# Is there a way to tell the difference between earth andesite from Mars

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I'm curios if there is a way to test if this sample might be Martian andesite.

What type of oxygen isotope (or other) test can be done to address this in some way?

As background, any information about such tests at the University of Utah would also be helpful to know.

If this is something that you have found (rather than purchased as a meteorite) the chances are very small that it is a meteorite. Even if it is a meteorite, the chances it's a Martian one are even smaller still and none have been found in the United States.

According to the Meteorites in the US page, which draws from the Meteoritical Society database, only 1821 meteorites have been found in the US over the past 200 years. Of all meteorites found in the world, less than 0.1% are from the Moon or Mars (source statement, graphs of meteorite fractions) and none of these have been found in the US, with the vast majority (99%) found in Antarctica or the African or Arabian deserts (lunar meteorites)).

There is a long "Meteorite Realities" page and a shorter, graphical "Self-Test Check-List" that it would be good to check and go through before it gets to chemical testing.

If you are determined to get testing done, the same meteorites.wustl.edu site on its page on meteorite chemical composition recommends chemical testing by Actlabs; there is more information on what they need (a 5g sample) and the type of tests to ask for on this page. Andesite is a type of basalt formed by volcanism and while it is true that most of the Martian meteorites are basalts (as discussed here), so are a lot of Earth rocks. On the chemical composition page, in plots of chemical composition such as silicon dioxide (SiO$$_2$$) vs total iron and magnesium oxide content e.g. the martian meteorites (red squares) separate from most terrestrial/Earth rocks and the "meteorwrongs" (white circles) due to having higher iron+magnesium content in the form of pyroxene, olivine and ilmenite (from 'Chemistry' section of How Do We Know That It's a Rock from the Moon?) However as noted on the basalt page:

Unfortunately, the only way to distinguish a terrestrial (Earth) basalt from a basaltic meteorite (Moon, Mars, asteroid) is with expensive chemical and mineralogical tests. If you find a basalt, it's probably not a meteorite.

So I would guess that these additional tests for the contents may be enough to distinguish a non-Earth basalt from an Earth one when the appearance to the eye or under a microscope is very similar (due to the similar formation mechanism via lava). However additional tests needed for trace elements may also be needed (Lunar basalts are Chromium-rich but have much lower concentrations of the alkali elements of potassium, sodium, rubidium, and cesium)

Chemical analysis for martian andesite for sio2 is 55.00 - 65.00, not anywhere close to korotevs out-dated charts. My number is sio2 59.32, the only number that brings up martian andesite when googled.

I witnessed the meteorite fall 11-15-2016.

Chemical analysis returns sio2 59.32 al203 16.62 fe203(t) 9.61 cao 1.32 mno .117 mgo 3.04 na2o 1.81 k20 5.78 tio .968

Oxygen isotope analysis results. From the ocean floor next to hydro thermal vent. 170( -0.033 1.5 mg o.o57. 1.4 mg. 0.061 1.8 mg

Can anyone help me on where I could get a noble gas analyzed or a microbe spit analysis on pyroxene?

Only two meteorites have been found on Earth that are composed of andesite. They were found at the Graves Nunataks ice shield in Antarctica during a US Antarctic search for meteorites in 2006/07. The meteorites are labelled GRA 06128 and GRA 06129.

Geologically, the samples are unusual because they are rare samples of felsic crustal material and they are extraterrestrial. Another thing that makes them unusual is,

these rocks also have unusual, isotopically light iron isotope compositions (negative values of δ56Fe). In contrast, all other planetary crust materials, including Earth's felsic crustal rocks (granites and andesites on the plot), have heavy iron isotope enrichments (positive values of δ56Fe).

The low NiO and low Fe/Mn of the mafic minerals in GRA suggest that its source was depleted of Ni and Fe relative to a chon-dritic precursor. Such depletions in eucrites and Martian rocks are interpreted to reflect segregation of metal via core formation; a similar inference could be made for the GRA parent body.

Sourced from a NASA Technical Report.

But,

The meteorites' composition has led scientists to rule out the possibility that they are chips off of the Moon, Mars or Venus. And the ratio of iron to manganese does not match that of Earth, ruling out the possibility that it is an old chunk blasted off our planet's surface that later returned.

