The eight planets of our solar system range from hot, rocky Mercury to the huge gas giants further out, but Earth is unique in that it is the densest of all the planets. The reasons behind that have to do with the way the planets formed in the first place. They coalesced from material spinning around the sun as it formed, all at different distances from the star that affected what they are made of.

If everything were based purely on the elements making them up, Mercury would be the densest planet. Mercury has a higher proportion of elements that are higher on the periodic table compared to any other known world in the Solar System. Even the asteroids that have had their volatile ices boiled off aren't as dense as Mercury is based on elements alone. Venus is #2, Earth is #3, followed by Mars, some asteroids, and then Jupiter's innermost moon: Io.

But it isn't just the raw material composition of a world that determines its density. There's also the issue of gravitational compression, which has a greater effect for worlds the larger their masses are. This is something we've learned a lot about by studying planets beyond our own Solar System, as they've taught us what the different categories of exoplanet are. That's allowed us to infer what physical processes are at play that lead to the worlds we observe.

The process of planet formation made Earth unique, and may go a long way toward explaining why it is habitable. The story is told in fascinating detail at Forbes. -via Damn Interesting

(Image credit: NASA)

When you are looking for recommendations of new movies (or movies new to you, that is) to watch, an esoteric list is more useful than a ranking of blockbusters. You already know about the blockbusters. Independent films are those made outside the Hollywood studio system, often on a shoestring budget.

In our attempt to assemble a list of the most important American indies, we have included works by mavericks, film school grads, and true outsiders; productions with multimillion-dollar budgets and labors of love financed through part-time jobs; movies that played the arthouse, the grindhouse, or barely anywhere at all.

Some were massive box office hits, while others languished in obscurity for decades. Not all of our selections would rank among the best American independent movies ever made. Instead, the films on this list are the ones that broke new ground, created genres, or first introduced important artistic voices and subjects into American film.

So while this list from the A.V. Club contains famous indie films you'd expect, like Night of the Living Dead, Eraserhead, and Clerks, it also has big films you might not have known were independents, like Dirty Dancing, Easy Rider, and Pulp Fiction. It also includes quite a few films that you have never heard of, but would be worth looking up and watching today.

(Image credit: Karl Gustafson)

Pull yourself together! Existence can be difficult at times, but with a little motivation, you can give it the honest effort it requires. This surreal animation is from AJ Jefferies. -via Boing Boing

Peter Dearman didn't come up with the idea of running a vehicle on liquid air; the concept goes back more than 100 years. But in 2001, he actually built one that worked. Dearman took that old idea and set to work fixing the problems that kept it off the market all that time.

Still, the underlying principle was sound. Most engines rely on heat differentials. In the case of, say, a gasoline-powered car, the fuel is mixed with air, crammed into a piston chamber, and set alight, causing it to jump more than 1,000 degrees in temperature. The gas rapidly expands, propelling the piston and, in turn, the wheels. Take the same process, slide it way down the Fahrenheit scale, and you've got a liquid air engine. The nitrogen fuel starts out at 320 degrees below zero. When it enters the (much warmer) piston chamber, it boils off into gas. The change in temperature is smaller than with gasoline, so the pistons move with a little less oomph—but it's enough to get the wheels going. The real problem comes later: All that frigid fuel coursing through the engine quickly freezes it, effectively wiping out the heat differential. The air stops expanding, and the car runs out of puff.

The roadblock was clear, Dearman told me recently. He'd been pondering how to get around it since he was a teen. In a car that runs on heat, you need something to keep it cool—a radiator. In a car that runs on cold, you need the opposite. “I had an idea in my head for how to make it work, but I knew I wasn't going to get anywhere until I had some research to go on,” he said.

Dearman not only came up with a way to dissipate the cold, but also harness it in a way that would make the vehicle efficient enough to justify its development, all while being eco-friendly. Read the story of Peter Dearman's liquid air engine at Wired.

