Comet Ice
Could I cool down the Earth by capturing a comet and dropping it in the ocean, like an ice cube in a glass of water? Daniel Becker No. In fact, it's honestly sort of impressive to find a solution that would actively make the problem worse in so many different ways. Dropping a comet into the ocean to cool the planet, famously suggested by the 2002 Futurama episode None Like It Hot,[1] wouldn't work for a few reasons. One is that dropping things from space creates heat. When water—or anything else—falls, it gains kinetic energy. When it stops falling, that energy has to go somewhere. Generally, it turns into heat. Water that goes over Niagara Falls, for example, gains enough kinetic energy during the 50-meter plunge to warm it up by about 0.1°C by the time it reaches the bottom. (This added heat is minor compared to the cooling effects of evaporation on the way down, so the actual temperature at the bottom is likely colder.) Outer space is a lot higher up than Niagara Falls,[citation needed] so the plunge down into the atmosphere at the bottom of Earth's gravity well adds a lot more than 0.1 degrees worth of heat. A chunk of ice from space that falls to Earth gains enough energy to warm the ice up, melt it, boil it into vapor, and then heat the vapor to thousands of degrees. If you built an icy waterfall from space, the water would arrive at the bottom as a river of superheated steam. Small chunks of ice falling from space disintegrate and boil away before they reach the ground, warming the upper atmosphere. Large comets can reach the ground intact and be vaporized on impact as their kinetic energy is converted to heat all at once. This heat energy would be about 100 times greater than the energy needed to bring even a very cold comet up to room temperature, so a comet falling from space would heat the Earth 100 times more than it cooled it. But let's suppose you figure out a way to lower the comet slowly, using some kind of magical crane,[2] and gently set the comet in the ocean. Comets are more dust than ice, but they're not particularly dense. A tiny piece of a comet would float for a short time until it became waterlogged, melted, and broke apart. A full-size comet wouldn't be strong enough to support its own weight, and would collapse like a drying sand sculpture. If the comet were placed in the ocean,[3] the added ice would cool the water down by only about a millionth of a degree. If you set the comet on land, it would soak up heat from the atmosphere—which contains much less stored heat than the oceans—briefly cooling the air by an average of one or two thousandths of a degree. Okay, so we just need thousands of comets, right? Each one will cool the air a little bit. With a large enough supply of comets, we can keep the Earth nice and cool, as long as we make sure they're lowered slowly. Unfortunately, comets would affect the Earth's temperature in another way. In addition to dust and water, they contain a small amount of CO2, which would be released into the atmosphere as the comet melted. This CO2[4] would change Earth's radiation balance, trapping heat near the surface and raising the planet's temperature. After a few years, the comet's greenhouse effect would have trapped more heat than the ice absorbed, and over the decades to follow, the extra heat would keep piling up. The CO2 released from the comet would raise the temperature of the Earth for centuries. It wouldn't just cancel out the cooling effect of the ice—over time, the comet's greenhouse effect would deliver as much heat as if you'd just let it slam into the planet and vaporize.[5] It's okay. Despite all this, your scenario could fix global warming. Remember that hypothetical crane that lets you lower comets to the surface? Well, if you hooked it up to a generator, you could use the slowly-descending comet to produce electricity. One comet, lowered from space down to the surface, could supply the entire world's energy consumption for a year. Sure, it would release a little CO2, but it would be nothing compared to the pollution from our current sources of energy. A comet crane generator could cut our energy-related greenhouse gas emissions to almost zero. The comet isn't the important part, the crane is. Sadly, we don't have the technology to build comet-lowering cranes—certainly not in time to help mitigate climate change. But harvesting orbital energy like this is a neat idea! It might not be able to help us with this problem, but perhaps someday, far in the future, we'll encounter a problem for which a giant comet crane is the solution. [1] I'm used to stuff making me feel old, but the fact that this episode aired 20 years ago is distressing in multiple ways. [2] Magical storks deliver babies, magical cranes deliver comets. [3] It actually wouldn't have much effect on global sea level, but the influx of cold water on the surface—and the dust released into the air—could definitely mess with the atmosphere. [4] Along with carbon monoxide, which indirectly affects the climate in a similar way—see pg. 718-719 of the IPCC WG1 AR5 report for more. [5] Although letting a comet slowly decay on the surface would definitely be preferable to a high-speed impact, as any dinosaur from the end of the Cretaceous can tell you.
