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| Pictured in natural
color in 2007. |
Mars
Mars is the fourth planet from the Sun and the
second-smallest planet in the Solar System after
Mercury. In English, Mars carries a name of the Roman
god of war, and is often referred to as the "Red Planet"
because the reddish iron oxide prevalent on its surface
gives it a reddish appearance that is distinctive among
the astronomical bodies visible to the naked eye. Mars
can easily be seen from Earth, as can its reddish
coloring.
Mars is a terrestrial planet with a thin atmosphere,
having surface features like those of the impact craters
of the Moon, and valleys, deserts, and polar ice caps of
Earth It has two moons, Phobos and Deimos, which are
small and irregularly shaped.
It is nearly 7,000 kilometres (km) wide; just over half
the width of the Earth. Its volume is about 15% of the
Earth. Since a lot of the Earth is covered by water, the
total surface area of the Mars is nearly as large as all
of the land on the Earth. It is possible that its size
may eventually permit human colonies. |
 |
| Galileo Galilei,
first person to see Mars via telescope in 1610. |
Ancient and medieval studies
Our records of watching and recording Mars started with
ancient Egyptian astronomers in the 2nd millennium BC.
Detailed observations of the location of Mars were made
by Babylonian astronomers who developed methods using
math to predict the future position of the planet. The
ancient Greek philosophers and astronomers developed a
model of the solar system with the Earth at the center
('geocentric'), instead of the sun. They used this model
to explain the planet's motions. Indian and Islamic
astronomers estimated the size of Mars and its distance
from Earth. Similar work was done by Chinese
astronomers.
In the 16th century, Nicholas Copernicus proposed a
model for the Solar System in which the planets follow
circular orbits about the Sun. This 'heliocentric' model
was the beginning of modern astronomy. It was revised by
Johannes Kepler, who gave an elliptical orbit for Mars
which better fit the data from our observations.
The first observations of Mars by telescope was by
Galileo Galilei in 1610. Within a century, astronomers
discovered distinct albedo features (changes in
brightness) on the planet, including the dark patch and
polar ice caps. They were able to find the planet's day
(rotation period) and axial tilt. Better telescopes
developed early in the 19th century allowed permanent
Martian features to be mapped in detail. The first crude
map of Mars was published in 1840, followed by better
maps from 1877 onward.
Yellow clouds on Mars have been observed since the
1870s, which were windblown sand or dust. During the
1920s, the range of Martian surface temperature was
measured; it ranged from –85 to 7 oC. The planetary
atmosphere was found to be arid with only traces of
oxygen and water. In 1947, Gerard Kuiper showed that the
thin Martian atmosphere contained extensive carbon
dioxide; roughly double the quantity found in Earth's
atmosphere. The first standard naming of Mars surface
features was set in 1960 by the International
Astronomical Union. |
|
 |
| The tenuous
atmosphere of Mars visible on the horizon. |
Gravity
If you were on Mars, you would be lighter, as Mars'
gravity only has a force about two fifths as strong as
the that of Earth's. You could lift objects that weigh
almost three times as much compared to similar objects
here on the Earth. You could jump up almost three times
higher, and it would take much longer to fall to the
ground from the same height. Even so there are some
things you couldn't do. Although a big rock would weigh
less and you could pick it up, it would still have the
same mass. If you tried to catch it, it would knock you
over, and if it landed on you it would crush you.
Atmosphere
Mars lost its magnetosphere 4 billion years ago,
possibly because of numerous asteroid strikes, so the
solar wind interacts directly with the Martian
ionosphere, lowering the atmospheric density by
stripping away atoms from the outer layer.
Physical characteristics
Mars has a very thin atmosphere with barely any oxygen
(it is mostly carbon dioxide). The atmosphere of Mars
consists of about 96% carbon dioxide, 1.93% argon and
1.89% nitrogen along with traces of oxygen and water,
Methane has been detected in the Martian atmosphere.
