Read the Sentence Mercury and Venus Relatively Close to the Sun

Lesson Objectives

Draw key features of each of the inner planets.
Compare each of the inner planets to Earth and to one some other.

Vocabulary

day
inner planets
terrestrial planets
year

Introduction

What evidence do planetary geologists take to go on to determine the geology of the inner planets? On Earth, scientists tin can collect and clarify the chemistry of samples, do radiometric dating to determine their ages, and look at satellite images to encounter large-calibration features. Rovers have landed on Mars and sent back enormous amounts of data simply much of the rest of what is known about the inner planets is from satellite images.

The Inner Planets

Theinner planets, orterrestrial planets, are the four planets closest to the Sun: Mercury, Venus, World, and Mars.Effigy below shows the relative sizes of these 4 inner planets.

This composite shows the relative sizes of the four inner planets. From left to right, they are Mercury, Venus, World, and Mars.

Different the outer planets, which accept many of satellites, Mercury and Venus do not have moons, Earth has one, and Mars has two. Of course, the inner planets have shorter orbits around the Dominicus, and they all spin more slowly. Geologically, the inner planets are all made of cooled igneous rock with atomic number 26 cores, and all have been geologically active, at least early on in their history. None of the inner planets has rings.

Earth

Although Earth is the third planet out from the Dominicus this lesson will start hither. Nosotros know a lot more about Earth, and then what we know tin can exist used for comparison with the other planets.

What are Globe's well-nigh distinctive features? This famous prototype of World was taken during the Apollo 17 mission to the moon. Tin can you find a hurricane? A tempest spinning in the opposite direction from the hurricane?

World's Surface and Life

As you tin see in (Figure above), World has vast oceans of liquid water, big masses of exposed land, and a dynamic temper with clouds of h2o vapor. Earth also has ice covering its polar regions. Earth's average surface temperature is 14°C (57°F). Water is a liquid at this temperature, but the planet also has water in its other 2 states, solid and gas. The oceans and the temper help keep World's surface temperatures adequately steady.

Every bit nevertheless World is the only planet known to have life. The presence of liquid water, the power of the atmosphere to filter out harmful radiation, and many other features make the planet uniquely suited to harbor life. Life and Earth now affect each other; for example, the evolution of plants immune oxygen to enter the atmosphere in large enough quantities for animals to evolve. Although life has non been found elsewhere in the solar system, other planets or satellites may harbor primitive life forms. Life may also be found elsewhere in the universe.

Structure and Plate Tectonics

The rut that remained from the planet's accretion, gravitational pinch, and radioactive disuse allowed the Globe to cook, probably more than than once. As it afterwards cooled, gravity pulled metal into the center to create the core. Heavier rocks formed the curtain and lighter rocks formed the crust.

Earth'south crust is divided into tectonic plates, which move around on the surface considering of the convecting curtain below. Movement of the plates causes other geological activity, such as earthquakes, volcanoes, and the formation of mountains. The locations of these features are mostly related to current or one-time plate boundaries. Globe is the only planet known to accept plate tectonics.

Earth's Motions and Satellites

Earth rotates on its centrality in one case perday, past definition. Earth orbits the Lord's day one time every 365.24 days, which is divers equally ayr. Earth has i large moon, which orbits Earth in one case every 29.5 days, a catamenia known as a month.

World's moon is the only large moon orbiting a terrestrial planet in the solar system. The Moon is covered with craters; it besides has large plains of lava. The huge number of craters suggests that Moon's surface is ancient. In that location is evidence that the Moon formed when a large object — perhaps every bit large as the planet Mars — struck Earth in the distant past (Figure below).

Too its Moon, World is orbited past a bully bargain of space debris, the remains of satellites, and rocket stages.

Mercury

The smallest planet, Mercury, is the planet closest to the Sun. Because Mercury is and so close to the Dominicus, it is hard to find from Earth, even with a telescope. Nonetheless, the Mariner x spacecraft, shown inEffigy below, visited Mercury from 1974 to 1975. The MESSENGER spacecraft has been studying Mercury in detail since 2005. The craft is currently in orbit around the planet, where it is creating detailed maps. MESSENGER stands for Mercury Surface, Infinite Surround, Geochemistry and Ranging.

