Stemming from the Greek word for "wanderers," planets have long captured humanity's attention as they moved across the sky against a backdrop of fixed stars. Planets are distinct from stars in that they have no internal source of radiation and typically orbit stars. While our solar system has eight planets, astronomers continue to discover more throughout the universe as technology advances. Find out more about your favorite or least familiar planet with our collection of the internet's best resources on planets.
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Its original size was deduced from the orbits of its moons, Amalthea and Thebe. The planet's magnetic field was also 50 times stronger than today, or 400 times stronger than Earth's.
Hubble captured the collisions, which created massive black impact sites visible from space. It represented the first time scientists could prepare for and observe an interplanetary collision in real time, allowing them to gather valuable information about Jupiter’s atmosphere.
In 2006, the International Astronomical Union formally defined a planet as an object in orbit around the sun with a nearly spherical shape and an orbital path clear of significant debris. Because Pluto shares its neighborhood with comets from the Kuiper Belt, it was reclassified as a dwarf planet.
After NASA’s Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, Carl Sagan used the image to reflect on humanity’s fragility and the responsibility to protect "the only world we’ve ever known."
Mercury deviates within 7 degrees of the ecliptic that marks the path of the sun, with the other planets varying from 3 degrees to approximately flat. Even an alignment within 1 degree between all eight planets is estimated to occur only once every 13.4 trillion years.
Since its discovery over 350 years ago, the anticyclonic storm—with a high-pressure center and flows opposite to the low-pressure system underneath it—has fascinated astronomers due to its size, which is larger than Earth's, and its prominent features, including winds that surpass 250 miles per hour.
One of Hubble’s early images captured 30 young star systems in the Orion region, each surrounded by material that looked like it was forming planets. These systems increased the number of data points scientists had to test planetary formation models.
Asteroids contributed to planet formation and carried water from the solar system's outer reaches toward the center. They were also early providers of the necessary elements and conditions for life to evolve on Earth.
Once classified as planets, Ceres and Vesta are now considered a dwarf planet and an asteroid, respectively. The discovery of many similarly sized objects led to the creation of the asteroid belt category.
The group was formed in 1800 to find a planet some astronomers believed existed between Mars and Jupiter. Prior to their disbanding in 1815, the group instead discovered Vesta, Juno, and other objects they would call asteroids.
From roughly 60 miles above the Earth's surface to farther than light has traveled during the entire age of the universe, space has captured human imagination for millennia. Explore the final frontier with the best resources curated from across the internet.