Space Oddity

Last post, we began a tour of the Solar System.¹ What was supposed to be a single piece on our cosmic neighbourhood morphed into a multi-post extravaganza. Turns out, it’s hard to write a short-ish blog entry on the entirety of the Solar System. Who knew?

We ended with Venus, Earth’s angry twin. The two planets are similar in size, mass, and composition, but Venus’s atmosphere has become absurdly thick, about 92 times the pressure of Earth’s at sea level, and incredibly toxic. Its clouds are made of sulphuric acid, which can corrode most metals and damage organic material. Yeesh! Easy on the sky acid, Venus!

Next up is our own backyard. Earth may seem familiar, but when you look at it alongside its neighbours, it becomes clear just how lucky we are. From liquid water to a magnetic field that shields us from solar radiation, Earth has a long list of features that make life possible. It’s not just our home planet, it’s a rare gem in the vastness of space.

After Earth, we will move on to Mars. The Red Planet has fascinated sky-watchers for centuries,² and for good reason. It’s cold, dry, and dusty, but there are signs that water once flowed across its surface. With each new rover mission, we peel back another layer of its past, and maybe even its potential to host life. Finally, we will take a detour into the asteroid belt, the wide band of rocky leftovers between Mars and Jupiter.

Our planet. The only place we know for sure hosts life, and is perfectly suited to support it. (so, you would think we would try harder to keep it that way, but *waves arms in existential dread* here we are.) Earth sits in the habitable zone, the range around a star where liquid water can exist.³ As we saw with Venus, just being in this zone doesn’t guarantee oceans, but water is widely seen as essential for life to emerge.⁴ With about 70% of Earth’s surface covered in it, life took hold rather quickly and eventually evolved into awkward, self-aware apes who send DMs, shop for outfits, and blog about the cosmos.

Our planet’s early days are referred to as the Hadean eon,⁵ named after Hades, the Greek god of death. This name reflects the intense heat, volcanic activity, and constant bombardment that made Earth a hostile and molten world. During this time, the planet was still forming its crust and cooling from its chaotic birth. Artist recreations of this period often include rocky crusts separated by giant streams of lava, being fed by vast chains of volcanos. So metal! 🤘 

The earliest signs of life we’ve found on Earth are microfossils and isotopic signatures in rocks dating back about 3.5 to 3.8 billion years.⁷ So it looks like life took hold pretty quickly once the Earth cooled from its hellish creation. 

If water was essential for life to begin, where did it come from? Some of Earth’s water likely emerged from within, released by volcanic eruptions as the young planet’s surface cooled and solidified. But a significant portion may have arrived from space, delivered by icy asteroids and comets during a violent era of frequent impacts.⁸ The hydrogen isotope ratios in Earth’s water closely match those found in certain carbon-rich asteroids, supporting this idea.⁹

This chaotic period, known as the Late Heavy Bombardment,¹⁰ left lasting marks on the Moon’s surface. Unlike Earth, which constantly reshapes itself through plate tectonics, erosion, and weathering, the Moon lacks any geological activity to erase surface features. It has no atmosphere, no liquid water, and no tectonic recycling.¹¹ This means impact craters and surface scars remain intact for billions of years, offering a preserved record of the early Solar System’s turbulent history.¹²

The origin of the Moon remains one of the solar system’s great puzzles. The leading explanation is the giant impact hypothesis,¹³ which proposes that a Mars-sized planet named Theia collided with Earth, and some of the resulting debris eventually came together to form the Moon. This idea is supported by the Moon’s composition, which closely resembles Earth’s mantle, particularly in oxygen isotope ratios. The similarity is greater than would be expected if the Moon had formed on its own. ¹⁴

Because of their gravitational interaction and close proximity, the Earth and Moon have become tidally locked.²⁴ This means the Moon rotates at the same rate it orbits Earth, so we always see the same side when we look up.

Long ago, the Moon spun faster than it orbited, as both bodies revolved around their shared baricenter (center of mass). Earth’s gravity raised tidal bulges on the Moon, and because of its faster spin, those bulges were slightly offset from the Earth and Moon line. Earth’s gravity pulled back on those off-center bulges, creating friction that gradually slowed the Moon’s rotation. Over millions of years, that drag synchronized the Moon’s spin with its orbit, locking one hemisphere permanently toward Earth.