(a) Mariner 10 made three flybys of Mercury in 1974 and 1975. (b) A 2008 image of compiled from a flyby by MESSENGER.

AsFigure beneath shows, the surface of Mercury is covered with craters, similar World's moon. Aboriginal impact craters means that for billions of years Mercury hasn't inverse much geologically. Likewise, with very little temper, the processes of weathering and erosion exercise non wearable downwardly structures on the planet.

Mercury is covered with craters, like World'due south moon. MESSENGER has taken extremely detailed pictures of the planet's surface.

There are many images, movies and activities on the MESSENGER site: http://messenger.jhuapl.edu/alphabetize.php.

Short Year, Long Days

Mercury is named for the Roman messenger god, who could run extremely quickly, just as the planet moves very speedily in its orbit around the Sun. A year on Mercury — the length of time it takes to orbit the Sun — is just 88 World days.

Despite its very brusk years, Mercury has very long days. A day is defined as the fourth dimension it takes a planet to turn on its centrality. Mercury rotates slowly on its axis, turning exactly three times for every ii times it orbits the Lord's day. Therefore, each twenty-four hours on Mercury is 57 Earth days long. In other words, on Mercury, a twelvemonth is only a Mercury day and a half long!

Extreme Temperatures

Mercury is close to the Sun, so information technology tin go very hot. However, Mercury has almost no atmosphere, no h2o to insulate the surface, and information technology rotates very slowly. For these reasons, temperatures on the surface of Mercury vary widely. In direct sunlight, the surface tin exist equally hot as 427°C (801°F). On the night side, or in the shadows inside craters, the surface can be as common cold every bit -183°C (-297°F)! Although nearly of Mercury is extremely dry, scientists retrieve there may exist a small amount of water in the grade of ice at the poles of Mercury, in areas that never receive directly sunlight.

A Liquid Metal Cadre

Effigy below shows a diagram of Mercury's interior. Mercury is 1 of the densest planets. It'southward relatively large, liquid core, fabricated by and large of melted iron, takes upwards virtually 42% of the planet's volume.

Mercury contains a thin chaff, a mantle, and a large, liquid core that is rich in iron.

Venus

Named afterwards the Roman goddess of love, Venus is the only planet named after a female. Venus' thick clouds reflect sunlight well then Venus is very bright. When it is visible, Venus is the brightest object in the sky besides the Lord's day and the Moon. Considering the orbit of Venus is within Earth's orbit, Venus always appears close to the Sunday. When Venus rises merely before the Sun rises, the bright object is called the morning star. When it sets but later on the Dominicus sets, it is the evening star.

Of the planets, Venus is near similar to Earth in size and density. Venus is besides our nearest neighbor. The planet'southward interior structure is like to Earth'due south with a big iron core and a silicate mantle (Figure below). Only the resemblance betwixt the two inner planets ends there.

Notice out more about Venus at the post-obit link: http://www.nasa.gov/worldbook/venus_worldbook.html.

Venus's interior is like to Earth's.

Motion

Venus rotates in a management contrary the other planets and contrary to the direction it orbits the Sun. This rotation is extremely slow, only 1 plough every 243 days. This is longer than a year on Venus—it takes Venus just 224 days to orbit the Sun.

Extreme Temper

Venus is covered past a thick layer of clouds, as shown in pictures of Venus taken at ultraviolet wavelengths (Effigy below).

This ultraviolet image from the Pioneer Venus Orbiter shows thick layers of clouds in the atmosphere of Venus.

Venus' clouds are non made of water vapor like Earth'due south clouds. Clouds on Venus are made by and large of carbon dioxide with a chip of sulfur dioxide — and they besides contain corrosive sulfuric acid. Because carbon dioxide is greenhouse gas, the atmosphere traps heat from the Sun and creates a powerful greenhouse upshot. Even though Venus is further from the Sun than Mercury, the greenhouse event makes Venus the hottest planet. Temperatures at the surface achieve 465°C (860°F). That's hot enough to cook lead.