If every country's airspace extended up forever, which country would own the largest percentage of the galaxy at any given time? Reuven Lazarus Today's question is adapted from What If 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions, which contains many more What If answers and is available now! Congratulations to Australia, new rulers of the galaxy. The Australian flag has a number of symbols on it, including five stars that represent the stars of the Southern Cross.[1] Based on the answer to this question, maybe their flag designers should think bigger. Countries in the southern hemisphere have an advantage when it comes to star ownership. Earth's axis is tilted relative to the Milky Way; our North Pole points generally away from the galaxy's center. If each country's airspace extended upward forever, the core of the galaxy would stay under the control of countries in the southern hemisphere, changing hands over the course of each day as the Earth rotates. At its peak, Australia would control more stars than any other country. The supermassive black hole at the core of the galaxy would enter Australian airspace every day south of Brisbane, near the small town of Broadwater. After about an hour, almost the entire galactic core—along with a substantial chunk of the disk—would be within Australian jurisdiction. At various times throughout the day, the galactic core would pass through the domain of South Africa, Lesotho, Brazil, Argentina, and Chile. The United States, Europe, and most of Asia would have to be content with outer sections of the galactic disk. The northern hemisphere isn't left with the dregs, though. The outer galactic disk has some cool things in it—like Cygnus X-1, a black hole currently devouring a supergiant star.[2] Each day, as the core of the galaxy crossed the Pacific, Cygnus X-1 would enter the United States's airspace over North Carolina. While owning a black hole would be cool, the United States would also have millions of planetary systems constantly moving in and out of its territory—which might cause some problems. The star 47 Ursae Majoris has at least three planets and probably more. If any of those planets have life on them, then once a day all that life passes through the United States. That means that there's a period of a few minutes each day where any murders on those planets technically happen in New Jersey. Luckily for the New Jersey court system, altitudes above about 12 miles are generally considered "high seas." According to the American Bar Association's Winter 2012 issue of the Admiralty and Maritime Law Committee Newsletter, this means that deaths above these altitudes—even deaths in space—are arguably covered by the 1920 Death on the High Seas Act, or DOHSA. But if any aliens on 47 Ursae Majoris are considering bringing a lawsuit in a US court under DOHSA, they're going to be disappointed. DOHSA has a statute of limitations of 3 years, but 47 Ursae Majoris is more than 40 light-years away... ...which means it's physically impossible for them to file charges in time. [1] Epsilon Crucis has five points, while the others have seven, implying that the view of Epsilon is from a telescope with different lens geometry from the others. Minor symbolic/graphic design choice? Or clue to a secret multiversal alliance between parallel universe Australias? No way to know for sure! [2] Cygnus X-1 was the subject of a famous bet between astrophysicists Stephen Hawking and Kip Thorne over whether it was a black hole or not. Hawking, who had spent much of his career studying black holes, bet that it wasn't. He figured that if black holes turned out not to exist, at least he would win the bet as a consolation prize. In the end, luckily for his legacy, he lost.