Methane can exist in the Martian atmosphere for only a
limited period before it is destroyed—estimates of its
lifetime range from 0.6–4 years. Its presence despite
this short lifetime indicates that an active source of
the gas must be present. Volcanic activity, cometary
impacts, and the presence of microbial life forms are
among possible sources. Mars's atmosphere is too thin to
protect Mars from meteors, which is why the lower half
of Mars has so many craters.
The atmosphere is quite dusty, containing incredibly
tiny particles which give the Martian sky a tawny color
when seen from the surface. It may take on a pink hue
due to iron oxide particles suspended in it. Because
there is an atmosphere, however thin it is, the sky does
change colour when the sun rises and sets.
When Mars comes closest to the Sun, the atmosphere can
stir up storms of dust. Mars has the largest dust storms
in the Solar System. These can vary from a storm over a
small area, to some storms that are so gigantic they can
cover the entire planet in clouds of dust. Dust storms
on Mars can last for hundreds of days, with wind speeds
of up to 200 kilometres per hour, and have been shown to
increase the global temperature. Huge storms like these
have been seen from the Earth through telescopes.
Water on Mars
Liquid water is necessary for life and metabolism, so if
water was present on Mars, the chances of life evolving
is improved. The Viking orbiters found evidence of
possible river valleys in many areas, erosion and, in
the southern hemisphere, branched streams. Since then,
rovers and orbiters have also looked closely and
eventually proved water was on the surface at one time,
and is still found as ice in the polar ice caps and
underground.
Liquid water cannot exist on the surface of Mars due to
low atmospheric pressure, which is less than 1% of the
Earth's, except at the lowest elevations for short
periods. The two polar ice caps appear to be made
largely of water. The volume of water ice in the south
polar ice cap, if melted, would be sufficient to cover
the entire planetary surface to a depth of 11 meters (36
ft).
In November 2016, NASA reported finding a large amount
of underground ice in the Utopia Planitia region of
Mars. The volume of water detected has been estimated to
be equivalent to the volume of water in Lake Superior.
Mars does not have any liquid water on the surface now,
but signs of run-off on the surface were probably caused
by water. Landforms seen on Mars strongly suggest that
liquid water at some time existed on the planet's
surface. Huge areas of ground have been scraped and
eroded. These are known as 'outflow channels', and cut
across the surface in about 25 places. |
 |
| Exposure of
silica-rich dust uncovered by the Spirit rover. |
Polar caps
Like the Earth, Mars has ice caps at its poles. However,
they are made from frozen carbon dioxide as well as ice.
During the Martian winter at each pole, the cap grows as
carbon dioxide from the atmosphere freezes. The cap
shrinks again during the Martian summer. As on Earth,
when it is winter at one pole it is summer at the other.
Geology
Today, features on Mars are named from a variety of
sources. Albedo features (how reflective and bright
something is) are named for classical mythology. Craters
larger than 60 km are named for deceased scientists and
writers and others who have contributed to the study of
Mars. Craters smaller than 60 km are named for towns and
villages of the world with populations of less than
100,000. Large valleys are named for the word "Mars" or
"star" in various languages; small valleys are named for
rivers.
Because Mars is the one of the closest planets to Earth
in the Solar System, many wondered if there was any kind
of life there. Today we know that the kind of life, if
any, would be some simple bacteria-type organisms. The
surface of Mars is a lot like a desert on Earth; it is
very dry and dusty, but it is also very cold.
The outer, rocky surface of Mars is called the crust.
Most of the crust is made from basalt, a type of rock
made when lava grows cold. Like the Earth, Mars has a
thick layer of rock below the crust called the mantle.
The mantle is much hotter than the crust, and the mantle
rock is partly molten. But the crust on Mars has grown
thick, so the lava from the mantle no longer reaches the
surface. There are volcanoes on Mars, but they are no
longer active.
The planet Mars is made of rock. The ground there is red
because of iron oxide (rust) in the rocks and dust. The
planet's atmosphere is very thin and contains a lot of
carbon dioxide and a very tiny amount of oxygen. The
temperatures on Mars are colder than on Earth, because
it is farther away from the Sun and has less air to keep
warmth in. There is water ice and frozen carbon dioxide
at the north and south poles. The average thickness of
the planet's crust is about 50 km (31 mi), with a
maximum thickness of 125 km (78 mi).