The atmosphere of Venus is full of acid, its pressure is burdensome, and the enormous corporeality of carbon dioxide causes delinquent greenhouse effect(4d): http://world wide web.youtube.com/lookout man?five=HqFVxWfVtoo (two:05).

The atmosphere of Venus is and then thick that the atmospheric pressure level on the planet's surface is 90 times greater than the atmospheric pressure level on Earth's surface. The dense temper totally obscures the surface of Venus, fifty-fifty from spacecraft orbiting the planet.

Venus'south Surface

Since spacecraft cannot run across through the thick atmosphere, radar is used to map Venus' surface. Many features found on the surface are similar to Earth and yet are very unlike.Figure below shows a topographical map of Venus produced by the Magellan probe using radar.

This imitation color image of Venus was fabricated from radar data collected by the Magellan probe between 1990 and 1994. What features can yous identify?

Orbiting spacecraft accept used radar to reveal mountains, valleys, and canyons. Most of the surface has large areas of volcanoes surrounded past plains of lava. In fact, Venus has many more volcanoes than any other planet in the solar system and some of those volcanoes are very large.

Most of the volcanoes are no longer active, but scientists have institute prove that there is some active volcanism (Figure beneath). Think about what you lot know about the geology of World and what produces volcanoes. What does the presence of volcanoes propose about the geology of Venus? What show would you lot look for to find the causes of volcanism on Venus?

This image of the Maat Mons volcano with lava beds in the foreground was generated by a figurer from radar information. The reddish-orange color is shut to what scientists think the color of sunlight would wait like on the surface of Venus.

Venus besides has very few touch on craters compared with Mercury and the Moon. What is the significance of this? World has fewer affect craters than Mercury and the Moon also. Is this for the same reason that Venus has fewer impact craters?

It's difficult for scientists to figure out the geological history of Venus. The environment is too harsh for a rover to go there. It is even more hard for students to figure out the geological history of a afar planet based on the information given here. Still we can piece together a few things.

On Earth, volcanism is generated because the planet's interior is hot. Much of the volcanic activity is caused past plate tectonic activity. Just on Venus, there is no evidence of plate boundaries and volcanic features do non line upwardly the manner they exercise at plate boundaries.

Considering the density of bear on craters tin can be used to determine how old a planet's surface is, the small number of impact craters means that Venus' surface is young. Scientists call up that in that location is frequent, planet-broad resurfacing of Venus with volcanism taking place in many locations. The cause is heat that builds up beneath the surface that has no escape until finally information technology destroys the crust and results in volcanoes.

Mars

Mars is the quaternary planet from the Dominicus, and the commencement planet beyond Earth's orbit (Figure below). Mars is a quite different from Earth and nonetheless more than similar than any other planet. Mars is smaller, colder, drier, and appears to accept no life, merely volcanoes are common to both planets and Mars has many.

Mars is easy to find so Mars has been studied more thoroughly than any other extraterrestrial planet. Infinite probes, rovers, and orbiting satellites have all yielded information to planetary geologists. Although no humans take ever set human foot on Mars, both NASA and the European Space Agency accept prepare goals of sending people to Mars one-time between 2030 and 2040.

Find out all yous desire to know about Mars at http://mars.jpl.nasa.gov/extreme/.

This image of Mars, taken by the Hubble Infinite Telescope in October, 2005, shows the planet's blood-red color, a small water ice cap on the south pole, and a dust tempest.

A Cherry Planet

Viewed from Earth, Mars is reddish in color. The aboriginal Greeks and Romans named the planet later on the god of war. But the surface is not reddish from blood just from large amounts of iron oxide in the soil.

The Martian atmosphere is very thin relative to Earth's and has much lower atmospheric pressure. Although the temper is fabricated upwards mostly of carbon dioxide, the planet has only a weak greenhouse effect so temperatures are just slightly higher than if the planet had no atmosphere.

Surface Features

Mars has mountains, canyons, and other features similar to Earth. Some of these surface features are amazing for their size! Olympus Mons is a shield volcano, like to the volcanoes that brand up the Hawaiian Islands. But Olympus Mons is too the largest mount in the solar organization (Effigy beneath).

