Mars Has Seasons

Mars Poles

Of all the planets in our solar system, Mars is the most similar to Earth. It has icy north and south poles, shown in the photo to the left. It has seasons just like Earth except the Martian year is approximately twice that of Earth, due to its much longer path around the sun. The tilt towards the Sun is 25 degrees compared to 23 degrees for Earth. In the winter season Mars' poles of ice expand and then contract during their summer.

Mars orbits closest to the Sun when its southern hemisphere is tilted towards it, while the northern hemisphere is tilted towards the Sun when it is furthest away. The southern summer is therefore much hotter than the northern summer. This extra heat pouring into the southern hemisphere causes greater turbulence and drives stronger winds, stirring up the largest storms.

In springtime, the polar ice caps starts to recede and may even disappear from view altogether by their summer. The carbon dioxide released from the melting ice makes the atmosphere thicker. Once autumn arrives, the polar cap of that hemisphere starts to grow again as temperatures drop, sometimes reaching the middle latitudes in winter.

In northern summer, clouds can form, especially around the top of volcanoes. At other times of the year, heat rising from the tropics, the region either side of the equator, can make cloud bands form in this region, in much the same way as on Earth.

Landing near one of the poles would have the advantage of a lot of easy to mine water from the ice. On the other hand when winter sets in, it becomes extremely cold - temperatures can be as cold as -150°C and are dark for months at a time. So a polar landing would be a very risky venture.  Top

What makes Up a Good Landing Spot?

Mars Photo

"I'm picking landing sites that I may be visiting in the future," says planetary scientist Zachary Gallegos of the University of New Mexico, one of the final 100 candidates for the Mars One mission, a proposed one-way trip to Mars.

The first thing Mars explorers will need is a safe place to land. The goal is a flat area roughly 25 kilometers large suitable for landing many supply vessels and crew ships over a number of missions, Gallegos says. See the Mars illustration to the left - a nice flat area to lend.

"In addition, you don't want something that's super-rocky, since boulders are hazardous to landing and make roving difficult," says planetary scientist Fred Calef at NASA's Jet Propulsion Laboratory. "But you don't want something super-soft either. Some places on Mars have pockets of dust that are several meters deep, and you wouldn't want to land on fluffy powder."

Low altitudes could also offer better landing sites "since you'll have more atmosphere above you," Calef says. Having more air makes it easier to land safely with parachutes or other braking mechanisms.  Top

Local Resources


Life for astronauts on Mars will depend largely on making use of resources already on the Red Planet. The most important resource that astronauts need on Mars is water. Water is useful not only for drinking, but also for radiation shielding, and as fuel when it is split into hydrogen and oxygen. "The cost of bringing water from Earth to Mars is very expensive," Calef says.

There may be five sources of water on Mars — sheets of water ice; water-rich hydrated minerals; underground aquifers; seasonal flows of water; and atmospheric humidity. "There's going to be a vigorous debate about which of these is the best source of water," says Richard Davis, Jr.., assistant director for science and exploration at NASA's science mission directorate.

At first glance, the most obvious choice for water might be sheet ice, but Mars can be very cold, "and the colder ice gets, the harder it gets. "It will take a lot of energy to dig rock-hard ice out of the ground and melt it," Calef says. Still, getting water involves dredging sand or rock and baking it until the water comes out. The energy needed for this is generally considered to be higher than melting sheet ice. More research is needed to see which option for water is best, Davis says.

The European Space Agency has released a nice image of the Mars Korolev Crater shown at the left above. It is a 50-mile wide crater that is filled with water ice all year long. The crater is pretty deep, a mile and a quarter, so it is an ample supply of future water for a long time. The Korolev Crater is in the northern lowlands of Mars.  Top

Geological Features

Rim Crater

Astronauts will not simply want to land and live on Mars, but they will also want to check out local attractions as well. That is, places where scientific discoveries might be made. Geology is a science that deals with the history of a celestial body and its life, especially as recorded in rocks and other features. Astronauts will want to explore some geological features of Mars.

Features such as craters, outcrops, canyons and dune fields (ridges of sand) promise to shed light on the the geological history of Mars. Although such features may be challenging for astronauts to navigate, those are usually the kind of features planetary scientists want to study. See the photo to the left of the rim of Victoria Crater.

