What is the creepiest planet in the universe?

 It's 2M1207b.

This gigantic planet (with about four times the mass of Jupiter) lies 170 light-years from Earth, and its distinctive atmosphere is hellish. Temperatures can reach 1400 degrees Celsius, and its rotation speed is astonishing (it completes one rotation in 10 hours compared to Earth's 24 hours, which is remarkable considering it's about 4000 times the size of Earth). And in the planet's stratosphere, highly sophisticated chemical reactions occur, causing glass droplets to rain down on its surface, so sometimes the rain contains not only glass but also molten iron and other materials.

Could humans survive on another planet without a spacesuit?

 If you step onto another planet without a spacesuit, suffocation is the least of your worries. In our solar system alone, you could be crushed, melted, or have your blood literally boil.

Venus offers a crushing atmospheric pressure 90 times that of Earth, temperatures hot enough to melt lead, and rains of sulfuric acid. Mars visually resembles an arid terrestrial desert, but its environment is just as lethal.

A view of the sandy, rocky surface inside Jezero Crater on Mars. Source: Wikimedia Commons.

Standing on this barren surface without a pressurized suit, a human would face an atmosphere 100 times thinner than Earth's, composed almost entirely of carbon dioxide. They would quickly succumb to ebullism—a condition where the boiling point of bodily fluids drops below the body's internal temperature, causing the water in tissue and blood to vaporize. Asphyxiation would follow in minutes. Gas giants like Jupiter and Saturn lack solid surfaces entirely, offering only a descent into crushing pressure and turbulent storms.

To survive without a spacesuit, a person would need an Earth-like exoplanet located in its star's habitable zone—the orbital region where temperatures allow liquid water to pool. This hypothetical planet must meet strict criteria: surface gravity close to 1G, a magnetic field to deflect stellar radiation, and a breathable atmospheric pressure. Crucially, the atmosphere must contain enough oxygen to sustain human metabolism without being so rich that it becomes highly flammable, mixed with an inert buffer gas like nitrogen.

Even if astronomers identify a planet with the perfect temperature and atmospheric composition, the biological reality of stepping outside remains hazardous. On Earth, free oxygen is continuously replenished by photosynthetic life. If an exoplanet has a breathable oxygen atmosphere, it likely harbors its own biosphere. A human arriving on such a world without a spacesuit might face alien microorganisms, allergens, or protein structures that the human immune system is completely unprepared to handle, making the alien air fatal for entirely biological reasons.

An artist's concept of Kepler-186f, an Earth-size exoplanet orbiting within its star's habitable zone. Photo by NASA Ames/SETI Institute/JPL-CalTech. is licensed under CC BY 4.0.

Can you explain how gravity works on a spherical planet?

 Gravity doesn't actually pull you "down." You are locked in a tug-of-war with every speck of dust and chunk of rock on Earth, being yanked in billions of directions at once.

Every atom in the planet exerts a tiny, invisible pull on your body. Because the Earth is a sphere, the rock thousands of miles to your left is pulling you to the left, and the rock thousands of miles to your right is pulling you to the right. The pull from the northern hemisphere cancels out the pull from the southern hemisphere. The only direction that doesn't get canceled out is the straight path toward the center of the planet.

In 1687, Isaac Newton proved this mathematically with what is now called the Shell Theorem. He showed that for any uniform sphere of matter, all the individual gravitational pulls from every particle add up perfectly to simulate a single point of mass at the exact center. As far as physics is concerned, the gravitational pull you feel on the surface is exactly the same as if all of Earth's mass were concentrated into a microscopic dot at the core.

This geometry means "down" is not a fixed direction in space, but simply a local vector pointing toward the center of mass. A person standing in Australia and a person standing in Canada are both pointing their feet toward the same central point without either of them "falling off."

Gravity is also the reason planets are spherical in the first place. Once a rocky body in space reaches a certain mass—usually about 400 miles across—its gravitational pull becomes so strong that it crushes its own material inward. The solid rock behaves like a slow-moving liquid, collapsing under its own weight until all matter is as close to the center of gravity as geometrically possible.

The 'Blue Marble' photograph taken by the Apollo 17 crew in 1972. Earth's gravity pulls its matter inward from all sides, molding it into a sphere over billions of years. Source: Wikimedia Commons.

How close are we to discovering another habitable planet?

 Astronomers have already discovered dozens of "habitable" planets. The catch? Many of these promising worlds are actually bare, irradiated rocks blasted by violent solar flares.

The "habitable zone"—often called the Goldilocks zone—simply refers to the orbital distance from a star where temperatures allow liquid water to exist on a rocky surface. Researchers have identified several promising Earth-sized candidates in these zones, such as Proxima Centauri b, located just four light-years away, and the seven-planet TRAPPIST-1 system.

