Earth

Why Does Earth Have an Atmosphere?

Earth's atmosphere is enormous, so far reaching that it even affects the International Space Station's route. But how did this giant gaseous envelope form?

That is, why does Earth have an atmosphere?

In short, our atmosphere is here because of gravity. When Earth formed, about 4.5 billion years ago, the molten planet barely had an atmosphere. But as the world cooled, its atmosphere formed, largely from gases spewed out of volcanoes, according to the Smithsonian Environmental Research Center (SERC). This ancient atmosphere was very different from today's; it had hydrogen sulfide, methane and 10 to 200 times as much carbon dioxide as the modern atmosphere does, according to SERC. [Infographic: Earth's Atmosphere Top to Bottom]

"We believe the Earth started out with an atmosphere a bit like [that of] Venus, with nitrogen, carbon dioxide, maybe methane," said Jeremy Frey, a professor of physical chemistry at the University of Southampton in the United Kingdom. "Life then began somehow, almost certainly in the bottom of an ocean somewhere."

After around 3 billion years, the photosynthetic system evolved, meaning that single-celled organisms used the sun's energy to turn molecules of carbon dioxide and water into sugar and oxygen gas. This dramatically increased oxygen levels, Frey told Live Science. "And that is the biggest pollution event, you might say, that life has ever done to anything, because it slowly transformed the planet," he said.

Nowadays, Earth's atmosphere consists of approximately 80 percent nitrogen and 20 percent oxygen, Frey said. That atmosphere is also home to argon, carbon dioxide, water vapor and numerous other gases, according to the National Center for Atmospheric Research (NCAR).

It's a good thing these gases are there. Our atmosphere protects the Earth from the harsh rays of the sun and reduces temperature extremes, acting like a duvet wrapped around the planet. Meanwhile, the greenhouse effect means that energy from the sun that reaches Earth gets waylaid in the atmosphere, absorbed and released by greenhouse gases, according to the NCAR. There are several different types of greenhouse gases; the major ones are carbon dioxide, water vapor, methane and nitrous oxide. Without the greenhouse effect, Earth's temperature would be below freezing.

However, today, greenhouse gases are out of control. As humans release more carbon dioxide into the atmosphere, Earth's greenhouse effect gets stronger, according to NCAR. In turn, the planet's climate gets warmer.

Intriguingly, no other planet in the universe has an atmosphere like Earth's. Mars and Venus have atmospheres, but they cannot support life (or, at least, not Earth-like life), because they don't have enough oxygen. Indeed, Venus' atmosphere is mainly carbon dioxide with clouds of sulfuric acid, the 'air' is so thick and hot that no human could breathe there. According to NASA, the thick carbon dioxide atmosphere of Venus traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system. Surface temperatures there are hot enough to melt lead.

"The fact that Earth has an atmosphere is extremely unusual in respect of the planets in the solar system, in that it's very different from any of the other planets," Frey said. For example, the pressure of Venus is about 90 atmospheres, the equivalent to diving 3,000 feet (914 meters) beneath the ocean on Earth. "The original Russian spaceships that went there [to Venus] just recorded for a few seconds and then got crushed," Frey said. "Nobody ever really understood how hot it was."

So, Earth's atmosphere is life — and without it, life as we know it wouldn't exist. "Earth needed the right atmosphere [for life] to get started," Frey said. "It has created that atmosphere, and it has created circumstances to live in that atmosphere. The atmosphere is a totally integral part of the biological system."

Originally published on Live Science.

Earth's atmosphere is so big the moon flies through it

The boundaries between planet Earth, the moon, and deep space just got fuzzier.

According to a new analysis of data recorded by a spacecraft more than 20 years ago, the outer fringes of our cozy planet's atmosphere stretch far beyond what is typically imagined.

In fact, Earth's supply of hydrogen gas — the lightest air molecule and element on the Periodic Table— may extend nearly 400,000 miles out.

That's plenty of reach to envelope the moon, which orbits our planet at an average distance of 238,856 miles away.

"The moon flies through Earth's atmosphere," Igor Baliukin, a space physicist at Russia's Space Research Institute in Moscow, said in a European Space Agency (ESA) press release. "We were not aware of it until we dusted off observations made over two decades ago by the SOHO spacecraft."

Formally known as the Solar and Heliospheric Observatory, SOHO is operated jointly by NASA and the European Space Agency.

