Weird science that makes giant arthropods impossible

Some of Sci Fi’s most interesting aliens look like or share traits with Earth’s arthropods.  Arthropods include insects (like, ants), centipedes and millipedes, arachnids (like, spiders) and crustaceans (like, crabs and lobsters).  Think of the giant sandworms of Arrakis in Dune, the spider-like buggers of Ender’s Game, and the Bugs of Starship Troopers, which are very cool alien space bugs.  All of these aliens are human-size or larger.

But on Earth, physics and genetic history have kept arthropods much smaller than humans.  The largest arthropods alive are certain crabs and lobsters, and even the largest of these, the American Lobster, does not grow to 50 pounds.  Yes, that’s big for a lobster, but not exactly the match of a human in a gladiator ring or in a space battle.  It’s certainly not large enough to develop the large, complex brain needed for sentience.

Photo of crayfish. Crayfish exoskeletons form natural armor. Photo by Anton Ahlberg (
Crayfish exoskeletons form natural armor. Photo by Anton Ahlberg (

On Earth, arthropods developed exoskeletons (skeletons on their outsides), which provide great protection from enemies and allow the evolution of an amazing range of weapons and tools.  Consider the giant claws of a crab or the sting of a scorpion.  But exoskeletons restrict how large arthropods can afford to grow.  Molting — the process of replacing an exoskeleton as the animal grows — takes longer the larger the animal grows.  Some crabs take an entire month to climb out of their old skeleton and allow the new one to harden up.  Exoskeletal legs are also basically tubes filled with muscle and tissue.  If an arthropod grew to human size, the exoskeleton would not be strong enough to hold up the ‘pod’s weight.  And the arthropod’s muscles would not be strong enough to move the exoskeleton around.

Arthropods also evolved in a way that their cells get oxygen through gills, their skin, or tubes in their bodies, called tracheae, that open directly to the outside air.  Humans and other vertebrates have lungs and feed oxygen to the cells through the blood.  As ‘pods grow larger, it becomes harder and harder to get enough oxygen through their skin or tracheae to every cell.  A ‘pod as large as a human might easily suffocate.

As ‘pods grow larger, it becomes harder and harder to get enough oxygen to every cell.

But a ‘pod-like animal that evolved on another planet might not have those limits.  For example, we can imagine an alien “Pod” that evolved from simpler ancestors with both an internal and external skeleton.  Such creatures might have an internal skeleton in their arms and legs to support the weight of a large body.  But with a partial exoskeleton, the Pod might have a natural helmet for its head, giant claws, or possibly a scorpionlike tail.  With lungs instead of tracheae, the Pods could breathe like we do.  Finally, on an alien world with different elements in the rocks and soil, the Pods might evolve with exoskeletons made from lighter, stronger materials that would allow them to grow mighty armor and still move quickly.

Photo of two red crab claws clasping. Could a Pod with giant crablike claws evolve on some distant planet? 
Photo by Joshua Théophile (
Could a Pod with giant, crablike claws evolve on some distant planet?
Photo by Joshua Théophile (

Check out this great University of California at Berkeley website that explains the reasons that limit the size of arthropods on Earth.

Photo of bee.  Bees and wasps can fly AND sting. Photo by USGS (
Bees and wasps can fly and sting.
Photo by USGS (

Design a Pod

Let’s design our own alien Pod.

What two features that exist on Earth’s arthropods would you add to your Pod?  Would they make it a fearsome foe?  Would it have any weaknesses?

Please post your comments below.

Be stellar!

Matthew Cross

Cyborg parts–machine hands and feet in Sci Fi can do incredible things

Image of metal android
Cover of Cinder by Marissa Meyer

In the Cinder by Marissa Meyer, Linh Cinder is a licensed mechanic living in New Beijing in the Eastern Commonwealth on Earth. “Cinder was the only full-service mechanic at New Beijing’s weekly market. Without a sign, her booth hinted at her trade only by the shelves of stock android parts that crowded the walls. It was squeezed into a shady cove between a used netscreen dealer and a silk merchant, both of whom frequently complained about the tangy smell of metal and grease that came from Cinder’s booth, even though it was usually disguised by the aroma of honey buns from the bakery across the square. Cinder knew they really just didn’t like being next to her.”

Linh harbors several secrets, some that even she does not know. But one is that she is a cyborg, part human and part machine. In fact, she is 32.68 percent machine.

