The Geography of Mars

Technically, the correct term for the title of this post is Areology, from Ares (the Greek god of war) and -logy (the study of something).
Mars has mountains much like Earth.  However, unlike many of the mountain ranges on Earth, Martian mountains were not created by plate techtonics.  Olympus Mons, Ascraeus Mons, Arsia Mons, and Elysium Mons are all taller than Mount Everest. Pavonis Mons is slightly shorter, but has a much wider base.

All five of those mountains are shield volcanoes, which erupt but have low viscosity lava. The lava flows down the sides of the volcano, which lead to wide bases and low profiles.  For the Martian volcanoes, lack of plate tectonics lead to all the shield volcanoes on Mars to get really wide and really tall.

Olympus Mons is the largest of these volcanoes.  It is 21.4 km tall (from the peak to average surface elevation around its locality)and as shown in the picture below, the base has an area equivalent to the size of Arizona.  This means that the slope of Olympus Mons is only 5 degrees from base to peak.  Olympus Mons is not the tallest mountain in the solar system. That honor belongs to Rheasilvia on the asteroid Vesta. It has a height from base to peak of 22 km, though only 12 km are above the average surface elevation of Vesta.  Mauna Kea and Mauna Loa are two shield volcanoes in the Hawaiian island chain. They have peaks only 4.2 km above sea level, but from base to peak they are 10.2 km.


Olympus Mons

Tharsis Montes

Elysium Mons

Mars is also home to one of the most extensive canyon systems in the solar system.  Valles Mariners is a huge scar running across the landscape in the southern hemisphere.  If we were able to place it on Earth, it would run from New York to Los Angeles.  It is approximately 4000 km long send has a maximum depth of 7 km.  Compare this to the Grand Canyon in Arizona, which is "only" 446 km long and 1.8 km deep.  The Grand Canyon was shaped by the Colorado River, but it is unknown what formed the Valleys Marineris.  It is believed that liquid water or volcanism formed it, but it could be a combination of both.

Valles Mariners



Lastly, Mars may have at one time liquid oceans. It does not anymore because of the atmospheric pressure (future post) and the low temperature. Images from Martian probes show evidence of ancient shorelines.

Astronomy Picture of the Day 

Mars Global Surveyor

 



Mars

Space.com



 

Mars is the fourth planet from the Sun, the third largest terrestrial planet, and the seventh largest planet in the Solar System (only Mercury is smaller). 

• Distance from the Sun: 1.5 AU
• Solar Day equivalent to 24.5 Earth hours
• Tropical Year (how long it takes to complete one orbit around the Sun: 687 Earth days 
• Inclination of 5.65° from the Solar equator and 1.85° from the ecliptic
• Martian density is 3.9 g/cm³ or about 3.9 times that of water
• Mass is 10.7% of Earth and Radius is 53.2% of Earth
• Gravity on Mars is 0.376 times that of Earth (a 100-lb person would weigh 37.6 lbs on Mars)

Mars has a geography that you would find on Earth, but to a larger scale.  Mars boasts the largest mountain in the solar system, the longest and deepest canyon, and strange polar caps.  Mars is also well known for its reddish color, which you can see above, but is also apparent when seeing it in the sky.  Another strange feature is that Mars is criss-crossed by a multitude of channels, has high spots and low spots, and has features that on Earth, were created by flowing water.

 

Mars has two satellites that did not form in the same location as Mars.  Phobos and Deimos were probably captured by Mars and will be discussed in a later post.

 

Mars has an atmosphere, which can be seen as the bluish ring in the above photo of Mars. The major component of its atmosphere is carbon dioxide, like Venus, but that is where the similarities end.  It has an atmospheric pressure at the surface of 0.636 kPa, compared to Earth's surface pressure of 101.3 kPa and Venus' surface pressure of 9.2 MPa (9,200 kPa).  Despite the low pressure, the surface of Mars can reach 35°C (95°F) in direct sunlight, but drops to as low as -143­­­°C (-225.4°F) at night.  Unlike Earth and Venus, it does not retain heat as well because of its thin atmosphere.  The average surface temperature of Mars is -63°C (-81.4°F) so liquid water does not really exist on the surface.

Tides

The tides on Earth are driven by gravity, but not Earth's gravity.  The main reason we have tides is from the Moon.  The Sun affects the tides to some extent, but the Moon is the chief driver of the tides.  The gravitational pull from the Moon on the Earth attracts the oceans in a way to create tides.

High tides occur when the Moon is directly overhead or overhead on the opposite side of the Earth. Low tides are when the Moon is on the horizon.  When the Moon is directly overhead, the Moon is pulling water towards it, creating a bulge.  This is called a sublunar tide.  When the Moon is at the other side, it is pulling the Earth away from the water.  We call this an antipodal tide.  At the horizon, it is basically pulling the water along the surface of the Earth, and we have low tide.

In reality, since the Earth is rotating, the tides actually follow a couple hours after the location of the Moon.  But for our purposes, we can safely assume the Moon is directly overhead or at the horizon.

During the lunar cycle, there are times when the Sun, Earth, and Moon line up in a condition called syzygy.  These are when the Moon is full or at new phase.  Tides are higher than normal because of the combined gravitational attraction of the Sun and the Moon.  During the Full Moon and New Moon, the high tides are called spring tides. During the first quarter or third quarter, the Moon and the Sun are 90° apart in the sky and high tides are at the lowest heights.  We refer to these high tides as neap tides.

