4: MARS

MARS

(NASA/JPL/Malin Space Science Systems)

Formation Mars formed about 4.5 billion years ago from swirling gas and dust in the solar nebula. Gravity pulled matter in the nebula together, forming a ball about one half the diameter of the Earth. Like other terrestrial (rocky) planets, Mars has a hot central core surrounded by a rocky mantle and an outer crust.

Mars' crust is about 25 km thinner in the northern hemisphere, compared to the south. Also, the land elevation is about 3 km lower. It is theorized that these differences were caused by a very large object (Pluto-sized) colliding with Mars soon after its formation.

(NASA/JPL)

Structure, Atmosphere and Magnetosphere Mars is a dry dusty planet, hostile to complex lifeforms. Nevertheless, it is the most studied planet in the solar system, after the Earth. Mars has a dense core, with a radius of approximately 1800 km. The core is composed primarily of iron and nickel and is at least partially molten. Surrounding the core is a silicate (rocky) mantel, which seems to be dormant. It was active in the past, giving rise to large-scale tectonic features on the surface (mountains, volcanoes, ridges and canyons). The surface crust is approximately 50km thick, about 25% thicker than the Earth’s. Seismometers on the surface have detected several “Marsquakes” indicating that the planet is still geologically active.

Mars has a very thin atmosphere. The average surface atmospheric pressure is only 0.6% that of Earth, and its highest atmospheric pressure is equivalent to the pressure at about 35km above the Earth’s surface. The main atmospheric gas is carbon dioxide (96%); the rest is made up primarily of argon and nitrogen.

There is strong evidence that the Mars of today is radically different from the Mars of the past. Surface features such as outflow channels, networks of valleys, gullies, deltas and alluvial fans strongly suggest there was significant surface water in the past. This hypothesis is further supported by the discovery of minerals such as hematite, goethite, jarosite and gypsum which form in the presence of water.

Jezero Crater region, showing a segment of the crater wall in the background, an inflow channel and delta with a small impact crater. (NASA/JPL-Caltech/USGS)

Liquid water cannot exist on the present-day Martian surface, due to the low atmospheric pressure. Mars must have had a thicker atmosphere in the past for liquid water to have existed. There is evidence that Mars lost its magnetic field about 4 billion years ago. It is possible that Mars’ thicker atmosphere was stripped off by the solar wind (charged particles streaming from the sun) once Mars lost its protective magnetic field.

(NASA/JPL-Caltech/Cornell Univ)

The Martian year is 687 Earth days- nearly two Earth years. Mars has a similar axial tilt to that of the Earth, and a similar day/night cycle. It therefore experiences seasons, although each is about twice as long as a season on Earth. Temperatures range from about -150 C to +20 C. Mars has permanent polar ice caps made from water ice beneath a layer of frozen carbon dioxide. The carbon dioxide layer on the north pole turns directly into a gas (sublimates) during its “summer.” The amount of water ice in the polar caps substantial. If melted, the water in the south polar cap alone could cover the entire planet to a depth of 11 meters. (Remember though, that liquid water cannot exist on present-day Mars!)

The area of Mars is about the same as the dry land area of Earth. Mars’ reddish colour comes from the high concentration of iron oxide (rust) in the surface soil. Robotic drilling (which began with Nasa's Curiosity rover in 2013) shows that many of the rocks are gray or white beneath the surface layer of rust. Mars has the largest dust storms in the solar system. Wind speeds reach 160 km/h. and can cover the entire planet, blotting out surface features normally visible from Earth-bound telescopes.

Stormy weather on Mars. (NASA/JPL-Caltech/MSSS)

Mars has many surface features of great interest. Valles Marineris (shown) is an enormous canyon, 10 times the size of the Grand Canyon. It is 320 km wide and 7 km deep, and would stretch from Victoria BC to Montreal QC. To the north west lies Olympus Mons, an extinct shield volcano that is three times the height of Mount Everest and ranks as the tallest volcano in the Solar System. Further to the west, almost opposite to Valles Marineris, lies the Jezero crater (see photo, above), the landing site for the Perseverance rover, which touched down in 2020. This site was carefully selected from evidence that the crater was once water-filled, with an inflowing river, leaving a delta. It is a perfect spot to begin searching for signs of ancient life!

(NASA/JPL-Caltech)

Moons Mars has two moons, Deimos and Phobos. They are quite small (16km and 26km diameter respectively) and irregularly shaped. They are formed of material similar to that found in asteroids, and they may be captured objects from the asteroid belt. Phobos orbits Mars at an altitude of only 6,000 km. It is predicted that within 50 million years it will either crash into the planet or break apart, forming a ring.

(NASA/JPL-Caltech/University of Arizona)

Missions There have been at least 40 successful missions to Mars as of 2021. These Missions have been launched by the USA (NASA), USSR/Russia, the European Space Agency (ESA), India, China and the United Arab Emirates. The earliest successful mission was the flyby of Mariner 4 in 1964. The first successful landing on Mars was in 1971 by the USSR, however, communications from the craft ceased within two minutes following touchdown. The first operational lander was NASA's Viking 1, which touched down in 1976 and transmitted for more than six years. The first rover on the Martian surface was Sojourner, in 1996. It was operational for 84 days.

Within the last decade, there have been many rovers on Mars, and many more orbital missions. The extent of our scientific knowledge of this other world could easily fill several large books. As of 2021, three rovers are operating on Mars- Perseverance (NASA), Curiosity (NASA) and Zhurong (China), and there are eight orbiting probes from various nations.

It seems missions to Mars have almost become routine, yet it is hard to overstate the technical challenges on the pathway to success. Nearly two-thirds of the missions to Mars have failed in some way. But there is no "Martian Curse", it's just really hard to go there! Currently, NASA, Russia, and several private companies in the USA are planning crewed missions to Mars.

Mariner 4 completed the first successful flyby of Mars in 1964

Perseverance rover and Ingenuity helicopter on the surface of Mars (NASA/JPL-Caltech)