Posted on by Fraser Cain

Pictures of Rivers

Mississippi river delta

Here are some cool pictures of rivers taken by various spacecraft.

Here’s a picture of the Mississippi river delta. The image was captured by Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard NASA’s Terra satellite.

Betsiboka River flooding
Betsiboka River flooding

This is an image of flooding on the Betsiboka River in Madagascar. The flooding was created by Tropical Storm Eric, which swept through the region in early 2009. This photograph was taken by astronauts on board the International Space Station.

Colorado River Delta
Colorado River Delta

People rely on the Colorado River so much that very little of it actually reaches the ocean. Instead, almost all of the water that flows through the river is used for irrigation along its route.

Ganges river delta. Image credit: NASA
Ganges river delta. Image credit: NASA

This is a picture of the river delta for the Ganges. In fact, the Ganges combined with the Brahmaputra River make up the largest river delta in the world. The rivers flood from snow melt in the nearby Himalayas.

Niger River
Niger River

This is a picture of the Niger River. It was captured by the ASTER instrument on board NASA’s Terra Earth Observation satellite.

We have written many articles with pictures of rivers for Universe Today. Here’s an article about flooding in the Red River, and here’s an image of the Yangtze River from space.

We have also recorded an episode of Astronomy Cast all about the Earth. Listen to it here, Episode 51: Earth.

Posted on by Jean Tate

Abiogenesis

What are Fossils
Fossil stromatolite, Barberton Mountains South Africa (2.5 billion years old)

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How did life on Earth arise? Scientific efforts to answer that question are called abiogenesis. More formally, abiogenesis is a theory, or set of theories, concerning how life on Earth began (but excluding panspermia).

Note that while abiogenesis and evolution are related, they are distinct (evolution says nothing about how life began; abiogenesis says nothing about how life evolves).

Intensive study of the Earth’s rocks has turned up lots and lots of evidence that some kinds of prokaryotes lived happily on Earth about 3.5 billion years ago (and there’re also pointers to the existence of life on Earth in the oldest rocks). So, if life arose on Earth, it did so from the chemicals in the water, air, and rocks of the early Earth … and in no more than a few hundred million years.

Because there are no sedimentary rocks older than about 3.7 billion years (and no metamorphic ones older than about 3.9 billion years), and because the oldest such rocks already contain evidence that there was life on Earth then, testing abiogenesis theories must be done by means other than geological.

There is a long history of attempts to create various organic molecules – such as amino acids – from simple precursors such as carbon dioxide, ammonia, and water, in conditions which simulate those of the early Earth. Those of Miller and Urey, in 1953, are the most famous (and the first).

It turns out that it’s pretty easy to form many kinds of organic molecules, in a wide range of environments … so the focus of research today is on how life could arise from any particular brew. And the hard part is how reliable self-replication get going (if you can make some sort of primitive cell in a test tube, it isn’t a form of life if it can’t reproduce itself!). So far, it seems that RNA and DNA cannot have been involved (too hard to form and stay stable), but several simpler kinds of molecules may work.

Well, that’s one hard part; another is how can a stable bag of chemicals form? (There have been some exciting recent discoveries which may help answer at least part of this question).

A different approach – than reproduction – to finding the key to how life got started involves asking how metabolism arose; how can a bag of chemicals take in ‘food’, process it (to supply energy to all the other chemical processes going on in the bag), and get rid of the waste?

The TalkOrigins website has a summary of abiogenesis, though it is now somewhat dated (much has happened in just the last three years)!

Abiogenesis in its strict sense (origin of life on Earth) is a bit off the track for Universe Today; however, conditions under which life might spontaneously arise, on other planets (etc) is not. Some Universe Today stories on this are Sub-surface Oceans In Comets Suggest Possible Origin of Life, Add Heat, Then Tectonics: Narrowing the Hunt for Life in Space, and Has Liquid Water Been Detected on Mars?

Posted on by Fraser Cain

Earth’s Circumference

Blue marble Earth. Image credit: NASA

The Earth’s circumference – the distance around the equator – is 40,075 kilometers around. That’s sounded nice and simple, but the question is actually more complicated than that. The circumference changes depending on where you measure it. The Earth’s meridional circumference is 40,008 km, and its average circumference is 40,041 km.