(Image credit: Jan Siemen)

drive on ice they said! this got me pic.twitter.com/VHxwSEhIAY

— Dan Mace (@Dannmace) March 27, 2020

Driving on ice is pretty scary, but some folks won't let that stop them. Watch this SUV take on a frozen lake that seems to be on the verge of melting, considering the sheen of water on top of the ice. This video has been all over the internet, but this version is the full story, including footage from inside the vehicle. If you're expecting a failure, you've come to the right place. But stay to the end. -via Geekologie

When did women start wearing their hair cut short? You might think the style dates back about a hundred years to the rise of the flapper, but it is actually quite a bit older, before the days of motion pictures or even photographic evidence. Specifically, back to the French Revolution. And even then, fashion trends followed pop culture entertainment.

During the later years of the French Revolution, many fashionable young men and women of the upper and middle classes began to cut their hair short. It was called the Titus haircut, or coiffure à la Titus. The name is a reference to Titus Junius Brutus, the elder son of Lucius Junius Brutus, who founded the Roman Republic in 509 BC by famously overthrowing the Roman monarchy.

The unlikely connection between an ancient Roman nobleman and a late-18th-century French haircut begins in 1729, with the French Enlightenment writer Voltaire, who had just finished composing a five-act play called Brutus. The play draws material from the legendary story of Lucius Junius Brutus, who condemned his son Titus to death for taking part in a conspiracy to reinstate the monarchy and put the overthrown king Lucius Tarquinius Superbus back on the throne. Titus was blindly in love with the Etruscan king’s daughter Tullie, and it was through this relationship that the conspirators dragged Titus into betraying Rome. When the Senate handed Titus over to his father, Brutus forgave his son but insisted on his execution to ensure the safety of the Republic.

What does any of this have to do with short hair? The actor who portrayed Titus during a 1791 revival of the play had his hair cropped short. Read how that became a viral fashion and what it meant to the French at Amusing Planet.

According to Merriam-Webster, concatenation is "a group of things linked together or occurring together in a way that produces a particular result or effect," or else the process of linking those things. The experimental film CONCATENATION by Donato Sansone strings together all kinds of film clips that have only one thing in common: motion. Placed just right in sequence, they remind one of a chain-reaction domino fall, marble run, or Rube Goldberg machine. It's a lot of clips, but they move so fast the video still comes in at less than a minute. Genius! -via Colossal

You may have already thought giraffes are weird, but you really have no idea. Many parts of the giraffe are over-engineered to deal with its ridiculous height and lifestyle. Ze Frank is here to explain just how strange giraffes can be. This video, unlike his other animal videos, contains no explicit mating footage, but does have one dead giraffe near the end.

On the internet, you can find recipes for all kinds of homemade weirdness. But when it comes to ice cream, Sato Shigeaki probably thought of it first. His sardine ice cream recipe is already 26 years old.

In 1994, the Japanese Patent Office granted Sato Shigeaki a patent for sardine-flavored ice cream. In his patent application, Shigeaki explained that his intention was to to promote the fishing industry by encouraging children who don't like fish to eat them. He also provided the basic recipe for his sardine ice cream. It involved cooking the sardines with onions, soybeans, rice wine, and walnut paste. Then adding this concoction to a base of chocolate ice cream.

It turns out that Shigeaki was in the business of making ice cream to promote businesses that weren't ice cream. He also patented ice cream flavors that incorporated trees, beer, wine, and even silk! Read about Shigeaki's odd ice creams at Weird Universe.

One of the things that seems very weird in Star Wars is the planet Tatooine, which has two suns. Binary suns? How could a planet revolve around two suns? The most logical explanation is that the planet moves orbitally in the same plane, or disk, that the suns use to revolve around each other. Binary stars have been found in the Milky Way galaxy, some with planetary discs in their revolutionary plane, but others are much stranger. Some revolve perpendicular to their planetary disks, and one system has four stars!  

The stars in the binary system Ea and Eb are both low mass, about 0.93 and 0.28 times the mass of the Sun. They orbit each other in just 19 days on a mildly elliptical orbit, and are surrounded by a lovely disk of gas and dust about 4 billion kilometers in radius (a disk that orbits both stars in a binary like that is called a circumbinary disk).

