Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

How was popcorn discovered? – Kendra, age 11, Penn Yan, New York

You have to wonder how people originally figured out how to eat some foods that are beloved today. The cassava plant is toxic if not carefully processed through multiple steps. Yogurt is basically old milk that’s been around for a while and contaminated with bacteria. And who discovered that popcorn could be a toasty, tasty treat?

These kinds of food mysteries are pretty hard to solve. Archaeology depends on solid remains to figure out what happened in the past, especially for people who didn’t use any sort of writing. Unfortunately, most stuff people traditionally used made from wood, animal materials or cloth decays pretty quickly, and archaeologists like me never find it.

We have lots of evidence of hard stuff, such as pottery and stone tools, but softer things – such as leftovers from a meal – are much harder to find. Sometimes we get lucky, if softer stuff is found in very dry places that preserve it. Also, if stuff gets burned, it can last a very long time.

Corn’s ancestors

Luckily, corn – also called maize – has some hard parts, such as the kernel shell. They’re the bits at the bottom of the popcorn bowl that get caught in your teeth. And since you have to heat maize to make it edible, sometimes it got burned, and archaeologists find evidence that way. Most interesting of all, some plants, including maize, contain tiny, rock-like fragments called phytoliths that can last for thousands of years.

Scientists are pretty sure they know how old maize is. We know maize was probably first farmed by Native Americans in what is now Mexico. Early farmers there domesticated maize from a kind of grass called teosinte.

Before farming, people would gather wild teosinte and eat the seeds, which contained a lot of starch, a carbohydrate like you’d find in bread or pasta. They would pick teosinte with the largest seeds and eventually started weeding and planting it. Over time, the wild plant developed into something like what we call maize today. You can tell maize from teosinte by its larger kernels.

There’s evidence of maize farming from dry caves in Mexico as early as 9,000 years ago. From there, maize farming spread throughout North and South America.

Popped corn, preserved food

Figuring out when people started making popcorn is harder. There are several types of maize, most of which will pop if heated, but one variety, actually called “popcorn,” makes the best popcorn. Scientists have discovered phytoliths from Peru, as well as burned kernels, of this type of “poppable” maize from as early as 6,700 years ago.

You can imagine that popping maize kernels was first discovered by accident. Some maize probably fell into a cooking fire, and whoever was nearby figured out that this was a handy new way of preparing the food. Popped maize would last a long time and was easy to make.

Ancient popcorn was probably not much like the snack you might munch at the movie theater today. There was probably no salt and definitely no butter, since there were no cows to milk in the Americas yet. It probably wasn’t served hot and was likely pretty chewy compared with the version you’re used to today.

It’s impossible to know exactly why or how popcorn was invented, but I would guess it was a clever way to preserve the edible starch in corn by getting rid of the little bit of water inside each kernel that would make it more susceptible to spoiling. It’s the heated water in the kernel escaping as steam that makes popcorn pop. The popped corn could then last a long time. What you may consider a tasty snack today probably started as a useful way of preserving and storing food.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Sean Rafferty, Professor of Anthropology, University at Albany, State University of New York

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Is it possible that one day we could make Mars like Earth? – Tyla, age 16, Mississippi

When I was in middle school, my biology teacher showed our class the sci-fi movie “Star Trek III: The Search for Spock.”

The plot drew me in, with its depiction of the “Genesis Project” – a new technology that transformed a dead alien world into one brimming with life.

After watching the movie, my teacher asked us to write an essay about such technology. Was it realistic? Was it ethical? And to channel our inner Spock: Was it logical? This assignment had a huge impact on me.

Fast-forward to today, and I’m an engineer and professor developing technologies to extend the human presence beyond Earth.

For example: I’m working on advanced propulsion systems to take spacecraft beyond Earth’s orbit. I’m helping to develop lunar construction technologies to support NASA’s goal of long-term human presence on the Moon. And I’ve been on a team that showed how to 3D-print habitats on Mars.

To sustain people beyond Earth will take a lot of time, energy and imagination. But engineers and scientists have started to chip away at the many challenges.