The Moon is far more than just a visual delight in the night sky. It helps stabilise Earth’s axial tilt by exerting gravitational torque on the planet’s equatorial bulge. This reduces wobble and keeps the tilt relatively steady over long periods.²⁵ Without this influence, Earth’s tilt could drift dramatically, possibly swinging between zero and ninety degrees over millions of years. Such changes would lead to extreme climate shifts, including intense ice ages and prolonged heat.

The Moon also drives ocean tides through its gravitational pull on Earth’s water.²⁶ These regular tidal movements circulate nutrients, move sediments, and support coastal ecosystems such as estuaries, salt marshes, and tidal flats.²⁷ These habitats foster biodiversity and contribute to climate regulation and shoreline protection.

Without the Moon, Earth’s climate would be unstable and its ecosystems far less supportive of life.

The Moon was the first and so far only place beyond Earth where humans have landed and walked. On July 20, 1969, NASA’s Apollo 11 mission made history when Neil Armstrong became the first person to set foot on the lunar surface, followed by Buzz Aldrin.²⁹ Their landing in the Sea of Tranquility marked a major milestone in space exploration, proving that crewed missions beyond Earth were possible.

Later Apollo missions expanded on this success, with five more crewed landings between 1969 and 1972. Astronauts collected hundreds of kilograms of rock and soil samples, set up scientific instruments, and drove the lunar rover across the surface.³⁰ These missions revealed that the Moon is geologically inactive and covered in fine dust called regolith.³¹ Each mission added new insights into the Moon’s history, surface conditions, and its connection to our own planet.

After decades of staying away, we may finally be heading back to the Moon. The Artemis Program,³³ launched by NASA in 2017, is a modern lunar exploration programme with a long-term goal to establish a permanent base on the Moon as a stepping stone for future human missions to Mars. If successful, it will mark the first human presence on the Moon since Apollo 17 in 1972. (Artemis was Apollo’s twin sister in Greek mythology.³⁴ Gotta love when they nail the names. 🎩 *tips hat*) It’s still in the early stages, but we can expect more impressive Moon footage from NASA in the near future.

Named after the Roman god of war,³⁵ Mars is our next stop. Mankind has learned a lot about the red planet, and even though it’s farther from Earth than Venus, its surface is far more human-friendly. You would still die in minutes without protection and breathing gear, but it’s not the “clouds can strip paint and skin” kind of planet. (Looking at you, Venus.) Unlike the crushing and toxic Venusian environment, Mars has more moderate conditions: dry, cold, and thin-aired, but manageable with the right technology.³⁶

Mars is the outermost of the three rocky planets in the Sun’s habitable zone. Unlike Venus, which offers only scant evidence of ancient water, Mars provides compelling geological and mineralogical proof that it once hosted abundant surface water. Satellite imagery reveals dried-up river valleys, lake basins, delta deposits, and alluvial fans.³⁷ Orbital and rover instruments have detected water-altered minerals such as clay-rich phyllosilicates, hydrated salts, sulfates, and chlorides, along with layered sedimentary strata indicative of ancient lakes.³⁸ Together, these geological markers support a picture of early Mars with a thicker atmosphere and long-lived liquid water, possibly persisting for millions of years.³⁹

Mars has seasons like Earth thanks to its 25.2° axial tilt, which causes its polar ice caps to grow and shrink throughout the year. Its surface is coated in iron oxide, giving the planet its distinct rusty red colour, visible even through amateur telescopes.⁴⁰ Mars is also known for massive dust storms that can cover the entire planet for weeks at a time, blocking sunlight and creating serious challenges for solar-powered missions.⁴¹ The planet’s two small, irregularly shaped moons, Phobos and Deimos, are thought to be captured asteroids.⁴² Phobos, the closer of the two, is slowly spiralling inward and may eventually break apart or crash into the Martian surface.⁴³

Mars’ thin atmosphere and lack of magnetic shielding make it vulnerable to harsh solar radiation and incapable of sustaining surface water or life as we know it.⁵⁰ These factors also explain its cold, dry, and barren state today, despite early signs that it may once have been warmer and wetter.⁵¹

Based on computer models, Mars should have grown to be much bigger, more like Earth or Venus, because the building material (called planetesimals) extended well past its orbit. But Mars is only about 11% the mass of Earth, and much less dense. So what happened?

