Every year the robots and satellites scientists have sent to Mars make discoveries that help us learn more about the Red Planet's past and take us a step closer to humanity's potential future living there — and this year was no exception.
Despite the death of NASA's Ingenuity helicopter and a gaping hole in one of the Curiosity rover's wheels, 2024 was still a banner year for Martian discoveries, including what happened to the Red Planet's magnetic field and whether or not the alien world once harbored extraterrestrial life.
From the iconic "spiders on Mars" and a giant dog-shaped blob to an underground ocean and other newly discovered water deposits, here are our 10 favorite things found on Mars this year.
Related: 32 things on Mars that look like they shouldn't be there
Giant underground ocean
Arguably the most significant development on Mars this year was the revelation that a massive reservoir, containing enough water to cover the Red Planet with a 1-mile-deep (1.6 kilometers) ocean, is lurking beneath the Martian surface.
NASA's InSight lander discovered the underground reservoir in a layer of rock 7 to 13 miles (12 to 20 km) beneath the planet's surface by analyzing more than four years of "Marsquake" data. Although no existing drilling methods can reach these depths on Earth, this reservoir could be hugely important to future astronauts if we can find a way to reach it.
Researchers also noted that the buried ocean could harbor extraterrestrial life.
"Spiders" swarm "Inca City"
Spiders on Mars is the name given to spindly crack-like features that appear on the Red Planet's surface during the Martian springtime when carbon dioxide ice sublimates — or turns directly into a gas — and drags up dust from below that settles into strange shapes on the ground.
Scientists have known about these arachnid lookalikes for decades. But in April, photos from the European Space Agency's (ESA) Mars Express orbiter and ExoMars Trace Gas Orbiter revealed that the spiders had emerged in great numbers at a region near Mars' south pole, known as the "Inca City" formation.
In September, researchers also created these spiders on Earth for the first time, which will help scientists learn more about these strange structures in the future.
Martian dog and mystery blobs
In September, dozens of mysteriously dense blobs — including a structure with a surprisingly canine shape — were found lurking beneath an ancient seabed surrounding Mars' north pole, thanks to a first-of-its-kind "gravity map."
The new map was created using data from the InSight lander and Mars Express orbiter, revealing 20 underground structures with densities between 19 to 25 pounds per cubic foot (300 and 400 kilograms per cubic meter) higher than the surrounding bedrock. However, it is currently unclear how they formed and what they are made of.
The same research also confirmed the presence of a gigantic, solidified lava plume spanning 1,100 miles (1,750 km) beneath the solar system's tallest peak, Olympus Mons — a giant volcano standing more than 16 miles (25 km) above Mars' equator.
Massive volcano "hiding in plain sight"
Until recently, scientists assumed that we had already uncovered all of Mars' largest structures. But in March, scientists announced the surprise discovery of an enormous, long-dead volcano, spanning more than 280 miles (450 km) across.
The giant volcano, which is still unnamed, had gone unnoticed until now because it has been massively eroded, meaning little of it remains above ground. However, researchers studying the region noticed the area was surrounded by the remains of ancient slopes that would have once towered above the surrounding landscape.
Researchers also spotted what appears to be the remains of a sheet of buried glacier ice near the base of the volcano, which could make the volcano a "prime location" for astrobiological research.
A salty smile
In September, researchers spotted a surprising "smiley face" beaming up from the surface of Mars as they surveyed the alien landscape.
The grinning shape, which is made up of a ring of ancient chloride salt deposits with a pair of meteor-crater eyes, was snapped by ESA's ExoMars Trace Gas Orbiter. The chloride salt appears pink in the image because it was snapped in infrared. Normally, the smile would be invisible to the naked eye.
The photo was taken as part of a study that surveyed almost 1,000 similar deposits, which are all thought to "provide optimal conditions for biological activity and preservation," researchers wrote.
Frosty peaks full of water
To the naked eye, Martian volcanoes look as dry and barren as the rest of the Red Planet. However, in June, researchers revealed that the lofty peaks of these dormant mountains are covered in water — in the form of frost.
In total, researchers believe there could be at least 150,000 tons of water frost — the equivalent of 60 Olympic swimming pools — on the four largest Martian peaks at any given time, images captured by ESA's Trace Gas Orbiter revealed.
Researchers had previously assumed this would be impossible because the sunlight at the equator, where all the volcanoes are located, is strong enough to turn any ice directly into gas. However, the new study shows that while the frost sublimates away every day, it reforms overnight.
Weird rocks
Mars' surface is littered with loose rocks, and this year NASA's rovers found a bunch of weird ones.
In January, the Curiosity rover spotted an arrowhead-shaped rock on the slopes of Mount Sharp that drew comparisons to the Starfleet badge from "Star Trek."
In June, the Perseverance rover discovered a first-of-its-kind lightly colored boulder in the Jezero Crater. Researchers said the pale rock, dubbed "Atoko Point" after a similarly strange rock in the Grand Canyon, is in a "league of its own" and could shed new light on Mars' past.
And in September, Perseverance also found a strange black-and-white striped "zebra rock" that is unlike anything else seen on the Red Planet. The exact origin of this rock, dubbed "Freya Castle," is unknown, but researchers suspect it was made via volcanic processes.
"Cryptic terrain" and dark dust
In April, ESA's Mars Orbiter captured images of surface features around the planet's south pole that researchers said were "surprisingly dark compared with their icy surroundings."
The scientists dubbed these areas "cryptic terrain" and believe they are caused by patches of CO2 ice that repeatedly freeze and sublimate throughout the year. This is a seasonal cycle, where the ice appears during the Martian autumn and disappears in spring.
The team also identified specific places where they believe that dark dust gets pulled up from the surface through the ice, similar to how "spiders on Mars" form, creating polygonal shapes where the dust absorbs additional sunlight and causes ice to sublimate faster.
Green spots
Thanks to early science fiction, most people's mental picture of potential Martians probably resembles little green men. But while these stereotypical aliens have remained elusive so far, the Perseverance rover did discover little green spots on the Red Planet this year.
The tiny spots, which measure around 0.08 inches (0.2 centimeters) across, were photographed by the rover in August as it surveyed an area dubbed "Serpentine Rapids." The colorful patches were embedded within rocks alongside white dots. Green spots like these can be found in rocks on Earth when iron gets oxidized, giving the rocks a similar composition to rust — and researchers believe the same thing is probably happening on Mars.
On Earth, microbes often help oxidize rocks, hinting that the same could have happened on the Red Planet. However, the spots can also form via abiotic factors.
Buried ice chunks
In addition to the newly revealed underground ocean and the abundant frost discovered on top of Mars' volcanoes, researchers also discovered massive chunks of ice buried beneath the Red Planet's equator this year.
The submerged blocks, which extend 2.3 miles (3.7 km) below the surface, were spotted using radar images captured by ESA's Mars Express Orbiter. They are hiding beneath a geological formation called the "Medusae Fossae Formation" and are covered by thick layers of ash and dust.
It is unclear how the ice got buried, but this is not the first time that frozen water has been found beneath Mars' equator, suggesting it could be a good idea to set up future Martian bases near the planet's middle.
