Janus is the Roman god of transitions and the nickname for a 'two-faced' white dwarf, with hydrogen and helium in opposite atmospheres.

In 46 BCE, Julius Caesar introduced the Julian calendar, which established Jan. 1 as the beginning of the new year. The month was named after Janus, the Roman god of transitions, who had two faces—one looking back at the past, the other forward to the future. While the Babylonians also made promises as part of their celebration of the new year, the Roman tradition became more focused on looking backwards to plan for the coming year.

The continent-sized cyclones at Jupiter’s poles generate strong winds and ammonia-laden storms. The spacecraft has also collected data on Jupiter’s unique magnetic field, which resembles a blend of Earth’s and Uranus/Neptune's.

Discovered in 1995, hot Jupiters are a class of exoplanets—planets orbiting stars other than the sun—with size and mass similar to Jupiter. They are most commonly found orbiting metal-rich stars and have become essential for testing theories of planetary system formation.

This state of hydrogen has metallic properties, including conductivity, which powers these planets' magnetic fields. First theorized in the 1930s, its existence was confirmed through indirect evidence before being created in a Harvard lab in 2017.

NASA introduces you to the fifth planet from the sun, the gas giant Jupiter. When it comes to our solar system, Jupiter is the biggest kid on the block. Named after the king of the Ancient Roman gods, Jupiter is a planet of storms and chaos, most famously in its Great Red Spot, a hurricane larger than the earth itself.

Since solar winds remove gases from protoplanetary disks within millions of years of a star’s birth, models needed to provide a mechanism to jump-start Jupiter’s formation and growth. The solution involved incorporating pebbles of matter into the disk.

As seen from space, Jupiter’s most striking feature is an anticyclone 30% larger than Earth, with winds twice the speed of Category 5 hurricanes. The descent into the storm brings enough pressure to strip atoms of their electrons.

The auroras flicker faster and brighter than those seen on Earth. This contrasts with earlier predictions that the lights would fade slowly over several minutes, providing insights into how Jupiter's magnetosphere operates.

Despite decreasing in size, the anticyclone remains larger than Earth, rotating with winds up to 933 km/h. Its longevity may be because it is trapped between two opposite-flowing jet streams, which act like two conveyor belts.

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.

On worlds like WASP 76b, which orbits its host star approximately 3% the Earth-sun distance, temperatures on its day side can vaporize iron. Winds more than 14 times the speed of sound blow this material to its night side, where it condenses and falls as liquid metal.

January is named after two-faced Janus, February stems from a festival known as Februa, March comes from the god of war, Mars, and so on. Learn the origins and see ancient statues or art for the inspiration for each name of the month.

Jupiter has never seemed closer and clearer than it does in these images gathered by the James Webb Telescope. Behold beautiful auroras, hazy clouds, and more. This may not be the classic image of Jupiter (and its stormy Great Red Spot) you're used to, but it tells scientist, and us, more about the largest planet in our solar system.

The innermost and third-largest of Jupiter’s four Galilean moons, Io’s volcanic activity is driven by tidal heating from Jupiter’s gravitational pull. Its atmosphere is very thin and primarily composed of sulfur dioxide, and its volcanic eruptions can exceed 1,000°C.

Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune are named after the messenger of the gods, the goddess of love, the god of war, the king of gods, the god of agriculture, the god of the sky, and the god of the sea, respectively. "Earth" comes from Old English and Germanic words meaning "ground."

NASA provides a profile of the seventh planet from the sun and the third largest—Uranus. More than just a punchline, the planet is cold, windy, and utterly inhospitable. It's also a lovely blue-green, due to the large amounts of methane it contains, with faint rings and two dozen moons. Learn more about this not-so-gentle gas giant.

The nebular hypothesis proposes that a swirling cloud of gas and dust coalesced into a dense center, forming a star amid nuclear fusion. Lighter elements were blown far from the star while heavier elements remained nearby, serving as primary materials for terrestrial and jovian planets, respectively.

Following in the footsteps of the Neptune image released in 2022, NASA’s James Webb Space Telescope has taken a stunning image of the solar system’s other ice giant, the planet Uranus. The new image features dramatic rings as well as bright features in the planet’s atmosphere.

Unlike Earth-like planets, hycean worlds with thick hydrogen atmospheres and deep oceans could allow biosignature gases like methyl halides to accumulate in detectable levels. These gases, linked to microbial life on Earth, are easier for the James Webb Space Telescope to identify than traditional markers like oxygen or methane.

One theory of Jupiter’s formation involves the planet spiraling inwards from the asteroid belt, gathering material and disrupting the initial formation of terrestrial planets. Saturn’s gravitational pull would then reverse its course.

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.

Jupiter's moons were first discovered on Jan. 7, 1610. They include Ganymede, the largest moon in the solar system and larger than Mercury, Io, the most volcanically active moon, and Europa, which has a saltwater ocean.

These stars maintain an atmosphere of hydrogen, helium, and carbon at approximately 2,000,000 degrees Celsius (3,600,000 degrees Fahrenheit), only a few thousandths of a millimeter thick, which envelops "mountains" about a millimeter high. Its interior consists of an inner and an outer crust surrounding inner and outer cores, all held together by enormous gravitational forces despite spinning multiple times a second.

Despite covering almost three-quarters of its surface, water only makes up about 0.12% of Earth's volume. Water in some of Jupiter's and Saturn's moons comprises a larger share of those celestial bodies and of the total water in the solar system. For example, Jupiter's moon Ganymede is believed to harbor almost nine times Earth's oceans beneath its icy shell.

Scientists from the University of Zurich and NCCR PlanetS proposed the mechanism after using computer modeling to replicate Jupiter’s formation to match its observed concentration of heavy elements. The work may help understand how Jupiter-like exoplanets exist near host stars.

The model suggests Jupiter migrated inward early in its formation and cleared debris from the inner orbits of terrestrial planets. Saturn's gravitational pull saved what was left of the inner solar system to form Mercury, Venus, Earth, and Mars.

Using the JunoCam, scientists have observed several of Jupiter's features, including cyclones, the Great Red Spot, and cloud bands and zones. The mission's effectiveness has resulted in its extension from July 2021 to September 2025.

Using a telescope inspired by Dutch designs, Galileo spotted four moons orbiting Jupiter in 1610, providing undeniable evidence against geocentrism and fueled support for the heliocentric model. Galileo’s original telescope design stretched 20 meters long—a feat of optical engineering for its time.

Primarily composed of visible matter, this celestial object would also contain a significant amount of dark matter that would annihilate with itself, converting its mass into energy. This energy would prevent the star from collapsing under its own gravity and from triggering nuclear fusion until its dark matter fuel was exhausted.

Despite its reputation as Earth’s cosmic shield, Jupiter’s gravity pulls more asteroids into Earth-crossing orbits. Simulations show that Earth experiences over three times more asteroid impacts because of Jupiter’s influence than if Jupiter didn’t exist.

Decades in the making, JWST is designed to study the universe in infrared light, allowing it to see through cosmic dust and observe ancient galaxies, star formation, and potentially life-supporting exoplanets. The Webb will orbit the sun at a stable point 1.5 million kilometers from Earth.