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Mars 101 | National Geographic

To the ancient Romans, the planet Mars was symbolic of blood and war. But to many people today, the red planet may hold the key for a bright, new future for humanity.

The story of Mars began about 4.5 billion years ago, when gas and dust swirled together to form the fourth planet from the Sun.

Mars is the second-smallest planet in the solar system, with a diameter just shy of the width of Africa. In fact, its entire surface area is similar to that of all of Earth’s continents combined. Much like its terrestrial cousin, Mars is dense and has a rocky composition. At the center of the planet is a core made of iron, nickel, and sulfur, which may have created a protective magnetic field during Mars’s earlier years.

Enveloping the core is a rocky mantle made of silicate minerals and a crust rich in iron. These iron minerals react with the trace amounts of oxygen in Mars’s atmosphere and rusts, giving the planet its signature reddish hue. While its blood-like appearance inspired the ancient Romans to name Mars after their god of war, the planet’s rusty color could be considered symbolic of the planet’s prime days long past.

Today, Mars is dry, desolate, and cold (with temperatures dropping as low as -225 degrees Fahrenheit). But billions of years ago, the planet was much warmer, more geologically active, and had a watery surface. While its blood-like appearance inspired the ancient Romans to name Mars after their god of war, the planet’s rusty color could be considered symbolic of the planet’s prime days long past.

Lake-beds and river valleys snake along the face of Mars, indicating that liquid water was, for a time, present. Volcanoes, such as Olympus Mons, the largest volcano in the solar system at three times the height of Mt. Everest, once erupted with lava. But by about 50 million years ago, soon after Earth’s dinosaurs died out, Mars’s volcanoes also went extinct. Water on the red planet still exists today, but mostly in the form of polar ice caps.

Because of factors such as the presence of water, some scientists believe life may have existed on the red planet — and may exist again.

Since the 1960’s, space programs from around the world have launched missions to Mars in attempts to understand the planet’s past, present, and potential for sustaining life.

Life on another planet may well be out of reach for the near future.

But if any planet could give us hope, Mars may hold the key to the survival of humanity.

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Mercury 101 | National Geographic

The planet Mercury is named after the messenger of the Roman gods because even the ancients could see how swift and fleeting it is in the sky.

But it wasn’t until recently, that scientists began unraveling Mercury’s many mysteries.

Mercury is the smallest planet in our solar system. Its diameter currently measures just over 3,000 miles, about the size of the continental United States. Like Earth, Mercury is a terrestrial planet with three main layers: A core, a mantle, and a crust. Only Mercury’s crust has no tectonic plates. Also, its iron core is enormous by comparison, making up 85 percent of its radius, while Earth’s inner and outer core account for just 55%.

Because of the core’s exceptional size, it has had a surprising influence on Mercury’s overall size – by causing it to shrink. The hot iron core has slowly cooled and contracted over the planet’s 4.5 billion years. In doing so, it pulled Mercury’s surface inward, and has caused the planet to shrink radially by more than four miles. So far…

This shrinking planet is also the planet closest to the Sun, orbiting our Solar System’s star at an average distance of roughly 36 million miles. Such proximity affects Mercury’s atmosphere, or rather, the lack of one. It only has a very thin exosphere, which is traditionally the outermost layer of a planet’s atmosphere. This exosphere is made of oxygen, sodium, hydrogen, helium, and potassium, all whipped up from the planet’s surface by solar winds.

The lack of atmosphere and close proximity to the Sun also makes Mercury a planet of extremes. The surface temperature can climb to 800 degrees Fahrenheit during the daytime and fall to 290 degrees below zero at night.

Mercury’s proximity to the Sun is also the reason behind its age-old reputation of being swift and fleeting. The Sun’s gravity pulls harder on Mercury than any other planet. And like all planets, Mercury travels in an elliptical orbit, slowing down when it’s farther away from the Sun, and accelerating as it draws closer. Clocking in at an average speed of over 100,000 miles per hour, Mercury slings around the Sun in just 88 days.

From Earth, Mercury is difficult to observe because it’s fleeting and so close to the Sun.

And so far, it’s only been visited by two spacecraft: NASA’s Mariner 10 and MESSENGER.

Those missions gave us much of what we know today, but future ventures are in the works with high hopes of revealing more of Mercury’s secrets.

Excerpts from the National Geographic | 101 Videos on Solar System

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