During the planets’ creation, Jupiter may have formed very early and migrated inward toward the Sun, possibly reaching as close as 1.5 AU, just beyond where Mars orbits today. This scenario is part of what is known as the grand tack hypothesis (Walsh et al., 2011).⁵²

According to this idea:

• As Jupiter moved inward, it disrupted or cleared out much of the material in the region where Mars was beginning to form. This early migration would have scattered or ejected many of the planetesimals that Mars needed to grow.
• Then, as Saturn formed, it exerted a gravitational pull that caused Jupiter to reverse course and migrate outward to its present location.
• By the time this outward migration occurred, the area beyond Earth’s orbit had already been stripped of mass, leaving only a thin population of building material behind.

Simulations that include Jupiter’s migration produce smaller Mars-sized planets at the correct orbital distance, matching our observations. This also helps explain the low mass of the asteroid belt, which lies just beyond Mars and would also have been depleted.

Mars has the tallest volcano in the solar system, Olympus Mons.⁵³ At ~22 km high, it’s 2.5 times taller than Mount Everest. Since the planet has only about 38% of Earth’s gravity, it allows mountains to grow taller before collapsing under their own weight. And unlike Earth, Mars doesn’t have active tectonic plates, so, volcanic hotspots stay in one place for millions of years.⁵⁴

On Earth, a moving plate creates volcanic chains (like Hawaii). On Mars, the crust doesn’t move, so lava builds up in one location, creating a supervolcano. Olympus Mons likely erupted repeatedly for hundreds of millions of years. With no plate movement and few erosional forces, it just kept growing.⁵⁵

If tallest volcano wasn’t enough, the red planet is also home to the solar system’s deepest canyon. Valles Marineris⁵⁶ is 7 to 10 km deep, over 6 times deeper than the Grand Canyon. It’s also one of the longest canyons at over 4,000 km long, about the width of Canada. It’s a giant rift valley⁵⁷ so it wasn’t carved by water. Instead, it likely formed as the crust stretched and cracked while the nearby Tharsis volcanic region (home of Olympus Mons) swelled. The massive weight of the Tharsis rise added stress to the crust, causing it to crack and pull apart to the east, creating this huge chasm system.⁵⁸ Plus, Mars has little wind and almost no liquid water, so the canyon has stayed intact over time, whereas on Earth, erosion would’ve worn it down.⁵⁹

Both Olympus Mons and Valles Marineris are reminders that Mars is geologically unique, with slower-moving surface dynamics and fewer natural erasers like water or tectonics to flatten things out.

Being close to Earth and the most viable planet we could realistically call home one day, Mars has become a focus for future human exploration.⁶⁰ There has been plenty of excitement in recent years about sending people to the Red Planet, whether through international space agencies⁶¹ or ambitious private ventures.⁶² The idea of colonising Mars or using it as a backup plan for Earth’s troubles shows up often in media and public talks.⁶³ But in reality, we are still a long way off from making any of this happen.⁶⁴

The biggest barriers are technical. A round trip to Mars takes many months, and we do not yet have spacecraft, habitats, or life support systems ready for such a long and dangerous journey.⁶⁵ Astronauts would face deep space radiation, reduced gravity, and serious psychological stress from isolation.⁶⁶ Even landing safely on Mars is a challenge. Its thin atmosphere makes it hard to slow down large payloads, which is something we would need for humans and their equipment.⁶⁷ And once on the ground, they would still need oxygen, food, water, and energy, all in a freezing, dusty environment.⁶⁸

Despite all that, plans are slowly moving forward. Space agencies have mapped out possible crewed missions in the 2030s or 2040s, using the Moon as a testbed.⁶⁹ Meanwhile, private groups are working on rocket designs, landing systems, and early-stage habitat concepts.⁷⁰ For now, Mars remains a dream worth pursuing, but one that still requires decades of steady progress, strong funding, and international cooperation to become reality.

