Igneous rock (aka. "fire rock") is formed from cooled and solidified magma. Credit: geologyclass.org
When it comes to the composition of the Earth, three main types of rock come into play. These are known as metamorphic rock, sedimentary rock, and igneous rock, respectively. Also known as “fire rock” (derived from the Latin “ignus”), these type of rock are the most common type of rock in the Earth’s surface. In fact, combined with metaphoric rock, igneous rock makes up 90 to 95% of all rock to a depth of 16 km from the surface.
Igneous rocks are also very important because their mineral and chemical makeup can be used to learn about the composition, temperature and pressure that exists within the Earth’s mantle. They can also tell us much about the tectonic environment, given that they are closely linked to the convection of tectonic plates. But just how are these rocks formed?
A depiction of the atomic structure of the helium atom. Credit: Creative Commons
Since the beginning of time, human beings have sought to understand what the universe and everything within it is made up of. And while ancient magi and philosophers conceived of a world composed of four or five elements – earth, air, water, fire (and metal, or consciousness) – by classical antiquity, philosophers began to theorize that all matter was actually made up of tiny, invisible, and indivisible atoms.
Since that time, scientists have engaged in a process of ongoing discovery with the atom, hoping to discover its true nature and makeup. By the 20th century, our understanding became refined to the point that we were able to construct an accurate model of it. And within the past decade, our understanding has advanced even further, to the point that we have come to confirm the existence of almost all of its theorized parts.
Artist's conception of Mars, with asteroids nearby. Credit: NASA
Mars represents something of a conundrum for scientists. In many respects, it is significantly different from Earth. It’s cold, it’s dry, there is little atmosphere or precipitation to speak of, and nothing grows there. By our standards, that makes it an incredibly inhospitable place. And yet, in many other respects, it is quite similar to our world.
For instance, Mars’ internal structure is differentiated between a metallic core and a silicate mantle and crust. It also has plenty of water, though the majority of it is concentrated in the polar regions as water ice (and as a permanent layer of permafrost under much of the surface). But perhaps most striking of all, a day on Mars is almost the same as a day here on Earth.
In fact, a day on Mars is roughly 40 minutes longer than a day is here on Earth. Compared to other bodies in our Solar System where a day is either incredibly short (Jupiter’s rotates once on its axis every 9 hours, 55 minutes and 29.69 seconds) or incredibly long (a day on Venus lasts for 116 days and 18 hours), this similarity is quite astounding.
However, there are some things that need to be addressed before we go about declaring just how long a day is on another planet. In fact, there are two ways to determine the length of a day on a celestial body, the sidereal day and the solar day; both of which are used by astronomers for determining the passage on time.
Sidereal vs. Solar:
By definition, a sidereal day on Mars is the length of time that it takes the planet to rotate once on its axis so that stars appear in the same place in the night sky. On Earth, this takes exactly 23 hours, 56 minutes and 4.1 seconds. In comparison, on Mars, a sidereal day lasts 24 hours, 37 minutes, and 22 seconds.
The solar day, by contrast, is the time it takes for the Earth to rotate on its axis so that the Sun appears in the same position in the sky. This position changes slightly each day, but on Earth, a mean solar day works out to being 24 hours long. On Mars, a solar day lasts 24 hours, 39 minutes, and 35 seconds. Rounding that out, we say that a day here on Earth works out to an even 24 hours while on Mars, a day lasts 24 hours and 40 minutes.
Want to know about some other interesting similarities Mars has with Earth? Read on!
Seasonal Changes:
Mars also has a seasonal cycle that is similar to that of Earth’s. This is due in part to the fact that Mars also has a tilted axis, which is inclined 25.19° to its orbital plane (compared to Earth’s axial tilt of approx. 23.44°). It’s also due to Mars orbital eccentricity, which mean that it ranges in distance from 206.7 million to249.2 million kilometers from the Sun.
This change in distance causes significant variations in temperature. While the planet’s average temperature is -46 °C (51 °F), this ranges from a low of -143 °C (-225.4 °F) during the winter at the poles to a high of 35 °C (95 °F) during summer and midday at the equator. This high in temperatures is what allows for liquid water to still flow, albeit intermittently, on the surface of Mars.
It also snows on Mars. In 2008, NASA’s Phoenix Landerfound water ice in the polar regions of the planet. This was an expected finding, but scientists were not prepared to observe snow falling from clouds. The snow, combined with soil chemistry experiments, led scientists to believe that the landing site had a wetter and warmer climate in the past.
The eccentricity in Mars’ orbit is what causes some significant variations in temperature. Credit: NASA
And then in 2012, data obtained by the Mars Reconnaissance Orbiter revealed that carbon-dioxide snowfalls occur in the southern polar region of Mars. For decades, scientists have known that carbon-dioxide ice is a permanent part of Mars’ seasonal cycle and exists in the southern polar caps. But this was the first time that such a phenomena was detected, and it remains the only known example of carbon-dioxide snow falling anywhere in our solar system.
For starters, soil samples and orbital observation have demonstrated conclusively that roughly 3.7 billion years ago, the planet had more water on its surface than is currently in the Atlantic Ocean. Similarly, atmospheric studies conducted on the surface and from space have proven that Mars also had a viable atmosphere at that time, one which was slowly stripped away by solar wind.
Weather Patterns:
Like Earth, Mars can have some pretty extreme weather. In the Red Planet’s case, this takes the form of dust storms that can dominated the surface from time to time. These storms have been known to grow to be thousands of kilometers across, occasionally encircling the entire planet and covering everything in a thick haze of dust. When these storms become that large, they prevent direct observation of the Martian surface.
Case in point: when the Mariner 9 orbiter became the first spacecraft to orbit Mars in 1971, it sent pictures back to Earth of a world consumed in haze. The entire planet was covered by a dust storm so massive that only Olympus Mons, the giant Martian volcano that measures 24 km high, could be seen above the clouds. This storm lasted for a full month, and delayed Mariner 9‘s attempts to photograph the planet in detail.