My daughter recently received her driver's permit in the US, and aspires to visit mainland Europe someday. She has learned enough about the rules of the road to know never to drive into the ocean; however, she jokingly suggested that given a sufficient quantity of rental cars, she could eventually get to Europe by driving east repeatedly. The question is, how many vehicles would it take to build a car-bridge across the Atlantic? Eric Munson After extensive research, I can conclusively state that this would be a violation of your rental car agreement. Also, you would disrupt ocean circulation in the North Atlantic, potentially seriously altering the climate in the northern hemisphere. That's very bad, although not necessarily a violation of your rental car agreement. If you try to drive from the US to Europe, your car will stop working pretty quickly, since according to Google Maps there's a large hole between them and it's full of water. Once your car gets stuck, you'll have to leave it there and go get another one. Driving your second car onto the roof of the sunken first one could get you a little closer to Europe. If we assume you're starting in Boston and heading toward Lisbon, using a car as a bridge would get you about a millionth of the way there, since Boston and Lisbon are about a million car-lengths apart. If the Atlantic Ocean were two feet deep, you could make a bridge out of a million cars placed end to end. Unfortunately, a quick rewatch of Titanic (1997) suggests that the Atlantic Ocean is more than two feet deep. You'll quickly have to start piling up cars in multiple layers. At first, when the bridge would be just one or two cars high, you could stack them in a single vertical column. But as the water gets deeper, you'll need to create a wider base to keep the wall of cars from tipping over.[1] The North Atlantic current would push against the car causeway, but the tipping force from the water motion would be relatively minor compared to the pile's tendency to topple under its own weight.[2] As you built your bridge out into the deep ocean, the cars on the bottom of the stack would be crushed. The pressure crushing them wouldn't be the water pressure. Once the windows broke and the interior of the car flooded, the pressure would equalize and the cars would hold their shape, relatively unaffected by the weight of the ocean above them. Instead, what would crush the cars would be the weight of the other cars sitting on top of them. Even when they're underwater, cars weigh a lot. About 50% of the weight of modern cars is steel and iron, which is much denser than water,[3] so submerged cars are still quite heavy—about 60% to 70% of their surface weight, depending on their exact composition. The cars on the bottom of a mile-high stack would be subjected to extreme pressures, even greater than what they experience in hydraulic car crushers. Those crushers[4] are capable of flattening a car into a pancake a foot or two thick, and the same thing would happen to the cars on the bottom of our stack. The first part of your bridge to Europe would be over the continental shelf, where the water is relatively shallow—just a few hundred crushed cars deep. You'd still need a lot of cars to form this shallow-water portion of the bridge; getting out to the edge of the continental shelf would take about a billion of them, which is probably close to the total number of cars in the world. Parking lots hold about 1 car per 30 square meters, so a billion cars would cover a large portion of eastern Massachusetts.[5] After the continental shelf, the water gets a lot deeper. The deep-ocean portion of your bridge would require a lot more cars—likely about a trillion of them. This is far more cars than exist in the world; a parking lot big enough to hold them would take up most of the Earth's land area. So you can't rent anywhere close to a billion or a trillion cars—Enterprise, for example, only has about half a million cars in its fleet. But if you tried, you'd run into other problems, too. I got a copy of a recent Enterprise rental car agreement, and I have some bad news: 4. Prohibited Use and Termination of Right to Use. a. Renter agrees to the following limits on use: [...] (4) Vehicle shall not be used for: any illegal purposes; in any illegal or reckless manner; in a race or speed contest; or to tow or push anything. [...] (8) Vehicle shall not be loaded in excess of Vehicle’s Gross Vehicle Weight Rating [...] (9) Vehicle shall not be driven on an unpaved road or off-road. You'd clearly be in violation of 4(a)(9) by driving it off-road. I think you'd also be violating 4(a)(4) and probably 4(a)(8) as well. This would result in you being—at minimum—on the hook for the total cost of the rental car.[6] Some credit cards offer coverage for rental car damage, so you might think that—if you're a high-status cardholder—you could try to get the company to foot the bill. Unfortunately, I took a look at the agreement for the American Express Centurion card, and the "What is Not covered" section clearly addresses this scenario: What is Not Covered? ANY COVERED EVENT BASED UPON OR ARISING OUT OF: [...] 3. Use of the Rental Vehicle in violation of the terms and conditions of the Rental Agreement [...] 8. off-road operation [...] of the Rental Vehicle [...] 11. intentional damage [...] to the Rental Vehicle Interestingly, American Express will also not cover damages incurred by using the rental car in a war: [...] 1. War or acts of war (whether declared or undeclared), service in the armed forces or units auxiliary to it [...] This rule could actually end up being relevant here. Your car bridge across the Atlantic, in addition to potentially disrupting ocean circulation, would cut off shipping access to northern Europe and much of Atlantic Canada... ...which may qualify as a naval blockade. [1] A glance at piles of cars in a junkyard suggests that they often end up in stacks with an angle of repose of 30 or 45 degrees, but a stack with a 10°-15° angle of repose at the bottom should be stable once the cars are sufficiently crushed. [2] Mike Ashby's Useful Solutions to Standard Problems is a fantastic resource for these kinds of calculations. In this case, you could use it to figure out how a column of cars will topple, which would require an estimate of the compressibility of a stack of cars at different stages of flattening. I used specs from hydraulic car crushers to come up with my rough estimates here, but these estimates could probably be refined with experiment if you know someone with a lot of cars. [3] Citation: You don't see a lot of anchors floating around. [4] Most famous, of course, for imperiling George Frankly in an episode of MathNet, the detective show on PBS's Square One TV. [5] Apparently all the world's cars would take up slightly more space than all the world's people. [6] If you continue to operate the vehicle in such a manner, 4(d) says the company has the right to notify police that it has been stolen.