The shield volcano Olympus Mons (Mount Olympus) is an
extinct volcano in the vast upland region Tharsis, which
contains several other large volcanoes. Olympus Mons is
roughly three times the height of Mount Everest, which
in comparison stands at just over 8.8 km (5.5 mi).
It is also home to Valles Marineris, the third largest
rift system (canyon) in the Solar System, 4,000 km long.
It is called a terrestrial planet because its outer
layers are made of rocky material like the Earth. |
 |
| Newly formed impact
crater (est 2016 – 2019). False blue color
highlights exposed bedrock. |
Meteorite craters
After the formation of the planets, all experienced the
"Late Heavy Bombardment". About 60% of the surface of
Mars shows a record of impacts from that era. Mars is
scarred by a number of impact craters: a total of 43,000
craters with a diameter of 5 km (3.1 mi) or greater have
been found. The largest confirmed of these is the Hellas
impact basin, clearly visible from Earth.
Due to the smaller mass of Mars, the probability of an
object colliding with the planet is about half that of
Earth. Mars is located closer to the asteroid belt, so
it has an increased chance of being struck by materials
from that source. Mars is more likely to be struck by
short-period comets (those that lie within the orbit of
Jupiter). In spite of this, there are far fewer craters
on Mars compared with the Moon, because the atmosphere
of Mars provides protection against small meteors.
Some meteorites hit Mars with so much force a few pieces
of Mars went flying into space – even to Earth. Rocks on
Earth are sometimes found which have chemicals that are
exactly like the ones in Martian rocks. These rocks also
look like they fell really quickly through the
atmosphere, so it is reasonable to think they came from
Mars.
NASA maintains a catalog of 34 Mars meteorites, that is,
meteorites which originally came from Mars. These assets
are highly valuable since they are the only physical
samples available of Mars.
Studies at NASA's Johnson Space Center show that at
least three of the meteorites contain possible evidence
of past life on Mars, in the form of microscopic
structures resembling fossilized bacteria (so-called
biomorphs). Although the scientific evidence collected
is reliable, and the rocks are correctly described, what
made the rocks look like they do is not clear.
Orbit and rotation
A Martian day is called a sol, and is a little longer
than an Earth day. Mars's average distance from the Sun
is roughly 230 million km (143 million mi), and its
orbital period is 687 (Earth) days. The solar day (or
sol) on Mars is only slightly longer than an Earth day:
24 hours, 39 minutes, and 35.244 seconds. A Martian year
is equal to 1.8809 Earth years, or 1 year, 320 days, and
18.2 hours.
It rotates on a tilt, just like the Earth does, so it
has four different seasons. Of all the planets in the
Solar System, the seasons of Mars are the most
Earth-like, due to the similar tilts of the two planets'
rotational axes. The lengths of the Martian seasons are
about twice those of Earth's, because its orbital period
is that much longer.
Martian surface temperatures vary from lows of about
−143 °C (−225 °F) (at the winter polar caps) to highs of
up to 35 °C (95 °F) (in equatorial summer). The wide
range in temperatures is due mostly to the thin
atmosphere which cannot store much solar heat. The
planet is also 1.52 times as far from the Sun as Earth,
resulting in just 43% of the amount of sunlight. |
|
 |
| The descent stage of
the Mars Science Laboratory mission carrying the
Curiosity rover deploys its parachutes to
decelerate itself before landing, photographed
by Mars Reconnaissance Orbiter. |
Observation and exploration
Dozens of crewless spacecraft, including orbiters,
landers, and rovers, have been sent to Mars by the
Soviet Union, the United States, Europe, and India to
study the planet's surface, climate, and geology.
Mariner 9 and Viking made maps of Mars using the data
from their missions, and another was the Mars Global
Surveyor mission, launched in 1996 and operated until
late 2006, that allowed complete, extremely detailed
maps of the Martian topography, magnetic field and
surface minerals. These maps are available online; for
example, at Google Mars. Mars Reconnaissance Orbiter and
Mars Express continued exploring with new instruments,
and supporting lander missions.
