A journey through our Solar System and its characteristics
The Solar System is the planetary system in which Earth is located. It consists of a group of astronomical objects that orbit around a single star—known as the Sun—from which it takes its name.
This star, which concentrates 99.75% of the system’s mass, is the only celestial body that emits its own light.
(Source: Wikipedia)
The Solar System formed 4.568 billion years ago from the collapse of a molecular cloud.
The remaining material gave rise to a protoplanetary circumstellar disk where the physical processes leading to the formation of planets took place.
The Solar System is currently located in the Local Interstellar Cloud within the Local Bubble of the Orion Arm, a spiral arm of the Milky Way galaxy, about 28,000 light-years from its center.
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Birth of the Solar System (National Geographic)
Among the numerous objects orbiting the star, most of the remaining mass is concentrated in eight planets, whose orbits are nearly circular and lie within a nearly flat disk called the ecliptic plane.
The four closest, significantly smaller, are Mercury, Venus, Earth, and Mars, also known as the terrestrial planets, and are mainly composed of rock and metal.
The outer planets, gas giants also known as "Jovian planets," are substantially more massive than the terrestrial ones.
The two largest, Jupiter and Saturn, are primarily composed of helium and hydrogen, while the ice giants, Uranus and Neptune, are mostly made of frozen water, ammonia, and methane.
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Planets of the Solar System
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The True and Incredible Motion of the Solar System
Mercury is the planet closest to the Sun in the Solar System and the smallest. It is part of the so-called inner or rocky planets and lacks moons.
It was once thought that Mercury always showed the same face to the Sun, like the Moon with Earth; however, in 1965, it was discovered that its rotational period is 58.7 days.
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Getting to Know Mercury Better
We know Mercury better thanks to the work of the Messenger probe (launched by NASA in 2004, reaching the planet in 2011).
Messenger is an acronym for MErcury Surface, Space ENvironment, GEochemistry and Ranging. During its journey, it flew by Earth, Venus (twice), and Mercury itself (three times).
Venus is the second planet from the Sun and the third-largest in size, from smallest to largest.
It is a rocky and terrestrial planet, often referred to as Earth’s sister planet because they are similar in size, mass, and composition, though they differ greatly in thermal and atmospheric conditions.
Its atmospheric pressure is 90 times that of Earth’s, making it the planet with the highest atmospheric pressure among all the rocky planets. Despite being further from the Sun than Mercury, Venus has the hottest atmosphere, as it traps more heat due to being primarily composed of greenhouse gases.
Venus has the longest day in the solar system: 243 Earth days, and its motion is retrograde, meaning it rotates clockwise, opposite to the other planets.
When Venus is brightest, it can be seen during the day, being one of the only three celestial bodies visible to the naked eye in daylight, alongside the Moon and the Sun. Venus is commonly known as the morning star (Lucifer) or the evening star (Hesperus), and when visible in the night sky, it is the second-brightest object after the Moon.
For this reason, Venus must have been known since prehistoric times.
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Getting to Know Venus Better
Venus Express was the European Space Agency’s (ESA) first mission dedicated to the planet Venus.
The mission was launched in November 2005 and officially concluded in December 2014, although ESA managed to extend its operation until 2015. During its final phase, the spacecraft performed experimental maneuvers at very low altitudes before losing contact.
The main scientific goals of Venus Express included a detailed study of Venus' atmosphere, its plasma environment, the interaction between the surface and atmosphere, and the search for possible active volcanism. These data helped improve understanding of Venus' climatic and atmospheric evolution.
Earth is the densest and the fifth-largest planet in the Solar System. It is also the largest of the four terrestrial planets.
Earth formed approximately 4.55 billion years ago, and life emerged about a billion years later. Its atmosphere and other abiotic conditions have been significantly altered by the planet’s biosphere, favoring the proliferation of aerobic organisms and the formation of an ozone layer which, along with Earth's magnetic field, blocks harmful solar radiation, thus allowing life to thrive on Earth.
Earth’s physical properties, geological history, and orbit have allowed life to persist. It is estimated that the planet will continue to support life for another 500 million years, as, according to current predictions, after that time, the Sun’s increasing brightness will lead to the extinction of the biosphere.
No other planet is known to have this balance of liquid water, essential for any known form of life. The Earth's poles are mostly covered in solid ice. The planet’s interior is geologically active, with a thick, relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core of approximately 88%.
Earth interacts with other objects in space, especially the Sun and Moon. Earth has a single natural satellite, the Moon, which began orbiting the planet 4.53 billion years ago; it causes tides, stabilizes Earth’s axial tilt, and gradually slows its rotation.
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Mars is the fourth planet from the Sun in the Solar System. It is sometimes nicknamed the Red Planet due to its reddish appearance caused by iron oxide dominating its surface. It has a thin atmosphere made of carbon dioxide and two moons: Phobos and Deimos. It is part of the so-called terrestrial planets (rocky in nature, like Earth) and is the most distant inner planet from the Sun. In many ways, it is the planet most similar to Earth.