Why are there different numbers for the Earth’s circumference? It happens because the Earth is spinning. Think about what happens when you spin around holding a ball on a string. Your rotation creates a force that holds the ball out on the end of the string. And if the string broke, the ball would fly away. Even though the Earth is a solid ball of rock and metal, its rotation causes it to flatten out slightly, bulging at the equator.

That bulge isn’t very much, but when you subtract the meridional circumference (the equator when you pass through both poles), and the equatorial circumference, you see that it’s a difference of 67 km. In other words, if you drove your car around the equator of the Earth, you would drive an extra 67 km than you would if you drove from pole to pole to pole.

And that’s why the average circumference of Earth is 40,041 km. Which answer is correct? It depends on how accurate you want to be with your calculation.

We have written many articles about the Earth for Universe Today. Here’s an article about how fast the Earth rotates, and here’s an article about how round the Earth is.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Posted on by Abby Cessna

Magnetic North Pole

The movement of Earth's north magnetic pole across the Canadian arctic, 1831--2001 (Geological Survey of Canada)
The movement of Earth's north magnetic pole across the Canadian arctic, 1831--2001 (Geological Survey of Canada)

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The Earth has a magnetic field, known as the magnetosphere, that protects our planet from the particles of the solar winds. One point of that field is known as the Magnetic North Pole. The Magnetic North Pole is not the geographic North Pole; it is actually hundreds of miles south of the geographic North Pole and north of Canada.

Hundreds of years ago, European navigators believed that the needles of compasses were attracted to some “magnetic mountain” or “island” thought to be located in the far north. Some also believed that the needles could be attracted to the Pole Star, which is part of the Ursa Minor constellation and has long been used in navigation. One English philosopher, William Gilbert, proposed that the Earth acts like a giant magnet; he also was the first person to state that the Earth’s magnetic field points vertically downward at the Magnetic North Pole. It took hundreds of years before scientists came to properly understand our planet’s magnetic field, although this is known to be correct now.

All magnets have two poles, like the “plus” and “minus” signs found on batteries. Instead of these locations being named plus and minus though, they were named the North and South Magnetic Poles. It is toward the Magnetic North Pole that your compass points not the geographic North Pole, which makes sense considering it utilizes magnets to determine direction. At the Magnetic North Pole, the magnetic fields points down vertically; in other words it has a 90° “dip” toward the Earth’s surface. The counterpart of the Magnetic North Pole is the Magnetic South Pole. Because the Earth’s magnetic field is not perfectly symmetrical, the magnetic fields are not antipodal. That means that if you draw a straight line between them, it does not pass through the Earth’s center. It is off by approximately 530 km. The North and South Magnetic Poles are also known as Magnetic Dip Poles because they “dip” at a 90° angle towards the Earth.   

The Magnetic North Pole continues to move around. According to the Geological Survey of Canada, which routinely studies the Magnetic North Pole, the pole moves as much as 40 km per year. It also moves daily. Every day, the Magnetic North Pole has an elliptical movement of approximately 80 km from the average point of its center. That means when you are using a compass, you have to be aware of the difference between magnetic north and geographic north.

Universe Today has articles on Earth’s magnetic field and modeling the Earth’s magnetic field.

For more information, check out the Magnetic North Pole and geomagnetism.

Astronomy Cast has an episode on Earth.

References:
Earth’s Inconstant Magnetic Field
Earth’s Magnetic Field and its Changes in Time

Posted on by Fraser Cain

Exosphere

Exosphere

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The Earth’s atmosphere is broken up into several distinct layers. We live down in the troposphere, where the atmosphere is thickest. Above that is the stratosphere, then there’s the mesosphere, thermosphere and finally the exosphere. The top of the exosphere marks the line between the Earth’s atmosphere and interplanetary space.

