object

mars

Mars is a rocky planet in our solar system, often used as a mass reference for exoplanets.
66 related articles

Description

Mars is the fourth planet from the Sun and the second smallest in the solar system, with a mass about one-tenth that of Earth. In planetary science, it serves as a convenient reference point for rocky planets, particularly when comparing exoplanets: astronomers often describe a super-Earth as 'a few Mars masses' or 'several times Mars's mass' to give a sense of scale. Mars is also a prime target for studying planetary evolution, as its surface preserves a record of dramatic climate shifts and geological activity.

History

The first accurate measurement of Mars's mass came in 1877 when Asaph Hall discovered its moons and used their orbits to calculate the planet's gravitational pull. Earlier estimates, based on perturbations of Earth's orbit, had been rough but roughly correct.

How it works

Mars's mass is determined from the orbits of its two small moons, Phobos and Deimos, using Kepler's laws of motion. Its rocky composition, with a core of iron and sulfur, a silicate mantle, and a thin crust, is inferred from spacecraft measurements of its gravity field and the composition of meteorites that originated on Mars. The planet's low surface gravity (about 38% of Earth's) means it retains only a thin atmosphere, mostly carbon dioxide, and its surface pressure is too low for liquid water to persist today.

In practice

Mars serves as a calibration standard for exoplanet masses, and its geology and climate history inform models of habitability on rocky worlds elsewhere. It is also the target of ongoing robotic exploration missions.

Fun fact

Mars's mass is so small that a person weighing 100 kg on Earth would weigh only 38 kg there, yet the planet still has the largest volcano in the solar system, Olympus Mons, which is about 22 km high.