Although it might appear to be a dead planet, it is not. Its dune fields are still moved by the Martian wind, its polar ice caps change with the seasons, and there even seem to be some small seasonal water flows.
It is one of the superior planets relative to Earth, meaning it never passes between the Sun and Earth.
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Jupiter is the fifth planet in the Solar System. It is one of the outer or gaseous planets.
It is the brightest planet throughout the year depending on its phase. Additionally, after the Sun, it is the largest celestial body in the Solar System, with a mass nearly two and a half times that of all the other planets combined (318 times the mass of Earth and three times that of Saturn).
Jupiter is a massive gaseous body, mainly composed of hydrogen and helium, lacking a defined solid surface. Notable atmospheric features include the Great Red Spot, a huge anticyclone located in the southern tropical latitudes, cloud bands in dark and bright zones, and a global atmospheric dynamic characterized by intense alternating zonal winds reaching speeds of up to 140 m/s (504 km/h).
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Getting to know Jupiter better
The Juno probe arrived at Jupiter in July 2016 to investigate the planet, in a mission that has been extended beyond the originally planned timeframe.
Its primary goal is to study Jupiter’s atmosphere, origin, structure, and evolution, as well as to map its gravitational and magnetic fields and analyze its auroras. These studies help to understand the formation of Jupiter and the Solar System.
Juno follows a polar orbit to protect itself from the planet’s radiation, which has allowed the mission to be extended and key information to be obtained about Jupiter’s internal layers and atmosphere.
Saturn is the sixth planet from the Sun, the second-largest in size and mass after Jupiter, and the only one with a ring system visible from Earth.
It is one of the outer or gaseous planets. The most characteristic feature of Saturn is its bright rings. - Galileo was the first to observe the rings in 1610, but the low tilt of the rings and the low resolution of his telescope initially made him think they were large moons.
- Christiaan Huygens, with better observational tools, was able to clearly observe the rings in 1659.
- James Clerk Maxwell demonstrated mathematically in 1859 that the rings could not be a single solid object but had to be composed of millions of smaller particles.
The particles within Saturn’s rings orbit at a speed of 48,000 km/h, 15 times faster than a bullet.
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Getting to know Saturn better
Cassini-Huygens is a joint project between NASA, ESA, and ASI. It is an unmanned space mission aimed at studying Saturn and its natural satellites, commonly referred to as moons. The spacecraft consists of two main elements: the Cassini orbiter and the Huygens probe.
The probe reached Saturn’s largest moon, Titan, on January 14, 2005, when it descended to its surface to collect scientific data. It is the first spacecraft to orbit Saturn and the fourth human-made artifact to visit the planet.
Uranus is the seventh planet in the Solar System, the third-largest in size, and the fourth-most massive.
Although it is visible to the naked eye in the night sky, it was not cataloged as a planet by ancient astronomers due to its faint brightness and slow orbit. Uranus is also the first planet discovered using a telescope.
Uranus is similar in composition to Neptune, and both differ from the other two gas giants (Jupiter and Saturn). Because of this, astronomers sometimes classify them as a different category: ice giants.
Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration compared to the other planets, as its axis of rotation is tilted nearly to its orbital plane. Therefore, its north and south poles are located where most other planets have their equators.
Winds on Uranus can reach or even exceed 250 meters per second (900 km/h).
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Neptune is the eighth planet from the Sun and the most distant in the Solar System. It is one of the outer or gas giant planets and is the first to be discovered through mathematical predictions. It is the fourth-largest planet in diameter and the third most massive. Its mass is 17 times that of Earth and slightly more massive than its “twin” planet, Uranus, which has 15 Earth masses and is less dense.
Neptune is a dynamic planet with storms reminiscent of Jupiter’s. The largest one, the Great Dark Spot, was about the size of Earth, but it disappeared in 1994, and another has since formed. Neptune has the strongest winds of any planet in the Solar System.
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Pluto is a dwarf planet in the Solar System, located beyond Neptune’s orbit. During the General Assembly of the International Astronomical Union (IAU) held on August 24, 2006, the category of plutoids was created, which includes Pluto, and it is also the prototype of the trans-Neptunian objects known as plutinos.
Pluto was first visited by a space probe when NASA’s New Horizons mission flew by in July 2015, providing detailed images and data on its surface and surroundings.
Discovered on February 18, 1930, by astronomer Clyde William Tombaugh from the Lowell Observatory in Arizona, Pluto was considered the ninth planet in the Solar System until 2006 when, after a long debate, it was reclassified as a dwarf planet due to the criteria established by the IAU.
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Journey Through the Solar System
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The Scale of the Solar System's Planets
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