Pecans have a storied history in the United States. Today, American trees produce hundreds of million of pounds of pecans – 80% of the world’s pecan crop. Most of that crop stays here. Pecans are used to produce pecan milk, butter and oil, but many of the nuts end up in pecan pies.

Throughout history, pecans have been overlooked, poached, cultivated and improved. As they have spread throughout the United States, they have been eaten raw and in recipes. Pecans have grown more popular over the decades, and you will probably encounter them in some form this holiday season.

I’m an extension specialist in Oklahoma, a state consistently ranked fifth in pecan production, behind Georgia, New Mexico, Arizona and Texas. I’ll admit that I am not a fan of the taste of pecans, which leaves more for the squirrels, crows and enthusiastic pecan lovers.

The spread of pecans

The pecan is a nut related to the hickory. Actually, though we call them nuts, pecans are actually a type of fruit called a drupe. Drupes have pits, like the peach and cherry.

The pecan nuts that look like little brown footballs are actually the seed that starts inside the pecan fruit – until the fruit ripens and splits open to release the pecan. They are usually the size of your thumb, and you may need a nutcracker to open them. You can eat them raw or as part of a cooked dish.

The pecan derives its name from the Algonquin “pakani,” which means “a nut too hard to crack by hand.” Rich in fat and easy to transport, pecans traveled with Native Americans throughout what is now the southern United States. They were used for food, medicine and trade as early as 8,000 years ago.

Pecans are native to the southern United States, and while they had previously spread along travel and trade routes, the first documented purposeful planting of a pecan tree was in New York in 1722. Three years later, George Washington’s estate, Mount Vernon, had some planted pecans. Washington loved pecans, and Revolutionary War soldiers said he was constantly eating them.

Meanwhile, no one needed to plant pecans in the South, since they naturally grew along riverbanks and in groves. Pecan trees are alternate bearing: They will have a very large crop one year, followed by one or two very small crops. But because they naturally produced a harvest with no input from farmers, people did not need to actively cultivate them. Locals would harvest nuts for themselves but otherwise ignored the self-sufficient trees.

It wasn’t until the late 1800s that people in the pecan’s native range realized the pecan’s potential worth for income and trade. Harvesting pecans became competitive, and young boys would climb onto precarious tree branches. One girl was lifted by a hot air balloon so she could beat on the upper branches of trees and let them fall to collectors below. Pecan poaching was a problem in natural groves on private property.

Pecan cultivation begins

Even with so obvious a demand, cultivated orchards in the South were still rare into the 1900s. Pecan trees don’t produce nuts for several years after planting, so their future quality is unknown.

To guarantee quality nuts, farmers began using a technique called grafting; they’d join branches from quality trees to another pecan tree’s trunk. The first attempt at grafting pecans was in 1822, but the attempts weren’t very successful.

Grafting pecans became popular after an enslaved man named Antoine who lived on a Louisiana plantation successfully produced large pecans with tender shells by grafting, around 1846. His pecans became the first widely available improved pecan variety.

The variety was named Centennial because it was introduced to the public 30 years later at the Philadelphia Centennial Expedition in 1876, alongside the telephone, Heinz ketchup and the right arm of the Statue of Liberty.

This technique also sped up the production process. To keep pecan quality up and produce consistent annual harvests, today’s pecan growers shake the trees while the nuts are still growing, until about half of the pecans fall off. This reduces the number of nuts so that the tree can put more energy into fewer pecans, which leads to better quality. Shaking also evens out the yield, so that the alternate-bearing characteristic doesn’t create a boom-bust cycle.

US pecan consumption

The French brought praline dessert with them when they immigrated to Louisiana in the early 1700s. A praline is a flat, creamy candy made with nuts, sugar, butter and cream. Their original recipe used almonds, but at the time, the only nut available in America was the pecan, so pecan pralines were born.

During the Civil War and world wars, Americans consumed pecans in large quantities because they were a protein-packed alternative when meat was expensive and scarce. One ounce of pecans has the same amount of protein as 2 ounces of meat.

After the wars, pecan demand declined, resulting in millions of excess pounds at harvest. One effort to increase demand was a national pecan recipe contest in 1924. Over 21,000 submissions came from over 5,000 cooks, with 800 of them published in a book.

Pecan consumption went up with the inclusion of pecans in commercially prepared foods and the start of the mail-order industry in the 1870s, as pecans can be shipped and stored at room temperature. That characteristic also put them on some Apollo missions. Small amounts of pecans contain many vitamins and minerals. They became commonplace in cereals, which touted their health benefits.

In 1938, the federal government published the pamphlet Nuts and How to Use Them, which touted pecans’ nutritional value and came with recipes. Food writers suggested using pecans as shortening because they are composed mostly of fat.

The government even put a price ceiling on pecans to encourage consumption, but consumers weren’t buying them. The government ended up buying the surplus pecans and integrating them into the National School Lunch Program.

While you are sitting around the Thanksgiving table this year, you can discuss one of the biggest controversies in the pecan industry: Are they PEE-cans or puh-KAHNS?

Shelley Mitchell, Senior Extension Specialist in Horticulture and Landscape Architecture, Oklahoma State University

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

When astronomers search for planets that could host liquid water on their surface, they start by looking at a star’s habitable zone. Water is a key ingredient for life, and on a planet too close to its star, water on its surface may “boil”; too far, and it could freeze. This zone marks the region in between.

But being in this sweet spot doesn’t automatically mean a planet is hospitable to life. Other factors, like whether a planet is geologically active or has processes that regulate gases in its atmosphere, play a role.