By measuring the radioactive decay of elements in the meteorite…

shown that the rock must have formed around 4.5 billion years ago, when Earth and the other planets were coalescing.

Studying these fragments of a now-vanished object from that era provides a rare window into the early solar system

## What’s the difference between an astronaut and a cosmonaut?

Two Russian cosmonauts took an important trip outside of the International Space Station (ISS) this week.

Oleg Novitsky and Pyotr Dubrov left the ISS to prepare for the undocking and disposal of an old space station module which has been attached to the spacecraft for almost two decades!

The module will be sent back to Earth before the arrival of a brand new new Russian Multi-Purpose Laboratory Module called 'Nauka' which is Russian for the word science.

It's the very first time either of the cosmonauts, who arrived on the ISS in April this year, has gone on a spacewalk and their special mission lasted over seven hours!

## Is there a way to tell the difference between earth andesite from Mars - Astronomy

Astronomers calculated the distance between the Earth and Sun in about 1769 when Venus passed across the sun. Please could you explain this calculation?

It goes like this: By 1769, Kepler's laws of planetary motion and Newton's law of gravity had been laid out and shown to work. The period of each planetary orbit had been measured, but not the absolute distances. Kepler's Third Law (which, really, is Newton's law of gravity written in a special form) relates the orbital period of each planet to its relative distance from the Sun. For instance, Kepler's Third Law tells us that if the orbit of Venus is 0.62 years (Earth years, that is), then its average distance from the Sun is 72% of the Earth-Sun distance. So astronomers knew the relative distances between each planet and the Sun, but they did not know how those distances compared to terrestrial units of length (like miles) or to the size of the Earth. Since the planets' orbital periods were all known, knowing a single absolute distance would give the distances to all other planets. Thus, if we knew the distance from the Earth to the Sun, then we'd know the size of Venus's orbit too, and the speed at which it moves. So all of these details can be related to one number: the Earth-Sun distance.

The rest was determined by what astronomers call parallax.

Imagine you and a friend are standing on one side of a street, but separated by a sizable distance. You friend is to your right, for concreteness. And both of you are staring at a single lamppost in front of you on the other side. A car approaches from your left. As you're staring at the lamppost, the car cuts through your line of sight first, then a short time later, it cuts through your friend's line of sight, right? Because your friend is looking at the lamppost from a different angle.

If you knew how far away you and your friend were standing, and the velocity of the car, and the time difference between you and your friend's crossing, you could use geometry to find your distance to the lamppost.

Now, move that analogy to the transit of Venus. You and your friend are at two separate observatories (at two far-apart locations on Earth), staring at the Sun, waiting for the transit. You will each see the transit happen at slightly different times. More importantly, you will each see Venus take a slightly different path across the Sun's surface, and you will measure slightly different durations for the transit. With those measurements, and some trigonometry, one can calculate the absolute distance to the Sun. In 1771, based on analysis of observations of the transits of Venus that occurred in 1761 and 1769, French astronomer Jérôme Lalande calculated a value of the astronomical unit that was just 2% higher than its actual (modern) value.

Here are some pages with more information on the transit observations (and some illustrations) and how they can be used to determine the Earth-Sun distance:

Note that there had been another fairly accurate calculation of the astronomical unit a century earlier, using the same principle (parallax) for observations of Mars. When Mars came close to Earth in 1672, simultaneous observations by Giovanni Cassini (in Paris) and Jean Richer (in French Guiana), comparing where Mars appeared relative to background stars, yielded a value of an astronomical unit that was about 7% higher than the modern value. This is discussed in more detail at:

This page was last updated by Sean Marshall on January 17, 2016.

### About the Author

#### David Bernat

David received his PhD in Physics in 2011. He studies extrasolar planets, brown dwarfs, and theoretical cosmology.

## Is there a way to tell the difference between earth andesite from Mars - Astronomy

Often I look up at the stars and once in a while I will see what looks like a star but is obviously a planet because its light is not bent by the Earth's atmosphere. However, I am always curious to know WHICH planet am I looking at. How can I find information that can tell me which planets I see in the sky at what positions and times?

Each planet also looks slightly different from the others.

Mercury is difficult to see because it is always close to the sun. Venus is white and very bright, and is never seen late at night. (hey, that rhymes!) Mars is the red planet. Jupiter is yellow and very bright. Saturn is also yellow, but not as bright as Jupiter.