And then on June 9th, 2001, the Hubble Space Telescope spotted a dust storm in the Hellas Basin on Mars. By July, the storm had died down, but then grew again to become the largest storm in 25 years. So big was the storm that amateur astronomers using small telescopes were able to see it from Earth. And the cloud raised the temperature of the frigid Martian atmosphere by a stunning 30° Celsius.
Therein lies another thing Mars has in common with Earth – global warming! Much like warming trends here on Earth, warming on Mars is caused by the presence of particulate matter in the air that absorbs energy from the Sun and radiates it outward into the atmosphere. causing average temperatures to rise.
These storms tend to occur when Mars is closest to the Sun, and are the result of temperatures rising and triggering changes in the air and soil. As the soil dries, it becomes more easily picked up by air currents, which are caused by pressure changes due to increased heat. The dust storms cause temperatures to rise even further, so you could say Mars has a “greenhouse effect” of its own!
As you have probably concluded from all the facts listed above, Mars can be a harsh and volatile planet. Just knowing the answer to ”how long is a day on Mars?” only provides a small glimpse of what is going on there. At the end of the day (no pun intended!) there is plenty happening on Mars that makes it similar enough to Earth that many people are actually contemplating living there someday. And knowing exactly what sets Mars apart, and what we can work with, will be intrinsic to making that happen!
Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL
Neptune is a truly fascinating world. But as it is, there is much that people don’t know about it. Perhaps it is because Neptune is the most distant planet from our Sun, or because so few exploratory missions have ventured that far out into our Solar System. But regardless of the reason, Neptune is a gas (and ice) giant that is full of wonder!
Below, we have compiled a list of 10 interesting facts about this planet. Some of them, you might already know. But others are sure to surprise and maybe even astound you. Enjoy!
The Sun provides energy for life here on Earth through light and heat. Credit: NASA Goddard Space Flight Center
There is a reason life that Earth is the only place in the Solar System where life is known to be able to live and thrive. Granted, scientists believe that there may be microbial or even aquatic life forms living beneath the icy surfaces of Europa and Enceladus, or in the methane lakes on Titan. But for the time being, Earth remains the only place that we know of that has all the right conditions for life to exist.
One of the reasons for this is because the Earth lies within our Sun’s Habitable Zone (aka. “Goldilocks Zone”). This means that it is in right spot (neither too close nor too far) to receive the Sun’s abundant energy, which includes the light and heat that is essential for chemical reactions. But how exactly does our Sun go about producing this energy? What steps are involved, and how does it get to us here on planet Earth?
Democritus, ancient Greek philosopher who is credited with the birth of atomic theory. Credit: phil-fak.uni-duesseldorf.de
As the philosopher Nietzsche famously said “He who would learn to fly one day must first learn to stand and walk and run and climb and dance; one cannot fly into flying.” This is certainly true when it comes to humanity’s understanding of the universe, something which has evolved over many thousands of years and been the subject of ongoing discovery.
And along the way, many names stand out as examples of people who achieved breakthroughs and helped lay the foundations of our modern understanding. One such person is Democritus, an ancient Greek philosopher who is viewed by many as being the “father of modern science”. This is due to his theory of universe that is made up of tiny “atoms”, which bears a striking resemblance to modern atomic theory.
Though he is typically viewed as one of Greece’s many pre-Socratic natural philosopher, many historians have argued that he is more rightly classified as a scientist, at least when compared to his contemporaries. There has also been significant controversy – particularly in Germany during the 19th century – over whether or not Democritus deserves credit for atomic theory.
This argument is based on the relationship Democritus had with contemporary philosopher Leucippus, who is renowned for sharing his theory about atoms with him. However, their theories came down to a different basis, a distinction that allows Democritus to be given credit for a theory that would go on to become a staple of the modern scientific tradition.
Democritus, by Hendrik ter Brugghen – Heraclitus, 1628. Credit: rijksmuseum.nl
Birth and Early Life:
The precise date and location of Democritus birth is the subject the debate. While most sources claim he was born in Abdera, located in the northern Greek province of Thrace, around 460 BCE. However, other sources claim he was born in Miletus, a coastal city of ancient Anatolia and modern-day Turkey, and that he was born in 490 BCE.
It has been said that Democritus’ father was from a noble family and so wealthy that he received the Persian king Xerxes on the latter’s march through Abdera during the Second Persian War (480–479 BC). It is further argued that as a reward for his service, the Persian monarch gave his father and other Abderites gifts, and left several Magi among them. Democritus was apparently instructed by these Magi in astronomy and theology.
After his father had died, Democritus used his inheritance to finance a series of travels to distant countries. Desiring to feed his thirst for knowledge, Democritus traveled extensively across the known world, traveling to Asia, Egypt and (according to some sources) venturing as far as India and Ethiopia. His writings include descriptions of the the cities of Babylon and Meroe (in modern-day Sudan).
Upon returning to his native land, he occupied himself with the study of natural philosophy. He also traveled throughout Greece to acquire a better knowledge of its cultures and learned from many of Greece’s famous philosophers. His wealth allowed him to purchase their writings, and he wrote of them in his own works. In time, he would become one of the most famous of the pre-Socratic philosophers.
The ruins of the ancient Greek city of Abdera, with the west gate shown. Credit: Wikipedia Commons/Marysas
Leucippus of Miletus had the greatest influence on him, becoming his mentor and sharing his theory of atomism with him. Democritus is also said to have known Anaxagoras, Hippocrates and even Socrates himself (though this remains unproven). During his time in Egypt, he learned from Egyptian mathematicians, and is said to have become acquainted with the Chaldean magi in Assyria.
In the tradition of the atomists, Democritus was a thoroughgoing materialists who viewed the world in terms of natural laws and causes. This differentiated him from other Greek philosophers like Plato and Aristotle, for whom philosophy was more teleological in nature – i.e. more concerned with the purpose of events rather than the causes, as well things like essence, the soul, and final causes.
According to the many descriptions and anecdotes about Democritus, he was known for his modesty, simplicity, and commitment to his studies. One story claims he blinded himself on purpose in order to be less distracted by worldly affairs (which is believed to be apocryphal). He was also known for his sense of humor and is commonly referred to as the “Laughing Philosopher” – for his capacity to laugh at human folly. To his fellow citizens, he was also known as “The Mocker”.