However, discovering a planet's orbit is only the first step. The current hurdle is proving these worlds actually have atmospheres and water. Most of the best candidates orbit M-dwarf stars (red dwarfs). While these stars are the most common in the galaxy, they are highly volatile and prone to the exact type of magnetic activity that strips away a nearby planet's atmosphere over billions of years.

Scientists are currently using the James Webb Space Telescope (JWST) to analyze these worlds, and the initial results highlight the immense difficulty of the task. JWST observations of the innermost planets in the TRAPPIST-1 system—TRAPPIST-1b and c—suggest they completely lack substantial atmospheres. Hope remains for planets further out in the system, like TRAPPIST-1e, but extracting clear atmospheric data is incredibly challenging because the star's own magnetic activity often mimics or obscures the chemical signatures instruments are looking for.

To actually confirm a habitable planet—one with an atmosphere, water, and perhaps biosignatures like oxygen and methane—astronomers need next-generation tools. NASA is currently developing the Habitable Worlds Observatory (HWO), a flagship mission targeted for the 2040s. Instead of analyzing silhouettes as planets pass in front of their stars, HWO will use advanced coronagraphs to block out starlight. This will allow the telescope to directly image approximately 25 potentially habitable worlds and scan them for the chemical signatures of life.

While scientists have mapped the locations of the most promising interstellar neighbors, definitive proof of an alien atmosphere capable of supporting life is likely waiting on the technology of the 2040s.

An artist's illustration of Kepler-186f, an Earth-sized exoplanet discovered in its star's habitable zone. Photo by Jack Madden is licensed under CC BY-SA 4.0.

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Is a planet's gravity directly proportional to its mass?

 Uranus has 14.5 times the mass of Earth. Yet if you could somehow stand on its cloud tops, you would actually weigh 11% less than you do right now.

A planet's surface gravity is not determined by mass alone. According to Newton's law of universal gravitation, the gravitational force you feel on a planet's surface depends on two variables: the planet's mass and its radius. While gravity is directly proportional to mass, it is inversely proportional to the square of the radius. This means the distance from the center of the planet matters significantly more than the sheer amount of matter it contains.

When a planet gains mass, its physical size usually increases as well. If a planet's radius grows, you are pushed further away from its center of mass. Because the radius is squared in the gravity equation, a large increase in volume can easily overpower a substantial increase in mass.

Saturn is a perfect example of this dynamic. The gas giant contains 95 times more mass than Earth. However, because it is composed mostly of hydrogen and helium, it is far less dense, giving it a radius more than nine times that of Earth. Since you would be so far from Saturn's center of mass, its surface gravity is only 10.44 m/s²—barely stronger than Earth's 9.8 m/s².

This mathematical relationship is also why ultra-dense cosmic objects possess such extreme gravitational pulls. A neutron star has roughly the same mass as the Sun, but it is compressed into a sphere just 20 kilometers across. Because the radius is incredibly small, the surface gravity is billions of times stronger than Earth's. Ultimately, surface gravity is a contest between how much mass a celestial body has and how closely you can stand to the center of it.

Uranus contains significantly more mass than Earth, but its larger radius means its surface gravity is actually weaker. Source: Wikimedia Commons.

Would it be possible for a planet of giants to exist?

 Yes, but you’d need very specific conditions.

Lower gravity, abundance resources, food, and water.

The lower gravity part is important because it becomes more difficult for life to support its own mass as gravity goes up.

This is because of the square-cube trap. As an animal doubles in linear size, it’s volume multiples by eight. It’s leg bones only become four times stronger in this process.

This is, in part, why you see larger animals (like elephants and giraffes) having a much more lumbering gait and movement. They aren’t agile at all and are only just strong enough to support their weight. Whereas you compare this to ants—which are breathtakingly strong for their height.

The low gravity aspect is also well illustrated by the fact that the largest living creatures on Earth are, by far, aquatic species such as whales.

A man petting a blue whale.

Conversely, in higher gravity planets that could support life, I suspect we’d see much smaller species overall.

So yes—it’s entirely possible there are planets with giant lumbering beasts walking about. Or at a minimum, ocean planets with even larger species than we currently have.

What is the most dangerous planet?

 The richest and most dangerous planet.

This planet is renowned for its valuable mineral resources. It is also known as the diamond planet, as almost all of the rocks that make up the planet are diamonds.

