A Field Guide to the Planets
Sabine Stanley, Ph.D., is a Bloomberg Distinguished Professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins University. She received a HBSc degree in Physics and Astronomy from the University of Toronto and then completed M.A. and Ph.D. degrees in Geophysics from Harvard University. Prior to joining Johns Hopkins, Professor Stanley was a postdoctoral researcher at the Massachusetts Institute of Technology and a professor at the University of Toronto. At Johns Hopkins, she also holds appointments in the Henry A. Rowland Department of Physics and Astronomy, the Applied Physics Laboratory’s Space Exploration Sector, and the Hopkins Extreme Materials Institute.
Professor Stanley has received several honors and awards for both her research and teaching. Her research honors include the American Geophysical Union’s William Gilbert Award for her major theoretical contributions to the study of planetary magnetism, and her teaching awards include the Dean’s Outstanding Teaching Award from the University of Toronto.
Professor Stanley’s research includes studies of the magnetic fields of Earth, Mercury, Mars, Saturn, Uranus, Neptune, and exoplanets. She is also a coinvestigator on NASA’s Mars InSight mission. In addition to her research work, Professor Stanley has served as the editor of the Journal of Geophysical Research: Planets and has chaired the Women in Physics Canada Conference.
01: How the Solar System Family Is Organized
Since 1962, robots have been exploring our solar system to help answer this most important question: Who are we? With fascinating data and images now in hand, explore this family album overview of our planets, dwarf planets, moons, asteroids, Kuiper Belt objects, and long-period comets—and fly through some of our solar system’s most unique features!
02: Mercury, the Extreme Little Planet
Mercury is a planet of many solar system extremes—smallest planet, closest to the Sun, shortest year, most elliptical orbit, smallest axis tilt, and largest fraction of iron. Learn how these characteristics and others have resulted in a planet where the Sun sometimes moves backwards across the sky, where water ice has been found at the poles, and a magnetic field that offers more protection than Mars’.
03: Venus, the Veiled Greenhouse Planet
While the Venusian carbon dioxide atmosphere has resulted in a runaway greenhouse effect and the hottest surface temperature in the solar system, the Earth and Venus actually contain about the same amount of carbon. Explore the forces that resulted in the extreme atmospheric differences between these two otherwise-similar planets.
04: Earth: How Plate Tectonics Sets Up Life
Given the striking similarities between the four terrestrial planets, why is Earth the only one teeming with life? Proposed as a bold theory less than 70 years ago, could plate tectonics be a main driver of life on Earth? Explore the fascinating movement of our planet’s surface and the many ways in which a geologically-active Earth has sustained our biologically-active planet.
05: Orbiting Earth: Up through the Atmosphere
Compared to Venus or the giant planets, Earth has a relatively thin atmosphere. And yet, without this single, fragile layer, life would not have evolved and thrived. Discover the unique properties of each atmospheric layer— and encounter specific ways we’ve explored each layer as a springboard to exploring the rest of our solar system.
06: Exploring the Earth-Moon System
Our Moon, formed from the Earth about 4.5 billion years ago, is by far the largest moon in the solar system relative to its planet’s size. Explore the many ways in which this uniquely coupled system affects the tides on Earth and on the Moon, our rotation and revolution, the process of tidal locking, and even the planetary stability that has allowed for the development of life on Earth.
07: Humans on the Moon: A Never-Ending Story
Even before the invention of telescopes, humans were familiar with the dark lunar highlands and bright maria on the Moon’s surface. But now, with knowledge gained from both robotic and crewed missions, you can also explore fascinating and complex lunar swirls, sinuous rilles, and the lava tubes that hold promise as ideal locations for future lunar bases.
08: Exploring Mars from Space and the Ground
Humanity’s fascination with Mars is never-ending—from the days when we posited a planet covered in straight-line canals and vegetation to NASA’s current Moon to Mars program. Learn how the intriguing similarities and differences between Earth and Mars have resulted in Mars’ planet-wide dust storms, migrating polar ice caps, and 3.9-billion-year-old impact craters.
09: Water on Mars and Prospects for Life
Recent robotic exploration provides tantalizing evidence: Mars’ barren landscape could have been much more Earth-like in the past. With warmer temperatures, a thicker atmosphere, and the possibility of water oceans and tsunamis, could Mars have an Earth sibling that supported life? Learn about the thrilling recent discoveries that will guide future exploration and scientific inquiry on the red planet.
10: Near-Earth Asteroids and the Asteroid Belt
Fans of science fiction, or the natural history of our planet, know that a collision with an asteroid has the potential to obliterate civilization as we know it. With 20,000 asteroids identified in near-Earth orbit, how can collision be avoided? Learn why these rocky bodies, and those in the Asteroid Belt between Mars and Jupiter, never accreted into planets and how we might harness their resources for future space travel.
11: Mighty Jupiter, The Ruling Gas Giant
Does Jupiter have a greater similarity to the Earth or to the Sun? It depends on which characteristics you consider. Explore the many ways in which Jupiter is unique among the planets and consider what our solar system would be like without it. This gas giant might seem too far away to make a difference in your daily life, but without Jupiter, life on Earth might never have had a chance.
