Scientists continued to make major advancements in 2014, particularly in the area of space exploration.
The advancements ranged from rocket testing to experiments aboard the International Space Station to landing a spaceship on a comet.
Here are five of the major scientific accomplishments of 2014.
1. Orion Launched a Test Mission
NASA sent into orbit, on Dec. 5, its first major launch vehicle since the Apollo program, a major step for sending humans into deep space with destinations such as Mars.
After a weather and technical delay, NASA launched Orion with a new heavy-lift rocket. It tested Orion's launch and high-speed re-entry systems.
Two orbits later, the Orion unmanned spacecraft successfully splashed down in the Pacific Ocean at the end of a mission that lasted about four-and-a-half hours.
2. Pluto Became a Planet Again
The debate renewed in October over the fate of the once-planet Pluto.
Pluto, which was discovered in 1930 by astronomer Clyde Tombaugh, was demoted by the International Astronomical Union (IAU) to dwarf planet status in 2006. The IAU now considers the solar system to consist of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Smithsonian Center for Astrophysics held a debate in September about whether Pluto should be a planet. Voters listened to three scientists who presented various views in a debate and decided that Pluto is indeed a planet.
For the record, the IAU still lists Pluto as a dwarf planet.
3. Astronauts Print First 3-D Object in Space
Astronauts aboard the International Space Station made the first 3-D object in space in November, thanks to a new printer.
NASA and officials with Made In Space Inc., the company that worked with NASA to design, build and test the 3-D printer, said the process may change how the way ISS crews get replacement tools and parts.
The first objects built in space will be returned to Earth in 2015 for detailed analysis to verify that the 3-D printing process works the same in microgravity as it does on Earth, NASA said.
4. Researchers Find Five Previously Undetected Greenhouse Gases
Five new man-made greenhouse gases that may play a role in climate change and ozone depletion were discovered during two separate research projects.
Increasing greenhouse gases trap additional heat in the lower atmosphere, which results in higher surface temperatures, AccuWeather.com Senior Meteorologist Brett Anderson said.
The discovery of three chlorofluorocarbons (CFCs) and one hydrochlorofluorocarbon (HCFC) were reported online March 9, 2014, in the journal "Nature Geoscience" by researchers from the United Kingdom, Germany, Australia, France and the Netherlands.
At their current concentrations, the new gases do not pose a major threat to the ozone layer as they are tens to hundreds of times smaller than those of the known seven types of CFCs, which are still around, Johannes C. Laube of the University of East Anglia, Norwich, U.K., said.
A fifth compound, perfluorotributylamine (PFTBA), a perfluoroalkyl amine, was discovered by researchers at the University of Toronto, Memorial University of Newfoundland and the Ford Motor Co.
That finding was published in late November 2013 in the journal "Geophysical Research Letters," a journal of the American Geophysical Union.
5. Philae Comet Landing ‘Named Top Breakthrough of 2014'
Nov. 12 saw the successful landing of a spacecraft on a comet - the first-ever attempt to do so.
The European Space Agency-designed Rosetta spacecraft included special instruments from NASA and landed its 220-pound Philae lander on Comet 67P/Churyumov-Gerasimenko.
"This is the most exciting spacecraft mission since Cassini reached Saturn a decade ago," Slooh Astronomer Bob Berman said.
The landing was more than 10 years in the making as the mission began in March 2004.
Rosetta journeyed through the solar system, using a series of gravity slingshots from Earth and Mars before reaching its final destination, the ESA said.