The One About MARS
ABOUT OUR PLANETS
The eight planets fall under two main categories — small, rocky, terrestrial inner planets and large, hydrogen rich jovial planets. The rocky planets also known as the inner planets are closer to the Sun and are closer to each other as well. These planets are made of rocks with an abundance of metals deep in their interiors. They have few moons, if any, and no rings. Mars is the last of the four inner rocky planets of our Solar system. Other rocky planets include Mercury, Venus, and Earth. The jovian planets make up the outer planets and are further from the Sun as well as from each other. These planets lack solid surfaces and are mostly made of hydrogen, helium, and hydrogen compounds, such as water, ammonia, and methane. These planets contain many moon and rings. These giant outer planets are Jupiter, Saturn, Neptune, and Uranus.
BIRTH
Our entire solar system formed from the gravitational collapse of a spinning interstellar cloud of gas. Reference my older post — The one about Star life cycle — for more information on this. This is known as the nebular hypothesis as an interstellar gas is called a nebula. The original cloud is large and diffuse, and rotates relatively slowly. Because of conservation of energy, the cloud heats up as it collapses. And because of conservation of angular momentum, the cloud spins faster as it contracts. Collisions between particles flatten the cloud into a disk. The result is a spinning, flattened disk, with mass concentrated near the center and the temperature highest near the center. This heated, mass heavy center forms our sun and planets form in the flattened disk. The formation of spinning disk explains the orderly motions of our solar system today. The planets all orbit the Sun in nearly the same plane because they formed in the flat disk. The direction in which the disk was spinning became the direction of the Sun’s rotation and the orbits of planets — though the small sizes of planets compared to the entire disk allowed some exceptions to arise (Venus & Uranus).
The terrestrial planets formed in the warm, inner regions of the swirling disk that allowed metal and rock to condense. The jovian planets formed in the colder, outer regions. This planet forming process is known as accretion. Our planets formed from the accretions about 4.5 billion years ago, around the same time as the formation of our Sun. This nebular hypothesis holds true for other stars and their planetary systems as well.
COMPARISON TO EARTH
Mars’s size and distance from the Sun have dictated most of its geological history. The present-day Mars looks much like some deserts or volcanic plains on Earth. Mars is only half of Earth’s size in diameter. Its mass is about 10% that of Earth. A Martian day is 24 hours and 37 minutes. Martian polar caps resemble that of Earth, although they contain frozen carbon dioxide in addition to water and ice. Martian year is almost twice as long as an Earth year. Mars’s rotation axis is tilted about the same as Earth’s, and as a result it has seasons much like those on Earth. However, Mars’s orbit is much more elliptical than Earth. For this reason, seasons on Mars are affected by its orbit as well as its tilt. The higher ellipticity of Mars’s orbit puts it significantly closer to the Sun during the southern hemisphere summer and farther from the Sun during the northern hemisphere winter. For this reason, seasons on Mars are more extreme with shorter, warmer summers in southern hemisphere and longer, colder winters in northern hemisphere.
Though Mars’s surface looks almost Earth-like, you wouldn’t want to visit without a spacesuit. The atmosphere is so thin that it creates only a weak greenhouse effect despite being made mostly of greenhouse gas — carbon dioxide. This makes the air pressure on Mars far less than that on top of Mount Everest (or less than 1% of that of Earth’s surface). The trace amounts of oxygen would not be nearly enough to breathe, and the lack of atmospheric ozone would leave you exposed to deadly ultraviolet radiation from the Sun.
Even Martian winds are very different from those on Earth. Winds on earth are driven primarily by effects of Earth’s rotation and by heat flow from the equator to the poles. In contrast, winds on Mars are strongly affected by its extreme seasonal changes. Unlike Earth, a dust storm on Mars could affect the entire planet (image below).
The temperature is usually well below freezing, with a global average of about -58F. The temperatures at winter pole drop so low (about -200F) that carbon dioxide condenses into dry ice at polar caps. At the same time, frozen carbon dioxide at the summer pole sublimates into carbon dioxide gas. During peak of summer, nearly all the carbon dioxide may sublime from the summer pole, leaving only a residual polar cap of water ice. The atmosphere pressure therefore increases at the summer pole and decreases at winter pole. As much as one-third of the total carbon dioxide of the Martian atmosphere moves seasonally between north and south polar caps. Sometimes these pressure differences initiate huge dust storms, particularly when the more extreme summer approaches in the southern hemisphere.