Olympus Mons is about 27 km (sixteen.vii miles/88,580 ft) in a higher place the Martian surface, more than 3 times taller than Mount Everest. The volcano'due south base is about the size of the land of Arizona.

Mars besides has the largest canyon in the solar organisation, Valles Marineris (Figure below).

Valles Marineris is iv,000 km (two,500 mi) long, every bit long as Europe is broad, and i-fifth the circumference of Mars. The canyon is vii km (four.iii mi) deep. By comparing, the Grand Coulee on Globe is simply 446 km (277 mi) long and about two km (1.2 mi) deep.

Mars has more impact craters than Earth, though fewer than the Moon. A video comparing geologic features on Mars and World is seen hither: Mars tectonics video http://news.discovery.com/videos/space-three-questions-mars-tectonics.html

Is There Water on Mars?

Water cannot stay in liquid form on Mars because the atmospheric pressure is as well low. Notwithstanding, there is a lot of water in the course of ice and fifty-fifty prominent ice caps (Figure below). Scientists likewise think that at that place is a lot of water water ice present just under the Martian surface. This ice can melt when volcanoes erupt, and h2o can period beyond the surface temporarily.

The north polar ice cap on Mars.

Scientists think that water one time flowed over the Martian surface because at that place are surface features that look like water-eroded canyons (Figure below). The presence of h2o on Mars, even though it is at present frozen as ice, suggests that information technology might take been possible for life to exist on Mars in the past.

The Mars rover collected rounded clumps of crystals that, on Earth, are known to form in water.

A video of the top 5 Phoenix Lander sites on Mars is seen here: http://news.discovery.com/videos/infinite-height-v-mars-phoenix-lander-images.html.

Two Martian Moons

Mars has 2 very small moons that are irregular rocky bodies (Figure below). Phobos and Deimos are named after characters in Greek mythology — the ii sons of Ares, who followed their begetter into war. Ares is equivalent to the Roman god Mars.

Mars has two small moons, Phobos (left) and Deimos (right). Both were discovered in 1877 and are thought to be captured asteroids.

An animation of the moons orbiting Mars is seen hither: http://commons.wikimedia.org/wiki/File:Orbits_of_Phobos_and_Deimos.gif.

KQED: Searching for Life on Mars

The Mars Science Laboratory was launched on November 26, 2011 and will search for whatsoever show that the Red Planet was in one case capable of supporting life. Curiosity is a car-sized rover that is scouring the cerise planet for clues; it landed in August 2012. Acquire more than at:http://science.kqed.org/quest/video/searching-for-life-on-mars/.

Lesson Summary

The four inner planets, or terrestrial planets, accept solid, rocky surfaces.
World, the third planet from the Sun, is the only planet with large amounts of liquid h2o, and the only planet known to back up life. Earth has a large round moon.
Mercury is the smallest planet and is the closest to the Sun. With its extremely thin temper, Mercury has a large temperature range. Similar the Moon, it is covered with craters.
Venus is the 2d planet from the Sun and the closest planet to Earth, in distance and in size. With its thick, corrosive temper, the surface temperature is extremely high.
Venus has mountainous areas, too as volcanoes surrounded past plains of lava.
Mars is the quaternary planet from the Sun. Mars is ruddy in color and has the largest mount and the largest canyon in the solar system. It has two pocket-size moons.
H2o ice is found in the polar ice caps and under the surface of Mars.

Review Questions

1. Name the inner planets from the Lord's day outward. Then name them from smallest to largest.

two. Why practice the temperatures on some planets vary widely? Why are some temperatures much less variable?

iii. Why does Venus have college temperatures than Mercury?

4. How are maps of Venus made?

5. Name two major ways in which World is unlike whatsoever other planet.

6. Why is Mars red?

vii. Suppose y'all are planning a mission to Mars. Place two places where yous might be able to become water on the planet. Why is this important?

Points to Consider

The first humans may reach Mars sometime in the next few decades. What atmospheric condition will they face? Why do y'all retrieve nosotros are going to Mars instead of Mercury or Venus?
Why are the iv inner planets called terrestrial planets? What might a planet be similar if it weren't a terrestrial planet?

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Source: https://courses.lumenlearning.com/earthscience/chapter/inner-planets/