Observations from Hubble contributed to Pluto's demotion from planetary status

Officially discovered in 1930, Pluto was reclassified as a dwarf planet in 2006 after the International Astronomical Union revised its definition of a planet, requiring that its orbit be free of significant cosmic debris.

Gaming out how our solar system might catch a new planet

If Pluto's downgraded status to a dwarf planet has got you down, consider this: Scientists think there's a chance our solar system could catch a new planet. The first ever observed so-called Interstellar Object was reported in 2017, a reddish, cigar-shaped rock astronomers named Oumuamua. Although it left in 2022, scientists believe an object with the right mass and trajectory might take a seat at the planetary table. Learn how it would work here.

Categorization of celestial objects has changed over history

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.

There may be over one trillion comets in the Kuiper Belt

Named after Gerard Kuiper, who theorized the existence of a band of icy objects beyond Neptune in 1951, direct evidence for its existence did not arrive until 1992, when the first trans-Neptunian object, besides Pluto and its moon Charon, was observed. Comets with periods of less than 200 years originate from this belt.

What is the Kuiper Belt?

The Kuiper Belt is a collection of extraterrestrial objects that might've been a planet if it hadn't been for Neptune. Still, the belt is a fascinating collection of dwarf planets, rocks, ice, and comets. Extending beyond Neptune's orbit, the Kuiper Belt provides an endless selection of interesting objects and anomalies for astronomers to explore.

The Hubble Space Telescope made discoveries within our solar system and across the universe

The observatory helped confirm the presence of water on Jupiter's moon Europa, and uncovered seasonal variations on planets like Uranus. It also observed exoplanets and gravitational lensing, proved the existence of supermassive black holes at the centers of galaxies, and detected the accelerated expansion of the universe.

A return to Uranus

There's been only one mission to Uranus before—Voyager 2 passed by the ice giant in 1986 before heading off into interstellar space. NASA's recent planned itinerary for space missions lists Uranus as the highest priority over the next decade. The seventh planet is 20 times as far from the sun as Earth, and researchers say its study will shed light on how the outer half of the Solar System formed.

Since 1989, storms resembling Jupiter's Great Red Spot have been observed on Neptune, but darker and lasting no more than a few years.

A look at Uranus, our distant icy cousin

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.

While published images have suggested that Neptune is much bluer than Uranus, the two ice giants are a similarly pale shade of greenish-blue.

The majority of exoplanets—planets outside the solar system—have been discovered through mini-eclipses created when they pass in front of their host star and block some of its light from reaching Earth.

Astronomers inferred Neptune's existence through mathematics while attempting to explain irregularities in Uranus' orbit, but Neptune had been directly observed 234 years earlier by Galileo.

Although no such planet exists in our solar system, the most common subtype of exoplanet in the galaxy is the sub-Neptune world, which is larger than Earth but smaller than the ice giants.

Explore a 3D interactive visualization of Neptune, the smallest of the solar system's giant planets.

In 1994, fragments of comet Shoemaker-Levy 9 crashed into Jupiter

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.

View galleries of images taken by the Voyager spacecraft, including close-ups of Uranus, Jupiter's Great Red Spot, Saturn's ring system, and Neptune's Great Dark Spot.

Hubble overcame early optical failure and became a critical scientific instrument

The flaw in Hubble's mirror was smaller than the width of a human hair, but fixing it required a space mission as complex as a Hollywood rescue story—with astronauts installing corrective optics like contact lenses for a giant eye in the sky.

View galleries of images taken by the Hubble Space Telescope

With more than 1.7 million observations made since 1990, the Hubble Space Telescope has captured images of space missions, planets, stellar nurseries, interstellar comets, star clusters, galaxies, and more. This search tool allows users to sort and filter across these celestial objects to explore over 35 years of Hubble's astrophotography.

Asteroids are often unobserved until they are days away from Earth

Even those large enough to cause local or regional damage are too small, dim, and far away to be observed readily from cosmological distances. New tools, like NASA's NEO Surveyor telescope, aim to address gaps in detection systems.

Brown dwarfs are nicknamed 'failed stars' because, while much more massive than planets, they lack sufficient mass to initiate nuclear fusion in their cores and become stars.

Hot Jupiters are giant planets that orbit very close to their host star

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.

Hubble revealed that planet-forming disks are common around young stars

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.

Ice found in another star system for the first time

NASA's James Webb Space Telescope has discovered frozen water in a young star system. The ice is similar to that found in Kuiper Belt objects in our solar system, and provides insights into planetary formation processes.

Asteroids were discovered by 18th-century planet hunters

While looking for a planet between Mars and Jupiter to coincide with an apparent mathematical pattern in the distances of known planets from the sun, a group calling themselves the "Celestial Police" discovered multiple objects that fell into a new classification.

Atmospheric drag is causing the Hubble Space Telescope to drift toward Earth slowly

Without interventions to boost the observatory to a higher orbit, Hubble is expected to fall to Earth's surface in the mid-2030s. In the meantime, the telescope is expected to continue to be productive by shifting its mode of operation to rely on a single gyroscope, down from three.

James Webb telescope shows new views of Uranus

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.