If there hadn't been a Moon, we would still have tides, but they would only be affected by the Sun.  High tides and low tides would be much different than we have today.  In fact, if there hadn't been a Moon, ground-based life might not exist.  Biologists believe that life began in the oceans and as tides rose and fell, some of that life might have been left behind on the shores, especially during spring tides.  This would force that life to adapt to life on land and evolve into air-breathing creatures.  If there hadn't been a Moon, intelligent life might still have evolved, but would have developed in cetaceans, rather than primates.

The Moon also affects atmospheric tides, but since air is less dense than water, the tides are not as pronounced.  Atmospheric tides do add to weather and climate on Earth.

Lastly, as mentioned in a previous post (The Origin of the Moon), the Moon is slowly receding from the Earth.  As it gets farther and farther away, the size of the tides will decrease.  Since the recession is only 2 cm/century, it will take millenia for the size of the tides to be noticable.

Perseid Meteor Shower

If you go outside at night this week, you might be able to see an annual event called the Perseid meteor shower.  It occurs yearly when the Earth passes through the comet Swift-Tuttle's debris trail.  This year, the shower will peak on the night of August 12-13, with the maximum being before dawn on August 13th.

The Perseids are called that because if you were to trace the origin of the meteors, they would appear to originate in the constellation Perseus.   This origination point is called the radiant, since the meteors seem to radiate out from this point.

When we experience meteor showers, the Earth passes through a debris trail left by comets or asteroids that have orbits that cross near our orbit around the Sun.  The debris is caught by the Earth and falls through the sky and what we see is the meteor.

There are a couple of definitions you should learn.

• Meteoroid - the actual object falling through the sky.  This can be as tiny as a dust particle or as big as an asteroid (which we really don't want)
• Meteor - this is actually what we see.  As the meteoroid falls through the atmosphere, friction causes the gas to heat up around the meteoroid and glows.
• Meteorite - if the meteoroid is large enough, it will not completely burn up as it falls and what is left when it hits the ground is a meteorite.

For your viewing pleasure, this week, Perseus is a little north of the Moon.

Supermoon

I probably should have posted this a couple of days ago, but oh well.

The Supermoon of 2014 just occured this past weekend (August 10). 

The Supermoon is not the newest superhero of DC or Marvel.

The Supermoon is the full moon happened to occur during perigee.  The Moon appeared the largest because it happened to be at its closest in its orbit to Earth.  Tides (which will be discussed further in a future post) happened to be a tad higher, but nothing else really is affected by a Supermoon.  It's just cool to see the Moon so large.

Return to the Moon

We have not been to the Moon since Apollo 17 in 1972.  The reason the United States went to the Moon, originally, was not for science or exploration, but rather for political reasons.  The US wanted to beat the Soviet Union to the Moon.  On July 20, 1969, when Neil Armstrong made one small step for man and a giant leap for all mankind, a human being stood on another celestial body other than Earth for the first time in history.

Why haven't we been back?  One, it is extremely expensive to travel to the Moon.  Not only do we have to have enough fuel to get there, but we need enough to get back.  We'd also have to worry about keeping the astronauts safe while on the Moon.  Two, there really is no economic or political gain from going to the Moon.  At the moment, the only gains we would receive would be purely scientific.  There is no profit to travelling to the Moon, though sometime in the future, it may be profitable to mine the Moon.  Politically, it wouldn't make one country better than any other.  The only advantage would be if there was a multi-nation coalition to go the Moon and make it worthwhile for all humanity.  Lastly, we don't have the technology to go back to the Moon.  A whole class of new spacecraft would have to be designed, tested, and constructed for man to go to the Moon once again.

Why is this important?  There has been talk of a crewed mission to Mars, which is all well and good.  But to skip going back to the Moon first would be a huge mistake.  The Moon is much easier to get to from the Earth than Mars; it would only take a few days travel to get to the Moon, with a round trip only taking about a week.  To get to Mars, it would require at least 6 months of travel from Earth to Mars and almost two years for a round trip.  If humanity built a lunar base, it would be easier to use as a launching point for exploration of the rest of the Solar System.  It would require less energy to launch a ship from the Moon than the Earth because the Moon is much smaller and its gravity would not work as hard against launching a rocket or spacecraft.  Once we set up a permanent presence on the lunar surface, exploration of the Solar System should follow, with Mars being the most logical first step.

Another nice thing about using the Moon as a launching pad is that the materials needed to build rockets and habitats and create fuel for spacecraft are already on the Moon.  The challenge would be to harvest the material and convert it into useful products. That is obviously many years in the future, but we still need to return to the Moon before thinking about going to Mars.

The Origin of the Moon

When we first explored the Moon, we weren't sure what we would find.  We expected to find similar material that we find on Earth.  What we found is even more unusual.

First, why did we expect similar material on the Moon?  Based on the location of the Earth in the Solar System (and by default, the location of the Moon), we expected to find refractory elements because they have a higher boiling point than volatile elements, i.e. they vaporize at high temperatures which in the early Solar System included the location of the Earth.  All planets close to the Sun are generally made up of this type of material because they are close to the Sun.  This is why we believed that terrestrial planets are close to their central star and Jovian planets are far from their star.  Because of this, we expected to find the Moon was made up of refractory elements.

However, when we actually went to the Moon, we discovered something really strange; the composition of the Moon is nearly identical to that of the interior of the Earth.  Not that we found the same material, but that the concentrations were the same.  So what does this tell us?

This tells us that when the Earth was very young, something collided with the infant Earth to create the Moon.  A Mars-sized body collided with the Earth to create the Moon and to leave some material on the Earth.  This helps explain three things:

1. The Moon's composition and why it is nearly identical to the Earth's composition
2. The Moon is receding from Earth. Recall that the Moon is moving about 2 cm away from the Earth every century (See blog post on the eclipses)
3. The 1:1 Moon-Earth resonance since the Moon formed from the Earth

Daily Galaxy