The Last Frontier: How much of space have we explored so far?
Last Updated: August 29, 2023
Since the dawn of time, humans have gazed at the heavens, their curiosity piqued by the vast expanse of space. This fascination took a decisive turn in the 1950s, when we started propelling objects beyond Earth’s atmosphere to probe the universe more closely.
But even as we inch further into the cosmos, the question remains – how much of this infinite frontier have we truly explored by 2023? Join us as we journey through the annals of space exploration, charting the scope of our celestial explorations within this vast cosmic neighborhood.”
Let's start with the beginning
Since the times of Galileo, we’ve been observing planets and other astronomical objects with telescopes, expanding the limited view that our eyes provide. And we’ve continued doing so, building bigger and better telescopes, including ones that can detect wavelengths that our eyes can’t, opening the doors to new insights.
However, launching off Earth and actually going somewhere in space is quite the engineering feat and it took us years to reliably send objects and then humans into space using rockets. Many of our instruments are in orbit around Earth at various levels, with telescopes and other observatories and instruments that are constantly being used by scientists to further research.
In addition, since November 2000, we’ve held continuous human occupation of the International Space Station (ISS) almost 250 miles (400 km) above the surface. We’ve also been tracking Near Earth Objects such as Near Earth Asteroids, better understanding potential risks close by.
But let’s focus on missions beyond Earth.
Lunar missions
There have been over 30 at least partially successful missions to the moon including both manned and probe missions as well as dozens of unsuccessful ones, especially from the 1950s and 60s when we were just starting and in the middle of the space race. As our closest body in space, it has been a popular target for space exploration and study.
Below is a table of the manned missions to the moon as of May 2023.
Mission Name and Space Agency | Mission Launch Date | Lunar Arrival Date | Mission End Date | Mission Goals/ Accomplishments |
Apollo 11 (NASA) | Jul 16, 1969 | Jul 20, 1969 | Jul 24, 1969 | 1st manned mission to land on the Moon. Neil Armstrong and Buzz Aldrin became the first humans to walk on the lunar surface. |
Apollo 12 (NASA) | Nov 14, 1969 | Nov 19, 1969 | Nov 24, 1969 | 2nd manned mission to land on the Moon. Conducted scientific experiments and explored lunar surface. |
Apollo 14 (NASA) | Jan 31, 1971 | Feb 5, 1971 | Feb 9, 1971 | 3rd manned mission to land on the Moon. Conducted experiments, collected lunar samples, and deployed scientific instruments. |
Apollo 15 (NASA) | Jul 26, 1971 | Jul 30, 1971 | Aug 7, 1971 | 4th manned mission to land on the Moon. Conducted extensive scientific experiments, including the use of the Lunar Roving Vehicle (LRV). |
Apollo 16 (NASA) | Apr 16, 1972 | Apr 20, 1972 | Apr 27, 1972 | 5th manned mission to land on the Moon. Conducted geological surveys, collected samples, and deployed scientific instruments. |
Apollo 17 (NASA) | Dec 7, 1972 | Dec 11, 1972 | Dec 19, 1972 | 6th and final manned mission to land on the Moon. Conducted extensive geological surveys, collected samples, and deployed scientific instruments. |
Note: Apollo 13 was deemed a “successful failure” when an oxygen tank blew, causing damage to the other oxygen tank as well as damaged electric and other life support systems. The crew eventually had to escape in the Lunar Module and make their way back to Earth. While the mission was a failure, the crew and NASA learned invaluable lessons in how to get the crew back home safely in the event of a failure.
In addition, below are a few of the notable unmanned missions, ranging from the early days of the space race to the present times. This is not an exhaustive list for which I would recommend NASA’s Moon Missions page and their Solar System Exploration Missions Archive.
