History of Discovery in Our Solar System Quiz

The hypothesis that the Earth revolves around the Sun had been proposed in the 3rd century BC by Aristarchus of Samos, based on a concept by Philolaus of Croton (c. 470 - 385 BC). However, this received little attention in medieval Europe due to the loss of scientific works of the Hellenistic period.

The hypothesis of the geocentric model of the solar system, developed by Ptolemy (100 - 170 CE), served as the basis for astronomical science for 1,500 years. It was ultimately superseded by the correct heliocentric model.

In the early 16th century CE, Nicolaus Copernicus developed a mathematical model of a heliocentric solar system. He developed his theory in 1510 CE, but only presented it in 1543 CE in his book "De revolutionibus orbium coelestium". He resisted publishing his theories because he didn't want to risk the scorn of the establishment, which had been following Ptolemy's geocentric model for centuries.

Nearly a century later, Galileo was convicted of heresy for "following the position of Copernicus, which is contrary to the true sense and authority of Holy Scripture", as charged by the Inquisition's sentence of June 22, 1633. He was placed under house arrest for the rest of his life, which was the next 9 years.

The first record of a telescope was a Dutch patent submitted by Middleburg spectacle maker Hans Lipperhey for a refracting telescope, in 1608. Galileo heard about it and built his own version, using it to make his own telescopic observations of the heavens.

Uranus is visible to the naked eye, but is very dim. Therefore, it was not classified as a planet until 1781, when it was observed by William Herschel. It was not named "Uranus" until seven decades later. It has only been visited by one Earth probe -- Voyager 2 -- which was utilizing a rare periodic alignment of the outer planets to use gravity-assisted accelerations to direct it to Uranus and Neptune after it visited Jupiter and Saturn.

Neptune is not visible to the naked eye. It is the only current planet not initially observed by direct empirical observation. Instead, changes in the orbit of Uranus led Alexis Bouvard to hypothesize that an as-of-then undiscovered planet was perturbing Uranus's orbit.

Neptune is more massive than Uranus, but smaller. Its orbital period is 164.8 Earth years, meaning that it has just barely completed one full orbit since its discovery. It won't complete a second until the mid 2170s.

The moons were named from characters in Book XV of the "Iliad", where Ares (the Greek counterpart of the Roman god of war, Mars) summons Dread (Deimos) and Fear (Phobos).

Asaph Hall III discovered both moons within a week in August 1877 at the US Naval Observatory in Washington, DC. He had been actively searching for Martian moons.

Both moons are very small and irregular compared to other planetary moons, at maximum diameters of 16 miles and 10 miles (Phobos and Deimos respectively). This gives rise to the hypothesis that they are captured asteroids from the neighboring asteroid belt between Mars and Jupiter.

Pluto was discovered on February 18, 1930 by Clyde Tombaugh. Though it was discovered by perceived orbital irregularities in Uranus's orbit, its eventual mass was found to be too small to have affected Uranus as calculated. So its discovery is now considered as by chance.

Though it was initially classified as a planet, its orbital eccentricity led to the classification of Pluto as a "dwarf planet". Other celestial objects have also been called planets only to be reclassified, so Pluto is not being "picked on" by being demoted.

Its orbital path brings it within the orbit of Neptune. So when it was still considered a planet, it became the 8th planet and Neptune the 9th.

Sputnik 1 was launched into low Earth orbit by the Soviet Union on October 4, 1957. It sent a radio signal for three weeks until its batteries were depleted. It fell out of orbit on January 4, 1958, after completing 1,440 orbits and traveling approximately 70 million kilometers.

Its launch began the infamous "space race" between the USSR and USA, which was arguably won when the US landed humans on the Moon in July 1969.

The Apollo Program was the US's successful attempt to land humans on the Moon. Apollo 11 was the first of these missions to place men on the moon; subsequent missions also landed, with extended scientific experiments and exploration.

Apollo missions were planned up to Apollo 20. However, Apollo 20 was cancelled to allow resources to be diverted to allow Skylab to launch. Then missions 18 and 19 were canceled after the Apollo 13 incident and further budget cuts.

Pioneer 11 (or Pioneer G) is a robotic space probe whose mission was to study the asteroid belt between Mars and Jupiter, Jupiter itself, Saturn, the solar wind, and cosmic rays. It was the first probe to encounter Saturn. It is also one of five artificial objects so far to leave the solar system, the others being Pioneer 10, Voyagers 1 & 2, and the New Horizons.