All in all, surface conditions on mars today make it seem utterly inhospitable to life. However, careful study of Martian geology offers evidence that Mars had a warmer and wetter past.
WATER ON PRESENT DAY MARS
No liquid water exists on surface of Mars today. We know this not only because we’ve studied most of the surface in reasonable detail but also because the surface conditions do not allow it. In most places and at most times, Mars is so cold that any liquid water would immediately freeze into ice. Even when the temperature rises above freezing, as it often does at midday near the equator, the air pressure is so low that liquid water would quickly evaporate. If you donned a spacesuit and took a cup of water outside your pressurized spaceship, the water would rapidly freeze or boil away (or do a combination of both).
Nevertheless, Mars offers ample evidence of past water flows.
WATER ON ANCIENT MARS
Although Mars is frozen today, the presence of dried-up river beds, rock-strewn floodplains, and minerals that form in water offers clear evidence that Mars had at least some warm and wet periods in past. Major flows of liquid water probably ceased at least 3 billions years ago, but some liquid water could persist underground, perhaps flowing to the surface on occasion.
Rocks at the Opportunity landing site contain tiny spheres — nicknamed “blueberries” — and odd indentations suggesting that they formed in standing water, or possibly groundwater percolating through rocks. Composite analysis shows that the “blueberries” contain the iron-rich mineral hematite, and other rocks contain sulfur-rich mineral jarosite. Both minerals form in water, and chemical analysis supports case for formation in salty environment such as pond or a lake, apparently made acidic by dissolving in some atmospheeric SO2. Other minerals may have been formed in environments like those of hot springs on earth. Taken together, the orbital and surface studies provide convincing evidence for abundant water in Mars’s past.
WHERE DID ALL THE WATER GO?
Even though ancient Mars has evidence of liquid water, much of that water was probably lost to space. However, significant amounts of water still remain frozen at the polar caps and in the top meter or so of the surface soil around much of the rest of the planet. The extent of this water ice is only beginning to become clear. Scientists were surprised to find surface ice sitting right under the Phoenix lander when it arrived in 2008. If all the ice that exists on Mars today melted, it could make an ocean 11 meters deep over the whole planet. Additional water ice probably lies deeper underground. It is even possible that some liquid water exists underground near sources of volcanic heat, providing a potential home to microbial life.
Orbital photographs also offer evidence of small scale water flows in recent times. The strongest evidence come from photos taken by Mars Reconnaissance Orbiter(MRO) of gullies on crater wall. These gullies look strikingly similar to the gullies we see on eroded slopes on Earth. One hypothesis is that gullies form when snow accumulates on the crater walls in winter and melts away from the base of the snowpack in spring. Alternatively, the gullies may be formed by landslides, which have been seen to occur elsewhere on Mars with the change of seasons.
WHY DID MARS CHANGE
There seems little doubt that Mars had wetter and possible warmer periods, probably with rainfall, before about 3 billion years ago. The idea that Mars once had a thicker atmosphere makes sense, because we would expect that its many volcanoes outgassed plenty of atmospheric gas. Much of this gas would have been water vapor and carbon dioxide, and these greenhouse gases would have warmed that planet. If Martian volcanoes outgassed greenhouse gases in the same proportion as do volcanoes on Earth, Mars would have had enough water to fill oceans. So, where did all this atmospheric gas go?
Mars must have somehow lost most of its carbon dioxide gas. This loss would have weakened the greenhouse effects until the planet essentially froze over. Some of the carbon dioxide condensed and became part of the polar caps, and some may be chemically bound to surface rock. However, the bulk of gas was probably lost to space. Recent data suggest a close link between the lost carbon dioxide and a change in Mars’s magnetic field. Early in its history, Mars probably had molten convection in its core, much like Earth today. The combination of this core’s convection and the planet’s rotation should have produced a magnetic field and a protective magnetosphere around Mars. The magnetic field would have weakened as Mars cooled and the core ceased to convect, leaving the atmosphere vulnerable to solar wind particles. These solar wind particles could have stripped gases out of the Martian atmosphere and into space.
