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The Planets Of Our Solar System

Composition Of The Solar System

Exoplanet Types: Worlds Beyond Our Solar System

Located at the centre of the solar system and influencing the motion of all the other bodies through its gravitational force is the Sun, which in itself contains more than 99 percent of the mass of the system. The planets, in order of their distance outward from the Sun, are Mercury, Venus, Earth, , Jupiter, Saturn, Uranus, and Neptune. Four planetsJupiter through Neptunehave ring systems, and all but Mercury and Venus have one or more moons. Pluto had been officially listed among the planets since it was discovered in 1930 orbiting beyond Neptune, but in 1992 an icy object was discovered still farther from the Sun than Pluto. Many other such discoveries followed, including an object named Eris that appears to be at least as large as Pluto. It became apparent that Pluto was simply one of the larger members of this new group of objects, collectively known as the Kuiper belt. Accordingly, in August 2006 the International Astronomical Union , the organization charged by the scientific community with classifying astronomical objects, voted to revoke Plutos planetary status and place it under a new classification called dwarf planet. For a discussion of that action and of the definition of planet approved by the IAU, seeplanet.

Magnetic Field And Core

In 1967, found Venus’s to be much weaker than that of Earth. This magnetic field is induced by an interaction between the and the , rather than by an internal as in the Earth’s . Venus’s small provides negligible protection to the atmosphere against .

The lack of an intrinsic magnetic field at Venus was surprising, given that it is similar to Earth in size and was expected also to contain a dynamo at its core. A dynamo requires three things: a liquid, rotation, and . The core is thought to be electrically conductive and, although its rotation is often thought to be too slow, simulations show it is adequate to produce a dynamo. This implies that the dynamo is missing because of a lack of convection in Venus’s core. On Earth, convection occurs in the liquid outer layer of the core because the bottom of the liquid layer is much higher in temperature than the top. On Venus, a global resurfacing event may have shut down plate tectonics and led to a reduced through the crust. This effect would cause the mantle temperature to increase, thereby reducing the heat flux out of the core. As a result, no internal geodynamo is available to drive a magnetic field. Instead, the heat from the core is reheating the crust.

Surface Conditions And Exosphere

The surface temperature of Mercury ranges from 100 to 700 K at the most extreme places: 0°N, 0°W, or 180°W. It never rises above 180 K at the poles, due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles. The reaches about 700 K during , but only 550 K at .On the dark side of the planet, temperatures average 110 K.The intensity of on Mercury’s surface ranges between 4.59 and 10.61 times the .

Although the daylight temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K, far lower than the global average. This creates a where ice can accumulate. Water ice strongly reflects , and observations by the 70-meter and the in the early 1990s revealed that there are patches of high radar near the poles. Although ice was not the only possible cause of these reflective regions, astronomers think it was the most likely.

The icy regions are estimated to contain about 10141015 kg of ice, and may be covered by a layer of that inhibits . By comparison, the ice sheet on Earth has a mass of about 4×1018 kg, and Mars’s south polar cap contains about 1016 kg of water. The origin of the ice on Mercury is not yet known, but the two most likely sources are from of water from the planet’s interior or deposition by impacts of comets.

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How To Remember The Order Of The Planets

There are many handy expressions to remember the order of the planets. These are typically mnemonics which use the first letter of each planet’s name to come up with a phrase that’s easier to remember.

Finally, if you are musically inclined, there are a few songs that may help you remember. Two popular ones are Mr. R’s Planet Song and The Planet Song from Kids Learning Tube.

Types Of Planets In The Solar System

Diagram of Planets in the Solar System 1132887 Vector Art at Vecteezy

The inner four planets closest to the sun Mercury, Venus, Earth and Mars are often called the “terrestrial planets” because their surfaces are rocky. Pluto also has a rocky, albeit frozen, surface but has never been grouped with the four terrestrials.

The four large outer worlds Jupiter, Saturn, Uranus and Neptune are sometimes called the Jovian or “Jupiter-like” planets because of their enormous size relative to the terrestrial planets. They’re also mostly made of gases like hydrogen, helium and ammonia rather than of rocky surfaces, although astronomers believe some or all of them may have solid cores.

If you were to order the planets by size from smallest to largest they would be Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn and Jupiter.

Jupiter and Saturn are sometimes called the gas giants, whereas the more distant Uranus and Neptune have been nicknamed the ice giants. This is because Uranus and Neptune have more atmospheric water and other ice-forming molecules, such as methane, hydrogen sulfide and phosphene, that crystallize into clouds in the planets’ frigid conditions, according to the Planetary Society . For perspective, methane crystallizes at minus 296 Fahrenheit , according to the U.S. National Library of Medicine .