Scientific Contributions:
Democritus is renowned for being a pioneer of mathematics and geometry. He was among the first Greek philosophers to observe that a cone or pyramid has one-third the volume of a cylinder or prism with the same base and height. While none of his works on the subject survived the Middle Ages, his mathematical proofs are derived from other works with contain extensive citations to titles like On Numbers, On Geometrics, On Tangencies, On Mapping, and On Irrationals.
Right circular and oblique circular cones. Credit: Dominique Toussaint
Democritus is also known for having spent much of his life experimenting with and examining plants and minerals. Similar to his work in mathematics and geometry, citations from existing works are used to infer the existence of works on the subject. These include On the Nature of Man, the two-volume collection On Flesh, On Mind, On the Senses, On Flavors, On Colors, Causes concerned with Seeds and Plants and Fruits, and to the three-volume collection Causes concerned with Animals.
From his examination of nature, Democritus developed what could be considered some of the first anthropological theories. According to him, human beings lived short lives in archaic times, forced to forage like animals until fear of wild animals then drove them into communities. He theorized that such humans had no language, and only developed it through the need to articulate thoughts and ideas.
Through a process of trial and error, human beings developed not only verbal language, but also symbols with which to communicate (i.e. written language), clothing, fire, the domestication of animals, and agriculture. Each step in this process led to more discoveries, more complex behaviors, and the many things that came to characterize civilized society.
In terms of astronomy and cosmology, Democritus was a proponent of the spherical Earth hypothesis. He believed that in the original chaos from which the universe sprang, the universe was composed of nothing but tiny atoms that came together to form larger units (a theory which bears a striking resemblance to The Big Bang Theory and Nebular Theory). He also believed in the existence of many worlds, which were either in state of growth or decay.
In a similar vein, Democritus advanced a theory of void which challenged the paradoxes raised by his fellow Greek philosophers, Parmenides and Zeno – the founders of metaphysical logic. According to these men, movement cannot exist because such a thing requires there to be a void – which is nothing, and therefore cannot exist. And a void cannot be termed as such if it is in fact a definable, existing thing.
To this, Democritus and other atomists argued that since movement is an observable phenomena, there must be a void. This idea previewed Newton’s theory of absolute space, in which space exists independently of any observer or anything external to it. Einstein’s theory of relativity also provided a resolution to the paradoxes raised by Parmenides and Zeno, where he asserted that space itself is relative and cannot be separated from time.
Democritus’ thoughts on the nature of truth also previewed the development of the modern scientific method. According to Democritus, truth is difficult, because it can only be perceived through senses-impressions which are subjective. Because of this, Aristotle claimed in his Metaphysicsthat Democritus was of the opinion that “either there is no truth or to us at least it is not evident.”
However, as Diogenes Laertius quoted in his 3rd century CE tract, Lives and Opinions of Eminent Philosophers: “By convention hot, by convention cold, but in reality atoms and void, and also in reality we know nothing, since the truth is at bottom.”
Diogenes Laertius, Lives and Opinions of Eminent Philosophers, makes mention of Democritus and his theories. Credit: Public Domain
Ultimately, Democritus’ opinion on truth came down to a distinction between two kinds of knowledge – “legitimate” (or “genuine”) and bastard (or “secret”). The latter is concerned with perception through the senses, which is subjective by nature. This is due to the fact that our sense-perception are influence by the shape and nature of atoms as they flow out from the object in question and make an impression on our senses.
“Legitimate” knowledge, by contrast, is achieved through the intellect, where sense-data is elaborated through reasoning. In this way, one can get from “bastard” impressions to the point where things like connections, patterns and causality can be determined. This is consistent with the inductive reasoning method later elaborated by Renee Descartes, and is a prime example of why Democritus is considered to be an early scientific thinker.
Atomic Theory:
However, Democritus greatest contribution to modern science was arguably the atomic theory he elucidated. According to Democritus’ atomic theory, the universe and all matter obey the following principles:
Everything is composed of “atoms”, which are physically, but not geometrically, indivisible
Between atoms, there lies empty space
Atoms are indestructible
Atoms have always been, and always will be, in motion
There are an infinite number of atoms, and kinds of atoms, which differ in shape, and size.
He was not alone in proposing atomic theory, as both his mentor Leucippus and Epicurus are believed to have proposed the earliest views on the shapes and connectivity of atoms. Like Democritus, they believed that the solidity of a material corresponded to the shape of the atoms involved – i.e. iron atoms are hard, water atoms are smooth and slippery, fire atoms are light and sharp, and air atoms are light and whirling.
Democritus’ model of an atom was one of an inert solid that interacted mechanically with other atoms. Credit: .science.edu.sg
However, Democritus is credited with illustrating and popularizing the concept, and for his descriptions of atoms which survived classical antiquity to influence later philosophers. Using analogies from our sense experiences, Democritus gave a picture or an image of an atom that distinguished them from each other by their shape, size, and the arrangement of their parts.
In essence, this model was one of an inert solid that excluded other bodies from its volume, and which interacted with other atoms mechanically. As such, his model included physical links (i.e. hooks and eyes, balls and sockets) that explained how connections occurred between them. While this bears little resemblance to modern atomic theory (where atoms are not inert and interact electromagnetically), it is more closely aligned with that of modern science than any other theory of antiquity.
While there is no clear explanation as to how scholars of classical antiquity came to theorize the existence of atoms, the concept proved to be influential, being picked up by Roman philosopher Lucretius in the 1st century CE and again during the Scientific Revolution. In addition to being indispensable to modern molecular and atomic theory, it also provided an explanation as to why the concept of a void was necessary in nature.
If all matter was composed of tiny, indivisible atoms, then there must also be a great deal of open space between them. This reasoning has also gone on to inform out notions of cosmology and astronomy, where Einstein’s theory of special relativity was able to do away with the concept of a “luminiferous aether” in explaining the behavior of light.