A partial checklist: Food, water, shelter, air

After the Moon, the next logical place for humans to live beyond Earth is Mars.

But is it possible to terraform Mars – that is, transform it to resemble the Earth and support life? Or is that just the musings of science fiction?

To live on Mars, humans will need liquid water, food, shelter and an atmosphere with enough oxygen to breathe and thick enough to retain heat and protect against radiation from the Sun.

But the Martian atmosphere is almost all carbon dioxide, with virtually no oxygen. And it’s very thin – only about 1% as dense as the Earth’s.

The less dense an atmosphere, the less heat it can hold on to. Earth’s atmosphere is thick enough to retain enough heat to sustain life by what’s known as the greenhouse effect.

But on Mars, the atmosphere is so slight that the nighttime temperature drops routinely to 150 degrees below zero Fahrenheit (-101 degrees Celsius).

So what’s the best way to give Mars an atmosphere?

Although Mars has no active volcanoes now – at least as far as we know – scientists could trigger volcanic eruptions via nuclear explosions. The gases trapped deep in a volcano would be released and then drift into the atmosphere. But that scheme is a bit harebrained, because the explosions would also introduce deadly radioactive material into the air.

A better idea: Redirecting water-rich comets and asteroids to crash into Mars. That too would release gases from below the planet’s surface into the atmosphere while also releasing the water found in the comets. NASA has already demonstrated that it is possible to redirect asteroids – but relatively large ones, and lots of them, are needed to make a difference.

Making Mars cozy

There are numerous ways to heat up the planet. For instance, gigantic mirrors, built in space and placed in orbit around Mars, could reflect sunlight to the surface and warm it up.

One recent study proposed that Mars colonists could spread aerogel, an ultralight solid material, on the ground. The aerogel would act as insulation and trap heat. This could be done all over Mars, including the polar ice caps, where the aerogel could melt the existing ice to make liquid water.

To grow food, you need soil. On Earth, soil is composed of five ingredients: minerals, organic matter, living organisms, gases and water.

But Mars is covered in a blanket of loose, dustlike material called regolith. Think of it as Martian sand. The regolith contains few nutrients, not enough for healthy plant growth, and it hosts some nasty chemicals called perchlorates, used on Earth in fireworks and explosives.

Cleaning up the regolith and turning it into something viable wouldn’t be easy. What the alien soil needs is some Martian fertilizer, maybe made by adding extremophiles to it – hardy microbes imported from Earth that can survive even the harshest conditions. Genetically engineered organisms are also a possibility.

Through photosynthesis, these organisms would begin converting carbon dioxide to oxygen. Eventually, as Mars became more life-friendly to Earthlike organisms, colonists could introduce more complex plants and even animals.

Providing oxygen, water and food in the right proportions is extraordinarily complex. On Earth, scientists have tried to simulate this in Biosphere 2, a closed-off ecosystem featuring ocean, tropical and desert habitats. Although all of Biosphere 2’s environments are controlled, even there scientists struggle to get the balance right. Mother Nature really knows what she is doing.

A house on Mars

Buildings could be 3D-printed; initially, they would need to be pressurized and protected until Mars acquired Earthlike temperatures and air. NASA’s Moon-to-Mars Planetary Autonomous Construction Technologies program is researching how to do exactly this.

There are many more challenges. For example, unlike Earth, Mars has no magnetosphere, which protects a planet from solar wind and cosmic radiation. Without a magnetic field, too much radiation gets through for living things to stay healthy. There are ways to create a magnetic field, but so far the science is highly speculative.

In fact, all of the technologies I’ve described are far beyond current capabilities at the scale needed to terraform Mars. Developing them would take enormous amounts of research and money, probably much more than possible in the near term. Although the Genesis device from “Star Trek III” could terraform a planet in a matter of minutes, terraforming Mars would take centuries or even millennia.

And there are a lot of ethical questions to resolve before people get started on turning Mars into another Earth. Is it right to make such drastic permanent changes to another planet?

