The Oort cloud, our solar system's theoretical icy shell

The Oort Cloud is a shell of icy objects surrounding the solar system, from which many comets originate

Proposed in 1950 by Jan Oort, the theoretical structure is believed to be the origin of comets with periods of more than 200 years. Leftover planetary building blocks from the early solar system formed the Oort Cloud after being flung out by the gravity of planets like Jupiter.

Comets serve as time capsules of the early solar system

The frozen objects preserve the molecular composition of the solar system's formation, dating back about 4.6 billion years. Spectral analysis of the gases they release when heated upon approaching the sun in eccentric orbits reveals this composition and helps assess solar system formation models.

The composition of comets earned them the nickname 'dirty snowballs'

The icy relics of the solar system are composed of rock, gravel, dust, and frozen molecules, such as carbon dioxide, carbon monoxide, methane, ammonia, and water. Once close to the sun, these compounds sublimate into gases, creating a fuzzy cloud that earned the comets another nickname in history: hairy stars.

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.

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.

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.

Comets can be categorized based on their orbital period

Short-period comets orbit around the sun once every 200 years or less and are made up of Jupiter-family (less than 20 years) and Halley-type (between 20 and 200 years) comet subgroups. Long-period comets have orbits greater than 200 years, while exocomets originate in solar systems outside our own.

How scientists study Earth's geocorona, the farthest portion of the planet's exosphere

Seen via ultraviolet radiation scattered by neutral hydrogen in the region, observations by the ESA/NASA Solar and Heliospheric Observatory indicate that the geocorona extends roughly 50 times Earth's diameter above its surface. At this distance, the geocorona extends beyond the Moon's orbit.

Find which comets are currently visible in the night sky

Incorporating sightings reported in the Comet Observation database and information from NASA's Jet Propulsion Laboratory, this list provides a finder chart, star map, tracker, simulated orbit, and key properties for each comet, all viewable based on a user's input position on Earth.

Our solar system is currently traveling through a 'dark matter hurricane'

The phenomenon refers to a stream of cosmic debris, including stars and dark matter, leftover from a small galaxy that passed too close to the Milky Way and was torn apart. There are over 30 such streams known in our galaxy, and the stream intersecting the solar system is predicted to continue to do so for millions of years.

Hypotheses on the origins of Earth's water, from comets and asteroids to magma oceans

Before Earth's atmosphere formed, any liquid water would have boiled off, preventing the accumulation of water early on to create today's oceans. Planetary scientists continue to debate whether this water was delivered later from comet or asteroid collisions or via reactions between iron oxide in Earth's molten surface and hydrogen gas from the planetary nebula.

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.

Read about the dangerous comet behind the Perseids meteor shower

Every summer, Earth passes through the debris trail of the Swift-Tuttle comet, producing the spectacle of the Perseids meteor shower. The phenomenon is a glorious opportunity for amateur stargazers, but astronomers have long noted the comet's orbit...

Asteroids are the rocky remains of the solar system's formation

These celestial bodies were not integrated into the precursors of planets about 4.6 billion years ago and instead continue to orbit the sun, primarily within a band between Mars and Jupiter—the asteroid belt.

Ceres—the largest object in the asteroid belt—may have once harbored a muddy ocean

NASA's Dawn mission revealed Ceres' surface composition, which contains salts, water ice, and organic material. Ceres' ocean likely froze over entirely in the past, when the presence of water may have allowed life to exist.

Cloud 9 is a dark-matter-dominated failed galaxy

Identified in 2023, the starless, gas-rich object is the first of its kind seen by astronomers and provides a window into the early stages of galactic formation without observations relying on visible matter as a proxy. The existence of such REHLICs, or Reionization-Limited-H I Clouds, was predicted by cold dark matter cosmological models.

A real-time 3D-explorer of the solar system

NASA's Eyes on the Solar System allows you to track all kinds of objects in space in real time, from observatories like the James Webb Telescope to all manner of comets and asteroids. Zoom in and out, read up on space missions, and see the solar system from a totally new angle with this incredible interactive site. Jump in here.