Concept graph →

Related articles · 67

Mars's Salt Thermos
Every Martian night, salt crystals on the planet's surface soak up moisture from the thin air, much like a sponge draws water from a damp cloth. By morning, a microscopic brine accumulates inside them, and during the day, as temperatures rise, that brine finds itself trapped in tiny cavities.
Scales Where Overly Heavy Planets Tip the System
Astronomers catch distant planets by the trembling of their stars: an invisible companion tugs the star toward us and away, and its light subtly shifts in color. But that trembling tells only half the truth. If the planet's orbit is tilted to our line of sight, only part of its weight rocks the star, so telescopes reveal not the true mass but its shadow.
The Neighbor Who Wasn't Kicked Out
On a sunny street, there's a house with a big family: a giant father who always sits by the window and a small child running around the yard. That's the TOI-4468 system: a gas giant hot Jupiter hugs the star, while a bit farther out circles a sub-Neptune — a planet smaller than Neptune but larger than Earth.
Exoplanets2026-08-201 minarXiv:2608.19892express
Martian Waves in Unison
On Mars, as on Earth, the air breathes: pressure rises and falls in rhythm with the daily tide — a wave heated by the Sun. But hidden in the InSight recordings was another, weaker wave. It's like an echo that gets lost in the loud sound of the main tone. This weak wave is called a Kelvin wave. It circles the planet like ripples on water from a thrown stone.
Exoplanets2026-08-051 minarXiv:2608.05054express
Martian Weather, Earthly Playbook
Meteorologists have grown used to trusting neural networks: the GraphCast model predicts Earth's weather days ahead by drawing on global snapshots of the atmosphere. But this 'brain' can be transplanted to another planet — where the air is thin and the Sun warms differently.
Galaxies2026-08-031 minarXiv:2608.02601express
Tiny Galaxy in the Milky Way's Halo
The night sky is like an ocean: the longer you stare, the more faint lights you notice in the depths. That's how astronomers, peering into the outskirts of the Milky Way, found Aquarius IV — a tiny stellar system that had been hiding in the dark until now. The system was spotted in images from an early survey by the future Vera Rubin Observatory.
Exoplanets2026-07-212 minarXiv:2607.19632express
Planetary Collisions and Their Hydrogen Coat
In a single star system, two teams of planets orbit. Some follow neat paths, like figure skaters on an ice rink, avoiding collisions. Others crowd together, their trajectories cross, and sooner or later a cosmic accident occurs — a giant impact.
Exoplanets2026-07-112 minarXiv:2607.10175express
How to Weigh a Planet by Its Shadow
When a distant planet passes in front of its star, it briefly blocks part of the light. Astronomers call this a transit and judge the planet's size by the depth of the dip. But light has a property: a massive body acts like a lens. Even a giant planet can slightly bend the star's rays, and the dip becomes a bit shallower than you might expect.
Exoplanets2026-07-112 minarXiv:2607.10403express
Lunar muons could illuminate subsurface voids
The Moon is an airless sphere of dense rocky grit called regolith. When fast particles from space slam into it, muons are born in the soil — unstable relatives of electrons, but two hundred times heavier. Most fly downward and fade away in the depths. But those that pop upward into the vacuum can travel tens of kilometers before decaying.
High Energy2026-07-081 minarXiv:2607.07668express
Strange Stars vs. Neutron Stars: A Duel in Gravitational Waves
Two ultradense spheres, each the size of a city, whirl in a dance. Their masses are less than the Sun's, but inside them is matter compressed to unimaginable limits. One sphere is a neutron star; the other is a strange star, made entirely of quarks — the elementary particles that build up protons and neutrons.
Waltz of Invisible Moons: The First Spectroscopic Find
The gravitational dances of celestial bodies long remained silent to astronomers. We learned to catch the shadows of planets against stars with the transit method — a breakthrough that delivered thousands of worlds thanks to William Borucki and his Kepler telescope.
Galaxies2026-07-053 minarXiv:2607.04216
Quasi-interstellar objects: when the Solar System meets its own exiles
Remember the sensational comet 1I/‘Oumuamua — the first object to come to us from another star? Its hyperbolic trajectory left no doubt: it was a wanderer from the interstellar void. But astronomers wondered: could some of these visitors not be strangers at all, but our own, escaped from the Solar System millions of years ago?
Invisible Planet in Warped Light
The light of a distant star is no perfect beacon. Passing through the gravitational field of another star, it bends, splits, and magnifies, creating a fleeting Einstein ring in the sky. This is how gravitational microlensing manifests, predicted by Fritz Zwicky back in the 1930s.
Cosmic Debt: How a Planet's Mass Locks Civilizations Forever
Every civilization is born with a gravitational debt. The home planet's mass determines the loan amount, and the Tsiolkovsky equation is the interest rate applied to each kilogram of payload. To send a probe to the stars, you have to pay with fuel, and the debt grows exponentially.
Exoplanets2026-06-222 minarXiv:2606.23483express
Mars's Subsurface Life: Radiation as Fuel
The Martian surface is a place where anything alive quickly dies. Cosmic rays and ubiquitous oxidizers sterilize the top layer of soil. But dig a little deeper, and the picture changes. There, beyond the reach of ultraviolet light, a zone suitable for life may lurk. This zone runs on a strange fuel — radiation.
Exoplanets2026-06-221 minarXiv:2606.23789express
James Webb Fishes Out an Invisible Planet from a Dusty Disk
Using James Webb, astronomers 'fished out' a third giant planet from the murky dust disk of the star β Pictoris. Two others were already known, but this one was hiding in the bright light, like a fish in muddy water.
Exoplanets2026-06-181 minarXiv:2606.20398express
Why the Moon Is a Copy of Earth? The Fluidity Clue
Young Earth was a boiling sphere of liquid rock, while Theia, which crashed into it, had had time to cool and solidify. It’s like dropping a chunk of cold butter into a pot of soup: the soup splashes out, but the butter barely moves. Similarly, Earth’s interior spewed into space, forming a cloud of cosmic dust and debris.
Exoplanets2026-06-161 minarXiv:2606.18219express
Inside Uranus and Neptune Lie Oceans of Magma
Previously, Uranus and Neptune were considered ice giants because of assumed thick layers of frozen water, methane, and ammonia. New calculations paint a different picture: deep inside them hides an ocean of hot magma, which under immense pressure has absorbed a colossal amount of hydrogen.
Exoplanets2026-06-161 minarXiv:2606.18355express
The Iron Planet Isn't So Iron After All
A cosmic sprinter on a short track: that's how you might describe planet GJ 367 b. It whips around its star in just 7.7 hours. This world is slightly smaller than Earth but has a personality: it was once thought to be nearly a solid ball of iron.