Voyager 2 is a space probe launched on August 20, 1977. Its mission was to explore Jupiter and Saturn, and to possibly encounter the ice giant planets Uranus and Neptune, which it did. It's the third spacecraft to leave the solar system.

Even though it was launched before Voyager 1, it was designated "2" because Voyager 1's path would accelerate it to pass Voyager 2 before either reached Jupiter. As a matter of fact, Voyager 2 came closest to Jupiter on July 9, 1979, while its sister Voyager 1 had its closest approach four months earlier.

Voyager 1, launched September 5, 1977, was launched two weeks after its sister Voyager 2. It was designated "1" because its path would accelerate it so that it would encounter Jupiter before Voyager 2; it did so by four months, on March 5, 1979.

Its mission was to explore Jupiter, Saturn, and either Pluto or Saturn's moon Titan. It was decided to have it explore Titan, as the moon had a substantial atmosphere.

Voyager 1 became the first artificial object to leave the solar system. It passed the previous probes Pioneer 10 & 11, even though the Pioneers were launched earlier.

In 2017, NASA successfully fired the probe's trajectory correction maneuver, enabling the probe to extend its mission by two to three years. It's expected to return scientific data until 2025, with a maximum lifespan going to 2030.

Voyager 2 is the only space probe to explore both Uranus and Neptune. It came within 81,500 kilometers of Uranus's cloudtops on January 24, 1986. Three years later, it came within 5,000 kilometers of Neptune.

Its initial mission was to explore Jupiter and Saturn (like its sister Voyager 1 had). As a backup, it was either going to explore the Saturnian moon Titan (if Voyager 1 couldn't) or continue on with gravity assist to explore the ice giants Uranus and Neptune. It did the latter, and has been the only probe to explore these planets.

Though not the first space telescope, Hubble, launched April 24, 1990, is one of the largest and most versatile. It was funded and built in the 1970s by NASA. It was initially intended to be launched in 1983, but technical issues, budgetary issues, and the Challenger disaster in January 1986 delayed its deployment.

After its 1990 launch, it was discovered that its main mirror had been ground incorrectly, resulting in an aberration that limited Hubble's capabilities. In 1993, a shuttle servicing mission corrected the issue, and it began its service.

After its various repairs, Hubble is expected to remain in service until the 2030s.

The definition of "planet" has changed quite a bit through history. In antiquity, any celestial object that didn't remain static in relation to the stars was termed a wandering star, or asteres planetai. This included the five naked-eye-visible modern planets (Mercury, Venus, Mars, Jupiter, and Saturn), the Moon, and the Sun.

With the heliocentric model becoming the accepted model of the solar system, the Moon and Sun were recognized for their difference and no longer called planets. Two other planets (Uranus and Neptune) were located after the invention of the telescope. Additionally, in 1801, Ceres was seen in the orbital space between Mars and Jupiter. It was initially called a planet, but then other objects (Pallas and Vesta) were discovered in this same region. Herschel, the discoverer of Uranus, suggested that these new objects have a separate classification of asteroids.

In the 21st century, more celestial objects were found in the region occupied by Pluto and named Quaoar, Sedna, and Eris. These were grouped with Pluto and given the designation trans-Neptunian object (TNO). This was applied to Pluto even though its eccentric orbit brings it within Neptune's orbit for a short time in its orbit. The discovery of Eris forced the International Astronomical Union (IAU) to create a new definition of "planet", as well as come up with a designation for TNOs that were not simple comets. This designation is "dwarf planet".

Voyager 1 crossed the heliopause and entered interstellar space on August 25, 2012, becoming the first space probe to do this.

New Horizons, launched January 19, 2006, was given a mission to explore Pluto and possibly Kuiper Belt Objects (KBOs). Using a gravity assist from Jupiter, it was then put into hibernation until its approach of Pluto. It was awakened in December 2014, and in January 2015 it began its approach to Pluto.

On July 14, 2015, it flew 12,500 kilometers above the surface of Pluto. After leaving the Plutonian system, it maneuvered for a flyby of KBO 486958 Arrokoth. Arrokoth is a primitive object, only 36 kilometers long, made of two smaller objects that are 21 and 15 kilometers.

Voyager 2 crossed the heliopause and entered interstellar space November 5, 2018.

The James Webb Space Telescope (JWST) is designed to conduct infrared astronomy. It was launched on December 25, 2021. Instead of being in low Earth orbit like Hubble, JWST is settled in the L2 Lagrange point, where it maintains basically a slightly greater orbital radius of the Sun. Gravitational attraction with the Earth keeps it from going too fast or slow.