When we meet her in the marketplace, she is removing the cyborg foot she has outgrown. “Her left hand was steel, tarnished and dark between the joints as if it needed a good cleaning.” She hid both her steel hand and her steel foot from everyone, embarrassed that she is a cyborg.


But by the end of the first volume of the Lunar Chronicles, Linh receives the gift of a new metal hand:

“‘State of the art,’ said Dr. Erland. “‘Fully accessorized. Plated with 100 percent titanium. And look!’ Like a child with a new toy, he fidgeted with the hand’s fingers, revealing a hidden flashlight, stiletto knife, a projectile gun, and screwdriver, and a universal connector cable. ‘It’s a pillar of usefulness. The tranquilizer darts are stored in here.’ He opened a compartment on the palm, revealing a dozen skinny darts. ‘Once your wiring synchronizes, you should be able to load it with a simple thought.”

Design your own cyborg hand!

You are a cyborg–a cybernetic organism–about to board a spaceship on a dangerous mission. What will you design for your own cyborg hand?

  • Will it include weapons, such as a knife or gun?
  • Will you include tools, like a screwdriver, wrench or wirecutters?
  • Will you include any exploring tools like a compass, a GPS, or a magnifying glass?

Please post your comments below.

Be stellar!

Matthew Cross

What is that?–LIGHT YEAR-a measure of distance–not a measure of time

Image: Prism refracting white light into a rainbow. Text: LIGHT YEAR--A measure of distance--not a measure of time--the light year helps astronomers describe the vast distances between the stars.

Today is Wednesday, so it’s time for our regular feature What is that? Here’s today’s term:

Light Year – a unit of length used to measure great distances in space

Light Year is a confusing term.  We all know what a year is.  A year is the length of time from your birthday to your next birthday.  It is also the length of time it takes the Earth to travel around the sun one time.  That idea may help us.

A year measures time.  It is how long the Earth takes to travel around the sun.  We could make up a term called an Earth Year.  It would mean how far the Earth travels in one year — or how far that trip around the sun is.  By the way, that is about 584,000,000 miles.  (If you live anywhere besides the United States, then that is about 940,000,000 kilometers.)

If an “Earth Year” (my made up term) is how far the Earth travels in one year, then a Light Year is how far a beam of light travels in one year.  Light travels very, very fast.  It can travel from the sun to the Earth in about 8 minutes.  That is about 92,960,000 miles (149,600,000 kilometers).  It takes me more than 8 minutes just to run one mile.

Sunlight on the Earth. Image: NASA.

According to scientists, light is the fastest traveler in the universe.  In fact, there is a rule of physics that says nothing in the universe can travel faster than light.

Light travels slower through glass and water than through air or a vacuum. Source: NASA.

Light also travels at a constant speed in the vacuum of space.  (It does slow down when it passes through air, a window, or water.  But even then, it travels super fast.  Michael Phelps is fast in water, but light is still faster.)  In the vacuum of space, light does not get tired and stop flying along.

A digital version of the Sun’s spectrum created from observations captured by the Fourier Transform Spectrometer at the McMath-Pierce Solar Facility at the National Solar Observatory on Kitt Peak, Arizona. Source: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.
Proxima Centauri. Image: NASA.

Because light travels so fast, it travels very far in one year.  That makes a Light Year–a measure of distance–very useful for measuring the vast distances between stars.  For example, the nearest star to our sun is Proxima Centauri.  It is about 25,000,000,000,000 miles away (40,000,000,000,000 kilometers).  It’s much easier to say (and to write) 4.25 light years.

So, when someone says “That is light years away,” they mean it is very far.  They are not talking about time or how quickly a human could travel that distance.  They are just talking about how large the distance is.

Invent your own measurement!

Let’s invent our own measurement of distance.

First, decide what you will use to set your measurement length. Will it be the length of an object? (To measure small distances, we could use the length of a twig we found.) Will it be the distance that something travels? (Like how far you can ride your bike in five minutes?)

What will you use your new measurement length to measure? The length of your hand? Then length of a car? The length of your neighborhood?

Finally, what will you name your measurement length? An “twig unit”? A “bike in 5”? Will you name it after yourself? (A “Matthew Mile”?) Or create a shiny, brand-new name you made up yourself? (A “plenth”?)

Please post your comments below.

Be stellar!