The planet 55 Cancri e has been my interest since I was 10 years old. With a mass eight times greater than Earth, it was only discovered by scientists in 2004. It's quite intriguing because it's believed to be a carbon planet, containing more carbon than oxygen. Interestingly, the side exposed to the planet's "sun" can reach temperatures of 1,700 degrees Celsius, hot enough to melt iron.

Although this is a "rich" planet whose rocks are diamonds that could be very profitable if sold on Earth, it is also very dangerous to visit. The diamonds there are not only found on the surface, but also fall from above like rain. Of course, the diamonds that fall there are not polished diamonds like those found in jewelry stores; they are raw, sharp, and capable of ripping through your skin.

I think that's all I can answer. It's been 7 years since I've been introduced to that planet, so explaining it is difficult because I've forgotten a bit.

Could there be a planet with 99% oxygen in space?

 We actually already know of one, but it's a moon, not a planet!

And yet it is so thanks to a small loophole.

This is Europa. It's a moon of Jupiter and is slightly smaller than our Moon. Its surface is composed of layers of ice, probably with liquid water deeper down. On the ice, this moon is constantly bombarded by deadly radiation (caused by the nearby volcanic moon Io and Jupiter's immense magnetic field).

Its atmosphere is composed almost exclusively of oxygen. But oxygen is so rare in the universe, so where does it come from? While oxygen on Earth is formed by plants, the oxygen on Europa is formed by radiation passing through the ice, splitting water molecules into hydrogen and oxygen gas (the hydrogen escapes into space).

But you couldn't breathe in it! Why?

Because Europa's atmosphere is actually very, very, very thin. The air pressure at its surface is only a billionth of that on Earth. So it can barely be said to have an atmosphere.

So here's the loophole: You asked about a planet whose atmosphere is 99% oxygen, which is a ratio. But you didn't ask how much atmosphere there is in the first place.

Is Pluto still a planet, or do astronomers call it a dwarf planet?

When it was discovered in 1930, Pluto was considered to be the ninth planet of the Solar System. It’s quite tiny, though: about half the size of our own Moon.

(Pluto is bottom left)

But over time, astronomers began to realise just how many similar objects there are out there beyond Neptune, in what is called the Kuiper Belt (which is kind of similar to the Asteroid Belt between Mars and Jupiter). Dozens, maybe hundreds or even thousands of them.

So if we are calling Pluto a planet, putting in the same category as Earth, Mars, etc., then there’s potentially a vast number more which should be added to the traditional list of planets. That’s not very convenient or clear.

So in 2006 the International Astronomical Union decided to define exactly what we mean by the word ‘planet’. An upshot of that was that Pluto didn’t fully qualify and came to be redefined as a ‘dwarf planet’. That is,

• it’s a round object and it’s orbiting the Sun just like a planet,
• however, it’s very small, more like the size of a moon or asteroid,
• and as such, it’s not big enough (gravitationally) to ever carve out an orbit all to itself like any big planet would.

Pluto is now just one of several dwarf planets that have been identified, including Haumea, Makemake, Eris and Ceres.

A couple of interesting facts about Pluto:

Pluto’s 248-year elliptical orbit around the Sun sometimes brings it closer to the Sun than Neptune’s orbit.

Pluto has a surprisingly big satellite (moon), called Charon. In effect, it’s a binary system.

A spider on Mercury..

 

It's called Apollodorus. A crater with hundreds of cracks.

The problem is, those cracks aren't made by the crater!

Back in 2008. The Messenger spacecraft zipped past Mercury. Snapped pictures of its side we had never seen before, and found many interesting things.

When scientists saw this weird, many-legged crater, they nicknamed it “The spider 🕷️”.

But something was off..

Those cracks turned out to be older than the crater. How do we know?

When an asteroid hits, it blasts off a lot of debris, which covers the surrounding. Like a blanket.

This debris covered the cracks. But if the cracks formed after the crater, they would have sliced through the debris.

Side-view of the crater

Also, not a single of those 100+ cracks cuts through the crater. They all stop exactly where the crater begins.

The question is, what made those cracks?

See, this crater sits in the middle of a much larger crater, called Caloris Basin. 1500 km across. The 5th largest crater in the Solar system.

Long ago, something happened deep beneath this basin. A massive plume of magma pushed it up. Caused it to bulge outwards.

But the surface is hard. It stretched and cracked.

Caloris Basin. The spider sits in the middle.

The cracks aren't random. They start from a point and spread outwards. Like a crack on your windshield.

Billions of years later, a completely unrelated asteroid hit Mercury. By pure fluke, it slammed exactly where the cracks converged.

Which planet in our solar system would be the most difficult for humans to land on safely?

 To find the hardest planetary landing in our solar system, you have to choose between a world with no surface at all, or one where the air is hot enough to melt lead.