Mission Name and Space Agency | Mission Launch Date | Mission End Date | Mission Type | Mission Goals/ Accomplishments |
Luna 2 (USSR) | Sep 12, 1959 | Sep 13, 1959 | Impact | 1st human-made object to reach the Moon. |
Luna 3 (USSR) | Oct 4, 1959 | Oct 7, 1959 | Flyby | Captured the first photographs of the far side of the Moon. |
Ranger 7 (NASA) | Jul 28, 1964 | Jul 31, 1964 | Impact | Captured high-resolution images of lunar surface before impact. |
Luna 9 (USSR) | Jan 31, 1966 | Feb 3, 1966 | Lander | 1st successful soft landing on the Moon. Transmitted panoramic images of the lunar surface. |
Surveyor 1 (NASA) | May 30, 1966 | Jan 7, 1967 | Lander | 1st successful soft landing of a U.S. spacecraft on the Moon. Conducted soil analysis and transmitted images of the lunar surface. |
Lunar Orbiter 1 (NASA) | Aug 10, 1966 | Oct 29, 1966 | Orbiter | Mapped potential landing sites for Apollo missions and captured the first photograph of Earth from the vicinity of the Moon. |
Luna 16 (USSR) | Sep 12, 1970 | Sep 24, 1970 | Lander, Sample Return | Successfully landed on the Moon, collected lunar soil samples, and returned them to Earth. |
Lunar Reconnaissance Orbiter (LRO) (NASA) | Jun 18, 2009 | Ongoing | Orbiter | Currently in orbit around the Moon. Maps the lunar surface, searches for potential landing sites, and studies the Moon’s environment and resources. |
Chang’e 4 (China) | Dec 7, 2018 | Ongoing | Lander/Rover | 1st mission to successfully land on the Moon’s far side. Conducted experiments, explored the lunar surface, and studied the geology of the Von Kármán crater. |
NASA’s ongoing Artemis missions are focusing on sending humans back to the moon for good in preparation for sending humans to Mars. The future missions will include installing a lunar base and a space station in orbit around the moon known as Gateway.
The next few years will be particularly exciting as the first crewed mission to orbit the moon is scheduled for 2024 and the first landing is scheduled for 2025.
Inner solar system missions
We’ve also sent missions to the inner solar system to better understand the area within our orbit around the Sun. There have been about 14 missions to asteroids and comets in the solar system depending on how you classify them since some visited more than one asteroid/ comet or even another body of the solar system as well.
Here we are going to focus on the planets and the Sun.
Mercury & Venus missions
The two planets between us and the Sun have fascinated us since ancient times and we used the early space race and decades after to explore both Mercury and Venus.
Below are the past missions to the two inner planets.
Mission Name | Destination | Mission Dates | Mission Type | Mission Goals/Achievements |
Venera program (Soviet Union) | Venus | 1961-1983 | Various | Series of 16 missions to study Venus’ atmosphere, surface conditions, and geological features |
Mariner 2 (NASA) | Venus | Launch: Aug 27, 1962 | Flyby | 1st successful mission to reach another planet (Venus) |
Mariner 10 (NASA) | Mercury | Launch: Nov 3, 1973 | Flyby | 1st mission to visit Mercury |
End: Mar 24, 1975 | Conducted three flybys of Mercury | |||
MESSENGER (NASA) | Mercury | Launch: Aug 3, 2004 | Orbiter | 1st mission to orbit Mercury |
End: Apr 30, 2015 | Detailed mapping and study of Mercury’s surface, composition, magnetic field, and exosphere | |||
Magellan (NASA) | Venus | Launch: May 4, 1989 | Orbiter | Mapped about 98% of Venus’ surface using radar |
End: Oct 13, 1994 | Provided detailed images and elevation data of Venus’ surface | |||
Venus Express (ESA) | Venus | Launch: Nov 9, 2005 | Orbiter | Studied Venus’ atmosphere, climate, and surface conditions |
End: Dec 16, 2014 | Investigated the planet’s dense atmosphere and its interaction with the solar wind | |||
Akatsuki (JAXA) | Venus | Launch: May 20, 2010 | Orbiter | A.k.a. the Venus Climate Orbiter |
Arrival: Dec 7, 2015 | Studies Venus’ atmospheric dynamics, cloud structure, and meteorology | |||
BepiColombo (ESA/JAXA) | Mercury | Launch: Oct 20, 2018 | Orbiter | Will study Mercury’s composition, structure, magnetic field, and exosphere |
Expected Arrival: 2025 |
Due to recent studies and observations that have increased the chance of finding the first sign of life off of Earth in the form of microbes in the atmosphere of Venus, three new missions have been approved for launch in the next decade.