If this all leaves you disappointed, don’t be. As scientists create innovations to terraform Mars, we’ll also use them to make life better on Earth. Remember the technology we’re developing to print 3D habitats on Mars? Right now, I’m part of a group of scientists and engineers employing that very same technology to print homes here on Earth – which will help address the world’s housing shortage.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Sven Bilén, Professor of Engineering Design, Electrical Engineering and Aerospace Engineering, Penn State

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Why do some planets have moons and some don’t? – Siddharth, age 6, Texas

On Earth, you can look up at night and see the Moon shining bright from hundreds of thousands of miles away. But if you went to Venus, that wouldn’t be the case. Not every planet has a moon – so why do some planets have several moons, while others have none?

I’m a physics instructor who has followed the current theories that describe why some planets have moons and some don’t.

First, a moon is called a natural satellite. Astronomers refer to satellites as objects in space that orbit larger bodies. Since a moon isn’t human-made, it’s a natural satellite.

Currently, there are two main theories for why some planets have moons. Moons are either gravitationally captured if they are within what’s called a planet’s Hill sphere radius, or they’re formed along with a solar system.

The Hill sphere radius

Objects exert a gravitational force of attraction on other nearby objects. The larger the object is, the greater the force of attraction.

This gravitational force is the reason we all stay grounded to Earth instead of floating away.

The solar system is dominated by the Sun’s large gravitational force, which keeps all of the planets in orbit. The Sun is the most massive object in our solar system, which means it has the most gravitational influence on objects such as planets.

In order for a satellite to orbit a planet, it has to be close enough for the planet to exert enough force to keep it in orbit. The minimum distance for a planet to keep a satellite in orbit is called the Hill sphere radius.

The Hill sphere radius is based on the mass of both the larger object and the smaller object. The Moon orbiting Earth is a good example of how the Hill sphere radius works. The Earth orbits around the Sun, but the Moon is close enough to Earth that Earth’s gravitational pull captures it. The moon orbits around the Earth, rather than the Sun, because it is within Earth’s Hill sphere radius.

Smaller planets like Mercury have a tiny Hill sphere radius, since they can’t exert a large gravitational pull. Any potential moons would likely get pulled in by the Sun instead.

Many scientists are still looking to see whether these planets may have had small moons in the past. Back during the formation of the solar system, they may have had moons that got knocked away by collisions with other space objects.

Mars has two moons, Phobos and Deimos. Scientists still debate whether these came from asteroids that passed close into Mars’ Hill sphere radius and got captured by the planet, or if they were formed at the same time as the solar system. More evidence supports the first theory, because Mars is close to the asteroid belt.

Jupiter, Saturn, Uranus and Neptune have larger Hill sphere radii, because they are much larger than Earth, Mars, Mercury and Venus and they’re farther from the Sun. Their gravitational pulls can attract and keep more natural satellites such as moons in orbit. For example, Jupiter has 95 moons, while Saturn has 146.

Moons forming with a solar system

Another theory suggests that some moons formed at the same time as their solar system.

Solar systems start out with a big disk of gas rotating around a sun. As the gas rotates around the sun, it condenses into planets and moons that rotate around them. The planets and moons then all rotate in the same direction.

But only a few moons in our solar system were likely created this way. Scientists predict that Jupiter’s and Saturn’s inner moons formed during the emergence of our solar system because they’re so old. The rest of the moons in our solar system, including Jupiter’s and Saturn’s outer moons, were probably gravitationally captured by their planets.

Earth’s Moon is special because it likely formed in a different way. Scientists believe that long ago, a large, Mars-sized object collided with the Earth. During that collision, a big chunk flew off the Earth and into its orbit and became the Moon.

Scientists guess that the Moon formed this way because they’ve found a type of rock called basalt in soil on the Moon’s surface. The Moon’s basalt looks the same as basalt found inside the Earth.

Ultimately, the question of why some planets have moons is still widely debated, but factors such as a planet’s size, gravitational pull, Hill sphere radius and how its solar system formed may play a role.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Nicole Granucci, Instructor of Physics, Quinnipiac University

This article is republished from The Conversation under a Creative Commons license. Read the original article.