Attempting to land on a gas giant like Jupiter is a paradox because the planet lacks a solid surface.

Jupiter, as seen by the Cassini spacecraft in 2000. It lacks a solid surface, making a traditional landing impossible.

Jupiter is composed almost entirely of hydrogen and helium. A crewed spacecraft entering its atmosphere would experience a descent with no end. After passing through turbulent, ammonia-rich clouds and lethal radiation belts, the ship would face exponentially increasing pressures and temperatures. Eventually, the pressure becomes so immense that hydrogen gas compresses into a bizarre state called liquid metallic hydrogen. Any vessel would be crushed, melted, and assimilated into the planet's interior long before reaching the core. Because there is no rocky crust to park a vehicle on, a safe landing is physically impossible.

For a true planetary landing on a solid surface, Venus provides the most hostile environment for human survival.

An illustration of a heavily armored spacecraft descending through the thick, hostile sulfuric acid clouds of Venus.

From orbit, Venus looks like a serene, bright marble, but its atmosphere is a nightmare for aerospace engineering. The atmosphere is composed primarily of carbon dioxide, with thick clouds of sulfuric acid. The atmospheric pressure at the surface is roughly 90 times greater than that of Earth. Standing on the surface of Venus would feel akin to being submerged 900 meters (about 3,000 feet) underwater. Any unreinforced habitat or spacesuit would instantly implode from the weight of the air alone.

In addition to the crushing pressure, Venus experiences a runaway greenhouse effect. The surface temperature averages around 475 degrees Celsius (887 degrees Fahrenheit). This is hot enough to melt lead, zinc, and tin. The extreme heat would instantly cook conventional life-support systems, melt electronics, and rapidly degrade spacecraft seals.

A panoramic view of the surface of Venus captured by the Soviet Venera 13 lander in 1982.

Despite these apocalyptic conditions, Soviet engineers managed to land robotic probes on Venus during the Cold War. Because the atmosphere is so incredibly dense, the later Venera landers did not even need parachutes for the final stages of their descent; they used aerodynamic braking discs to drift down through the thick, fluid-like air.

Once on the ground, the engineering challenge shifted entirely to survival. The Venera 13 robotic lander, which touched down in 1982, holds the record for the longest survival time on the Venusian surface. It lasted for just 127 minutes before the immense heat and pressure breached its protective titanium hull and destroyed its instruments. Designing a crewed lander to keep humans alive long-term on Venus would require specialized high-temperature refrigeration, massive titanium pressure hulls, and materials that push the boundaries of materials science.

While Mars presents difficulties with its thin atmosphere and dust storms, aerospace engineers plan to eventually send humans to visit and inhabit it. On Venus, achieving even a few hours of robotic surface time represents an engineering marvel, making it the single hardest planetary surface in the solar system for humans to reach and survive on.

Has a planet disappeared?

We think that our solar system lost at least one large planet in the past. Besides that, we thought we observed a planet disappear in the Fomalhaut system. Could it be evidence of extraterrestrial star wars?

Planets form in protoplanetary disks, and in their youth, many collisions and orbital instabilities can eject them, cause them to collide, or cause them to fall into stars and be destroyed. We think that our system hosted one more large planet located either between Saturn and Uranus or between Uranus and Neptune, and might have been similar in mass to Uranus and Neptune, making it an ice planet.

Robust evidence for its existence comes from computer simulations of the evolution of the orbits of the four largest planets. They don’t reproduce their current position unless a fifth world is added and ejected.

Furthermore, this banishment might have saved the inner four planets, including Earth, from instability caused by Jupiter's slow outward migration. When the fifth planet is added, its ejection propels Jupiter rapidly outwards, saving Earth, Venus, Mercury, and Mars from a sorry fate. Additionally, it sends Neptune moving outwards, and it can then capture a trans-Neptunian object, such as its moon Triton, which is thought to have been an independent dwarf planet.

It orbits Neptune in the opposite direction to other moons, and its destiny is sealed. It will fall into Neptune in about 3.5 billion years and be destroyed.

The ejection of this hypothetical fifth large planet probably occurred 3.9 to 4.1 billion years ago, and it coincides with the late heavy bombardment of Earth by asteroids, as seen in the geological record on our planet and even on the Moon and other worlds of our system. This might be additional evidence that something was going on at the time, and asteroids in the Kuiper belt and elsewhere were disrupted.

This lost planet is now a rogue world that jets through our galaxy alone without a star, probably very far away, because our system is also thought to have moved about 16,000 light-years from the place where it was born, closer to the galactic center, in the last 4.5 billion years.