The exosphere is the outermost layer of the Earth’s atmosphere. It starts at an altitude of about 500 km and goes out to about 10,000 km. Within this region particles of atmosphere can travel for hundreds of kilometers in a ballistic trajectory before bumping into any other particles of the atmosphere. Particles escape out of the exosphere into deep space.

The lower boundary of the exosphere, where it interacts with the thermosphere is called the thermopause. It starts at an altitude of about 250-500 km, but its height depends on the amount of solar activity. Below the thermopause, particles of the atmosphere have atomic collisions, like what you might find in a balloon. But above the thermopause, this switches over to purely ballistic collisions.

The theoretical top boundary of the exosphere is 190,000 km (half way to the Moon). This is the point at which the solar radiation coming from the Sun overcomes the Earth’s gravitational pull on the atmospheric particles. This has been detected to about 100,000 km from the surface of the Earth. Most scientists consider 10,000 km to be the official boundary between the Earth’s atmosphere and interplanetary space.

We have written several articles about the Earth’s atmosphere for Universe Today. Here’s an article about an evaporating extrasolar planet, and this article explains how far away space is.

You can learn more about the layers of the atmosphere, including the exosphere from this page at NASA.

We have recorded a whole episode of Astronomy Cast talking about the Earth’s (and it’s atmosphere). Check it out here, Episode 51: Earth.

Posted on by Fraser Cain

Satellite Map of the World

World satellite map. Image credit: NASA

There’s no better way to appreciate the planet you live on than to have a great big picture of it on your wall. Here are some ways you can get your hands on a satellite map of the world.

If you’ve got a nice printer and you’d like to save yourself some money, why not download a satellite map of the world for free from NASA. You can get free satellite images from the NASA Earth Observatory.

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Each month NASA releases a new composite satellite image of the entire planet. This lets you track changes from month to month. You can view the full images on this page.

NASA satellite map of the Earth
NASA satellite map of the Earth

You can also get a free satellite map of the world captured at night. This photo shows whole planet Earth, but now you’re seeing it at night. The bright spots are cities and populated areas. It’s easy to see the differences between 1st world countries and more developing nations.

Earth lights at night.

If you want to just buy a poster that you can put on your wall, you can find a bunch of satellite world maps from Amazon.com. Here’s a link to buy the Earth at night poster. And here’s an image of the whole Earth by day.

Posted on by Fraser Cain

Albedo Effect

Stains on the ice visible on this satellite image. Credit: British Antarctic Survey

Astronomers define the reflectivity of an object in space using a term called albedo. This is the amount of electromagnetic radiation that reflects away, compared to the amount that gets absorbed. A perfectly reflective surface would get an albedo score of 1, while a completely dark object would have an albedo of 0. Of course, it’s not that black and white in nature, and all objects have an albedo score that ranges between 0 and 1.

Here on Earth, the albedo effect has a significant impact on our climate. The lower the albedo, the more radiation from the Sun that gets absorbed by the planet, and temperatures will rise. If the albedo is higher, and the Earth is more reflective, more of the radiation is returned to space, and the planet cools.

An example of this albedo effect is the snow temperature feedback. When you have a snow covered area, it reflects a lot of radiation. This is why you can get terrible sunburns when you’re skiing. But then when the snow covered area warms and melts, the albedo goes down. More sunlight is absorbed in the area and the temperatures increase. Climate scientists are concerned that global warming will cause the polar ice caps to melt. With these melting caps, dark ocean water will absorb more sunlight, and contribute even more to global warming.

Earth observation satellites are constantly measuring the Earth’s albedo using a suite of sensors, and the reflectivity of the planet can actually be measured through Earthshine – light from the Earth that reflects off the Moon.

Different parts of the Earth contribute to our planet’s overall albedo in different amounts. Trees are dark and have a low albedo, so removing trees might actually increase the albedo of an area; especially regions typically covered in snow during the winter.

Clouds can reflect sunlight, but they can also trap heat warming up the planet. At any time, about half the Earth is covered by clouds so their effect is significant.

Needless to say, the albedo effect is one of the most complicated factors in climate science, and scientists are working hard to develop better models to estimate its impact in the future.