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Research With Space Probes


Reaching Mercury from Earth poses significant technical challenges, because it orbits so much closer to the Sun than Earth. A Mercury-bound spacecraft launched from Earth must travel over 91 million kilometres into the Sun’s gravitational . Mercury has an of 47.4 km/s , whereas Earth’s orbital speed is 29.8 km/s . Therefore, the spacecraft must make a large change in to get to Mercury and then enter orbit, as compared to the delta-v required for, say, .

The liberated by moving down the Sun’s potential well becomes , requiring a delta-v change to do anything other than pass by Mercury. Some portion of this can be provided from a during one or more fly-bys of Venus. To land safely or enter a stable orbit the spacecraft would rely entirely on rocket motors. is ruled out because Mercury has a negligible atmosphere. A trip to Mercury requires more rocket fuel than that required to the Solar System completely. As a result, only three space probes have visited it so far. A proposed alternative approach would use a to attain a Mercury-synchronous orbit around the Sun.

On March 24, 1975, just eight days after its final close approach, ran out of fuel. Because its orbit could no longer be accurately controlled, mission controllers instructed the probe to shut down. is thought to be still orbiting the Sun, passing close to Mercury every few months.




The Core Accretion Model

Approximately 4.6 billion years ago, the solar system was a cloud of dust and gas known as a solar nebula. Gravity collapsed the material in on itself as it began to spin, forming the sun in the center of the nebula.

With the rise of the sun, the remaining material began to clump together. Small particles drew together, bound by the force of gravity, into larger particles, according to the core accretion model. The solar wind swept away lighter elements, such as hydrogen and helium, from the closer regions, leaving only heavy, rocky materials to create terrestrial worlds. But farther away, the solar winds had less impact on lighter elements, allowing them to coalesce into gas giants. In this way, asteroids, comets, planets and moons were created.

Some exoplanet observations seem to confirm core accretion as the dominant formation process. Stars with more “metals” a term astronomers use for elements other than hydrogen and helium in their cores have more giant planets than their metal-poor cousins. According to NASA , core accretion suggests that small, rocky worlds should be more common than the large gas giants.

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The New Definition Of Planet

Here is the text of the IAUs Resolution B5: Definition of a Planet in the Solar System:

Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation “planets”. The word “planet” originally described “wanderers” that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

  • A planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape, and has cleared the neighbourhood around its orbit.
  • A “dwarf planet” is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape, has not cleared the neighbourhood around its orbit, and is not a satellite.
  • All other objects,except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.
  • Debateand DiscoveriesContinue

    Pluto: Once A Planet Now A Dwarf Planet

    The Planets of our Solar System Song (featuring The Hoover Jam)

    – Day: 6.4 Earth days

    – Number of moons: 5

    It is smaller than Earth’s moon its orbit is highly elliptical, falling inside Neptune’s orbit at some points and far beyond it at others and Pluto’s orbit doesn’t fall on the same plane as all the other planets instead, it orbits 17.1 degrees above or below.

    It is smaller than Earth’s moon its orbit is highly elliptical, falling inside Neptune’s orbit at some points and far beyond it at others and Pluto’s orbit doesn’t fall on the same plane as all the other planets instead, it orbits 17.1 degrees above or below, taking 288 years to complete a single orbit according to ESA.

    From 1979 until early 1999, Pluto had been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune’s path and once again became the solar system’s most distant planet until it was redefined as a dwarf planet. It’s a cold, rocky world with a tenuous atmosphere.

    Scientists thought it might be nothing more than a hunk of rock on the outskirts of the solar system. But when NASA’s New Horizons mission performed history’s first flyby of the Pluto system on July 14, 2015, it transformed scientists’ view of Pluto.

    Pluto is a very active ice world that’s covered in glaciers, mountains of ice water, icy dunes and possibly even cryovolcanoes that erupt icy lava made of water, methane or ammonia.

    Related: Why isn’t Pluto a planet anymore?

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    Uranus: The Tilted Sideways Planet In Our Solar System

    – Day: 18 Earth hours

    – Number of moons: 27

    Astronomers believe an object twice the size of Earth collided with Uranus roughly 4 billion years ago, causing Uranus to tilt. That tilt causes extreme seasons that last 20-plus years, and the sun beats down on one pole or the other for 84 Earth-years at a time.