Mars, Jupiter, and Saturn can be seen at any time in any position on the sky. Mercury is always very close to the sun and is very difficult to see. When Venus is visible, it is always seen right after sunset or right before sunrise, near the horizon in the direction of the sun.

### About the Author

#### Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.

## What is the difference between geology and Earth science?

So I am currently in grade 11 and extremely interested in getting a job in geology or Earth sciences, but I don't really know what the difference is. I tried looking up the course descriptions at the university I am planning to go to but they are the exact same.

One might say that geology is a subset of the earth sciences.

And those people would be right

At my highschool Earth Science 11 we had many units that branched out into Geology, Oceanography, Astronomy, and Meteorology. In Geology 12 our units were: Minerals, Igneous, Sedimentary, Metamorphic rocks, Mineral Resources, Tectonics, Earthquakes, Volcanoes, Faulting & Folding, Groundwater, Karst Topography, Glaciers, and Fluvial Processes. (I think that's all of them.) Earth Science is alot more broad.

Ya that helped a little, and wow I really wish that my high school would have an Earth science class.

All geology is earth science, but not all earth science is geology.

. except for planetary geology.

At the University of Michigan, they were both run out of the Geology Department (which they were threatening to re-name into some horribly long, all-inclusive bullshit department). The differences between the undergrad BS in Geology and BS in Earth Sciences were:

-Geology required an introductory field course held at Camp Davis. Earth Science did not.

-Geology majors were required to take two semesters each of math and physics, in addition to the University requirement for math. Earth Science traded these out for cognates (I took Organic Chemistry)

-Earth Science majors had to take a seminar course where weɽ listen-in on the weekly guest lecturer the department brought in to wow the faculty with their current research.

That's about it. Most of the actual geolgy/earth science courses were the same. Youɽ have both majors taking the same courses. The only way to tell if someone was on one track or the other was to ask them. The vast majority were geology majors though. The department was kind of geared to produce future grad students for other universities. Earth Science majors were usually "pre-" something, or double-majored with the school of education and meant to go into teaching. I didn't do that. Go me!

## Can you tell the date and your location from the stars?

Hi, I'm writing a story where the characters wake up and they don't know where they are and don't know how much time has passed. Since many of them are experienced sailors, one decides to use the stars to figure out where they are, and it turns out that it's the Atlantic ocean and 150 years in the future. Is that the kind of thing that's possible, and if it is, how accurate/precise would it be?

I started to answer "Yes", but after reading the full text of your post, I'll change it to "Yes, if they're really on their game and have something like an astrolabe around (or of course, a telescope)".

You can always use the stars to determine your latitude (how far north or south you are). In the Northern Hemisphere, you just look at the height of the north star above the horizon and that's your latitude north. On the horizon? You're on the equator. Straight up? You're on the north pole. The same principle applies to the Southern Hemisphere, though it's a bit more complicated because there's no star on the pole itself.

If you have a clock set to a particular place (like, say, Greenwich England) AND know the day of the year (which could be deduced through observations of the day's length to identify how long until the next solstice or equinox - you hit one every 3 months) then you can calculate longitude. For this reason, a clock that would keep accurate time at sea was groundbreaking technology, allowing accurate navigation and mapping around the world. In 1714, England's parliament offered a £20,000 prize for whoever could offer a solution accurate to a couple of minutes, the equivalent of almost £3 million today. To get "Atlantic ocean", a watch set to a particular time zone would do.

The only way to tell that 150 years had passed, though, would be by measuring the precession of Earth's axial tilt as it spins around every day. This has the effect of moving the north star, Polaris, away from the north pole - 2,000 years ago, Polaris was not the north star! There was no north star! The problem is that this precession cycle takes 26,000 years to complete. So 26,000 years ago, Polaris was the north star as well, and in 26,000 more years, it will be again. This works out to a change of about 50 seconds of arc per year (3600 arcseconds in a degree). In 150 years, the Earth's precession will definitely be measureable with the right tools, being about 2 degrees. It would be hard to notice without intentionally trying to measure it, though. Hipparchus first measured this precession by comparing his measurements to those about 150 years earlier, so there's certainly precedent for this time frame being measurable with ancient tools. So theyɽ have to know this precession rate and which direction it was moving to tell how far into the future and whether they were in the future or the past.