My 4 year old son and I were wondering about soccer ball sized hail today. How much damage would a hail storm with size 5 soccer ball sized hail do? Michael Grill When you think about it, it's honestly kind of weird that hailstones haven't killed all of us already. I mean, they're chunks of ice that plunge from the sky! Hailstones fall from really high up. There's a popular myth that a penny dropped from the Empire State Building can kill you. The myth isn't true,[1] but for anyone who believes it, hailstones should be terrifying—after all, they often fall from the height of ten Empire State Buildings. Luckily, the same thing that saves us from falling pennies also generally protects us from hailstones: Air resistance. As they fall, both pennies and hailstones quickly reach terminal velocity, the speed at which drag balances out gravity and prevents them from speeding up any more. For a small hailstone the size of a pea or a marble, terminal velocity might be only 10 or 20 miles per hour, the speed of an object tossed across a room. Getting hit by them isn't comfortable, but it's not likely to cause serious injury.[2] Large hailstones travel much faster than small ones and can be a lot more dangerous. The terminal velocity of a golf-ball-sized hailstone is about 60 miles per hour,[3] which could easily cause serious injury. Large hailstorms often cause extreme damage to cars, and the largest hailstones can be deadly. A storm in China in 2002 dropped egg-sized and baseball-sized hailstones that killed several dozen people and hospitalized many others. Luckily, deaths from hail aren't very common, for two main reasons: First, because hailstones big enough to be deadly are rare, and second, because when there's a thunderstorm severe enough to produce such large hail, people generally try to take shelter. A hailstone the size and shape of a regulation soccer ball would be more than twice the weight of the heaviest hailstones on record. It would have a terminal velocity of roughly 140 miles per hour, which is really fast. If one of them hit your car, it wouldn't just dent the body or crack the windshield, it could punch right through the roof. Sheltering indoors might not be enough to protect you, unless you had a particularly sturdy roof or possibly several floors above you. When a hailstorm is nearby, it's good to take shelter even if you're not right below the storm. As a hailstone forms in a thunderstorm updraft, it bounces around like popcorn in a popcorn machine. Usually, it falls out of the bottom of the storm, but sometimes it's ejected out of the top or sides, then carried by wind to fall some distance from the storm. Aircraft flying near thunderstorms have been hit by hail when they have nothing but blue sky above them. Real hailstones, especially large ones, aren't round like a soccer ball. As they tumble around in a thunderstorm, they grow via water freezing onto their sides. If they have a lump on one side, the protrusion can collect more water and grow faster than the areas around it, forming a blobby appendage. Liquid water can also run out to the edges of a rotating hailstone and freeze, forming icicle-like features. The weird shapes of large hailstones are good news for us ground-dwellers with breakable bones, because these protrusions tend to increase their drag and lower their terminal velocity. But the weird shapes of hailstones also raises an interesting possibility. If a hailstone had just the right combination of lobes, it's possible—if unlikely—that it might happen to form a lifting body. This strange category of aircraft—which includes the Space Shuttle, the M2-F1, and the Dream Chaser—can be unexpectedly aerodynamic despite their compact shapes, capable of gliding or even swoops. It's unlikely that any gliding hail has ever been observed, but in the 4 billion years that Earth has had water and thunderstorms, there have probably been some pretty strange hailstones. Not only has there likely been one the size of a soccer ball ... ... there might even have been one able to score a goal. [1] Mythbusters tried it in Season 1 Episode 7 and found that the penny would really sting and make you go "ow!!" [2] While dropping a penny on someone from the height of the Empire State Building wouldn't kill them, dropping the Empire State Building on a them from the height of a penny would, as demonstrated by the tragic demise of Jebediah Mythbuster in the pilot episode of the show eventually named in his memory. [3] A little slower than an actual golf ball, thanks to the golf ball's greater weight and those weird drag-reducing dimples.