Much of the water once present on Mars is also probably gone for good. Like the carbon dioxide, some water vapor may have been stripped away by the solar wind. However, Mars also lost water in another way. Because the Martian atmosphere lacks ultraviolet-absorbing gases, atmospheric water molecules would have been easily broken apart by ultraviolet photons. The hydrogen atoms that broke away from water molecules would have been lost rapidly to space. With these hydrogen atoms gone, the water molecules could not be made whole again. Initially, oxygen from the water molecules would have remained in the atmosphere, but over time this oxygen was lost too. Some was probably stripped away by solar wind, and the rest was drawn out of the atmosphere through chemical reactions with surface rock. This process literally rusted the Martian rocks, giving the “red planet” its distinctive tint.
All in all, there’s a huge chance that Mars may have harbored life in its ancient past, however microbial they may be. Finding organic evidence of this ancient life is what most Mars missions aim to do.
LANDMARKS
Olympus Mons is largest volcanic mountain in our solar system. It is has a height of 14 miles and dwarfs Earth’s Mount Everest.
Valles Marineris is a largest canyon of our solar system. It is 2,000 miles long, 400 miles wide, 5 miles deep.
MARTIAN MOONS
Mars has two tiny moons: Phobos and Deimos. These moons were probably asteroids once that were captured into Martian orbit early in the solar system’s history.
EXPLORATION
Mars is the most studied planet besides Earth. More than a dozen spacecraft have flown past, orbited, or landed on Mars. We have projects in place that are working to send humans to Mars within this decade.
ROVERS
SOJOURNER: Mars Pathfinder landed in the Ares Valley region in July of 1997. It was designed for a 7 day mission but lasted 83 martian days. This was the first wheeled vehicle to rove another planet.
SPIRIT: A Mars Exploration Rover (MER) sent around the same time as its twin Opportunity. It landed within the impact crater Gusev on January 4, 2004. Trover got stuck in a “sand trap” in 2009 which hampered recharging its batteries. It lost connection to Earth in 2010, after completing 20 times its originally planned mission duration.
OPPORTUNITY: A Mars Exploration Rover (MER) nicknamed “Oppy” was active from 2004 to 2018 when a global Martian dust storm engulfed the rover. It landed in Meridiani Planum, 3 weeks after its twin Spirit. This mission is considered one of NASA’s most successful ventures. Along with Spirit, this mission’s aim was to aim was to find evidence of past and current water on the planet.
CURIOSITY: Landed in Gale crater on August 6, 2012. The rovers goal include assessment of Martian climate and geology, as well as evidence of past or current microbial life. This rover is still active.
InSight LANDER: InSight successfully landed on Elysium Planitia (a broad plain on equator and second largest volcanic region) on November 26, 2018. The lander is designed to study the deep interior of planet, the structure of its core, and register any seismic activity.
PERSEVERANCE: This Mars 2020 rover is scheduled to launch in February, 2021. It will be accompanied by a helicopter drone — Ingenuity. Its objective is to find evidence on previous life on Mars.
ORBITERS
There are more than a dozen orbiter missions launched to Mars out of which 6 are still active. These include 2001 MARS ODYSSEY (NASA), MARS EXPRESS (ESA), MARS RECONNAISSANCE ORBITER (NASA), MARS ORBITER MISSION (ISRO), MAVEN (NASA), and ExoMars Trace Gas Orbiter (ESA & RosCosmos)
FUTURE MISSIONS
SPACE X’s BFR: The entire Elon Musk empire has been built on his desire to go to Mars. The Big falcon Rocket aka the Starship aims to send cargo to Mars as early as 2024. Mars opposition happens every 2 years, so by 2026 BFR will send the second cargo and then finally by 2028 the first inhabitants of Mars. Their aim will be to terraform the planet and start a martian colony.
NASA’s ARTEMIS: This programs aims to build a base on moon and use that as a workstation for missions to Mars. This is a great strategy as taking off from moon requires much less fuel due to its low gravity. Moon also has a plethora of underground ice which can be exploited for fuel cutting down costs significantly as well as leaving more room on board for cargo and crew.
Hope you enjoyed this post and found it informative.
REFERENCES:
Cosmic Perspective 6th edition; https://mars.nasa.gov/mer/
