If the moon were less than one-twelfth its current distance from Earth, the planet's tidal forces would overcome the moon's internal gravity, tearing it apart and forming a ring of debris.

While the leading hypothesis for the moon's origin involves a Mars-sized object called Theia striking ancient Earth and forming from the resulting debris, it cannot explain why lunar isotope abundances match Earth.

The moon is slowly contracting as its interior cools, creating moonquakes and lobate scarps—cliffs that are steep on one side and gently sloping on the other—as the moon's surface buckles.

Just as the moon deforms the Earth to create tides, Jupiter deforms its moon, Io, generating the thermal energy in Io's interior that powers the more than 400 volcanoes on its surface.

Remnants of another planet that helped form the moon may be beneath Earth's surface

Large mantle structures beneath Africa and the Pacific Ocean may be the buried remains of Thea, a large Mars-sized planet that collided with Earth. The theory is supported by isotopic evidence from volcanic and lunar rocks.

Geological tremors on the moon provide evidence that it is shrinking

Apollo seismometers have collected moonquake data, which scientists have analyzed to map the moon's interior and reveal that fault slips producing tremors are the result of sublunar cooling and contraction. It also revealed that the moon's inner core is about 500 kilometers (311 miles) across.

The moon's gravity exerts an overall pressure that displaces the oceans toward the opposite sides of Earth's equator, producing tides.

How the moon creates tides

Anyone who has visited large bodies of water virtually anywhere on Earth notices low and high tides occur at regular intervals, a process primarily driven by the moon’s gravitational pull. This explainer details how the motion of the Earth and Moon interact to create tides.

Instead of the tectonic plates found on Earth that produce earthquakes, volcanoes, and other geological activity when they interact, Mercury, Mars, and the moon have continuous, unbroken shells of rock called 'stagnant lids.'

Planets' high orbital speeds prevent them from falling into their host star

Although the gravitational force attracts a planet and the star it orbits around, the large speed the planet orbits with, which is acquired during its formation process, causes it to continuously miss the star as it orbits around it. This is analogous to theoretically throwing a baseball horizontally faster and faster until it's fast enough to orbit the Earth while attempting to fall to its surface.

The moon is moving 3.8 centimeters farther away from Earth each year

Driven by tidal forces, the effect is minimal and slow, ensuring stable tidal patterns and lunar cycles. Earth's rotation slows down as the Moon gains orbital momentum, slowly lengthening the day over time.

The sun will become a red giant after it exhausts the hydrogen fuel in its core, causing gravity to collapse the core and heat it enough for the surrounding hydrogen shell to ignite, releasing enough energy to cause the star to swell.

Spacecraft remnants and human waste left behind on the moon add to the trash in space

As more countries reach the moon with successful probe landings and unsuccessful crashes, more materials are left behind, adding to the amount of trash that needs to be retrieved. A United Nations treaty declared the moon a common heritage of humanity, exempting any one country from exclusive responsibility for cleanup.

Stars hold off gravitational collapse with the energy produced in nuclear reactions in their core, but when massive stars run out of fuel for these reactions, runaway collapse can produce a black hole.

Under the Big Rip scenario, dark energy becomes strong enough to tear atoms apart

If the density of dark energy, which produces a repulsive effect through the expansion of space, increases with time, then all structures of matter, including galaxies, stars, planets, and atoms, will be pulled apart once the strength of dark energy surpasses the magnitude of the forces holding those structures together, including the gravitational and electromagnetic forces.

Why the edge of Earth's atmosphere varies depending on which property is considered

As the distance from Earth's center increases, the planet's gravitational force weakens, causing it to gradually lose its ability to retain gases at the farthest edge of its atmosphere—the exosphere. At a height of approximately 200,000 kilometers (124,000 miles)—halfway to the Moon—the exosphere has so little density that it is indistinguishable from interstellar space.

Moon 101: NASA's complete overview of our lunar companion

From modulating our tides to impact our climate, Earth's lone natural satellite plays a key role forming the planet's habitat. Before diving into the rest of the resources on this page, check out NASA's overview of the basics of the Moon—how it got its name, its size and distance from Earth, its structure, and much more.

Why time ticks faster on the moon, which may need its own time zone

Because Earth exerts a stronger gravitational pull than the moon, it lags behind between 56 and 59 microseconds each day, or about one second every 46.5 years. This impacts essential synchronous operations of future electronic equipment on the lunar surface, which could be alleviated by a standardized conversion system between Earth and moon time zones.

How the moon moves, an interactive lesson

How exactly does the moon move, and why does it move that way? In this ridiculously comprehensive interactive explainer, you can conduct experiments to see how the moon rotates and as it moves around the Earth, while learning how gravity works by controlling the path and speed of different objects. Dive into this beautiful, simple explainer to learn the basics on gravity and the moon.

Black holes can disrupt the formation of galaxies

A team of astronomers in Munich detected a gas cloud being stretched and torn apart by the supermassive black hole at the center of the Milky Way, preventing matter from coalescing into new stars. Energy released from siphoned gas produced warm winds that may also prevent surrounding gas from coalescing.

Mar's moons, Phobos and Deimos, are thought to be captured asteroids

Of the two Martian moons, Phobos orbits more quickly, completing three revolutions a day. It gets 1.8 meters closer to Mars every year, and may crash into the planet in about 50 million years.

Because the half of Earth that faces the sun is larger than the area of the shadow cast by the moon during a solar eclipse, observers may experience a total, annular, or partial eclipse.

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.

Craters found on the moon and the calculated dates of these impacts, based on rocks returned by the Apollo missions, suggest that Earth was pummeled by asteroids for millions of years—a period known as the Late Heavy Bombardment.

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.

The moon's little-known, incredibly thin atmosphere

Earth's colorless, lifeless moon is often portrayed as devoid of an atmosphere. However, this fascinating article describes the very thin layer of gases floating above the surface of our celestial neighbor, a layer so thin it's technically known as...

Watch a simulation of a collapsing star becoming a black hole

When a massive star can no longer release enough energy through fusion in its core to fight off gravitational collapse, the dense core collapses first, producing an event horizon that traps light within it, including some light produced within the star at the time of collapse. As more material falls into the growing event horizon, the star will appear to eclipse itself from the inside.

Extraterrestrial volcanoes spew material present during their formation

Unlike Earth's volcanoes that release lava, cryovolcanoes on distant moons erupt cold jets of water, ammonia, and other light gases present during the formation of their host planet. The movement of internal heat produced during formation is thought to drive icy plume movement.

Explaining 'impossible' black holes

When stars collapse, the black holes they form can have the mass of either 50 suns or over 120—but current models claim strongly that no black hole should have a mass that falls in between that range. But in 2019, gravitational wave observatories detected two within it: one at 66 solar masses, the other at 85. The discovery disrupted established science and left researchers questioning the Standard Model of physics.

If there were a swimming pool on the moon, where gravity is about one-sixth that of Earth, championship finswimmers could potentially launch themselves up to 5 meters (16 feet) in the air.

Blood moons only occur during total lunar eclipses, when the Earth blocks the sun, but its atmosphere lets redder parts of sunlight through to reflect off the lunar surface.

Earth is constantly bombarded by material from space

Most of this matter is composed of small particles, with any smaller than 33 feet in diameter burning up in the atmosphere. Larger asteroids can reach the ground, and those larger than several thousand feet cause global damage, including earthquakes and tsunamis.

The masses of celestial objects can be determined by analyzing their orbits, observing how they bend light, or measuring their brightness.

Visualizing Earth's space garbage

An unsavory byproduct of humanity's brilliant exploration of space, the Moon, and more, is the rapid production of space debris floating around in orbit. Its estimated over 25,000 objects are in orbit, a number that grows everyday as satellites are decommissioned, rockets enter orbit, and more. Now, you can visualize what this debris looks like from a zoomed-out perspective with this brief video.

Tidally locked exoplanets experience extreme atmospheric temperatures

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.

Io, Jupiter’s moon, is the most volcanically active body in the 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.

Black holes do not 'suck' matter and energy in like a vacuum cleaner

Despite its immense magnitude, the force of gravity exerted by black holes acts in the same way as provided by stars and planets, allowing objects to maintain stable orbits around them. Even in cases where tidal forces and friction cause objects to change their orbit and fall towards a black hole, they are more likely to glance by, be whipped around, and get ejected rather than absorbed.

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.

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.

Why most atoms do not spontaneously break apart, despite protons repelling one another

At small scales, the strong nuclear force overwhelms electromagnetic repulsion between positively charged particles, keeping the nucleus intact. However, because the force's range is limited, it cannot provide the attraction needed to hold onto protons that are spread out across very large atomic nuclei.

Moon's visibility is determined by its declination, equivalent to Earth latitude

The Moon's declination varies between approximately +28.7 degrees and -28.7 degrees, ensuring it rises and sets between latitudes of approximately 61.3 degrees north and south. This means there are places on Earth where the Moon is never visible above the horizon and places where it temporarily does not set.

Space trash is making low Earth orbit increasingly dangerous for spacecraft

Millions of fragments from satellites, rockets, and other spacecraft that are no longer operational move thousands of meters per second as they circle Earth. Even a piece of debris a centimeter in size can cause mission-ending damage to space stations, telescopes, and astronauts.

Mars once had oceans and a thick atmosphere

It formed over millions of years as small clumps of matter orbiting the sun smashed together, solidified, and cooled. Geological features indicate the presence of past surface water, which evaporated away due to the planet's weak gravitational field.

Solar eclipses are a cosmic coincidence because the moon is 400 times smaller than the sun but about 400 times closer to Earth, allowing it to block sunlight for those on Earth within its shadow.

From the Greek words meaning 'rock blanket,' regolith is any layer of material covering solid rock, including soil, rock fragments, and dust.

Neutron stars, the remains of some massive stars after they explode in a supernova, are the densest directly observable objects in the universe.

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.

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.

Replacing the sun with a black hole would quickly collapse life on Earth

A black hole of the sun's mass would only be six kilometers wide, but it would exert the same gravitational pull as the sun. This means the planets would keep their current orbits but no longer receive solar radiation.

Although the moon passes between the sun and Earth each month, its orbit is tilted by five degrees, preventing Earth from experiencing a solar eclipse each month.

Just before and just after a total solar eclipse, sunlight can pass through uneven terrain on the lunar surface, producing disconnected bits of light around the moon called Baily's beads.