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Why humanity owes a lot to Jupiter
Our friendly neighborhood gas giant serves as a cosmic catcher's mitt.
- In 1994, a comet struck Jupiter, exploding on the gas giant's surface in an incredibly violent fireball.
- Such collisions are not uncommon for Jupiter. What is uncommon, however, are solar systems with planets like Jupiter.
- Without Jupiter, life on Earth might have been obliterated by comets and asteroids before it even got a chance to begin. The fact that Jupiter-like planets are so rare might be one of the reasons why we haven't found intelligent life yet.
In the two years leading up to 1994, astronomers had eagerly watched the progress of a comet called Shoemaker-Levy 9 as it journeyed through our solar system. It was the first comet to be observed orbiting a planet — Jupiter, in this case — and over the years, the gas giant's gravity had ripped the comet apart into several fragments up to 1.2 miles in diameter, swirling around at 134,000 miles per hour.
The comet itself wasn't what had attracted astronomers — instead, it was the chance to observe the predicted impact of Shoemaker-Levy 9 with Jupiter. And when Shoemaker-Levy 9 finally did strike Jupiter in July of 1994, there was one hell of an explosion. When the first fragment tore into the planet, a nearly 2,000-mile-high fireball exploded with temperatures in excess of 42,000 Fahrenheit.
It's not the only time Jupiter's been hit, too. Some studies estimate that the gas giant gets hit 8,000 times more than Earth. But that number might even be higher — we can't directly observe the far side of Jupiter, after all, and the Shoemaker-Levy 9 collision was one of the first times we thought to even look for celestial bodies impacting Jupiter. It makes sense: Not only is Jupiter a huge target, its mass attracts celestial bodies as they pass through our solar system.
So, this begs the question: What if we didn't have Jupiter in our solar system to suck up these rogue asteroids and comets?
This GIF shows the fireball created by Shoemaker-Levy 9's first impact with Jupiter.
How Jupiter protects us
Jupiter is big. Really big. Like a celestial clown car, Jupiter is so large that about 1,300 Earths could comfortably fit inside it. It's incredible girth is also an incredible boon for Earthlings. Jupiter attracts many asteroids and comets like Shoemaker-Levy 9 that, if not for Jupiter, might have struck the Earth.
Famously, one such asteroid snuck by and hit Earth about 65 million years ago, setting off a chain reaction that would ultimately lead to the extinction of the dinosaurs and provide mammals like us a shot at global domination. Now that humans are on top, we would very much like to stay there. Indeed, chances are a second major impact wouldn't be so fortuitous for us as the first was. Not only that, but if Jupiter were not there to suck up all of these other asteroids and comets, life may not even have had a chance to begin on Earth at all.
Jupiter's complicated, cloudy surface. Image source: NASA
The rare Earth hypothesis
As it turns out, solar systems with planets like Jupiter are fairly uncommon in the galaxy. This fact, coupled with Jupiter's protective role in our own solar system, lends credence to what scientists call "the rare Earth hypothesis."
One of the big mysteries in astronomy and astrobiology is how devoid of life the universe apparently is. Noting the many billions of stars similar to the sun, the probability of Earth-like planets orbiting those stars, and the probability of intelligent life to develop on those planets, physicist Enrico Fermi first asked the question "Where is everybody?" This would later become known as the Fermi paradox.
This paradox was put more formally by Frank Drake in the Drake equation, which lays out a statistical basis for estimating the number of intelligent civilizations in the Milky Way. His original estimates stated that there were between 1,000 and 100,000,000 civilizations in the galaxy. As we learned more about the universe, scientists have managed to narrow this number down. Current estimates put humanity's chance of being totally alone in the galaxy at 39 percent.
Part of why this is the case is because of Jupiter. Only about 1 in 1,000 stars are both similar to the sun and have a Jupiter-like planet with a relatively stable orbit in the outer rings of the solar system. When a Jupiter-like planet's orbit is a bit more eccentric than ours is, gradually the gas giant's orbit starts to bend towards its star. On its way, the planet rips apart any material that would have otherwise eventually formed into a planet like Earth. When they get close to their star, they become "hot" Jupiters.
