We wouldn't be here but for the solstices. Be thankful!

December 21 was the winter solstice in the Northern Hemisphere - the shortest day in the year. The solstices occur on most planets because they do not spin upright, or perpendicular to their orbits.

The Earth, for example, slouches 23.5 degrees on a tilted axis (inclination). This leaves the planet’s North Pole pointed toward the North Star over relatively long periods of time, even as Earth makes its year long migration around the sun. That means the Northern Hemisphere will spend half the year tilted slightly toward the sun, bathing in direct sunlight during summer’s long, blissful days, and half the year cooling off as it leans slightly away from the sun during winter’s short, frigid days. December 21 marks the day when the North Pole is most tilted away from the sun.

But every planet slouches at different angles.

The axial tilt of Venus, for example, is so extreme — 177 degrees — that the planet is essentially flipped upside down with its South Pole pointing up. Perhaps counter-intuitively, that means that there’s very little tilt to its upside-down spin and its hemispheres will never dramatically point toward or away from the sun. As such, the sun’s dance across the sky will remain relatively stable — shifting by a mere six degrees over the course of a Venusian year.

The axial tilt of Venus is so extreme that the planet is essentially flipped upside down with its South Pole pointing up

Had we evolved on Venus, it’s likely that we would not have noticed solstices or seasons at all.

The same can’t be said for Uranus!

An axial tilt of 98 degrees causes the ice giant to spin on its side. So, whereas one of Earth’s poles leans slightly toward the sun at solstice, one of Uranus’s poles points almost directly toward the sun at solstice — as though poised to make a perfect bulls eye. That means that one hemisphere will bask under the sun both day and night, while the other will experience a frigid and dark winter and not catch a glimpse of the sun for that entire season.

Two images of the same view of Uranus made by NASA’s Voyager 2 in 1986. The false-color image on the right shows how Uranus’s pole points towards the sun, its axis tilting at 98 degrees

Such a tilt on Earth would mean that the Arctic Circle didn’t begin 66 degrees north of the Equator, but at the Equator itself. All of North America, Europe, Asia and half of Africa would spend winters in permanent darkness and summers under constant sunlight. And on Uranus, which takes 84 Earth years to orbit the sun, these seasons last for decades.

But the king of extreme seasons is Pluto.

When NASA’s New Horizons spacecraft arrived at the dwarf planet in 2015, scientists discovered a unique world overflowing with surface features that look like networks of drainage channels and even a frozen lake. But given Pluto’s low atmospheric pressure and chilly surface temperature, liquids cannot flow across the surface — at least not today.

Scientists now have an explanation: seasons in Pluto’s past pushed atmospheric pressure high enough to allow liquids of methane and nitrogen to flow and pool on the surface.

A changing axial tilt is the biggest driver of wildly varying seasons on Pluto. Over the course of 4 million years, Pluto’s inclination shifts back and forth between 102 and 126 degrees, causing its equivalent of an Arctic Circle to grow and shrink. That occasionally creates seasons where the atmospheric pressure is high enough that liquid methane and nitrogen can flow.

Although, astronomers remain uncertain how a planet’s seasons might affect its likelihood to host life, it is believed that such dramatic swings — like those on Pluto — are likely a hindrance because they can make a planet unfit to live on for long stretches of time. Life needs a continuously habitable zone to thrive. Similarly, astronomers have long suspected that life would likely not survive on Earth should it have an axial tilt more akin to Uranus.

So, as the sun reaches its farthest point in the sky on December 21, be grateful. Never will the sun dip so far below the horizon that it plunges half of the globe into a months long night and the other half into an equally long summer. Nor does Earth’s tilt change drastically over millions of years, thanks to the influence of the moon. Instead, the sun appears to trot back and forth between the extremes, like the pendulum of a great clock, keeping the planet cozy while steadily counting off its years.

Source - The New York Times

Wayward moon is receding from Earth

From 1969 to 1972, Apollo astronauts had left laser reflectors on the moon’s surface, enabling astronomers to measure the moon’s distance from Earth with great accuracy. Although the moon’s distance from earth varies each month because of its eccentric orbit, the moon’s mean distance from Earth is nonetheless increasing at the rate of about 3.8 centimeters (1.5 inches) per year. That’s about the rate that fingernails grow.

Tidal friction with the Earth’s oceans is responsible for this long-term increase of the moon’s distance from Earth. It’s causing the moon to spiral into a more distant orbit. Tidal friction also slows down the Earth’s rotation, lengthening the day by about 1 second every 40,000 years. Hence, the number of days in a year is slowly diminishing over the long course of time.

Simulations suggest that at the time of the moon’s formation some 4.5 billion years ago, the moon was only about 20,000 to 30,000 kilometers from Earth. Way back then, Earth’s day might have been only 5 or 6 hours long. That would mean over 1,400 days in one year!

The Apollo 11 lunar laser ranging retroreflector array on the moon.

However, astronomers suspected the moon was receding from Earth before the heyday of the Apollo astronauts. Edmund Halley’s (1656 to 1741) studies of ancient solar and lunar eclipses suggested the possibility, as well. George Howard Darwin (1845 to 1912) is credited for figuring out mathematically how tidal friction affects the moon’s orbit.

