Discovery and exploration of the Solar System

[1] In ancient and medieval times, only objects visible to the naked eye—the Sun, the Moon, the five classical planets, and comets, along with phenomena now known to take place in Earth's atmosphere, like meteors and aurorae—were known.

[4] Systematic astronomical observations were performed in many areas around the world, and started to inform cosmological knowledge, although they were mostly driven by astrological purposes such as divination and/or omens.

Early historic civilizations in Egypt, the Levant, pre-Socratic Greece, Mesopotamia, and ancient China, recorded beliefs in a flat Earth.

[5] Ancient models were typically geocentric, putting the Earth at the center of the universe,[6] based solely in the common experience of seeing the skies slowly moving around above our heads, and by feeling the land under our feet to be firmly at rest.

[7] Though unclear if motivated by empirical observations, the concept of a spherical Earth apparently first gained intellectual dominance in the Pythagorean school in Ancient Greece in the 5th century BC.

Influenced by Pythagoran thinking and Plato, philosophers Eudoxus, Callippus, and Aristotle all developed models of the solar system based on concentric spheres.

Published in the Almagest, this model of celestial spheres surrounding a spherical Earth was reasonably accurate and predictive,[9] and became dominant among educated people in various cultures, spreading from Ancient Greece to Ancient Rome, Christian Europe, the Islamic world, South Asia, and China via inheritance and copying of texts, conquest, trade, and missionaries.

[9] Various astronomers, especially those who had access to more precise [citation needed] observations, were skeptical of the geocentric model and proposed alternatives, including the heliocentric theory where the planets and the Earth orbit the Sun.

German natural philosopher Johannes Kepler at first worked to combine Copernican system with Platonic solids in line with his interpretation of Christianity and an ancient musical resonance theory known as Musica universalis.

For example, with the Age of Discovery already well underway, astronomical thought in America was based on the older Greek theories,[11] but newer western European ideas began to appear in writings by 1659.

Italian polymath Galileo Galilei was an early user and made prolific discoveries, including the phases of Venus, which definitively disproved the arrangement of spheres in the Ptolemaic system.

[19] English astronomer and mathematician Isaac Newton, incidentally building on recent scientific inquiries into the speed at which objects fall, was inspired by claims by rival Robert Hooke of a proof of Kepler's laws.

Spectroscopy is a method that permits to study materials by means of the light they emit,[28] developed around 1835–1860 by Charles Wheatstone,[29] Léon Foucault,[30] Anders Jonas Ångström[31] and others.

[33] In 1868 Jules Janssen and Norman Lockyer discovered a new element in the Sun unknown on Earth, helium, which currently comprises 23.8% of the mass in the solar photosphere.

In ancient times, there was a common belief in the so-called "sphere of fixed stars", a giant dome-like structure or firmament centered on Earth which acted as the confinement of the whole universe, its edge, rotating daily around.

But by the European Renaissance, the possibility that such a huge sphere could complete a single revolution of 360° around the Earth in only 24 hours was deemed improbable,[35] and this point was one of the arguments of Nicholas Copernicus for leaving behind the centuries-old geocentric model.

When Galileo Galilei examined the skies and constellations through a telescope, he concluded that the "fixed stars" which had been studied and mapped were only a tiny portion of the massive universe that lay beyond the reach of the naked eye.

[40] By then it had been stablished beyond doubt that planets are other worlds, then the stars would be other distant suns, so the whole Solar System is actually only a small part of an immensely large universe, and definitively something distinct.

First, by 1835–1838, Thomas Henderson[41] and Friedrich Bessel[42] successfully measured two stellar parallax, an apparent shift in the position of a nearby star created by Earth's motion around the Sun.

This was not only a direct, experimental proof of heliocentrism (James Bradley already did it in 1729 when he discovered the cause of the aberration of starlight is the Earth's motion around the Sun),[43] but also accurately revealed, for the first time, the vast distance between the Solar System and the closest stars.

[46][47] Teams by Mike Brown, Chad Trujillo and David Rabinowitz discovered the trans-Neptunian objects (TNO) Quaoar in 2002,[48] Sedna in 2003,[49] Orcus and Haumea in 2004[50][51] and Makemake in 2005,[52] part of the most notable KBOs, some now regarded as dwarf planets.

Radar can also accurately measure the position and track the movement of such bodies, specially when they are small, as comets and asteroids, as well as to determine distances between objects in the Solar System.

All planets in the Solar System, plus their major moons along some asteroids and comets, have now been visited to varying degrees by spacecraft launched from Earth.

The first artificial object sent into space was the Soviet satellite Sputnik 1, launched on 4 October 1957, which successfully orbited Earth until 4 January the following year.

[needs update] In 1966, the Moon became the first Solar System body beyond Earth to be orbited by an artificial satellite (Luna 10), followed by Mars in 1971 (Mariner 9), Venus in 1975 (Venera 9), Jupiter in 1995 (Galileo), the asteroid Eros in 2000 (NEAR Shoemaker), Saturn in 2004 (Cassini–Huygens), and Mercury and Vesta in 2011 (MESSENGER and Dawn respectively).

[70] The Galileo orbiter also dropped a probe into Jupiter's atmosphere in 1995, this was intended to descend as far as possible into the gas giant before being destroyed by heat and pressure.

In 2022, the DART impactor crashed into Dimorphos, the minor-planet moon of the asteroid Didymos, with the explicit purpose of intentionally deviate (slightly) the orbit of a Solar System body for the first time ever, which it accomplished.

Other extraterrestrial materials came to Earth naturally, as meteorites, or became stuck to artificial satellites; they are specimens which also allows studying Solar System matter.

The first human being to reach space (defined as an altitude of over 100 km) and to orbit Earth was Yuri Gagarin, a Soviet cosmonaut who was launched in Vostok 1 on April 12, 1961.

In 2004, U.S. President George W. Bush announced the Vision for Space Exploration, which called for a replacement for the aging Shuttle, a return to the Moon and, ultimately, a crewed mission to Mars.