Moon Crashes, Martian Makeovers, and Other Minor Experiments

A Tour Through Digital Chaos with Universe Sandbox and Algodoo Physics

Introduction

I’ve mentioned in previous posts that I have a soft spot for simulators, including circuit simulators, factory simulators, and anything that lets me tinker and observe systems in motion. I’ve also shared a few quick Python examples built with Pygame, which rely heavily on simple physics to make the interaction feel alive. Watching a system react in real time satisfies a very specific curiosity of mine.

Recently, I finally tried out Universe Sandbox, inspired in part by the chaotic style of the YouTube channel GrayStillPlays. This tool offers a fascinating exploration of celestial mechanics, allowing you to smash planets together, alter the laws of gravity, or introduce a rogue star just to see the results. Alongside that, I revisited Algodoo Physics, a software more focused on terrestrial phenomena. It emphasizes hands-on experimentation with springs, liquids, pressure, and pulleys, offering a playful way to explore gravity and other forces.

Whether you’re experimenting, building, or simply testing the limits of what breaks first, these tools provide a fantastic educational opportunity. And, sometimes, it’s pure fun to drop a moon onto a planet and observe the resulting chaos.

A Quick Look at Universe Sandbox

Universe Sandbox has been around since 2015 and is available on Steam for approximately $30 USD. Despite its age, it remains impressive both visually and functionally. Although it is still listed as an Early Access title, the software runs smoothly and shows no noticeable issues with stability or compatibility.

The concept is simple yet powerful: you are given control over the universe. You can adjust the mass of the sun, replace Earth with a black hole, or experiment with other scenarios. Instead of a traditional "game," it functions more like an interactive physics lab where gravity, momentum, and celestial mechanics unfold in real time.

The community shares positive sentiments about it. On Steam, it has earned a 96% positive rating from nearly 24,000 reviews, securing the "Overwhelmingly Positive" label. This level of acclaim is quite rare, especially for a specialized educational simulator.

My Testing Plan (with a Little Help from ChatGPT)

These kinds of simulations scratch the same itch as Randall Munroe’s (of XKCD fame) What If? books, which explore absurd scientific questions with rigorous logic and a dose of humor. Universe Sandbox feels like the interactive version of that spirit. It lets you pose questions such as “What if the moon suddenly doubled in mass?” or “How close can a rogue planet get before Earth’s orbit collapses?” and then see the answers unfold along with all the spectacular consequences. It’s one thing to read the math on a page, but it’s entirely different to witness tidal waves, orbital shifts, and planetary destruction play out visually.

YouTube has a few channels with videos that feature all sorts of stunts you can try with Universe Sandbox. I recommend hopping over there and running a search.

While I’m not an astrophysicist, I’ll rely on ChatGPT to help me make sense of the math behind planetary habitability, mass thresholds, and impact dynamics. Universe Sandbox provides incredible tools, but it doesn’t guide you step-by-step, so having some outside calculations will definitely help. Here’s what I plan to try:

Scenario 1: Can I Add Sustainable Water to Mars?

One of the built-in tutorials introduces terraforming Mars by adding water. It’s a great starting point, but the scenario seems destined to fail. The planet either freezes or overheats, and the atmosphere never quite stabilizes. I plan to see if I can truly make it work by balancing temperature, pressure, and axial tilt to create conditions that are at least somewhat Earth-like. With the right adjustments and a few calculations, Mars might not have to remain dry and cold.

Scenario 2: Can I Turn Jupiter Into a Star?

Spoilers Ahead: If the movie 2010: The Year We Make Contact is on your list of movies to watch, skip ahead to the next scenario and avoid this scenario in the results section as well.

Inspired by the movie 2010: The Year We Make Contact or book 2010: Odyssey Two, where Jupiter ignites and becomes a second sun, I’ll explore whether stacking mass can cause it to shine without destabilizing the solar system. Science suggests Jupiter would need about 80 times its current mass to begin fusion and turn into a red dwarf. If successful, the consequences for the orbits of its moons and Earth would be fascinating to observe.

Scenario 3: What If Asteroid 2024 YR4 Hits Earth in 2032?

This concept is a little darker, but it perfectly exemplifies the type of “what if” scenario that Universe Sandbox is designed to explore. 2024 YR4 is a real asteroid that is currently being tracked. While it is not on a collision course, it serves as an excellent thought experiment. I will input its known size, velocity, and trajectory to simulate a hypothetical impact in 2032. Will the results show regional damage, a global event, or something in between?

The Results

Adding Water To Mars

Building on ChatGPT's suggestion and the in-game tutorial, I concentrated on increasing Mars' planetary rotation. ChatGPT proposed a day duration of approximately 10 hours, reasoning that this adjustment could enhance equatorial sunlight exposure, thereby fostering temperate zones near the equator.

After attempting to increase Mars' planetary rotation and shorten its day length, I found it challenging to raise peak temperatures beyond -30 degrees Celsius anywhere on the planet. ChatGPT further suggested introducing gaseous nitrogen or carbon dioxide to potentially enhance atmospheric conditions. Interestingly, after adding these gases, I noticed the formation of weather patterns and a semblance of an atmosphere. However, consistent with previous observations, any improvements in planetary temperature quickly dissipated.

Even when using the game’s planetary “heat tool” to artificially raise temperatures, such as applying 500 degrees Celsius to a surface area and maintaining it with a continuous mouse-down button click, you could observe that Mars quickly dissipated the added heat.