Studies in fossilized coral indicate that the Earth had spun faster upon its rotational axis when the moon was closer to Earth. Millions of years ago, days on Earth were shorter yet more abundant. For instance, around 900 million years ago, there were about 480 18-hours days in one year. Around 400 million years ago, there were about 400 22-hour days in one year. Looking into the future, astronomers expect longer days but fewer of them in one year.

If the lifetime of the Earth-moon system lasts long enough (which is doubtful), it is projected that after many billions of years, the same sides of the Earth and moon would face one another. In other words, the Earth’s rotational period and the moon’s orbital period would equal one another, representing a period of 47 days. At that time, the Earth/moon distance would expand to some 560,000 km, exceeding the present distance of 384,400 km by nearly 150%.

Source - EarthSky.org

What if photosynthesis stopped happening?

Photosynthesis converts light energy to chemical energy. Essentially, photosynthesis is the fueling process that allows plants and even algae to survive and grow. So what would happen if photosynthesis suddenly stopped happening?

If photosynthesis came to an abrupt end, most plants would die within short order. Although they could hold out for a few days -- or in some cases, a few weeks -- how long they lived would largely be a factor of how much sugar they had stored within their cells.

Large trees, for example, may be able to soldier on for several years — perhaps even a few decades — because of their energy stores and the slow rate of use. However, the majority of plants would meet a withering end, and so would the animals that rely on them for nourishment. With all the herbivores dead, the omnivores and carnivores would soon follow. Although these meat-eaters could feed on all the carcasses strewn about, that supply wouldn't last more than a few days. Then the animals that temporarily relied on them for sustenance would die.

That's because for photosynthesis to cease to exist, Earth would have to plunge into darkness. To do this, the sun would have to disappear and plunge Earth's surface temperatures into a never-ending winter of bitter cold temperatures. Within a year, it would bottom out at minus 73 degrees Celsius, resulting in a planet of purely frozen tundra.

Ironically, if the sun burned too bright, it could cause photosynthesis to stop occurring. Too much light energy would damage plants' biological structure and prevent photosynthesis from happening. This is why the photosynthetic process, in general, shuts down during the hottest hours of the day.

Whether the culprit were too much sunlight or not enough, if photosynthesis stopped, plants would stop converting carbon dioxide -- an air pollutant -- to organic material. Right now, we rely on photosynthetic plants, algae and even bacteria to recycle our air. Without them, there would be less oxygen production.

Even if all the plants on Earth were to die, people would remain resourceful -- especially if their lives depended on it. An artificial photosynthesis process being developed by scientists could just become the world's biggest problem-solver. Using an artificial "leaf," scientists have successfully harnessed sunlight and recreated photosynthesis. The leaf is actually a silicon solar cell that, when put in water and exposed to light, then generates oxygen bubbles from one side and hydrogen bubbles from the other - essentially splitting oxygen and hydrogen. Although the idea was designed as a way to potentially produce clean energy, there are implications for recreating a photosynthetic atmosphere as well.

Source - Laurie L. Dove "What if photosynthesis stopped happening?" 1 June 2015.
HowStuffWorks.com.

Is there an 8th continent? Searching.. Zealandia

An Underwater “Continent” Could Reveal Secrets About Earth’s Distant Past

Tens of millions of years ago, a landmass that’s being referred to as Zealandia was largely submerged beneath the Pacific Ocean.

This summer, more than thirty scientists set out on an underwater expedition using an advanced research vessel, and the results might yield brand-new insight into Earth’s prehistory. By drilling into the ocean floor some 4,000 feet below the surface, they were able to collect 8,000 feet of sediment cores that will give us a glimpse into geological processes that have taken place over the last 70 million years. The cores act as time machines allowing us to reach further and further back in time, first seeing the ancient underwater avalanches then evidence of rocks forged from a fiery origin.

It’s thought that Zealandia broke off from Australia between 60 and 85 millions years ago, forming New Zealand and other islands in the region. However, there’s still some debate as to whether or not it could be classified as a continent. Its relationship with Australia is thought to be similar to the link between North America and Greenland, and Africa and Madagascar.

Over the course of the expedition, over 8,000 fossils were found, giving the team an opportunity to study hundreds of different species. Knowing more about the creatures that inhabited Zealandia before it was submerged allows scientists to make informed guesses about what conditions were like. The discovery of microscopic shells of organisms that lived in warm shallow seas, and of spores and pollen from land plants, reveal that the geography and climate of Zealandia were dramatically different in the past. Based on the remains that have been found, it’s thought that land-based animals once roamed around Zealandia. The region would have served as a bridge that could be used to cross between continents.

It’s expected that the findings of this expedition will help us better comprehend how life propagated through the South Pacific, and offer some fresh perspective to the debate as to whether or not Zealandia is a continent. There are hopes that further study could produce more information about climate change, relating to the history of Zealandia’s climate millions of years ago and today.

A vessel equipped with drilling equipment is set to visit regions close to New Zealand, Australia, and Antarctica in 2018.

Sources - Futurism and National Geographic