PURPOSE: To learn about Jupiter and its moons be 4 billion years old—the oldest Moon rock found until then. ACCOMPLISHMENTS: Among its many discoveries, Galileo observed an electric field around Jupiter and vast on it; the temperature and CASSINI AND composition of volcanoes on its moon Io; an ocean of salty liquid water lying beneath the icy surface of its moon Europa; and a magnetic field DESTINATION: The Saturn system around its moon . Galileo also discovered a tiny moon orbiting WHEN: 1997–2017 an asteroid and observed a comet colliding with Jupiter’s atmosphere. PURPOSE: To learn about Saturn, its moons and rings, and the properties of gaseous planets ACCOMPLISHMENTS: From its orbit around Saturn, the Cassini space DESTINATION: Venus probe made an extensive survey of the planet, its moons, and its rings. It extended its mission twice, returning data and images for an extra WHEN: 1989–1994 nine years before plunging into Saturn’s atmosphere to its planned PURPOSE: To take high-resolution images of the surface of Venus, destruction in 2017. Among its many discoveries were the exact length and to study the planet’s , geology, and gravity of a on Saturn (10 , 33 minutes, and 38 seconds) and the ACCOMPLISHMENTS: During an extended mission of 243 days and more age of its rings (a mere 10 to 100 million years). Cassini carried the than 15,000 orbits, Magellan used cloud-piercing radar to map 83.7 Huygens probe that touched down on a world in the outer solar system. percent of the planet’s hitherto hidden surface. Its high-resolution On Titan, Huygens discovered and of methane and dunes images showed evidence of volcanic action, tectonic movement, lava made of particles of water ice. channels, and pancake-shaped domes.

VOYAGER 1 AND 2 MARS ORBITERS DESTINATION: Jupiter, Saturn, and interstellar space AND ROVERS WHEN: Launched 1977; ongoing DESTINATION: Mars PURPOSE: To learn about the Jupiter system, the Saturn system, and the WHEN: 1997–ongoing outer reaches of the solar system, and to carry messages beyond our solar system PURPOSE: To explore the surface of Mars ACCOMPLISHMENTS: Flying by Jupiter, Voyager 1 discovered a thin ring ACCOMPLISHMENTS: Little explored areas near Ares Vallis, its around the planet as well as two new moons; flying by Saturn, it landing site, discovering that water floods had shaped the terrain. discovered new moons and shed on the structure of Saturn’s and Opportunity found further evidence of water. has rings. flew by all four outer planets. Crossing into interstellar been searching for evidence that Mars could have supported life, and has space, both measured the interstellar environment. discovered organic materials—building blocks of life—in rocks. COME PREPARED CHECKLIST GLOSSARY Plan your visit. For information about asteroid: a small, rocky object that orbits the Sun; most are reservations, transportation, and lunchrooms, confined to the asteroid belt visit comet: a “dirty snowball” of frozen gases, rock, and ice that Read the Essential Questions in this guide to see orbits the Sun how themes in the space show connect to your interstellar: between the stars of our , beyond the curriculum. Identify the key points that you’d like solar system your students to learn. moon: a natural object that orbits a planet or asteroid Review the Synopsis for an advance look at what you and your class will be watching. planet: an object that orbits the Sun, is massive enough to have become spherical, is not a moon, and has removed small Download student activities objects from the area around its orbit, called its orbital zone; at a has not removed all objects from its orbital Designed for use before, during, and after your visit, zone, but it meets all the other criteria for a planet these activities on themes that correlate to the standards. CONNECTIONS TO OTHER HALLS ARRIVAL ARTHUR HALL OF Students can get close to meteorites and Please plan to arrive at the space show boarding look for clues about how our solar system area, located on the 1st floor of the Rose Center, formed and evolved. They can find out 15 minutes before the show starts. about sample-return missions to other worlds in the Building Planets section.

CULLMAN HALL OF THE UNIVERSE CORRELATION TO STANDARDS Students can visit the Planets Zone to A Framework for K-12 Education explore the variety of worlds. They can walk along the Cosmic Pathway to experience Scientific and Engineering Practices • Developing and the history of the universe and can using models • Planning and carrying out investigations the Scales of the Universe to understand • Analyzing and interpreting data the relative of different objects. Crosscutting Concepts • Patterns • Cause and effect • Scale, proportion, and quantity • Systems and system GOTTESMAN HALL OF models • Stability and change Students can examine an outstanding Disciplinary Core Ideas • PS2.A: Forces and Motion collection of geological specimens for a • PS2.B: Types of Interactions • ESS1.A: The Universe and close look at one planet: our own Earth. Its Stars • ESS1.B: Earth and the Solar System They’ll find sections on the Earth-Moon • ESS2.A: and Systems • ESS2.C: The system, , how Earth formed, Roles of Water in Earth’s Surface Processes and what makes Earth habitable.


Worlds Beyond Earth is dedicated to the memory of Charles Hayden Cover: All images courtesy of NASA. th Essential Questions: Solar system, © AMNH. in celebration of the 150 anniversary of his birth and made possible Synopsis: Moon and Io, courtesy of NASA; all other images, © AMNH. by the generous support of the Charles Hayden Foundation. Missions: , courtesy of NASA; Astronaut icon, Esteban Sandoval/ Noun Project; Satelite icon, Amiryshakiel/ Noun Project; Rover icon, Noun Project; Lander icon, Ben Davis/Noun Project. Proudly sponsored by: Back: All images © AMNH.

Generously sponsored in loving memory of Gilroy.

© 2020 American Museum of Natural History. All rights reserved.