Matthew Cross

Subterranean Cities–Underground cities fill literature going back hundreds of years. Sci Fi writers dig into these ideas and unbury fresh new worlds to explore.

Colorful image of a cave--Subterranean Cities--Underground cities fill literature going back hundreds of years.  Sci Fi writers dig into these ideas and unbury fresh new worlds to explore.
Cover of Fortuna by Kristyn Merbeth

Today, I want to focus on cities built beneath the ground.  One is a fortress built beneath the frozen crust of a distant planet, and the other is a secret, centuries-old city far beneath New York City.

In Fortuna by Kristyn Merbeth, Corvus is a soldier on the planet Titan, a frozen planet divided by an eternal civil war.  Because of the severe cold and the constant fighting, Titans live in caves and in cities built beneath the ground.

In Chapter 18, Corvus is leaving the military and taking a train from Fort Sketa to a fortress city filled with civilians.

Empty train tunnel curving to the left
Photo by Claudia Soraya (

“The next morning, I wake early to head to the train for the sake of avoiding unwanted company.  The station is just below the surface, chillier than the lower levels of the building, and the ceiling trembles under the weight of activity in the hangar above.

 . . . .
“When I first arrived on Titan, underground rooms made me feel caged and nervous.  Especially so in places like this, where the ceiling occasionally shakes loose clouds of dust, and the rumble of trains along the tracks makes it feel like the whole building could collapse on top of me.  Over the years it’s become normal.  Now, for the first time in a long time, I wonder if it will feel strange to walk in the sunlight again.

 . . . .
“The underground fortress of Drev Dravaask is beautiful.  It’s warm enough that I take off my outer coat, and not overcrowded with people and buildings like the major cities of other planets.  There is a simple elegance to its architecture and a surprising kindness in its people.  They all nod or smile at me as I pass, or press their fingers to their hearts if they notice the [military] brand on my wrist.  I return the gesture without thought, drinking in the quiet.  It’s so peaceful here compared to the rest of Titan.  Neither the storms nor the war can touch this place. 

There is a simple elegance to its architecture and a surprising kindness in its people.


“Drev Dravaask has held its ground for over a century while cities around it crumbled.  The stability allows people to build lives here that do not revolve around war.  There are restaurants and shops, bars and inns, families that aren’t missing pieces.  Of course, there is also a huge military recruitment center near the heart of the city, and posters advertising the perks of service on every street corner, so it is not possible to forget entirely.”

Image of light shining into a blue pool of waterbeneath stalagtites

Sister Scorpia sees Drev Dravaask, the undground city on Titan, very differently

Corvus was born on the planet Titan and returned as an adult to serve his mandatory three-year tour as a soldier in Titan’s eternal civil war.  His sister, Scorpia, was born on the family’s spaceship, Fortuna, and has a very different impression of the underground Drev Dravaask.  After storing Fortuna in a cave hangar on the surface, Scorpia and her family take a slow, rusty elevator deep into the planet.

Man in hoodie with eyes closed standing under a hole in a concrete ceiling
Photo by Stephen O. Duntan (

“The city of Drev Dravaask is carved into the earth beneath the surface of Titan, dark and damp caves forming homes and businesses and more.  The surface of the planet is too cold, too stormy; water freezes up there; and plants won’t grow, and people die slowly and numbly without realizing that they’re dying.  Down here, close to the hot springs that run beneath the surface, it’s a handful of degrees warmer.

“It would be easy to be miserable in a city like this, but the people of Drev Dravaask find pockets of happiness in their cold underground world.  As we head inward, a trio of soldiers sways past us arm in arm, belting a severely out-of-tune version of Titan’s planetary anthem.  A cluster of children giggle in an alleyway, finger-painting dirty words on the walls.  A hunched street vendor with a face full of battle scars hands a carefully wrapped meal to a gaunt teenager on the street corner.”

Gregor the Overlander finds a magical city of humans buried deep underground

In Gregor the Overlander by Suzanne Collins, Gregor and his baby sister, Boots, discover a mysterious land, called the Underland, filled with giant, talking rats, bats and cockroaches, that lies far beneath New York City.

View of a city full of lights seen through the mouth of a cavern

Gregor stumbles into the Underland and finds a city hidden deep beneath New York City

“There are but five known gateways to the Underland,” said Vikus.  “Two lead to the Dead Land, but you would never have survived those.  Two gateways open into the Waterway, but your clothing is quite dry.  You are alive, you are dry, from this I surmise you have fallen through the fifth gateway, the mouth of which I know to be in New York City.”