The habitable zone provides a useful guide to search for signs of life on exoplanets – planets outside our solar system orbiting other stars. But what’s in these planets’ atmospheres holds the next clue about whether liquid water — and possibly life — exists beyond Earth.

On Earth, the greenhouse effect, caused by gases like carbon dioxide and water vapor, keeps the planet warm enough for liquid water and life as we know it. Without an atmosphere, Earth’s surface temperature would average around zero degrees Fahrenheit (minus 18 degrees Celsius), far below the freezing point of water.

The boundaries of the habitable zone are defined by how much of a “greenhouse effect” is necessary to maintain the surface temperatures that allow for liquid water to persist. It’s a balance between sunlight and atmospheric warming.

Many planetary scientists, including me, are seeking to understand if the processes responsible for regulating Earth’s climate are operating on other habitable zone worlds. We use what we know about Earth’s geology and climate to predict how these processes might appear elsewhere, which is where my geoscience expertise comes in.

Why the habitable zone?

The habitable zone is a simple and powerful idea, and for good reason. It provides a starting point, directing astronomers to where they might expect to find planets with liquid water, without needing to know every detail about the planet’s atmosphere or history.

Its definition is partially informed by what scientists know about Earth’s rocky neighbors. Mars, which lies just outside the outer edge of the habitable zone, shows clear evidence of ancient rivers and lakes where liquid water once flowed.

Similarly, Venus is currently too close to the Sun to be within the habitable zone. Yet, some geochemical evidence and modeling studies suggest Venus may have had water in its past, though how much and for how long remains uncertain.

These examples show that while the habitable zone is not a perfect predictor of habitability, it provides a useful starting point.

Planetary processes can inform habitability

What the habitable zone doesn’t do is determine whether a planet can sustain habitable conditions over long periods of time. On Earth, a stable climate allowed life to emerge and persist. Liquid water could remain on the surface, giving slow chemical reactions enough time to build the molecules of life and let early ecosystems develop resilience to change, which reinforced habitability.

Life emerged on Earth, but continued to reshape the environments it evolved in, making them more conducive to life.

This stability likely unfolded over hundreds of millions of years, as the planet’s surface, oceans and atmosphere worked together as part of a slow but powerful system to regulate Earth’s temperature.

A key part of this system is how Earth recycles inorganic carbon between the atmosphere, surface and oceans over the course of millions of years. Inorganic carbon refers to carbon bound in atmospheric gases, dissolved in seawater or locked in minerals, rather than biological material. This part of the carbon cycle acts like a natural thermostat. When volcanoes release carbon dioxide into the atmosphere, the carbon dioxide molecules trap heat and warm the planet. As temperatures rise, rain and weathering draw carbon out of the air and store it in rocks and oceans.

If the planet cools, this process slows down, allowing carbon dioxide, a warming greenhouse gas, to build up in the atmosphere again. This part of the carbon cycle has helped Earth recover from past ice ages and avoid runaway warming.

Even as the Sun has gradually brightened, this cycle has contributed to keeping temperatures on Earth within a range where liquid water and life can persist for long spans of time.

Now, scientists are asking whether similar geological processes might operate on other planets, and if so, how they might detect them. For example, if researchers could observe enough rocky planets in their stars’ habitable zones, they could look for a pattern connecting the amount of sunlight a planet receives and how much carbon dioxide is in its atmosphere. Finding such a pattern may hint that the same kind of carbon-cycling process could be operating elsewhere.

The mix of gases in a planet’s atmosphere is shaped by what’s happening on or below its surface. One study shows that measuring atmospheric carbon dioxide in a number of rocky planets could reveal whether their surfaces are broken into a number of moving plates, like Earth’s, or if their crusts are more rigid. On Earth, these shifting plates drive volcanism and rock weathering, which are key to carbon cycling.

Keeping an eye on distant atmospheres

The next step will be toward gaining a population-level perspective of planets in their stars’ habitable zones. By analyzing atmospheric data from many rocky planets, researchers can look for trends that reveal the influence of underlying planetary processes, such as the carbon cycle.

Scientists could then compare these patterns with a planet’s position in the habitable zone. Doing so would allow them to test whether the zone accurately predicts where habitable conditions are possible, or whether some planets maintain conditions suitable for liquid water beyond the zone’s edges.

This kind of approach is especially important given the diversity of exoplanets. Many exoplanets fall into categories that don’t exist in our solar system — such as super Earths and mini Neptunes. Others orbit stars smaller and cooler than the Sun.

The datasets needed to explore and understand this diversity are just on the horizon. NASA’s upcoming Habitable Worlds Observatory will be the first space telescope designed specifically to search for signs of habitability and life on planets orbiting other stars. It will directly image Earth-sized planets around Sun-like stars to study their atmospheres in detail.

Instruments on the observatory will analyze starlight passing through these atmospheres to detect gases like carbon dioxide, methane, water vapor and oxygen. As starlight filters through a planet’s atmosphere, different molecules absorb specific wavelengths of light, leaving behind a chemical fingerprint that reveals which gases are present. These compounds offer insight into the processes shaping these worlds.

The Habitable Worlds Observatory is under active scientific and engineering development, with a potential launch targeted for the 2040s. Combined with today’s telescopes, which are increasingly capable of observing atmospheres of Earth-sized worlds, scientists may soon be able to determine whether the same planetary processes that regulate Earth’s climate are common throughout the galaxy, or uniquely our own.

Morgan Underwood, Ph.D. Candidate in Earth, Environmental and Planetary Sciences, Rice University

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