Early atomic theory stated that different materials had differently shaped atoms. Credit: github.com
Diogenes Laertius summarized Democritus atomic theory as follows in Lives and Opinions of Eminent Philosophers:
“That atoms and the vacuum were the beginning of the universe; and that everything else existed only in opinion. That the worlds were infinite, created, and perishable. But that nothing was created out of nothing, and that nothing was destroyed so as to become nothing. That the atoms were infinite both in magnitude and number, and were borne about through the universe in endless revolutions. And that thus they produced all the combinations that exist; fire, water, air, and earth; for that all these things are only combinations of certain atoms; which combinations are incapable of being affected by external circumstances, and are unchangeable by reason of their solidity.”
Death and Legacy:
Democritus died at the age of ninety, which would place his death at around 370 BCE; though some writers disagree, with some claiming he lived to 104 or even 109. According to Marcus Aurelius’ book Meditations, Democritus was eaten by lice or vermin, although in the same passage he writes that “other lice killed Socrates”, implying that this was meant metaphorically. Since Socrates died at the hands of the Athenian government who condemned him, it is possible that Aurelius attributed Democritus death to human folly or politics.
While Democritus was highly esteemed amongst his contemporaries, there were also those who resented him. This included Plato who, according to some accounts, disliked him so much that he wished that all his books would be burned. However, Plato’s pupil Aristotle was familiar with the works of Democritus and mentioned him in both Metaphysics and Physics, where he described him as a “physicist” who did not concern himself with the ideals of form or essence.
Democritus meditating on the seat of the soul, by Léon-Alexandre Delhomme (1868). Credit: Pubic Domain
Ultimately, Democritus is credited as being one of the founders of the modern science because his methods and theories closely resemble those of modern astronomers and physicists. And while his version of the atomic model differs greatly from our modern conceptions, his work was of undoubted value, and was a step in an ongoing process that included such scientists as John Dalton, Neils Bohr and even Albert Einstein.
As always, science is an process of continuing discovery, where new breakthroughs are built upon the foundations of the old and every generations attempts to see a little farther by standing on the shoulders of those who came before.
A photo of the full moon, taken from Apollo 11 on its way home to Earth, from about 18,520 km (10,000 nm) away. Credit: NASA
This might be a silly question, but what is the official name of that bright ball in the sky? You know, that thing we call the Moon? You might be surprised to know that the official name of the Moon is… the Moon. And this becomes all the more confusing when there are other moons orbiting other planets, and even asteroids.
But interestingly enough, the Moon has been given its fair share of special monikers, many of which are still used today. For example, a Full Moon occurs twelve times a year, and each one has a distinct name based on the season and the special significance this Moon has. Here is a list of all twelve Full Moon names and why they were bestowed upon Earth’s only satellite.
Tungurahua ("throat of fire"), an active stratovolcano in Ecuador. Credit: Patrick Taschler
Without a doubt, volcanoes are one of the most powerful forces of nature a person can bear witness to. Put simply, they are what results when a massive rupture takes place in the Earth’s crust (or any planetary-mass object), spewing hot lava, volcanic ash, and toxic fumes onto the surface and air. Originating from deep within the Earth’s crust, volcanoes leave a lasting mark on the landscape.
But what are the specific parts of a volcano? Aside from the “volcanic cone” (i.e. the cone-shaped mountain), a volcano has many different parts and layers, most of which are located within the mountainous region or deep within the Earth. As such, any true understanding of their makeup requires that we do a little digging (so to speak!)
While volcanoes come in a number of shapes and sizes, certain common elements can be discerned. The following gives you a general breakdown of a volcanoes specific parts, and what goes into making them such a titanic and awesome natural force.
Magma Chamber:
A magma chamber is a large underground pool of molten rock sitting underneath the Earth’s crust. The molten rock in such a chamber is under extreme pressure, which in time can lead to the surrounding rock fracturing, creating outlets for the magma. This, combined with the fact that the magma is less dense than the surrounding mantle, allows it to seep up to the surface through the mantle’s cracks.
Lava cooling after an eruption from Kilauea, a shield volcano near Kalapana, Hawaii Credit: kalapanaculturaltours.com
When it reaches the surface, it results in a volcanic eruption. Hence why many volcanoes are located above a magma chamber. Most known magma chambers are located close to the Earth’s surface, usually between 1 km and 10 km deep. In geological terms, this makes them part of the Earth’s crust – which ranges from 5–70 km (~3–44 miles) deep.
Lava:
Lava is the silicate rock that is hot enough to be in liquid form, and which is expelled from a volcano during an eruption. The source of the heat that melts the rock is known as geothermal energy – i.e. heat generated within the Earth that is leftover from its formation and the decay of radioactive elements. When lava first erupted from a volcanic vent (see below), it comes out with a temperature of anywhere between 700 to 1,200 °C (1,292 to 2,192 °F). As it makes contact with air and flows downhill, it eventually cools and hardens.
Main Vent:
A volcano’s main vent is the weak point in the Earth’s crust where hot magma has been able to rise from the magma chamber and reach the surface. The familiar cone-shape of many volcanoes are an indication of this, the point at which ash, rock and lava ejected during an eruption fall back to Earth around the vent to form a protrusion.
Throat:
The uppermost section of the main vent is known as the volcano’s throat. As the entrance to the volcano, it is from here that lava and volcanic ash are ejected.
Thurston lava tube is located on Kilauea in Hawaii. Credit: P. Mouginis-Mark, LPI
Crater:
In addition to cone structures, volcanic activity can also lead to circular depressions (aka. craters) forming in the Earth. A volcanic crater is typically a basin, circular in form, which can be large in radius and sometimes great in depth. In these cases, the lava vent is located at the bottom of the crater. They are formed during certain types of climactic eruptions, where the volcano’s magma chamber empties enough for the area above it to collapse, forming what is known as a caldera.
Pyroclastic Flow:
Otherwise known as a pyroclastic density current, a pyroclastic flow refers to a fast-moving current of hot gas and rock that is moving away from a volcano. Such flows can reach speeds of up to 700 km/h (450 mph), with the gas reaching temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill from their eruption site.
Their speeds depend upon the density of the current, the volcanic output rate, and the gradient of the slope. Given their speed, temperature, and the way they flow downhill, they are one of the greatest dangers associated with volcanic eruptions and are one of the primary causes of damage to structures and the local environment around an eruption site.