An international team of researchers including Baliukin published their research this month in the journal JGR Space Physics.

Apollo 16 astronauts took this ultraviolet photo of Earth passing in front of the sun in 1972. The image shows our planet's hazy "geocorona" or tenuous envelope of hydrogen gases.NASA

The internationally recognized boundary of space is called the Karman Line, and it's a border that exists 62 miles (100 kilometers) above Earth's surface. But contrary to popular belief, Earth's atmosphere has no clear or official boundary.

Earth's gravity hugs most of the densest gases close to its surface, including oxygen, nitrogen, carbon dioxide, and water vapor. Meanwhile, hydrogen and other very light gases drift deep into space.

Our planet has a magnetic field that thankfully protects the atmosphere — without it, a never-ending stream of particles from the sun, called the solar wind, might blow all these gases into space. (Mars' magnetic dynamo, by contrast, shut down billions of years ago, leading to a catastrophic loss of its air supply.)

Scientists knew that fleeting amounts of hydrogen drift far enough into space to merge with the solar wind. But the boundaries or envelope of that hydrogen cloud — called the geocorona — has never been fully clear.

The geocorona is invisible to human eyes. Hydrogen absorbs and re-emits sunlight in ultraviolet light, though, so Apollo 16 astronauts were able to photograph Earth's tenuous hydrogen cloud with ultraviolet-light-sensitive film during their moon mission in 1972.

Read more: SpaceX just launched an Israeli mission toward the moon. If successful, it would be the world's first private lunar landing.

SOHO, which has been in operation for about 23 years, carries an ultraviolet-light-recording instrument called SWAN (short for "Solar Wind ANisotropies"). It was designed to study the sun's particles, which can have huge ramifications on Earth, such as solar storms that can disrupt satellites and take out electrical grids.

However, by carefully reanalyzing two-decade-old observations from SWAN, an international team of scientists narrowed the data down to study hydrogen around Earth.

An illustration that shows how far Earth's geocorona extends into deep space.ESA

From that analysis, they learned that even the side of Earth that faces the sun has an envelope of hydrogen extending far beyond the moon's orbit.

Behind Earth, on its dark side, pressure from the solar wind pushes the planet's outermost atmosphere into a bulbous tail that extends around 391,000 miles (630,000 kilometers) into deep space.

"Astronauts on the lunar surface did not know that they were actually embedded in the outskirts of the geocorona," Jean-Loup Bertaux, a geophysicist and coauthor of the new study, said in the release.

The researchers noted that the density of the hydrogen cloud is so fleetingly low that it's still a vacuum out there. But the discovery could nonetheless have significant ramifications for new observatories that study the universe in normally invisible wavelengths of light.

"Space telescopes observing the sky in ultraviolet wavelengths to study the chemical composition of stars and galaxies would need to take this into account," Jean-Loup said in the release.

Parched Mars river valley looks surprisingly Earth-like

ESA's Mars Express caught sight of this dried-out river valley network in November 2018.

ESA/DLR/FU Berlin

Thanks to aerial and satellite views of Earth, we're all familiar with what river valleys look like from above. Seeing one on Mars highlights how similar our planets can appear despite their drastic differences.

The European Space Agency's Mars Express spacecraft has given us a spectacular view of a relic of the Red Planet's past. It's dry and dusty now, but we can see the remnants of a branching river valley network. 

ESA also generated a perspective view that makes it feel like you're soaring across the planet.

 

A perspective view of a dried-out river valley on Mars.

ESA/DLR/FU Berlin

Mars Express captured the image in November 2018 and ESA shared it on Thursday, saying it shows "clear signs of past water activity." The valley network is located in a highlands area east of the Huygens impact crater and north of the Hellas impact basin.

The valleys have undergone erosion over time, but the branch-like tributaries are still easily to spot.

ESA points to recent research indicating "the planet once had a thicker, denser atmosphere that was able to lock in far greater amounts of warmth, and therefore facilitate and support the flow of liquid water on the surface below."

The Mars Express imagery isn't the first sign of long-gone rivers on Mars, but it's one of the reasons we still hold out hope of one day finding signs of ancient life on the Red Planet. Scientists also suspect Mars is hiding a salty lake under its southern ice cap.

Mars is due to get a couple of new rovers from ESA/Roscosmos and NASA over the next few years. Both will be searching for signs of past life. ESA's river valley view just adds to the anticipation.