We have written many articles about the albedo effect for Universe Today. Here’s an article discussing the albedo of the Earth, and how decreasing Earthshine could be tied to global warming.

There are some great resources out on the Internet as well. Check out this article from Scientific American Frontiers, and some cool photos of different colors of ice.

We have recorded a whole episode of Astronomy Cast just about the Earth. Listen to it here, Episode 51: Earth.

Reference:
Encyclopedia of Earth

Posted on by Fraser Cain

Atmosphere Layers

Atmosphere layers. Image credit: NASA
Atmosphere layers. Image credit: NASA

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Seen from space, the Earth’s atmosphere is incredibly thin, like a slight haze around the planet. But the atmosphere has several different layers that scientists have identified; from the thick atmosphere that we breathe to the tenuous exosphere that extends out thousands of kilometers from the Earth. Let’s take a look at the different atmosphere layers.

Scientists have identified 5 distinct layers of the atmosphere, starting with the thickest near the surface, and then thinning out until it eventually merges with space.

The troposphere is the first layer above the surface of the Earth, and it contains 75% of the Earth’s atmosphere, and 99% of its water. Breathe in, that’s the troposphere. The average depth of the troposphere is about 17 km high. It gets deeper in the tropical regions, up to 20 km, and then shallower near the Earth’s poles – down to 7 km thick. Temperature and pressure are at the their highest at sea level, and then decrease with altitude. The troposphere is also where we experience weather.

The next atmosphere layer is the stratosphere, extending above the troposphere to an altitude of 51 km. Unlike the troposphere, temperature actually increases with height. Commercial airlines will typically fly in the stratosphere because it’s very stable; above weather, and allows them to optimize burning jet fuel. You might be surprised to know that bacterial life survives in the stratosphere.

Above that is the mesosphere, which starts at about 50-85 km above the Earth’s surface and extends up to an altitude of 80-90 km. Temperatures decrease the higher you go in the mesosphere, reaching a low of -100 °C, depending on the latitude and season.

Next comes the thermosphere. This region starts around 90 km above the Earth and goes up to about 320 and 380 km. The International Space Station orbits within the thermosphere. This is the region of the atmosphere where ultraviolet radiation causes ionization, and we can see auroras. Temperatures in the thermosphere can actually reach 2,500 °C; however, it wouldn’t feel warm because the atmosphere is so thin.

The 5th and final layer of the Earth’s atmosphere is the exosphere. This starts above the thermosphere and extends out for hundreds and even thousands of kilometers. Air molecules in this region can travel for hundreds of kilometers without bouncing into another particle.

We have written many articles about the Earth’s atmosphere for Universe Today. Here’s an article about the composition of the Earth’s atmosphere, and here’s information about the Earth’s early atmosphere.

Here’s a great article from NASA that explains the different layers of the atmosphere, and here’s more information from NOAA.

We have done a whole episode of Astronomy Cast just about Earth. Listen to it here, Episode 51 – Earth.

Posted on by Fraser Cain

Super Earths

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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The holy grail in the search for extrasolar planets will be the discovery of Earthlike planets orbiting other stars. With better telescopes and techniques, astronomers will eventually be able to even detect the atmospheres of extrasolar planets and determine if there’s life there. Although Earth-sized planets are impossible to detect with current observatories, astronomers are now finding super earths.

A super Earth is a terrestrial planet orbiting a distant star. But instead of having the mass of our own planet, it might have 2, 5, or even 10 times the mass of the Earth. Although that makes them large, very massive planets, they’re not as large or massive as gas giants.

And just because they’re called super Earths doesn’t mean they’re habitable, or even Earthlike in climate at all. Super Earths could be orbiting close to their parent star, or well outside the solar system’s habitable zone.

Scientists haven’t completely settled on a definition for super Earths. Some believe a planet should be considered a super Earth if it’s a terrestrial planet between 1 and 10 Earth masses, while others think it should be between 5 and 10 Earth masses.