One lesser-known hurdle is the return journey. Most mission concepts aim to bring astronauts back, which means launching off Mars, a planet with gravity about 38% that of Earth. This requires either bringing a return rocket along, which adds weight and complexity, or producing fuel on Mars itself.⁷¹ Scientists are researching how to extract oxygen from the Martian atmosphere⁷² and mine water from underground ice,⁷³ which could be split into hydrogen and oxygen for fuel.⁷⁴ These technologies are still in early development, but if successful, they could support return missions and also make longer stays and future settlements more realistic.

The poor, misunderstood asteroid belt. Despite dramatic sci‑fi portrayals, it’s mostly empty space. The objects are spread across a vast region, with average separations of about a million kilometres.⁷⁵ A spacecraft flying through it is unlikely to hit anything unless aiming for it.

The belt is made up of rocky leftovers from the early solar system, planetesimals that never formed into a planet because of Jupiter’s massive gravity.⁷⁶ In a way, it’s a time capsule of solar system formation.

Spectral analysis confirms many asteroids contain hydrated minerals, indicating past exposure to water. The dwarf planet Ceres, the largest object in the belt, hosts briny water beneath its crust. Salt deposits, such as sodium carbonate, point to a subsurface reservoir or slushy ocean.⁷⁷ This raises questions about whether the belt could have delivered water to early Earth. While most asteroids are rocky, some, like 16 Psyche, are largely made of metal, possibly remnants of a shattered protoplanet’s core. NASA’s Psyche mission is currently on its way to investigate. If it really is an exposed planetary core, Psyche could reveal what lies at the heart of rocky planets like Earth. It’s the first mission to visit a world made mostly of metal.⁷⁸

Most of the asteroid belt’s mass resides in a few large bodies. The four largest are Ceres,⁸⁰ Vesta,⁸¹ Pallas,⁸² and Hygiea,⁸³ and together they account for approximately 50 to 60 percent of the belt’s total mass. Ceres alone comprises roughly one third of the entire belt’s mass and is the only object in the belt large enough to meet the criteria as a dwarf planet. Vesta is the brightest object in the asteroid belt and has a layered interior similar to a small planet.⁸⁴ Pallas follows a highly tilted orbit that makes it challenging to observe. Hygiea may have formed from the debris of a massive ancient collision.

There are noticeable gaps in the asteroid belt called Kirkwood gaps,⁸⁵ which are caused by orbital resonances⁸⁶ with Jupiter. These gaps occur where an asteroid’s orbital period would align in a simple ratio with Jupiter’s, such as completing two or three orbits for every one made by Jupiter. When this happens, Jupiter’s gravity gives the asteroid a regular gravitational nudge, slowly shifting its orbit. Over time, this can destabilise the asteroid’s path and push it into a different part of the solar system. Some of these displaced asteroids eventually drift into the inner solar system and cross Earth’s orbit. In fact, many near-Earth asteroids are thought to have originated in the main belt before Jupiter’s influence set them on new trajectories.⁸⁷ These gaps act like invisible conveyor belts, carrying fragments into unexplored regions.

Meanwhile, sample return missions such as Japan’s Hayabusa⁹⁴ and Hayabusa2⁹⁵ and NASA’s OSIRIS‑REx⁹⁶ have targeted near‑Earth asteroids Itokawa, Ryugu, and Bennu. Although these asteroids are not in the belt, they likely originated there before being nudged into Earth‑crossing orbits.⁹⁷ The samples returned to Earth match the composition of particular meteorite classes, confirming that many of the space rocks landing on our planet are fragments from the main belt.⁹⁸

Looking ahead, the asteroid belt could become a valuable resource for missions beyond Mars. Many asteroids are rich in water‑bearing minerals that could be used for fuel or life support in deep space, and others contain high concentrations of metals such as nickel, platinum, and rare earth elements.⁹⁹

Ceres, the largest object in the belt, shows signs of water ice beneath its surface and maintains bright salt features, making it a potential strategic outpost for harvesting materials or resupplying missions destined for farther regions.¹⁰⁰ While mining the belt remains decades from realization, numerous studies and commercial ventures are now treating it as a serious future frontier in space exploration.¹⁰¹