I heard that bananas are radioactive. If they are radioactive, then they radiate energy. How many bananas would you need to power a house? Kang JI Bananas are radioactive. But don't worry, it's fine. Bananas are radioactive because they contain potassium, some of which is the radioactive isotope potassium-40. The factoid about banana radioactivity was popularized by nuclear engineers trying to reassure people[1] that small doses of radiation are normal and not necessarily dangerous. Of course, this kind of thing can backfire. Thanks to their use as a radiation dose comparison, bananas now have a reputation as an especially radioactive food, but they're really not. The CRC Handbook of Radiation Measurement and Protection, the source of the original data behind the banana factoid, lists lots of other foods with more potassium-40 than bananas, including coconuts, peanuts, and sweet potatoes. A large cheese pizza might be three times more radioactive than a banana,[2] and your own body emits a lot more radiation than either. Potassium-40 decays slowly, with individual atoms sitting around for millions or billions of years before quantum randomness finally triggers their decay. Imagine you're an atom of potassium; every second you roll 21 dice. If they all come up 6s, you decay. There are gazillions[3] of atoms of potassium-40 in a banana. In any given second, 10 or 15 of them make that all-sixes roll, spit out a high-energy particle, and become stable calcium or argon. That high-energy particle released by the expiring potassium atom[4] will promptly bonk[5] into other atoms, leaving everything vibrating with extra heat energy. In theory, you could use this heat energy to do work—that's how the Mars rovers Curiosity and Perseverance are powered. The Mars rovers use plutonium, which decays millions of times per second, releasing a lot of power. By comparison, the 15 decays per second from one banana work out to a couple of picowatts of power, roughly the power consumption of a single human cell. Even if you captured that decay energy with perfect efficiency, powering a house would require about 300 quadrillion[6] bananas, which would form a heap large enough to bury most of the skyscrapers in the NYC metro area.[7] The potassium-40 in bananas is a terrible source of energy. But that's okay, because you know what's a great energy source? The banana itself! A banana contains about 100 calories of food energy, and if you incinerate whole bananas as fuel, it would only take about 10 bunches per day to keep your house running. Unfortunately for New York City, which we buried in bananas a moment ago while trying to make the radiation idea work (sorry!), radioactivity vs chemical energy isn't an either/or thing. If you piled up a lot of bananas, they would start to release that chemical energy, one way or another. The sun-baked banana pile would start to rot. The heat from the bananas decomposing in the atmosphere would immediately swamp the heat from radioactivity. The sun-dried bananas would dry, crack, and eventually burn. Decomposition by anaerobic bacteria deep in the pile would produce various gases, including highly flammable methane. As they bubbled up to the surface of the burning banana swamp, they could ignite; gas buildup from food waste is a major industrial explosion hazard. So don't worry about the radioactivity in bananas. It's the rest of the banana that's the real threat. But if you're willing to risk the danger, you could power a lot more than just your house. With just a modest weekly supply of bananas—enough to cover Liberty Island in NYC... ...you could power the entire city. [1] After nuclear engineering, this is the main pastime of nuclear engineers. [2] Google has a handy tool for looking up the amount of potassium in foods, which even lets you select specific pizza brands. But for some reason, if you select Pizza Hut Pepperoni Pizza, your only serving size options are either "1 slice" or "40 pizzas." Nothing in between. [3] There are about 800,000,000,000,000,000 of them, which is probably quadrillions or quintillions or something, but life is too short to sit around counting zeros and then looking up the Latin prefixes for big numbers. [4] RIP [5] The technical term is THUNK. [6] Fine, I looked it up this time. [7] It's 300 quadrillion bananas, Michael—what can it cost, 3 quintillion dollars?