An exoplanet detection method involves measuring a host star's auroras

Astronomers have reported indirectly identifying a planet by observing its debris interacting with the magnetic field of the star it orbits. The interaction is a larger-scale version of the auroras observed on Jupiter, which are produced when material released by its moon, Io, interacts with the gas giant's magnetic field.

Visualize the size of countries on the sun and other planets

Pluto is roughly the size of Australia. What about Namibia and Nepal? How small would North America appear on the sun? Compare the relative size of continents and countries with this easy-to-use interactive.

As of 2026, 14 of Neptune's 16 moons have been named for mythological figures, with Triton, the largest of them, orbiting backward, or in retrograde.

An imperfection 1/50th the width of a human hair blurred Hubble's initial images

Not all parts of the space telescope's primary mirror focused incoming light to the same location, an effect known as spherical aberration. Because Hubble was designed to reside in low Earth orbit and be serviced by astronauts, service missions were deployed in the years after its launch to conduct repairs.

Play an interactive game to explore and learn about Hubble images

Aboard the fictional USS Hubble, users can choose their own adventure to investigate the solar system, our galaxy, and the universe beyond. Each option directs users to a real image accompanied by relevant information and additional media elements, such as a time-lapse of the moon Phobos orbiting Mars.

The names of comets can change based on subsequent observations

The International Astronomical Union's coded naming system uses the first letter to indicate a comet's category, which can change over time. "D" represents comets that have been lost or broken up, while "A" applies to former comets that are now asteroids or dwarf planets.

Fly through the deepest image of space ever taken by the Hubble Space Telescope

Taken over 11 days between 2003 and 2004, when the space telescope was aimed at a seemingly empty patch of the sky, the Hubble Ultra-Deep Field revealed about 10,000 sources of light, most of which are entire galaxies. This visualization expands the 2D image into a 3D view spanning 12 billion years.

Jupiter’s size forced the creation of modified planetary formation models

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.

New ways of seeing the cosmos have redrawn the map of human identity

From Galileo’s crude spyglass to the James Webb Space Telescope, each technological leap has expanded our observational reach and redefined philosophical and moral conceptions of our place in the universe. Identifying signs of life through the study of exoplanet atmospheres would represent the next great revolution.

In 2025, astronomers confirmed that Neptune has auroras, which were observed at mid-latitudes because its magnetic field is tilted 47 degrees from its rotation axis.

Images of Jupiter in unprecedented detail

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 breakthrough that changed our perception of the universe

In the 1920s, the Hooker Telescope helped Edwin Hubble make a discovery that forever changed how we see the universe. Building on the work of astronomers like Henrietta Leavitt and Harlow Shapley, Hubble used the telescope to prove that galaxies exist beyond the Milky Way—revealing a vast and expanding universe.

Watch a firsthand account of Hubble's first service mission to repair its faulty mirror

Hubble senior project scientist David Leckrone recalls initial public ridicule over the microscopic manufacturing error that put NASA's reputation at stake. In this behind-the-scenes interview, he breaks down the innovative fix deployed by space shuttle astronauts during Hubble's first servicing mission.

Evidence for a ninth planet in our solar system

Is there a massive ninth planet on the edge of our solar system? Many of our solar system's most distant objects tend to swing out in one direction, hinting at evidence for a previously unknown ninth planet potentially larger than Earth. This theoretical planet's orbital period is estimated to be roughly 20,000 years, revolving around the sun at a distance of 60 billion miles. Experts break down the evidence in this quick video.

Galileo's Jupiter discovery shattered Earth-centered universe beliefs

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.

Voyager 1 and 2 are the only spacecraft to reach and study interstellar space

The Voyager Interstellar Mission extended beyond the original planetary flybys to explore the solar system's edge and beyond. Voyager 1 and 2 crossed the heliosheath—the boundary between the solar wind and the interstellar medium—in 2012 and 2018, respectively.

View a gallery of photographs of Neptune taken during NASA missions.

When it formed 4.5 billion years ago, Jupiter was twice its current size

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.

View the Helix Nebula in different wavelengths of light to identify the structures surrounding the dying star, including shells of gas and dusty filaments.

Space telescope development was driven by a desire to bypass Earth's atmosphere

The most important figure in the effort to create what would become the Hubble Space Telescope was Lyman Spitzer, who first proposed a telescope in orbit in 1946. The nearly 50-year endeavor led to space-based observatories, which are not limited by Earth's atmosphere absorbing or distorting most wavelengths of light.

The European Space Agency placed a lander on the surface of a comet in 2014

Launched in 2004, the Rosetta spacecraft performed three flybys of Earth and one of Mars as gravitational slingshots to gain the necessary velocity to successfully place the Philae lander module on comet 67P/Churyumov-Gerasimenko. Philae achieved a soft landing only after bouncing twice from failed deployments of its anchoring harpoons.

According to the Grand Tack model, Saturn stopped Jupiter's inward migration

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.

View a gallery of photographs of Uranus taken during NASA missions.

Despite being called 'ice giants,' Uranus and Neptune do not contain plentiful frozen water—the term refers to their abundance of elements heavier than hydrogen and helium.