The stars themselves drift slowly around in the galaxy over time, so they could reasonably tell the difference between 150 years in the future and 26,150 years in the future - the constellations would look the same instead of somewhat distorted.

TLDR Atlantic, yes with a watch and time of year. 150 years in the future, yes with something like an astrolabe and an unusual knowledge of astronomy trivia.

## Differences Between Earth and Mars

Once in a while, people would wonder why life exists on Earth but not on other planets. Our planet, the third farthest from the sun in our solar system, is often compared to Mars. It’s our closest neighbor, and popular culture has stirred the notion that aliens, or extra-terrestrial beings, once lived on Mars. In fact, this sensational idea has some factual basis, especially in light of new scientific data which points out that water once existed abundantly on Mars. Water is a necessary ingredient in the creation of cellular species. The earliest form of life on our planet are plankton, which up to the present serves as food and sustenance for aquatic animals. Since water existed on Mars a long time ago, then there’s a high probability that cellular organisms also thrived in that planet. So far, however, no fossils have been found, and Mars remains just another planet in the solar system incapable of supporting life.

Comparing our planet with Mars would result in several similarities and differences. Some people do not know how to differentiate Earth with Mars, thus they get lost whenever the two planets are being compared. The first similarity deals with the structure of the two planets. Earth and Mars are made up of metal and rock, thus they are categorized as terrestrial planets. In terms of layers, both planets have a core of metal which is wrapped by a thicker mantle of solid rock. Above the mantle rests the crust. The second similarity deals with the presence of water. Earth has water in abundance, with oceans making up more than seventy percent of the crust. Mars’ water supply, on the other hand, is completely frozen at its poles. Even though there is a huge discrepancy between the two planets in terms of water content, both of them are capable of supporting water.

The differences between the two planets greatly outweigh their similarities. The first major difference is on plate tectonics. Earth has a shifting crust which continually changes the land forms, and replenishes the landscape. Mars, on the other hand, has a surface which never changes, and ancient meteorite scars from millions of years ago can still be seen today.

The second major difference deals with the discrepancy in planet size. Mars is much smaller than earth, measuring more or less six thousand eight hundred kilometers in diameter. Mars has only half of the Earth’s diameter, and approximately ten percent of the Earth’s mass. Mars’ small size means that it has only one-third of the Earth’s gravity. If people were able to jump on the surface of Mars, they would find out that their jumps are three times higher than their jumps on Earth.

The third, and greatest difference between the two planets is on sentient life. Life has yet to be found on Mars, while on Earth, almost every nook and cranny is filled with cellular life, from single-cellular bacteria to multi-cellular plants and animals.

Summary
1. Earth, the third planet in the solar system, has often been compared with Mars.
2. Earth and Mars are made up of metal and rock, thus they are categorized as terrestrial planets.
3. The first similarity is in terms of planetary structure. Both planets have a core of metal which is wrapped by a thicker mantle of solid rock. Above the mantle rests the crust.
4. The second similarity deals with the presence of water. Earth has water in abundance, with oceans making up more than seventy percent of the crust. Mars’ water supply, on the other hand, is completely frozen at its poles.
5. The first major difference between the two planets is on plate tectonics. Earth has a shifting crust which continually changes the land forms, and replenishes the landscape.
6. The second major difference deals with the discrepancy in planet size. Mars is much smaller than earth, measuring more or less six thousand eight hundred kilometers in diameter.
7. The third, and greatest difference between the two planets is on sentient life. Sentient life has yet to be found on Mars.

## Is there a way to tell the difference between earth andesite from Mars - Astronomy

Is it possible for the poles on Earth to switch places? Would we feel any effects from this happening? Why does this happen?

The poles on the Earth have changed places - many times! We can tell this has happened because the magnetic moment of the rocks that make up the ocean floor have an alternating direction. Which direction they exhibit depends on which way the poles were oriented when the rocks were being formed at the mid-ocean ridge.

During a reversal, which can take thousands of years, the magnetic poles start to wander away from the region around the spin poles, and eventually end up switched around. Sometimes this wandering is slow and steady, and other times it occurs in several jumps. One of the things that does consistently happen during a reversal is that the strength of the magnetic field decreases to almost zero. This is the part that has a lot people worried, as the magnetic field blocks a lot of incoming solar radiation that may be harmful to life.