Exoplanets2026-06-161 minarXiv:2606.18410express
Super-Earths and Mini-Neptunes: Two Fates
In the catalogs of exoplanets, there are many worlds with sizes between Earth and Neptune. They are divided into two groups: rocky super-Earths and gaseous mini-Neptunes. The Solar System has none of these, and scientists debate where they come from. The authors of the study looked into each planet's 'passport'—its orbit.
Popular Physics2026-06-141 minarXiv:2606.17105express
Gravitational Visitors: How Passing Planets Rewrote Earth's History
On the periphery of the Solar System lurk thousands of objects comparable in size to an exoplanet — a body of planetary mass not bound to our star. Their orbits are chaotic, and from time to time the trajectory of such a wanderer crosses Earth's path.
Exoplanets2026-05-312 minarXiv:2606.00974express
A Sulfur Key to Planetary Childhood
A kindergarten where some kids are busy making sandcastles while others are already assembling building blocks. That's roughly what the V1298 Tau system looks like: it's only 20 million years old — by cosmic standards, it just left the nursery. Several planets orbit it, and two of them, b and e, turned out to be surprisingly different.
Exoplanets2026-05-311 minarXiv:2606.01377express
Interstellar Visitor Slims Down Before Our Eyes
Among the icy chunks hurtling through the void, there are special travelers — interstellar comets. They were born around distant stars and happened to wander into our neighborhood. One of them, 3I/ATLAS, came under the gaze of telescopes as it approached the Sun. Its material, frozen gases and refractory dust, began to evaporate, leaving a glowing tail behind.
Exoplanets2026-05-302 minarXiv:2606.00612express
Planet X: The Dance of Twelve Stones
At the edge of the solar system, where the Sun is barely brighter than other stars, icy boulders, trans-Neptunian objects, circle around. Their orbits resemble hoops scattered by someone. But look closer: twelve of these hoops are not just floating in the void.
Exoplanets2026-05-252 minarXiv:2605.26216express
Planetary Budget Doesn't Add Up
The cosmic accounting has hit a snag. The bookkeeper is balancing the books: in one column, all the planets astronomers have counted in the galaxy; in the other, the stockpile of building material in the dusty cocoons of newborn stars. The numbers don't line up. Even if you gathered every last grain of dust and molded it into planets, there wouldn't be enough material.
Exoplanets2026-05-151 minarXiv:2605.15595express
Martian Spores: How Life Could Have Flown to Earth
The idea of extraterrestrial origin of life has long excited minds. Fred Hoyle believed bacteria travel between stars. A new study tested a similar but closer route: from Mars to Earth. In ancient times, Mars had water, and asteroid impacts knocked rocks with microbes into space.
Exoplanets2026-05-061 minarXiv:2605.04840express
Mars's dense layer reveals the fate of rocky planets
If you don’t stir a layered cocktail, the heavy syrup sinks to the bottom. A young planet is much the same — a seething ocean of molten rock. As it cools, minerals crystallize: some, like iron, get heavy and sink, while others float. You’d think a dense layer would pile up at the core.
Instrumentation2026-04-221 minarXiv:2604.20182express
A Swarm of Tiny Sails Heads to Proxima b
A handful of coins accelerates to one-fifth the speed of light. That's what Coracle interstellar probes will be like — tiny spacecraft weighing just a few grams, each with an ultrathin sail film. A powerful laser beam pushes them forward: light presses on the sail like wind fills a yacht's sails, except instead of air, it's a stream of photons.
Instrumentation2026-04-201 minarXiv:2604.18664express
Asteroids Instead of Trucks: Metal for Mars
The Red Planet is surrounded by the rubble of failed worlds — rocky boulders stuffed with metal. Shipping a kilogram of steel from Earth to Mars costs as much as several cars. It's far cheaper to pick up space junk right in orbit.
General Relativity2026-04-141 minarXiv:2604.12787express
Planet Nine Heats Up with Dark Matter
At the edge of the solar system, far beyond Neptune's orbit, something is knocking icy chunks off their paths. Their orbits are stretched and tilted in the same way, as if an invisible hand arranged them in a pattern.
Exoplanets2026-04-081 minarXiv:2604.07068express
How to Find a Planet Without Seeing It
At night, a distant streetlamp seems motionless, but if you walk closer and look carefully, you might notice it swaying slightly in the wind. That's roughly how astronomers hunt for planets around other stars: they measure how a star shifts ever so slightly under the gravitational tug of its invisible companions.
physics.gen-ph2026-04-051 minarXiv:2604.03916express
Life from Mars: How Realistic Is It?
A rock knocked off one planet by an asteroid impact hurtles through space and lands on another. If microbial spores are hiding inside, they might survive the cold, the radiation, and the rough landing. That's panspermia — the idea that life travels between worlds. But imagining such a journey is one thing; calculating every step is quite another.
Exoplanets2026-04-031 minarXiv:2604.03049express
Seven Planets March in Lockstep
Every 1151 years, seven planets of the Solar System, from Mercury to Neptune, find themselves at almost the same points in their orbits. Their positions scatter by less than a degree, as if the celestial mechanism is wound to the same tune. This rhythm was discovered by comparing planetary positions over 2600 years using precise tables of celestial motion.
Instrumentation2026-04-021 minarXiv:2604.02242express
Mars Without Biology: Three Paths to Warmth
Mars is an icy desert with an average temperature of minus 60. To warm it without biology, scientists propose three approaches with a single idea: create a thick heat-trapping blanket. First, deploy transparent film-blankets over bases. They let sunlight in but keep heat from escaping, allowing us to harvest water from the soil and grow plants.
Exoplanets2026-04-011 minarXiv:2604.00604express
Tilted Rings of Small Planets
Around distant icy bodies the size of a city, circling beyond Neptune, rings of dust and ice have been found. Small moons often whirl nearby. Mathematical analysis shows that a moon's gravity rocks the ring like a swing, making it tilt.
Exoplanets2026-03-302 minarXiv:2603.28238express
A Rocky Planet Around a Red Dwarf
The tiny star LHS 3844 is trembling. The invisible culprit is a rocky planet that whips around it every 11 hours. The planet pulls on the star, and the star responds with a barely perceptible wobble. Detecting that wobble is like noticing a 100-kilogram weightlifter step forward when a fly lands on his palm.
Exoplanets2026-03-182 minarXiv:2603.18233express
Stellar2026-03-172 minarXiv:2603.17040express
The Cosmic Waltz of Ultracool Dwarfs
Two dim stars whirl so close together that one siphons material off the other, like a spoon delicately skimming foam from broth. Astronomers have for the first time calculated the fate of such pairs — ultracool and brown dwarfs, the coldest and dimmest inhabitants of the galaxy. Previously, it was thought that mass exchange between them was impossible: they were too fragile.