The first super Earth ever discovered was found in 1991 orbiting a pulsar. Obviously that wouldn’t really be a very habitable place to live. The first super earth found orbiting a main sequence star was found in 2005, orbiting the star Gliese 876. It’s estimated to have 7.5 times the mass of the Earth, and orbits its parent star every 2 days. With such a short orbital period, you can expect that it’s orbiting very close to its parent star. Temperatures on the surface of the planet reach 650 kelvin.

The first super earth found within its star’ habitable zone was Gliese 581 c. It’s estimated to have 5 Earth masses, and orbits its parent star at a distance of 0.073 astronomical units (1 AU is the average distance from the Earth to the Sun). That’s pretty close to the star, and Gliese 581 c would probably have a runaway greenhouse effect, similar to Venus. But right beside that is Gliese 581 d, with a mass of 7.7 Earths and an orbit of 0.22 AU. This planet could very well have liquid water on its surface.

The smallest super Earth discovered so far is MOA-2007-BLG-192Lb, which has only 3.3 times the mass of the Earth, and was orbiting a brown dwarf star. But this record will probably be beaten by the time you read this, as planet hunters get better. It’s only a matter of time before a true Earthlike planet is discovered.

We have written many articles about super Earths. Here’s an article speculating on the kinds of atmospheres that super Earths might have, and another article about how similar super Earths really are to our own planet.

Here’s an artist’s impression of a super Earth features on NASA’s Astronomy Picture of the Day website, and here’s an article from NASA about super Earths.

We also recorded an episode of Astronomy Cast dealing with the different kinds of extrasolar planets you can find. Listen to it here. Episode 125: A Zoo of Extrasolar Planets.

Source: Wikipedia

Posted on by Fraser Cain

Destruction of Earth

Planet Killer
Artist's conception of an asteroid hitting Earth.

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Want to destroy the Earth? It’s harder than it sounds. That’s because the Earth is held together by the mutual gravity of 5.97 x 1024 tonnes of rock and metal. In order to blast the Earth apart, you would need to introduce more energy than the gravitational energy holding the whole planet together.

Think about it, if you wanted to bring about the destruction of Earth, you can’t just fly in your orbiting death star and fire a turbo laser at the planet. You might melt a little spot, but it’s not going to cause the planet to detonate like it did in Star Wars. Add up the mutual gravitational attraction of every atom in the Earth, and that’s how much energy you would need coming out of your laser. A laser powerful enough could vaporize the rock and metal and let it escape out into space. Keep that laser firing for billions of years and it should do the trick.

Another possibility would be to strike the Earth with an asteroid large enough to smash the planet. We’ve been hit by millions of asteroids in the past, and one was even thought to have formed the Moon. It would take an object the size of Mars slamming into Earth at more than 11 km/s to actually shatter the planet.

Instead of burning it, or smashing it, you could change the Earth’s orbit into a downward spiral into the Sun. After a few million years the planet would be burned up and destroyed by the Sun. Problem solved. In order to actually shift the Earth’s orbit, you would need to move a heavy asteroid so that it gently nudges the Earth into a spiraling orbit.

Of course, you could just bring an equivalent amount of antimatter, and let the Earth and anti-Earth collide together. The entire Earth would be annihilated in a heartbeat, leaving a flash of energy. Earth destroyed, problem solved.

But in the end, the Earth will likely be destroyed when it’s swallowed up by the Sun in about 7 billion years. When the Sun runs out of fuel, it will expand in size, becoming a red giant star. Astronomers agree it will swallow up Mercury and Venus, but they aren’t sure if it will get so large that it reaches the Earth. But whatever happens, the surface of the Earth will be scorched.

If that doesn’t completely destroy the Earth, you’ll need to wait trillions of years for the planet to get sucked into some black hole. And if that never happens, it might take 10100 years for the atoms that make up the Earth to decay into pure energy.

Then, the destruction of Earth will be complete.

This is a just a taste of the monumental amount of work it would take to bring about the destruction of Earth. Perhaps the best article every written on the subject is over here at Things of Interest.

You should also read Phil Plait’s book, Death from the Skies, which looks at all the different ways the Universe is trying to kill us.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded a two-part episode of Astronomy Cast about the End of Everything (including the Earth). Here’s part 1, and here’s part 2.

Reference:
NASA