Planetary science

Exploring the Solar System

Planetary Science


Mercury is the smallest and closest planet to the Sun in the Solar System. Its orbit around the Sun takes 87.97 Earth days, BepiColombo is looping inward to arrive in 2025. Messenger mapped the planet and crashed in 2015. Mariner 10 was first to reach Mercury, in 1974.


Akatsuki studies slow-spinning Venus, and launched with the IKAROS solar sail. Venus Express probed the Venusian atmosphere. Magellan mapped the planet and plunged through its clouds. Vega 1 and Vega 2 dropped landers before moving on to Halley’s comet. Pioneer Venus 1 dropped probes in 1978. Mariner 10 flew by in 1974. Venera 7 was first to land softly. More Venera spacecraft followed in the 70s and early 80s


The International Space Station presides over more than 2,600 smaller satellites in Earth orbit. Hubble just turned 30. Chandra watches stars explode in bursts of X-rays. TESS hunts for planets and orbits in resonance with the moon.Our amazing planet has been around for quite some time. ... Like all the planets, Earth orbits (travels around) around the sun. ... Have you ever wondered why we have different seasons? ... Not only does Earth zoom through space, it also spins on its axis.


Chandrayaan-2 studies the lunar surface. Its Vikram lander crashed near the moon’s south pole in 2019. Chang’e-4 was first to land softly on the moon’s far side, and released the Yutu-2 rover. It communicates with Earth through the Queqiao relay satellite. Chang’e 5-T1 passed the moon and sent a test capsule back to Earth. Chang’e-3 landed with the Yutu rover. Lunar Reconnaissance Orbiter maps the surface and spotted the Apollo landers. The twin ARTEMIS spacecraft study Earth’s magnetosphere. Beresheet crashed while landing in 2019. LADEE studied moon dust and crashed on the far side. Ebb and Flow mapped lunar gravity. Chang’e-1 mapped the moon. Chang’e-2 orbited and then left for the L2 Lagrangian point. LCROSS dove into the plume from a crashed Centaur rocket. Chandrayaan-1 found water. SMART-1 tested ion propulsion. Lunar Prospector searched for polar ice. Clementine tested equipment and cameras. Hiten counted dust and crashed in 1993. Selene followed to study the evolution of the moon. Luna 24 was the last of many successful Luna missions. It returned a sample to Earth in 1976. Explorer 49 was the last American mission to the moon for two decades, until Clementine in 1994.


InSight landed in 2018 and listens for marsquakes. The ExoMars Trace Gas Orbiter sniffs for methane and released the doomed Schiaparelli lander. MAVEN studies the history of Mars. Mars Orbiter Mission, also called MOM or Mangalyaan, is India’s first mission to another planet. Curiosity roves Gale Crater, an ancient Martian lake. Mars Reconnaissance Orbiter studies and photographs the Martian surface. Mars Express released the silent Beagle 2 lander, which was only located in 2015. Mars Odyssey maps water and ice on Mars. Phoenix landed in the Martian arctic. Opportunity rover died in 2019. Spirit rover became trapped in sand after roaming Mars for six years. Mars Pathfinder landed and released Sojourner, the first rover on another planet. Mars Global Surveyor mapped the planet. Viking 1 and Viking 2 dropped landers in 1976. Mariner 9 was the first craft to orbit another planet. Mariner 4 was first to pass Mars.


Juno spins in constant sunlight to study Jupiter. Galileo was first to orbit and crashed in 2003. Ulysses, Cassini and New Horizons passed Jupiter on their way to other destinations. Pioneer 10 was first to reach Jupiter in 1973, followed by Pioneer 11 in 1974 and Voyager 1 and Voyager 2 in 1979.


Cassini took stunning images of Saturn and its moons, dropped the Huygens lander on Titan and finally dove inside the rings and vanished. Pioneer 11 was first to pass Saturn in 1979, followed by Voyager 1 in 1980 and Voyager 2 in 1981.


The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects. New Horizons glimpsed the dwarf planet’s frozen heart during a flyby in 2015.


Rosetta passed asteroids, followed comet 67P/C-G and bounced and lost the Philae lander on its surface. Deep Impact slammed an impactor into comet Tempel 1 in 2005. Renamed EPOXI, the spacecraft flew on to visit comet Hartley 2. Stardust flew past an asteroid, returned a sample from comet Wild 2 and took a second look at Tempel 1. Deep Space 1 passed asteroid Braille in 1999 and comet Borrelly in 2001. Giotto, Suisei, Sakigake, Vega 1 and Vega 2 converged on Halley’s comet in 1986. ISEE-3 was renamed International Cometary Explorer and was first to visit a comet, in 1985. It zipped past Earth again in 2014.