Ash Cloud:
Volcanic ash consists of small pieces of pulverized rock, minerals and volcanic glass created during a volcanic eruption. These fragments are generally very small, measuring less than 2 mm (0.079 inches) in diameter. This sort of ash forms as a result of volcanic explosions, where dissolved gases in magma expand to the point where the magma shatters and is propelled into the atmosphere. The bits of magma then cool, solidifying into fragments of volcanic rock and glass.
Because of their size and the explosive force with which they are generated, volcanic ash is picked up by winds and dispersed up to several kilometers away from the eruption site. Due to this dispersal, ash an also have a damaging effect on the local environment, which includes negatively affecting human and animal health, disrupting aviation, disrupting infrastructure, and damaging agriculture and water systems. Ash is also produced when magma comes into contact with water, which causes the water to explosively evaporate into steam and for the magma to shatter.
Volcanic Bombs:
In addition to ash, volcanic eruptions have also been known to send larger projectiles flying through the air. Known as volcanic bombs, these ejecta are defined as those that measure more than 64mm (2.5 inches) in diameter, and which are formed when a volcano ejects viscous fragments of lava during an eruption. These cool before they hit the ground, are thrown many kilometers from the eruption site, and often acquire aerodynamic shapes (i.e. streamlined in form).
While the term applies to any ejecta larger than a few centimeters, volcanic bombs can sometimes be very large. There have been recorded instances where objects measuring several meters were retrieved hundreds of meters from an eruptions. Small or large, volcanic bombs are a significant volcanic hazard and can often cause serious damage and multiple fatalities, depending on where they land. Luckily, such explosions are rare.
Secondary Vent:
On large volcanoes, magma can reach the surface through several different vents. Where they reach the surface of the volcano, they form what is referred to as a secondary vent. Where they are interrupted by accumulated ash and solidified lava, they become what is known as a Dike. And where these intrude between cracks, pool and then crystallize, they form what is called a Sill.
Cross-section of a stratovolcano: 1. Magma chamber 2. Bedrock 3. Vent 4. Base 5. Sill 6. Dike 7. Layers of ash 8. Flank 9. Layers of lava 10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater 15. Ash cloud. Credit: MesserWoland
Secondary Cone:
Also known as a Parasitic Cone, secondary cones build up around secondary vents that reach the surface on larger volcanoes. As they deposit lava and ash on the exterior, they form a smaller cone, one that resembles a horn on the main cone.
Yes indeed, volcanoes are as powerful as they are dangerous. And yet, without these geological phenomena occasionally breaking through the surface and reigning down fire, smoke, and clouds of ash, the world as we know it would be a very different place. More than likely, it would be a geologically dead one, with no change or evolution in its crust. I think we can all agree that while such a world would be much safer, it would also be painfully boring!
In science fiction, wormholes are a method often used to travel great distances across space. Are these magic bridges really possible?
With all my enthusiasm for humanity’s future in space, there’s one glaring problem. We’re soft meat bags of mostly water, and those other stars are really really far away. Even with the most optimistic spaceflight technologies we can imagine, we’re never going to reach another star in a human lifetime.
Reality tells us that even the most nearby stars are incomprehensibly far away, and would require vast amounts of energy or time to make the journey. Reality says that we’d need a ship that can somehow last for hundreds or thousands of years, while generation after generation of astronauts are born, live their lives and die in transit to another star.
Science fiction, on the other hand, woos us with its beguiling methods of advanced propulsion. Crank up the warp drive and watch the stars streak past us, making a journey to Alpha Centauri as quick as a pleasure cruise.
You know what’s even easier? A wormhole; a magical gateway that connects two points in space and time with one another. Just align the chevrons to dial in your destination, wait for the stargate to stabilize and then just walk… walk! to your destination half a galaxy away.
Yeah, that would be really nice. Someone should really get around to inventing these wormholes, ushering in a bold new future of intergalactic speedwalking. What are wormholes, exactly, and how soon until I get to use one?.
A wormhole, also known as an Einstein-Rosen bridge is a theoretical method of folding space and time so that you could connect two places in space together. You could then travel instantaneously from one place to another.
We’ll use that classic demonstration from the movie Interstellar, where you draw a line from two points, on a piece of paper and then fold the paper over and jab your pencil through to shorten the journey. That works great on paper, but is this actual physics?
As Einstein taught us, gravity isn’t a force that pulls matter like magnetism, it’s actually a warping of spacetime. The Moon thinks it’s just following a straight line through space, but it’s actually following the warped path created by the Earth’s gravity.
And so, according to Einstein and physicist Nathan Rosen, you could tangle up spacetime so tightly that two points share the same physical location. If you could then keep the whole thing stable, you could carefully separate the two regions of spacetime so they’re still the same location, but separated by whatever distance you like.
Climb down the gravitational well of one side of the wormhole, and then instantaneously appear at the other location. Millions or billions of light-years away. While wormholes are theoretically possible to create, they’re practically impossible from what we currently understand.
Albert Einstein, pictured in 1953. Photograph: Ruth Orkin/Hulton Archive/Getty Images Ruth Orkin/Getty
The first big problem is that wormholes aren’t traversable according to General Relativity. So keep this in mind; the physics that predicts these things, prohibits them from being used as a method of transportation. That’s a pretty serious strike against them.
Second, even if wormholes can be created, they’d be completely unstable, collapsing instantly after their formation. If you tried to walk into one end, you might as well be walking into a black hole.
Third, even if they are traversable, and can be kept stable, the moment any material tried to pass through – even photons of light – that would make them collapse.
There’s a glimmer of hope, though, because physicists still haven’t figured out how to unify gravity and quantum mechanics.
This means that the Universe itself might know things about wormholes that we don’t understand yet. It’s possible that they were created naturally as part of the Big Bang, when the spacetime of the entire Universe was tangled up in a singularity.
Astronomers have actually proposed searching for wormholes in space by looking for how their gravity distorts the light from stars behind them. None have turned up yet.