    The collision is also thought to have knocked rock and ice into Uranus’ orbit. These later became some of the planet’s 27 moons. Methane in Uranus’ atmosphere gives the planet its blue-green tint. It also has 13 sets of faint rings.

    Uranus holds the record for the coldest temperature ever measured in the solar system minus 371.56 degrees F . The average temperature of Uranus is minus 320 degrees Fahrenheit .

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    Everyone Knows About The Solar System And The Planets That Make It Up Theyre In Space Orbiting The Sun In An Order We All At Least Used To Be Able To Recite

    But it was not always so. Until the likes of Copernicus, Kepler and Galileo came along, everyone thought the planets revolved around Earth, and before even that, no one was really sure what those big bright things in the sky even were.

    Thanks to thousands of years of observation, and careful study by some incredibly bright minds, we now have a good understanding of our Solar System. From the one with the ears, to the 11 year old girl that gave one of them their name, here are the stories behind each of the planets within it.

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    The Planets In Our Solar System In Order Of Size

    If youre interested in planets, the good news is theres plenty of variety to choose from in our own Solar System. From the ringed beauty of Saturn, to the massive hulk of Jupiter, to the lead-melting temperatures on Venus, each planet in our solar system is unique with its own environment and own story to tell about the history of our Solar System.

    What also is amazing is the sheer size difference of planets. While humans think of Earth as a large planet, in reality it is dwarfed by the massive gas giants lurking at the outer edges of our Solar System. This article explores the planets in order of size, with a bit of context as to how they got that way.

    What Has Hubble Taught Us About Storms In The Solar System

    Solar system simulation reveals planetary mystery

    Many astronomical phenomena occur over millions of years. But since its launch in 1990, the Hubble Space Telescope has kept a watchful eye on events within our own solar system, which happen on the timescale of days, weeks, and years. The short-term phenomena Hubble has witnessed on other planets includes the weather watching storms arise and dissipate across the faces of other worlds. Hubbles ability to see ultraviolet, infrared, and visible light makes it the ideal meteorologist for the solar system, allowing it to probe below the cloud tops and investigate the massive storms on distant planets.

    Among these constantly shifting weather patterns are dust storms on Mars. In 2018, a spring dust storm erupted in the southern hemisphere and ballooned into a global event enshrouding the entire planet. Hubbles Earth-orbit perspective allowed it to view the entirety of the global storm, while its long-term presence in space continues to allow it to monitor changes in Marss seasons over months and years.

    In the outer solar system, turbulent storms dot the atmospheres of the giant planets Jupiter, Saturn, Uranus, and Neptune allowing Hubble to become an expert storm tracker. For instance, Hubble has observed the downsizing of Jupiters most famous feature, the spinning, cyclone-like storm known as the Great Red Spot.

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    When Do The Planets In Our Solar System All Line Up

    Category: Space Published: August 28, 2013

    The planets in our solar system never line up in one perfectly straight line like they show in the movies. If you look at a two-dimensional plot of the planets and their orbits on a piece of paper you may be lead to believe that all the planets will circle around to the same line eventually. In reality, the planets do not all orbit perfectly in the same plane. Instead, they swing about on different orbits in three dimensional space. For this reason, they will never be perfectly aligned. It’s like waiting for a swarm of flies circling your head to all line up. It is not going to happen. When astronomers use words like “planetary alignment”, they don’t mean a literal lining up. They just mean that some of the planets are in the same general region of the sky. And this type of “alignment” almost never happens to all the planets, but instead happens to two or three planets at one time.

    Furthermore, “planetary alignment” depends on your viewpoint. If three planets are in the same region of sky from the earth’s point of view, they are not necessarily in the same region of sky form the sun’s point of view. Alignment is therefore an artifact of a viewpoint and not something fundamental about the planets themselves.

    The book Bad Astronomy by Philip C. Plait states,

    Astronomical Body
    All planets when closest 0.000064

    What Is A Planet

    This seemingly simple question doesn’t have a simple answer. Everyone knows that Earth, and Jupiter are planets. But both Pluto and Ceres were once considered planets until new discoveries triggered scientific debate about how to best describe thema vigorous debate that continues to this day. The most recent definition of a planet was adopted by the International Astronomical Union in 2006. It says a planet must do three things:

  • It must orbit a star .
  • It must be big enough to have enough gravity to force it into a spherical shape.
  • It must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun.
  • Discussionand debatewill continue as our view of the cosmos continues to expand.

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