While terraforming Mars within the game’s initial tutorial offers an intriguing challenge, it seems unlikely to achieve true success under its current constraints.

(Note, some elements of video difficult to see on small form factor devices.)

Turning Jupiter Into a Star

This challenge proved to be complex due to the immense mass requirements and potential disruptions to the solar system. Attempts to turn Jupiter into a sun revealed significant limitations, as artificially adding luminosity wouldn’t realistically impact Jupiter’s moons or the surrounding celestial dynamics. ChatGPT proposed an alternative: replacing Jupiter with a smaller star, such as Proxima Centauri. Among the game’s built-in stars, Proxima Centauri appeared to be the most suitable “small star” to substitute in place of Jupiter, offering a compelling compromise within the simulation.

The game doesn’t allow a drop-in place replacement. Unfortunately, I tried to focus on placing Proxima Centauri in an appropriate orbit around Sol at 5.2 AU that I’m sure I didn’t quite get it lined up in the place where Jupiter had been before deletion. So, as a result, I caused Jupiter’s moons to just be flung off into random directions. Sorry about that.

I had assumed this action would just cause all sorts of havoc with the solar system. The outer planets (or dwarf planets) did seem to get a little wonky upon this change. Pluto’s orbital plane seemed to get more spherical, taking random orbits around the sun with each of its years.

Proxima Centauri did eventually drift inward towards the sun by a few tenths of an AU over about 800 years. Meanwhile, things on planet earth seemed pretty tame, aside from a bit of global cooling and erratic seasons that I can’t explain.

(Note, some elements of video difficult to see on small form factor devices.)

Sending 2024 YR4 Crashing Into Earth

It took some time to figure out how to properly simulate this scenario. ChatGPT provided estimates for the asteroid's size, mass, and density, but I encountered challenges in getting Universe Sandbox to maintain consistency between these values when creating a generic asteroid. Eventually, I decided to spawn Apophis and adjusted its diameter to 300 meters to proceed with the simulation.

I initially believed that objects of this size would burn up or disintegrate upon entering Earth's atmosphere. However, after some research, I learned that even objects as small as 25 meters can survive atmospheric entry and reach the surface.

In earlier versions of the game, there was an apparent launch tool specifically designed for such scenarios. Unable to locate this feature, I employed a workaround by placing Apophis into orbit and then halting its orbital velocity, allowing Earth’s gravity to draw it toward the surface. Naturally, the rate of acceleration played a crucial role in this process. To execute the simulation, I positioned Apophis a few thousand kilometers above Earth when it was first spawned.

The aftermath of the simulation was profoundly destructive. The asteroid left a massive crater on Earth's surface, accompanied by widespread fires triggered by the impact blast. In the months following the collision, the resulting atmospheric pollutants led to global cooling, with temperatures stabilizing at six degrees Celsius lower than the game’s typical norms.

(Note, some elements of video difficult to see on small form factor devices.)

Honorable Mention: Algodoo Physics

If causing mayhem in the heavens doesn’t sound like fun to you, I’ll also suggest Algodoo Physics.

Algodoo is a unique 2D physics simulator that blends education and entertainment with a remarkably intuitive interface. Originally a commercial product priced at around $50 USD, it has since been made completely free and is available across various platforms, including Windows, Mac, and even iPad. This shift opened the door for a wider audience to explore the principles of physics in a highly visual and interactive way.

The software allows users to design and test an incredible range of real-world mechanical systems. You can simulate gravity, friction, air resistance, and fluids, and combine them with user-created objects like gears, pulleys, springs, and motors. For example, you can build a working car with suspension, a watermill powered by flowing liquid, or an elaborate Rube Goldberg machine just to watch how energy is transferred through a chain of reactions. The built-in tools let you graph force, velocity, and other data in real time, offering immediate feedback as you tweak your designs.

Algodoo is often praised as a fantastic learning tool for kids because of its colorful visuals and drag-and-drop simplicity. It is equally valuable for adults who are curious and want to explore questions like “what would happen if...”. The software provides a sandbox environment to test such curiosity-driven ideas without needing a lab or special equipment. Whether you're experimenting with the efficiency of inclined planes, testing buoyancy, or analyzing the mechanics behind spinning objects, Algodoo transforms abstract physics concepts into engaging, hands-on experiences.

While the graphics aren’t thrilling, they’re functional and fun.

(Note, some elements of video difficult to see on small form factor devices.)

Conclusion

These simulations are more than just digital toys, they spark curiosity. Whether experimenting with engineering a livable Mars or setting the solar system ablaze with a rogue star, the process inevitably generates new questions. Tools like Universe Sandbox and Algodoo transform physics into a dynamic experience, making it feel like a tangible system you can actively explore. Failures are not setbacks but opportunities for discovery, whether it’s more data, more explosions, or a planet reduced to a glowing crater.

Ultimately, that is what makes these tools so compelling. They reduce the obstacles to experimentation and encourage you to explore, tweak, break, and rebuild. You do not need a degree to indulge in questions like what might happen if an asteroid hit the Pacific or whether a steam-powered catapult could launch a car across a lake. All it takes is a little imagination and a willingness to click "unpause." From orbital disasters to Rube Goldberg contraptions, everything is an opportunity for discovery. There is no better way to learn than by watching your own cosmic mistakes unfold in real time.