Explore the known asteroids, comets, and spacecraft involved in asteroid studies within our solar system with 'Eyes on Asteroids,' a 3D visualization from NASA.

The most mysterious (known) star in the universe

Something massive, with roughly 1,000 times the area of Earth, is blocking the light coming from a distant star known as KIC 8462852. One of astronomers' more intriguing theories: Alien technology. Discovered via NASA's Kepler space telescope and a...

About 20% of asteroids are metal worlds similar to Earth's core

The biggest of these (that we know of) is 16 Psyche. Measuring 140 miles across, its iron and nickel content is potentially worth 10,000 quadrillion dollars. NASA’s mission to Psyche—reaching the asteroid in 2029—will study it to learn about its formation.

Most of the observable universe's volume consists of voids and supervoids—enormous regions of space with little to no galaxies, stars, or light.

As of 2025, scientific evidence strongly supports 3I/ATLAS being a comet

Claims of alien technology would require the celestial object to transmit measurable technological signals, which were not detected by the world's largest fully steerable radio telescope. Previous telescope observations identified that 3I/ATLAS's chemical composition, structure, and orbital characteristics are consistent with those of an interstellar comet.

The Southern Ocean's powerful circular current isolates organisms in its environment

The spiralling current churns up nutrients across the frigid waters, leading to the evolution of fantastical organisms, including century-old starfish and colossal squid, and unique adaptations, including the icefish's clear blood and organic antifreeze, over the past 30 million years.

Explore a gallery of O'Neill cylinder space settlements

The structures consist of a pair of cylinders with a total enclosed land area of 500 square miles and can house several million people. Each is approximately 20 miles long, 4 miles in diameter, and contains three mirrors that open and close to form a day-night cycle inside.

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

Light echoes are expanding shells of reflected starlight

Just as sound waves reveal the location of obstacles by reflecting off them, pulses of light emitted by stars illuminate rings of interstellar dust, giving the appearance of ejected material as the light travels outward.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Clouds' subtle climate effects require significant computational power to simulate

Responsible for reflecting sunlight and preventing thermal energy from entering the Earth system while also trapping energy and keeping it in the system, clouds are understood to substantially influence climate predictions. Because even supercomputers struggle to accurately model their dynamic behavior, researchers have used AI to indirectly incorporate clouds into climate models.

Who owns outer space?

More and more material ends up in Earth's orbit, posing threats to orbiting space stations and satellites. A 1960s treaty technically made space the common property of humankind, but with increasing chances of conflict in space, things can seem anarchic. This video breaks down the brewing tensions in space.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Planeterrellas create artificial auroras that mimic the atmospheric displays of light by setting up an electric field between two metal balls in a jar filled with a small amount of air.

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

The first image of a black hole was captured by creating an Earth-sized virtual observatory from a network of eight radio telescopes.

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

SpaceX's S-1 or 'prospectus' revealed many previously unknown details about the company, including its unprofitability despite doing $18.7B in revenue in 2025, exactly how many voting shares Elon Musk will have in the company (roughly 85%), and more.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

The name 'Silicon Valley' arose from the founding of Shockley Semiconductor Laboratory in Fairchild Semiconductor in 1956-57, founded near Stanford University in Palo Alto

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

Waves off the coast of Nazaré, Portugal, can reach over 100 feet and are caused by the area's deep underwater canyon geography

Georgia O'Keeffe's flower paintings are often assumed to be sexual, though the artist claimed she was simply interested in highlighting the beauty of flowers that most people neglect

Comedy legend Catherine O'Hara, star of 'Schitt's Creek' and 'Home Alone,' quit 'Saturday Night Live' after just one week to return to her old job.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

In 1963, a basement renovation in Turkey revealed a passageway to a hidden, multilevel underground city that once housed as many as 20,000 people

Search a massive database of over 4 decades of clues from the TV quiz show 'Jeopardy!'

The term 'algorithm' originated from the Latinized name of al-Khwārizmī, a 9th-century mathematician whose works introduced Arabic numerals and the decimal-based numeral system to Europe and whose treatise 'Al-Jabr' gave algebra its name.