Vikus, a mysterious, bearded man with silver hair and violet eyes, leads Gregor to the human capital of the Underland.

“He followed Vikus down a tunnel lined with stone torches to a small arch filled with something dark and fluttery.  Gregor thought it might be more bats, but on closer inspection he saw it was a cloud of tiny black moths.  Was this what he had passed through when he stumbled into the stadium?

Photo of bat enfolded in its wings hanging upside down
Bat hanging upside down in a cave. Credit: Tine Evanic (

“Vikus gently slid his hand into the insects.  ‘These moths are a warning system peculiar to the Underland, I believe.  The moment their pattern of flight is disturbed by an intruder, every bat in the area discerns it.  I find it so perfect in its simplicity,’ he said.  Then he vanished into the moths.”

Welcome to the city of Regalia!

“Behind the curtain of wings, Gregor could hear his voice beckoning.  ‘Gregor the Overlander, welcome to the city of Regalia!’

 . . . .

“Gregor didn’t know what he’d expected.  Maybe stone houses, maybe caves—something primitive.  But there was nothing primitive about the magnificent city that spread before him.

“They stood on the edge of a valley filled with the most beautiful buildings he’d ever seen.  New York was known for its architecture, the elegant brownstones, the towering skyscrapers, the grand museums.  But compared with Regalia, it looked unplanned, like a place where someone had lined up a bunch of oddly shaped boxes in rows.

Photo of cathedral of gray stone with domed towers
Photo by Barb McMahon (

“The buildings here were all a lovely misty gray, which gave them a dreamlike quality.  They seemed to rise directly out of the rock as if they had been grown, not made by human hands.  Maybe they weren’t as tall as the skyscrapers Gregor knew by name, but they towered high above his head, some at least thirty stories and finished in artful peaks and turrets.  Thousands of torches were placed strategically so that a soft, dusky light illuminated the entire city.

“And the carvings . . . Gregor had seen cherubs and gargoyles on buildings before, but the walls of Regalia crawled with life.  People and cockroaches and fish and creatures Gregor had no name for fought and feasted and danced on every conceivable inch of space.”

Your favorite underground cities

Sci fi has lots more underground cities.  Which ones are your favorites?  Were they built on Earth, on other planets, or in other universes?  Were they built by humans, alien life, or ancient creatures long gone?

Please post your comments below.

Be stellar!

Matthew Cross

Tanks–Sci Fi tanks sport strong armor, cool weapons, and sometimes even legs

Fire shooting from a tank gun
Photo by Ryoma Onita (

Spider Tank

In Kristyn Merbeth’s space opera Fortuna, she introduces the spider tank, a sturdy, four-legged machine that can carry a squad long distances over the treacherous, icy terrain of the planet Titan.

Cover of sci fi novel Fortuna by Kristyn Merbeth

The novel alternates between chapters told by Portia, the pilot of the family’s spaceship, Fortuna, and chapters told by her brother, Corvus, who is finishing his three-year enlistment in the military on Titan.

Here, Corvus describes the spider tank:

“The spider tank is designed to travel through dangerous terrain, able to navigate across ice and up almost-vertical cliffs, but the four legs plod along in jerky motions that always sicken my stomach.  Even after three years on Titan, I’m still not used to land vehicles, too accustomed to the smoother travel of hovercrafts that are common on every other planet.  Here the extreme winds and unpredictable weather make them too dangerous to operate.”

Traditional tanks on earth travel on wheels or on caterpillar treads, like those on a bulldozer.

A tank can really be any heavily armored vehicle with weapons. If it doesn’t have serious weapons, it should probably just be called an armored personnel carrier. Merbeth does not tell us about the weaponry in the spider tank. But in a battle scene, she writes of hand-held blasters and pulse rifles that shoot laser-fire. So I’m imagining the spider tank has some heavy-duty lasers and maybe a few other tricks besides.

Design your own tank!

If you were an engineer of the future, what kind of tank would you build?

  • Would it have wheels, treads, legs or hoverjets?
  • Would it fire cannonballs, shells, missiles or lasers?
  • Would soldiers ride in it, drive it remotely, or would it have artificial intelligence (AI) and drive itself?

Please post your comments below.

Be stellar!

Matthew Cross