Astronauts on Mars will not be limited to only making discoveries near their landing sites. "We expect crews to have significant mobility, to go up to 100 kilometers from where they land," says Ben Bussey, chief exploration scientist at NASA's human exploration and operations directorate.  Top

Land At The Equator Or Elsewhere

Mars Equator

One of the main dividing issues between scientists will be whether they propose human missions either near the equator or at higher latitudes. One of the primary advantages of landing at a high-latitude site is easy access to water, especially in the northern plains. We know that there is water ice within the uppermost meter of the surface, which means that astronauts won't have to dig deep into the subsurface. Since this ice is fairly pristine, it also means that they won't need to exploit a large region to get enough water to support a human crew.

Furthermore, water ice is potentially an important science target. It may preserve a record of the Martian climate from the time when it was deposited. Sort of like how we can use ice cores on Earth to learn about our planet's climate history, and it might even contain evidence for either past or present life.

However, higher latitudes would be an extremely challenging place to live. During the winter, an astronaut crew would not see the sun for months, causing a negative effect on crew morale. The base would have to be completely nuclear-powered because you could not use solar panels as an energy source. The colder temperatures seen during the winters at high latitudes can also prove hard on equipment.

An equatorial location will have more direct sunlight per year (just like on Earth). NASA's concept for human Mars exploration utilizes nuclear energy as a main power source, but many small outposts and devices will need to be solar powered. Finally, unless astronauts are on a one-way trip to the Red Planet (as the Mars One candidates are) they will want a good place to blast off from to return to Earth. The best place on Mars to launch from is the equator - planets spin faster there giving a velocity boost to launch vehicles. So you won't need as much rocket fuel.  Top

Mars Spacecraft Landing Issues

Mars Landscape2

A typical landing spacecraft will enter the Martian airspace traveling approximately 12,000 miles per hour. During the first four minutes into descent, friction with the atmosphere will slow down the spacecraft considerably. At the end of this phase, it will still be traveling about 1,000 miles per hour, but now there will only be about 100 seconds left and it will be about 30,000 feet high, the altitude that a commercial airliner typically flies. Things need to happen in a hurry.

A parachute will open to slow the spacecraft down to 200 miles per hour, but now there are only 6 seconds left and it is 100 yards above the ground. Then the retro rockets will fire to bring the spacecraft to almost zero velocity, and it will be about 40 feet above the surface. The spacecraft will free fall the rest of the way surrounded by airbags to cushion the blow. It will hit the ground about 20 miles per hour. This "extreme total deceleration" has to happen in just under seven minutes, a time frame known to NASA engineers as - "seven minutes of terror".

Mars doesn't exactly put out a welcome mat. Landing is complicated by its difficult terrain. The Martian surface is full of obstacles - massive impact craters, cliffs, cracks and jagged boulders. See an actual land scape photo at the left above. Even the toughest airbag can be punctured if it hits a large pointed rock. Unpredictable winds can also stir up further complications.  Top

Aerocapture vs Aerobraking


A technical landing process called "aerobraking" has been used successfully on Martian missions. Aerobraking uses propulsion to first insert the spacecraft into Mars orbit (orbit capture) and then circularizes it (to achieve the desired orbit) by having the spacecraft pass through the upper part of the atmosphere several times.

Typically, the final slowing down of a spacecraft is done by firing retro-rockets, rockets that fire in the opposite direction than the spacecraft is traveling. This method requires a lot of fuel that has to be carried all the way until the spacecraft reaches Mars. It adds additional weight to an already heavy vehicle and is very expensive.

"Aerocapture", a newer process, will perform the orbit capture in a single pass through the atmosphere. The aerocapture maneuver uses the drag caused by the planet's upper atmosphere to slow down the vehicle. See the illustration to the left.

The atmosphere, in this case, serves as a "brake" for the vehicle, eliminating the need for additional fuel for retro rockets. However, this approach requires significant thermal protection and "precision closed-loop guidance" during the maneuver. In addition, the trajectory must be constrained to avoid excessive deceleration loads on the crew. Although there are similar constraints on trajectories for robotic missions, human limits are typically more stringent. This is true especially in light of the effects of prolonged trip microgravity on deceleration tolerances. However, aerocapture is being planned for the first human landing on Mars. It will most likely be tested several times before then.