12: Jupiter’s Planetlike System of Moons
Today we know of 79 Jovian moons—the spherical Io, Europa, Ganymede, and Callisto, and dozens of other smaller, odd-shaped satellites. Learn why Jupiter’s gravitational forces plus the orbital resonance of the three interior moons make these some of the most promising places to search for extraterrestrial life—and why scientists believe the Jovian system once included generations of other moons, now gone.
13: Saturn and the Rings: Gravity’s Masterpiece
With its exquisitely complex ring system, NASA describes Saturn as the “jewel of our solar system.” Learn what decades of exploration have revealed about the origin and morphology of these ever-changing icy rings and how they interact with Saturn’s closest moons. From the rings to propeller moonlets, a massive hexagonal polar storm, and the giant vortex, our fascination with Saturn never ends!
14: Saturn’s Moons: Titan to Enceladus
With a system of 62 moons located in and far beyond its ring system, Saturn has outer moons that are some of the most fascinating worlds in the solar system. Learn why Titan and Enceladus hold such promise in our search for extraterrestrial life—from global subsurface oceans of water on both moons, to Titan’s Earth-like surface and organic molecules in its atmosphere. It’s no wonder that NASA has announced its Dragonfly mission to Titan, scheduled to launch in 2026.
15: Uranus: A Water World on Its Side
What a fascinating world Voyager 2 revealed in 1986 during its short flyby of Uranus! Learn why Uranus seems to orbit “on its side” surrounded by a delicate system of 13 rings and 27 moons, how we discovered its multi-polar magnetic field, and why scientists think Uranus might contain an ocean made of liquid diamond, with floating chunks of solid “diamond-bergs!”
16: Neptune: Windy with the Wildest Moon
Neptune is the coldest, but also the stormiest, planet in the solar system and the only planet that cannot be seen with the naked eye from Earth. Its moon Triton is the only spherical moon in the solar system that’s an irregular satellite that orbits opposite the direction of all the planets. Learn how tidal forces are not only changing that orbit, but also causing geologic activity on its surface—a surface that contains organic compounds.
17: Pluto and Charon: The Binary Worlds
Although Pluto is no longer categorized as a planet, Pluto the “dwarf planet” and its “moon” Charon are considered the closest thing in the solar system to a binary planet system. Explore the fascinating revelations from the New Horizons mission, including Pluto’s glacial flows, floating mountains, extreme seasons, unexpectedly complex atmosphere, and a surface that appears to be dusted in complex organic molecules.
18: Comets, the Kuiper Belt, and the Oort Cloud
Learn why scientists believe comets—the “leftovers” of planet formation in the outer solar system—could be partially responsible for the flourishing of life on Earth, bringing both water and organic material to the inner solar system. And explore the more distant Oort Cloud, where billions of cometary objects orbit at the outermost boundary of the solar system.
19: How Our Sun Defines Our Solar System
Fly through the corona of what is by far the largest, most massive, and most significant object in the solar system: the Sun. In fact, at 99.9 percent of the total mass of the system, you could say the Sun IS the solar system. With its gravity, heat, light, magnetic fields, and plasma storms, learn how the Sun affects every object in the system—and how we are in a race to learn more about coronal mass ejections before one destroys trillions of dollar’s worth of electronics on Earth.
20: A Solar System Time Machine and Meteorites
Today we see an orderly solar system with planets staying in their orbits around the sun, moons staying in their orbits around the planets, and comets coming and going in predictable fashion. But how did it all start? Learn how a molecular cloud gave rise to a proto-planetary disk in which our solar system developed step by step across time and space—and is developing still.
21: What the Biggest Exoplanets Reveal
Planets orbiting other stars used to be purely in the realm of science fiction. How did we begin discovering them by the thousands? Learn about the methods scientists have used to discover so many exoplanets so quickly. From “hot Jupiters” to “mini-Neptunes” to planets whose clouds rain molten glass, these discoveries demonstrate that ours is not the only type of planetary system possible!
22: Closing in on Earthlike Exoplanets
Beginning in 2009, the Kepler Space Telescope began staring intensively at a single patch of sky, about one quarter of one percent of the sky. After staring for four years straight, scientists had identified about 1,200 new planets. Sift through the Kepler discoveries for planets with a variety of Earth-like features, including presence in a “habitable” zone, and learn why billions of Earthlike planets are estimated to exist in our galaxy.
23: Planets Migrated in Our Early Solar System!
The surprising detection of gas giant planets orbiting extremely close to other stars has led to the realization that planets can form in one part of a stellar system and then migrate to another part. Did that happen in our own solar system? Learn about the evidence for a “Late Heavy Bombardment” on the Moon, Mars, and Mercury, how migration of one or more giant planets could have caused it, and how such migration could have affected the solar system we see today.
24: Human Futures in the Solar System
What are the next big ideas that will help us ask and answer the next big questions? Consider the fascinating future technologies of centimeter-sized satellites propelled by laser photons, liquid mirror telescopes on the Moon, a magnetic shield large enough to help terraform Mars, and more. Nourish your imagination, and experience the inspiration of space exploration!