Based on current research, the effects on humans and the Earth would actually be pretty negligible ("The Core" is hilarious, but a total scientific nightmare). Most of the harmful radiation the magnetic field blocks would be absorbed by the atmosphere, and wouldn't reach the surface (this is why it will be difficult to colonize Mars - no magnetic field OR atmosphere!). A few poorly built satellites might stop working, but overall, not much would happen to humans.

The cause of the reversals isn't well understood. The magnetic field is created by the Earth's "dynamo," or the extremely complicated set of currents of liquid iron in the outer core. Some models have shown that a reversal is the result of the reorganization of the currents, but we probably won't know for sure until it happens.

## Time delay between Mars and Earth

A photo of the Mars Express delay display on the control system, showing us the critical numbers of one-way light time, two-way light time and the distance from Earth.

One of the most difficult things about operating a spacecraft around Mars (not to mention the different time zones), compared with the Earth, is that it’s so far away!

Mars is so far away in fact that it takes radio signals quite a long time to get from the spacecraft back to Earth. During Curiosity EDL, this delay will be 13 minutes, 48 seconds, about mid-way between the minimum delay of around 4 minutes and the maximum of around 24 minutes.

This makes it a challenge to operate Mars Express because it’s hard to have a conversation with the spacecraft, or react if anything happens on board. If there is a problem and the spacecraft tells us, we won’t know for 13 minutes, and then even if we react straight away it’ll be another 13 minutes before our instructions get back to Mars – there’s a lot that can happen in half an hour at Mars (for example a whole Curiosity landing)!

To keep Mars Express flying safely, we load all the commands for the mission in advance and built in lots of autonomy to let the spacecraft take care of itself – you could say that for the Curiosity landing we’re running completely on autopilot!

The delay is nothing to do with the spacecraft or the hardware on the ground – it can’t be improved by a faster computer or a more powerful radio. In fact it is obeying the fundamental speed limit of the universe – the speed of light.

At 1,079,000,000 km/hour, light is pretty quick you could get from here to the Moon in a little over a second! But that just underlines how far away Mars is.

All light (or electromagnetic radiation, which includes radio signals) travels up to this speed, and radio waves from Earth to Mars Express and back are no exception. Take a look at the Wikipedia article on the speed of light and you’ll see how, in 1905, Einstein came upon the concept of this cosmic speed limit.

Above all, for tomorrow’s coverage of the Curiosity landing it makes it challenging for us to work out when to tell you what’s happening (as you’ve seen in our three column timeline)!

At ESOC, we talk about two different times – Spacecraft Event Time (SCET) and Earth Received Time (ERT). The former is what’s actually happening at Mars right now, although we won’t hear about it until over 13 minutes later, a time we call ERT.

The delay between the two is usually called the One-Way Light Time (OWLT) and the time for a message to go to Mars and come back is the Two-Way Light Time (TWLT), or round-trip time.

During all our coverage we’ll follow NASA’s lead and generally communicate events here and on Twitter to you in ERT because that’s when we’ll actually know what’s happened. If we do communicate something in SCET we’ll let you know so you (and us too) don’t get confused – it’s all part of the fun of exploring the Solar System!

## Mars compared to Earth

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 5.97×10 24 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 10 23 kg, which is around 15% that of Earth's.

Similarly, Earth's volume is a hefty 1.08321 x 10 12 km 3 , which works out 1,083 billion cubic kilometers. By comparison, Mars has a volume of 1.6318 x 10 11 km 3 (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/s 2 , 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 million km (1.666 AU). At perihelion, when it is closest to the Sun, it orbits at a distance of approximately 206,700,000 million 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.

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/cm 3 compared to 3.93 g/cm 3 (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).

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.

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.

Artistic representation of the orbits of Earth and Mars. Credit: NASA

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.

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.

Because 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.

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.

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).

Earth’s axial tilt (or obliquity) and its relation to the rotation axis and plane of orbit. Credit: Wikipedia Commons

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.

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 × 10 22 kg, its mass is 1.2% of the Earth's mass. It's mean density is 3.3464 g/cm 3 , 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/s 2 ).

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.

Artist’s impression of the interior of Mars. Credit: NASA/JPL

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.

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!

Color mosaic of Mars’ greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL