Pluto is discovered

On Feb. 18, 1930, astronomer Clyde W. Tombaugh discovered Pluto at the Lowell Observatory in Flagstaff, Arizona, U.S. Named after the Roman god of the underworld, Pluto is about 1,400 miles (2,380 kilometers) wide and takes 248 years to complete one revolution of the sun. It's temperature of -378 to -396 degrees Fahrenheit (-228 to -238 degrees Celsius) makes Pluto inhospitable. Considered the ninth planet of the solar system at the time of its discovery, Pluto was reclassified as a dwarf planet in 2006 by the International Astronomical Union because its orbit overlapped with that of Neptune’s.

Plasma shield around the heliosphere

When NASA's space probe Voyager 2 exited the solar system to enter interstellar space, it observed a giant wall of superhot plasma forming a border of what is called the heliosphere. According to scientists, who made the revelation in 2019, the plasma wall separates the solar winds from coming into contact with the interstellar medium. At the same time, the wall, located around 11 billion miles (17.7 billion km) from the sun, protects everything in the solar system from the devastating radiations of the galaxy.

Discovery of the first exoplanet

An exoplanet is a celestial body that orbits a star other than our sun. In 1995, astronomers Michel Mayor and Didier Queloz found a planet orbiting 51 Pegasi – a sun-like star in the constellation Pegasus. Quite similar to Jupiter, the planet was named 51 Pegasi b. Its discovery confirmed that the Earth’s sun is not the only one of its kind with a solar system, and heralded an evolution in astronomical research that led to findings of more exoplanets. In 2019, along with James Peebles for his “theoretical discoveries in physical cosmology,” Mayor and Queloz were awarded the Nobel Prize in Physics for their finding. As of Feb. 12, 2020, astronomers have identified 4,116 exoplanets in 3,056 planetary systems.

Discovery of Ceres

Ceres is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Discovered by Italian astronomer Giuseppe Piazzi in 1801, the celestial body was initially considered a comet and then a planet before the discovery of similar objects found in the belt got it reclassified as an asteroid. In 2006, the International Astronomical Union upgraded Ceres to the category of dwarf planet. In February 2017, NASA's spacecraft Dawn found evidence of organic material on Ceres.

Discovery of Uranus

Uranus was identified in 1781 by German-British astronomer William Herschel. The “ice giant” gets its bluish surface color from tiny frozen ammonia and methane crystals. The atmosphere is believed to be mostly hydrogen and helium. Scientists at the Kuiper Airborne Observatory discovered rings around the planet in 1977 – making Uranus the second planet with such a feature in the solar system. To date, NASA's Voyager 2 probe is the only spacecraft to have visited the planet.

Rings of Saturn 

Galileo Galilei was the first to observe Saturn in 1610 with a telescope. However, he could not describe the rings. In 1659, Dutch astronomer Christiaan Huygens was the first to theorize that the planet was encircled by rings. Composed of billions of particles of ice and rock, the rings are about 175,000 miles (281,635 kilometers) from the planet but relatively thin — a thickness ranging from about 32 feet (10 meters) to 0.60 miles (1 kilometer).