One possibility is that wormholes appear naturally like the virtual particles that we know exist. Except these would be incomprehensibly small, on the Planck scale. You’re going to need a smaller spacecraft.
Artist illustration of a spacecraft passing through a wormhole to a distant galaxy. Image credit: NASA.
One of the most fascinating implications of wormholes is that they could allow you to actually travel in time.
Here’s how it works. First, create a wormhole in the lab. Then take one end of the wormhole, put it on a spacecraft and fly away at a significant percentage of the speed of light, so that time dilation takes effect.
For the people on the spacecraft, just a few years will have occurred, while it could have been hundreds or even thousands for the folks back on Earth. Assuming you could keep the wormhole stable, open and traversable, then traveling through it would be interesting.
If you passed in one direction, you’d not only move the distance between the wormholes, but you’d also be transported to the time that the wormhole is experiencing. Go one direction and you move forward in time, go the other way: backwards in time.
Some physicists, like Leonard Susskind think this wouldn’t work because this would violate two of physics most fundamental principles: local energy conservation and the energy-time uncertainty principle.
Unfortunately, it really seems like wormholes will need to remain in the realm of science fiction for the foreseeable future, and maybe forever. Even if it’s possible to create wormholes, then you’ve got the keep them stable and open, and then you’ve got to figure out how to allow matter into them without collapsing. Still, if we could figure it out, that’d make space travel very convenient indeed.
If you could set up two ends of a wormhole to anywhere in the Universe, where would they be? Tell us your ideas in the comments below.
At one time, astronomers believed the surface of Mars was crisscrossed by canal systems. This in turn gave rise to speculation that Mars was very much like Earth, capable of supporting life and home to a native civilization. But as human satellites and rovers began to conduct flybys and surveys of the planet, this vision of Mars quickly dissolved, replaced by one in which the Red Planet was a cold, desiccated and lifeless world.
However, over the past few decades, scientists have come to learn a great deal about the history of Mars that has altered this view as well. We now know that though Mars may currently be very cold, very dry, and very inhospitable, this wasn’t always the case. What’s more, we have come to see that even in its current form, Mars and Earth actually have a lot in common.
Between the two planets, there are similarities in size, inclination, structure, composition, and even the presence of water on their surfaces. That being said, they also have a lot of key differences that would make living on Mars, a growing preoccupation among many humans (looking at you, Elon Musk and Bas Lansdorp!), a significant challenge. Let’s go over these similarities and the difference in an orderly fashion, shall we?
Sizes, Masses and Orbits:
In terms of their size and mass, Earth and Mars are quite different. With a mean radius of 6371 km and a mass of 5.97×1024 kg, Earth is the fifth largest and fifth most-massive planet in the Solar System, and the largest of the terrestrial planets. Mars, meanwhile, has a radius of approximately 3,396 km at its equator (3,376 km at its polar regions), which is the equivalent of roughly 0.53 Earths. However, it’s mass is just 6.4185 x 10²³ kg, which is around 10.7% that of Earth’s.
Artistic representation of the orbits of Earth and Mars. Credit: NASA
Similarly, Earth’s volume is a hefty 1.08321 x 1012 km3, which works out 1,083 billion cubic kilometers. By comparison, Mars has a volume of 1.6318 x 10¹¹ km³ (163 billion cubic kilometers) which is the equivalent of 0.151 Earths. Between this difference in size, mass, and volume, Mars’s surface gravity is 3.711 m/s², which works out to 37.6% of Earths (0.376 g).
In terms of their orbits, Earth and Mars are also quite different. For instance, Earth orbits the Sun at an average distance (aka. semi-major axis) of 149,598,261 km – or one Astronomical Unit (AU). This orbit has a very minor eccentricity (approx. 0.0167), which means its orbit ranges from 147,095,000 km (0.983 AU) at perihelion to 151,930,000 km (1.015 AU) at aphelion.
At its greatest distance from the Sun (aphelion), Mars orbits at a distance of approximately 249,200,000 km (1.666 AU). At perihelion, when it is closest to the Sun, it orbits at a distance of approximately 206,700,000 km (1.3814 AU). At these distances, the Earth has an orbital period of 365.25 days (1.000017 Julian years) while Mars has an orbital period of 686.971 days (1.88 Earth years).
However, in terms of their sidereal rotation (time it takes for the planet to complete a single rotation on its axis) Earth and Mars are again in the same boat. While Earth takes precisely 23h 56m and 4 s to complete a single sidereal rotation (0.997 Earth days), Mars does the same in about 24 hours and 40 minutes. This means that one Martian day (aka. Sol) is very close to single day on Earth.
Earth’s axial tilt (or obliquity) and its relation to the rotation axis and plane of orbit. Credit: Wikipedia Commons
Mars’s axial tilt is very similar to Earth’s, being inclined 25.19° to its orbital plane (whereas Earth’s axial tilt is just over 23°). This means that Mars also experiences seasons and temperature variations similar to that of Earth (see below).
Structure and Composition:
Earth and Mars are similar when it comes to their basic makeups, given that they are both terrestrial planets. This means that both are differentiated between a dense metallic core and an overlying mantle and crust composed of less dense materials (like silicate rock). However, Earth’s density is higher than that of Mars – 5.514 g/cm3 compared to 3.93 g/cm³ (or 0.71 Earths) – which indicates that Mars’ core region contains more lighter elements than Earth’s.
Earth’s core region is made up of a solid inner core that has a radius of about 1,220 km and a liquid outer core that extends to a radius of about 3,400 km. Both the inner and outer cores are composed of iron and nickel, with trace amounts of lighter elements, and together, they add to a radius that is as large as Mars itself. Current models of Mars’ interior suggest that its core region is roughly 1,794 ± 65 kilometers (1,115 ± 40 mi) in radius, and is composed primarily of iron and nickel with about 16-17% sulfur.
Both planets have a silicate mantle surrounding their cores and a surface crust of solid material. Earth’s mantle – consisting of an upper mantle of slightly viscous material and a lower mantle that is more solid – is roughly 2,890 km (1,790 mi) thick and is composed of silicate rocks that are rich in iron and magnesium. The Earth’s crust is on average 40 km (25 mi) thick, and is composed of rocks that are rich in iron and magnesium (i.e. igneous rocks) and granite (rich in sodium, potassium, and aluminum).