Careful examination of the data showed that the plane of the stars' orbits and the plane of the disk match to within a few degrees. In fact, looking at other short-period binaries they found the same thing.

But when they looked at binary stars that orbit farther out, the disk is highly tilted. An earlier paper from a different team of astronomers, for example, looked at a different young system, called HD 98800. This too is what's called a hierarchical quadruple system, with two pairs of binary stars orbiting each other. The inner pair (HD 98800 Ba and Bb) has a ring of dust surrounding it, but that ring is perpendicular to the binary orbital plane. The orbital period of that binary is 315 days, much longer than UZ Tau E. Again, the same is true for several other system they examined.

But back to Tattoine, which is more mundane than we realized in 1977. If the planet's revolution is circumbinary, its residents would see a solar eclipse about every day (although they shouldn't look at it). Read about both real and fictional binary and multiple star systems at Bad Astronomy.

(Image credit: Disney/Lucasfilm)

Tranquilizer darts are quite useful in that they allow us to sedate large and/or wild animals without getting dangerously close to them. They are also very handy in movies when needed. But they don't really work the way you see in film. Here's the real story about tranquilizer darts, which actually do hit humans from time to time. -via Digg

Africa contains many fossil remains of species that could be our ancestors -or could be evolutionary branches of ancestral species that didn't lead directly to Homo sapiens. The more species are found, the muddier the picture gets. Two-million-year-old fossils of Australopithecus africanus and another that could be Paranthropus robustus lived in the same area a few hundred thousand years apart. Both seem to have walked upright on two legs by their anatomy. But more recent tests show that the slightly older fossil did walk upright, while the newer one appears to have lived in trees, even though it was built for walking.   

It's hard to say exactly what that means, since we don't know the younger hominin's species for sure, or exactly where it fit into the family tree. However, it definitely spent some time in actual trees, hundreds of thousands of years after other hominins in the same area had taken up bipedalism. And two species which had clearly evolved for similar ways of life still practiced very different behavior. That means that our early cousins were a much more diverse group, both physically and behaviorally, than we've realized until fairly recently.

The researchers say they would like to CT scan the femurs of other early hominin specimens to help shed more light on how they moved in life. They also hope to study other bones, to better understand what their internal structure can tell us about what hominins did, rather than just what kinds of selective pressure their ancestors faced.

The real story here is how they determined the difference. While the fossil bones look alike, deep scans revealed where the hominin's lifestyle put stress on those bones. Read how they figured this out at Ars Technica. 

(Image credit: Georgiou et al. 2020)

People all over are working hard to keep themselves occupied and bring a smile to others at a safe social distance. In Seattle, Cristie Kearny converted her little free library box into a Peep Show! It's not at all x-rated, but a diorama made with marshmallow Peeps. The first show is "Mary Peepins," a candy takeoff on the Disney movie. Kearny plans to change it out and stage a different movie diorama every week. See more pictures of it at Boing Boing.

Most Star Wars geeks could retell the story of the first Star Wars movie pretty easily, possibly adding analysis along the way. But Liam's girlfriend Jessie has only seen the movie once, about three years ago. She recalls some things in great detail, but loses track of the overall scheme of things rather often. At least she remembers the character's names. Liam animated her account with appropriately stupid visuals. -via Geekologie

"Triple Self Portrait" by Norman Rockwell pic.twitter.com/LEr2e2bl7x

— Robert Etheredge (@BobEtheredge) March 28, 2020

The Getty Museum is challenging its Twitter followers to recreate famous artworks at home! Using just the objects around you and your imagination, see if you can bring a familiar painting to life. So far, quite a few folks have done it with results ranging from clever to hilarious to hilariously clever.

Meanwhile, in Iceland... pic.twitter.com/KKwbcIv1is

— RustyBertrand (@RustyBertrand) March 28, 2020

Magnificent

— busyness (@busyness) March 29, 2020

Add your creations to the Twitter thread here or just look through and see what others have done. See the top-ranked art so far at Bored Panda.