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Fomalhaut is one of the brightest stars in the sky, but it is a triple star system. Its main component is almost twice as massive as the Sun, an A-type star 440 million years old. This means that it's already in a quarter to a third of its lifespan, which is 1.5 to 2 billion years.

Since this system is as young as the solar system was at the time of the ejection of the fifth large gas planet, it's also as unstable, and we see absolutely vast debris disks there. We thought we had identified a planet in it, but it turns out we witnessed, for the first time, a collision of large asteroids that left a cloud of dust so large it mimicked a planet, which eventually disappeared as the dust dispersed.

We also need to update our models of such debris disks because, within a few years, we witnessed another asteroid collision in Fomalhaut. According to models, they shouldn’t happen more often than once every tens to hundreds of thousands of years, so either the models are wrong, or there is an extraterrestrial star war there.

Just joking. This system is too young to host advanced civilizations. It took almost 4 billion years in the solar system for multicellular life to emerge, and humans appeared even later.

What are some mind-blowing facts about the planet Earth?

 Earth looked like this 700 million years ago:

That’s right, the entire planet was covered in ice sheets that reached to the equator, the globe was on an ice age on massive steroids. This event is known as Snowball Earth, the most recent of which happened in the Cryogenian period (720–635 million years ago) during the Neoproterozoic era. Earlier global freezing did happen in the Paleoproterozoic (Huronian glaciation), but I’ll be focusing on the Sturtian and Marinoan glaciations in specific.

There are 2 main things that determine Earth’s temperature-

• The sun’s luminosity
• Atmospheric gases

Back in the Cryogenian, the sun was 6–7% dimmer than it is today (the sun gets brighter over time), meaning baseline temperatures were a lot lower on average, which made Earth much more vulnerable to an albedo runaway, which I’ll get to in a bit.

In the preceding Tonian period, continents were lined in the equator, this is huge as chemical weathering is strongest at the equator due to intense rainfalls. Chemical weathering locks CO2 gases into carbonate rocks, this happens when CO2 rains down upon silicate rocks, which are common in volcanic regions and continental merging. Carbon dioxide is a greenhouse gas, which means it traps the sun’s heat in the atmosphere, unlike how oxygen is. So when CO2 gets locked away in carbonate rocks, the amount of greenhouse gases in the atmosphere decreases.

This process happened over in the millions of years leading up to the Cryogenian, CO2 would keep plummeting as more and more carbonate rocks were formed due to chemical weathering, which continuously cooled the planet. Eventually, ice around the poles started to form, ice is one of the best deflectors of sunlight on Earth, otherwise known as albedo. As the amount of greenhouse gases lowered, more and more ice started to form, which reflected more sunlight, which made the Earth even colder, which meant more ice.

Once the ice reached around 40° degrees latitude, the albedo runaway effect became unstoppable, causing ice to eventually reach the equator, thus beginning Snowball Earth.

Cryogenian Earth 🧊

It’s estimated that at least 80–90% of the planet during this time would’ve been frozen rock solid, with possible small patches of equatorial ocean remaining intact, if any. Otherwise, the continents were covered in ice sheets kilometers thick, with oceans being covered in ice at least a couple hundred meters thick.

Temperatures around this time are estimated to have averaged around -50°C globally, with the equator being around -30°C on average, and the poles being a whopping -80°C on average! To put that into perspective, Antarctica's record low of -89°C is barely colder than the average South Pole day of Snowball Earth.

The absolute coldest days of Cryogenian period would’ve likely happened in the South Pole at winter, it’s been estimated that the record low could've reached a monumental -110°C to -130°C, that’s as freezing as the average day on Mars’s poles at night. These were very likely the coldest days in Earth’s history.

However, below the ice sheets covering the sea, life was still enduring, the earliest and most primitive of animals still hanged on in these hellish conditions, such as Otavia antiqua, possibly by being near hydrothermal vents and small patches of water where sunlight hit.

And as for how Snowball Earth ended? Volcanos. 🌋

Even during this global freezing, volcanos remained active and contributors of CO2 gases, and now that Earth was frozen, chemical weathering became pretty much nonexistent, so nothing was able to prevent CO2 gases from accumulating over millions of years.

Eventually, enough CO2 accumulated that ice began to melt at the equator before eventually, Earth was ice free.

Since then, Snowball Earth has never happened again, the last time this phenomena could’ve been possible under the perfect conditions was around 540–520 million years ago in the early Cambrian, afterwards, the sun became too bright to allow ice to reach the equator before melting. Even today, we are nearing the threshold for ice ages in the geological time scale. Snowball Earth will forever be exclusive to the Proterozoic eon.

-Cesar Alcaraz