Artist’s impression of the interior of Mars. Credit: NASA/JPL
Comparatively, Mars’ mantle is quite thin, measuring some 1,300 to 1,800 kilometers (800 – 1,100 mi) in thickness. Like Earth, this mantle is believed to be composed of silicate rock that are rich in minerals compared to the crust, and to be partially viscous (resulting in convection currents which shaped the surface). The crust, meanwhile, averages about 50 km (31 mi) in thickness, with a maximum of 125 km (78 mi). This makes it about three times as hick as Earth’s crust, relative to the sizes of the two planets.
Ergo, the two planets are similar in composition, owing to their common status as terrestrial planets. And while they are both differentiated between a metallic core and layers of less dense material, there is some variance in terms of how proportionately thick their respective layers are.
Surface Features:
When it comes to the surfaces of Earth and Mars, things once again become a case of contrasts. Naturally, it is the differences that are most apparent when comparing Blue Earth to the Red Planet – as the nicknames would suggest. Unlike other planet’s in our Solar System, the vast majority of Earth is covered in liquid water, about 70% of the surface – or 361.132 million km² (139.43 million sq mi) to be exact.
The surface of Mars is dry, dusty, and covered in dirt that is rich iron oxide (aka. rust, leading to its reddish appearance). However, large concentrations of ice water are known to exist within the polar ice caps – Planum Boreum and Planum Australe. In addition, a permafrost mantle stretches from the pole to latitudes of about 60°, meaning that ice water exists beneath much of the Martian surface. Radar data and soil samples have confirmed the presence of shallow subsurface water at the middle latitudes as well.
As for the similarities, Earth and Mars’ both have terrains that varies considerably from place to place. On Earth, both above and below sea level, there are mountainous features, volcanoes, scarps (trenches), canyons, plateaus, and abyssal plains. The remaining portions of the surface are covered by mountains, deserts, plains, plateaus, and other landforms.
Mars is quite similar, with a surface covered by mountain ranges, sandy plains, and even some of the largest sand dunes in the Solar System. It also has the largest mountain in the Solar System, the shield volcano Olympus Mons, and the longest, deepest chasm in the Solar System: Valles Marineris.
Earth and Mars have also experienced many impacts from asteroids and meteors over the years. However, Mars’ own impact craters are far better preserved, with many dating back billions of years. The reason for this is the low air pressure and lack of precipitation on Mars, which results in a very slow rate of erosion. However, this was not always the case.
Mars has discernible gullies and channels on its surface, and many scientists believe that liquid water used to flow through them. By comparing them to similar features on Earth, it is believed that these were were at least partially formed by water erosion. Some of these channels are quite large, reaching 2,000 kilometers in length and 100 kilometers in width.
Color mosaic of Mars’ greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL
So while they look quite different today, Earth and Mars were once quite similar. And similar geological processes occurred on both planets to give them the kind of varied terrain they both currently have.
Atmosphere and Temperature:
Atmospheric pressure and temperatures are another way in which Earth and Mars are quite different. Earth has a dense atmosphere composed of five main layers – the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere. Mars’ is very thin by comparison, with pressure ranging from 0.4 – 0.87 kPa – which is equivalent to about 1% of Earth’s at sea level.
Earth’s atmosphere is also primarily composed of nitrogen (78%) and oxygen (21%) with trace concentrations of water vapor, carbon dioxide, and other gaseous molecules. Mars’ is composed of 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. Recent surveys have also noted trace amounts of methane, with an estimated concentration of about 30 parts per billion (ppb).
Because of this, there is a considerable difference between the average surface temperature on Earth and Mars. On Earth, it is approximately 14°C, with plenty of variation due to geographical region, elevation, and time of year. The hottest temperature ever recorded on Earth was 70.7°C (159°F) in the Lut Desert of Iran, while the coldest temperature was -89.2°C (-129°F) at the Soviet Vostok Station on the Antarctic Plateau.
Space Shuttle Endeavor silhouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere. Credit: NASABecause of its thin atmosphere and its greater distance from the Sun, the surface temperature of Mars is much colder, averaging at -46 °C (-51 °F). However, because of its tilted axis and orbital eccentricity, Mars also experiences considerable variations in temperature. These can be seen in the form of a low temperature of -143 °C (-225.4 °F) during the winter at the poles, and a high of 35 °C (95 °F) during summer and midday at the equator.
The atmosphere of Mars is also quite dusty, containing particulates that measure 1.5 micrometers in diameter, which is what gives the Martian sky a tawny color when seen from the surface. The planet also experiences dust storms, which can turn into what resembles small tornadoes. Larger dust storms occur when the dust is blown into the atmosphere and heats up from the Sun.
So basically, Earth has a dense atmosphere that is rich in oxygen and water vapor, and which is generally warm and conducive to life. Mars, meanwhile, is generally very cold, but can become quite warm at times. It’s also quite dry and very dusty.
Magnetic Fields:
When it comes to magnetic fields, Earth and Mars are in stark contrast to each other. On Earth, the dynamo effect created by the rotation of Earth’s inner core, relative to the rotation of the planet, generates the currents which are presumed to be the source of its magnetic field. The presence of this field is of extreme importance to both Earth’s atmosphere and to life on Earth as we know it.
Map from the Mars Global Surveyor of the current magnetic fields on Mars. Credit: NASA/JPL
Essentially, Earth’s magnetosphere serves to deflect most of the solar wind’s charged particles which would otherwise strip away the ozone layer and expose Earth to harmful radiation. The field ranges in strength between approximately 25,000 and 65,000 nanoteslas (nT), or 0.25–0.65 Gauss units (G).
Today, Mars has weak magnetic fields in various regions of the planet which appear to be the remnant of a magnetosphere. These fields were first measured by the Mars Global Surveyor, which indicated fields of inconsistent strengths measuring at most 1500 nT (~16-40 times less than Earth’s). In the northern lowlands, deep impact basins, and the Tharsis volcanic province, the field strength is very low. But in the ancient southern crust, which is undisturbed by giant impacts and volcanism, the field strength is higher.