As of 2018, Mars is host to eight functioning
spacecraft: six in orbit—2001 Mars Odyssey, Mars
Express, Mars Reconnaissance Orbiter, MAVEN, Mars
Orbiter Mission and ExoMars Trace Gas Orbiter and two on
the surface—Mars Science Laboratory Curiosity (rover)
and InSight (lander).
Another rover, Opportunity, is inactive now, but NASA
still hopes to reestablish contact with it. The public
can request images of Mars via the Mars Reconnaissance
Orbiter's HiWish program.
The Mars Science Laboratory, named Curiosity, launched
on November 26, 2011, and reached Mars on August 6, 2012
UTC. It is larger and more advanced than the Mars
Exploration Rovers, with a movement rate up to 90 m (300
ft) per hour.
Experiments include a laser chemical sampler that can
deduce the make-up of rocks at a distance of 7 m (23
ft). On February 10, 2013, the Curiosity rover obtained
the first deep rock samples ever taken from another
planetary body, using its on-board drill. The same year,
it discovered that Mars's soil contains between 1.5% and
3% water by mass (though it is attached to other
compounds and thus not freely accessible).
The European Space Agency will launch the ExoMars rover
and surface platform in July 2020. The United Arab
Emirates' Mars Hope orbiter is planned for launch in
2020, reaching Mars orbit in 2021. The probe will make a
global study of the Martian atmosphere.
Several plans for a human mission to Mars have been
proposed throughout the 20th century and into the 21st
century, but no active plan has an arrival date sooner
than the 2020s. SpaceX founder Elon Musk presented a
plan in September 2016 to, optimistically, launch space
tourists to Mars in 2024 at an estimated development
cost of US$10 billion.
In October 2016, President Barack Obama renewed U.S.
policy to pursue the goal of sending humans to Mars in
the 2030s, and to continue using the International Space
Station as a technology incubator in that pursuit. The
NASA Authorization Act of 2017 directed NASA to get
humans near or on the surface of Mars by the early
2030s.
NASA provides two online tools: Mars Trek, which
provides visualizations of the planet using data from 50
years of exploration, and Experience Curiosity, which
simulates traveling on Mars in 3-D with Curiosity. |
|
 |
| Martian tripod
illustration from the 1906 French edition of The
War of the Worlds by H. G. Wells. |
Popular culture
The depiction of Mars in fiction has been stimulated by
its dramatic red color and by nineteenth century
scientific idea's that its surface conditions might
support not just life but intelligent life. Thus
originated a large number of science fiction stories,
among which is H. G. Wells' The War of the Worlds,
published in 1898, in which Martians seek to escape
their dying planet by invading Earth.
Influential works included Ray Bradbury's The Martian
Chronicles, in which human explorers accidentally
destroy a Martian civilization, Edgar Rice Burroughs'
Barsoom series, C. S. Lewis' novel Out of the Silent
Planet (1938), and a number of Robert A. Heinlein
stories before the mid-sixties.
Jonathan Swift made reference to the moons of Mars,
about 150 years before their actual discovery by Asaph
Hall, detailing reasonably accurate descriptions of
their orbits, in the 19th chapter of his novel
Gulliver's Travels.
A comic figure of an intelligent Martian, Marvin the
Martian, appeared in Haredevil Hare (1948) as a
character in the Looney Tunes animated cartoons of
Warner Brothers, and has continued as part of popular
culture to the present.
After the Mariner and Viking spacecraft had returned
pictures of Mars as it really is, an apparently lifeless
world, these ideas about Mars had to be abandoned, and a
trend for accurate, realist depictions of human colonies
on Mars developed, the best known of which may be Kim
Stanley Robinson's Mars trilogy. Theories about the Face
on Mars and other mysterious landmarks spotted by space
probes have meant that ancient civilizations continue to
be a popular theme in science fiction, especially in
film. |
|
 Kiddle:
Mars
Wikipedia: Mars |
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