In solar systems with hot Jupiters, Earth-like planets are exceedingly rare. And for those solar systems where a potentially habitable, Earth-like planet does exist don't have the benefit we have from our Jupiter. In effect, we're protected by a giant, gaseous catcher's mitt; when asteroids and comets go hurtling through our solar system, Jupiter catches them before they wipe us out.
The idea of 'absolute time' is an illusion. Physics and subjective experience reveal why.
- Since Einstein posited his theory of general relativity, we've understood that gravity has the power to warp space and time.
- This "time dilation" effect occurs even at small levels.
- Outside of physics, we experience distortions in how we perceive time — sometimes to a startling extent.
Physics without time<p>In his book "The Order of Time," Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.</p><p style="margin-left: 20px;">"If I observe the microscopic state of things," writes Rovelli, "then the difference between past and future vanishes … in the elementary grammar of things, there is no distinction between 'cause' and 'effect.'"</p><p>So, why do we perceive time as flowing <em>forward</em>? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.</p><p>Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.</p><p style="margin-left: 20px;">"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the <a href="https://www.ft.com/content/ce6ef7b8-429a-11e8-93cf-67ac3a6482fd" target="_blank"><em>Financial Times</em></a>. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."</p>
The strange subjectivity of time<p>Time moves differently atop a mountain than it does on a beach. But you don't need to travel any distance at all to experience strange distortions in your perception of time. In moments of life-or-death fear, for example, your brain would release large amounts of adrenaline, which would speed up your internal clock, causing you to perceive the outside world as moving slowly.<br></p><p>Another common distortion occurs when we focus our attention in particular ways.</p><p style="margin-left: 20px;">"If you're thinking about how time is <em>currently</em> passing by, the biggest factor influencing your time perception is attention," Aaron Sackett, associate professor of marketing at the University of St. Thomas, told <em><a href="https://gizmodo.com/why-does-time-slow-down-and-speed-up-1840133782" target="_blank">Gizmodo</a></em>.<em> "</em>The more attention you give to the passage of time, the slower it tends to go. As you become distracted from time's passing—perhaps by something interesting happening nearby, or a good daydreaming session—you're more likely to lose track of time, giving you the feeling that it's slipping by more quickly than before. "Time flies when you're having fun," they say, but really, it's more like "time flies when you're thinking about other things." That's why time will also often fly by when you're definitely <em>not</em> having fun—like when you're having a heated argument or are terrified about an upcoming presentation."</p><p>One of the most mysterious ways people experience time-perception distortions is through psychedelic drugs. In an interview with <a href="https://www.theguardian.com/books/2018/apr/14/carlo-rovelli-exploding-commonsense-notions-order-of-time-interview" target="_blank"><em>The Guardian</em></a>, Rovelli described a time he experimented with LSD.</p><p style="margin-left: 20px;">"It was an extraordinarily strong experience that touched me also intellectually," he said. "Among the strange phenomena was the sense of time stopping. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing any more. It was a total subversion of the structure of reality."<br></p><p>It seems few scientists or philosophers believe time is completely an illusion.</p><p style="margin-left: 20px;">"What we call <em>time</em> is a rich, stratified concept; it has many layers," Rovelli told <em><a href="https://physicstoday.scitation.org/do/10.1063/PT.6.4.20190219a/full/" target="_blank">Physics Today</a>.</em> "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."</p>What <em>is</em> an illusion is the idea that time flows at an absolute rate. The river of time might be flowing forever forward, but it moves at different speeds, between people, and even within your own mind.
The world's 10 most affected countries are spending up to 59% of their GDP on the effects of violence.
- Conflict and violence cost the world more than $14 trillion a year.
- That's the equivalent of $5 a day for every person on the planet.
- Research shows that peace brings prosperity, lower inflation and more jobs.
- Just a 2% reduction in conflict would free up as much money as the global aid budget.
- Report urges governments to improve peacefulness, especially amid COVID-19.
The lush biodiversity of South America's rainforests is rooted in one of the most cataclysmic events that ever struck Earth.
- One especially mysterious thing about the asteroid impact, which killed the dinosaurs, is how it transformed Earth's tropical rainforests.
- A recent study analyzed ancient fossils collected in modern-day Colombia to determine how tropical rainforests changed after the bolide impact.
- The results highlight how nature is able to recover from cataclysmic events, though it may take millions of years.