This would seem to indicate that Mars had a magnetosphere in the past, and explanations vary as to how it lost it. Some suggest that it was blown off, along with the majority of Mars’ atmosphere, by a large impact during the Late Heavy Bombardment. This impact, it is reasoned, would have also upset the heat flow in Mars’ iron core, arresting the dynamo effect that would have produced the magnetic field.
Another theory, based on NASA’s MAVEN mission to study the Martian atmosphere, has it that Mars’ lost its magnetosphere when the smaller planet cooled, causing its dynamo effect to cease some 4.2 billion years ago. During the next several hundred million years, the Sun’s powerful solar wind stripped particles away from the unprotected Martian atmosphere at a rate 100 to 1,000 times greater than that of today. This in turn is what caused Mars to lose the liquid water that existed on its surface, as the environment to become increasing cold, desiccated, and inhospitable.
Satellites:
Earth and Mars are also similar in that both have satellites that orbit them. In Earth’s case, this is none other than The Moon, our only natural satellite and the source of the Earth’s tides. It’s existence has been known of since prehistoric times, and it has played a major role in the mythological and astronomical traditions of all human cultures. In addition, its size, mass and other characteristics are used as a reference point when assessing other satellites.
The Moon is one of the largest natural satellites in the Solar System and is the second-densest satellite of those whose moons who’s densities are known (after Jupiter’s satellite Io). Its diameter, at 3,474.8 km, is one-fourth the diameter of Earth; and at 7.3477 × 1022 kg, its mass is 1.2% of the Earth’s mass. It’s mean density is 3.3464 g/cm3 , which is equivalent to roughly 0.6 that of Earth. All of this results in our Moon possessing gravity that is about 16.54% the strength of Earth’s (aka. 1.62 m/s2).
The Moon varies in orbit around Earth, going from 362,600 km at perigee to 405,400 km at apogee. And like most known satellites within our Solar System, the Moon’s sidereal rotation period (27.32 days) is the same as its orbital period. This means that the Moon is tidally locked with Earth, with one side is constantly facing towards us while the other is facing away.
Thanks to examinations of Moon rocks that were brought back to Earth, the predominant theory states that the Moon was created roughly 4.5 billion years ago from a collision between Earth and a Mars-sized object (known as Theia). This collision created a massive cloud of debris that began circling our planet, which eventually coalesced to form the Moon we see today.
Mars has two small satellites, Phobos and Deimos. These moons were discovered in 1877 by the astronomer Asaph Hall and were named after mythological characters. In keeping with the tradition of deriving names from classical mythology, Phobos and Deimos are the sons of Ares – the Greek god of war that inspired the Roman god Mars. Phobos represents fear while Deimos stands for terror or dread.
Phobos measures about 22 km (14 mi) in diameter, and orbits Mars at a distance of 9,234.42 km when it is at periapsis (closest to Mars) and 9,517.58 km when it is at apoapsis (farthest). At this distance, Phobos is below synchronous altitude, which means that it takes only 7 hours to orbit Mars and is gradually getting closer to the planet. Scientists estimate that in 10 to 50 million years, Phobos could crash into Mars’ surface or break up into a ring structure around the planet.
Meanwhile, Deimos measures about 12 km (7.5 mi) and orbits the planet at a distance of 23,455.5 km (periapsis) and 23,470.9 km (apoapsis). It has a longer orbital period, taking 1.26 days to complete a full rotation around the planet. Mars may have additional moons that are smaller than 50- 100 meters (160 to 330 ft) in diameter, and a dust ring is predicted between Phobos and Deimos.
Scientists believe that these two satellites were once asteroids that were captured by the planet’s gravity. The low albedo and the carboncaceous chondrite composition of both moons – which is similar to asteroids – supports this theory, and Phobos’ unstable orbit would seem to suggest a recent capture. However, both moons have circular orbits near the equator, which is unusual for captured bodies.
So while Earth has a single satellite that is quite large and dense, Mars has two satellites that are small and orbit it at a comparatively close distance. And whereas the Moon was formed from Earth’s own debris after a rather severe collision, Mars’ satellites were likely captured asteroids.
Conclusion:
Okay, let’s review. Earth and Mars have their share of similarities, but also some rather stark differences.
Mean Radius: 6,371 km 3,396 km
Mass: 59.7×1023 kg 6.42 x 10²³ kg
Volume: 10.8 x 1011 km3 1.63 x 10¹¹ km³
Semi-Major Axis: 0.983 – 1.015 AU 1.3814 – 1.666 AU
Air Pressure: 101.325 kPa 0.4 – 0.87 kPa
Gravity: 9.8 m/s² 3.711 m/s²
Avg. Temperature: 14°C (57.2 °F) -46 °C (-51 °F)
Temp. Variations: ±160 °C (278°F) ±178 °C (320°F)
Axial Tilt: 23° 25.19°
Length of Day: 24 hours 24h 40m
Length of Year: 365.25 days 686.971 days
Water: Plentiful Intermittent (mostly frozen)
Polar Ice Caps: Yep Yep
In short, compared to Earth, Mars is a pretty small, dry, cold, and dusty planet. It has comparatively low gravity, very little atmosphere and no breathable air. And the years are also mighty long, almost twice that of Earth, in fact. However, the planet does have its fair share of water (albeit mostly in ice form), has seasonal cycles similar to Earth, temperature variations that are similar, and a day that is almost as long.
All of these factors will have to be addressed if ever human beings want to live there. And whereas some can be worked with, others will have to be overcome or adapted to. And for that, we will have to lean pretty heavily on our technology (i.e. terraforming and geoengineering). Best of luck to those who would like to venture there someday, and who do not plan on coming home!
![Space Shuttle Endeavour sillouetted against the atmosphere. The orange layer is the troposphere, the white layer is the stratosphere and the blue layer the mesosphere.[1] (The shuttle is actually orbiting at an altitude of more than 320 km (200 mi), far above all three layers.) Credit: NASA](https://www.universetoday.com/wp-content/uploads/2012/03/Endeavour_silhouette_STS-130.jpg)