Named after Renaissance artist and scientist Leonardo da Vinci, NASA’s DAVINCI mission (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging) will study the origin, evolution, and present state of our sister planet from both an orbiter and atmospheric probe. It is scheduled to launch in 2029.
The joint ESA-NASA EnVision mission aims to provide a detailed study of the interaction between the planet’s atmosphere, surface/subsurface, and interior, creating a holistic view of its history, activity, and climate. It is scheduled to launch in 2030.
NASA’s VERITAS “Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy” will be an orbiter focused on discovering how the evolution of Earth and Venus differed, leading to their very different present environments as well as providing detailed present-day observations of volcanic activity and searching for water. It is scheduled to launch in 2031.
Mars missions
Mars missions have been particularly popular since Mars is relatively close to Earth and rocky making it the easiest planet in the solar system to send landers and rovers for study. In addition, studies from past visits have shown that Mars likely used to be like Earth with liquid water and possibly even life, which if we can find proof would be the first confirmation of life off Earth.
In total, there have been 15 Mars missions so far. Some of the notable ones include:
Mission Name | Space Agency | Mission Dates | Mission Type | Mission Goals/Achievements |
Mariner 4 | NASA | Launch: Nov 28, 1964 | Flyby | 1st successful flyby of Mars |
End: Dec 21, 1967 | Obtained the first close-up images of Mars | |||
Viking 1 | NASA | Launch: Aug 20, 1975 | Lander/Orbiter | 1st successful landing on Mars |
End: Nov 13, 1982 | Conducted experiments to search for signs of life | |||
Mars Global Surveyor | NASA | Launch: Nov 7, 1996 | Orbiter | Mapped the entire surface of Mars in high resolution |
End: Nov 2, 2006 | Studied Martian atmosphere, climate, and geology | |||
Spirit | NASA | Launch: Jun 10, 2003 | Rover | Explored Martian surface and conducted experiments to search for signs of past water activity |
End: Mar 22, 2010 | Discovered evidence of past water-related environments and volcanic activity | |||
Opportunity | NASA | Launch: Jul 7, 2003 | Rover | Explored Martian surface and investigated the geology and mineralogy of Mars |
End: Feb 13, 2019 | Discovered evidence of past water-related environments and played a crucial role in advancing our understanding of Mars | |||
Mars Reconnaissance Orbiter | NASA | Launch: Aug 12, 2005 | Orbiter | Studied Martian surface, atmosphere, and climate |
Ongoing | Detected underground ice deposits and served as a communications relay for other Mars missions | |||
Phoenix | NASA | Launch: Aug 4, 2007 | Lander | Confirmed the presence of water ice near the Martian pole |
End: Nov 2, 2008 | Analyzed Martian soil and investigated the potential habitability of Mars | |||
Curiosity | NASA | Launch: Nov 26, 2011 | Rover | Investigated Martian climate, geology, and potential habitability |
Ongoing | Discovered evidence of past habitable environments and collected data on Mars’ geological history and potential for ancient life | |||
Perseverance | NASA | Launch: Jul 30, 2020 | Rover | Designed to explore the Jezero Crater, search for signs of past microbial life, collect samples for future return to Earth, and demonstrate new technologies |
Ongoing | Conducted detailed investigations of geology, climate, and astrobiology, and carried out the first-ever powered flight on another planet |
Mars has also long been considered as an eventual second home to humans and NASA has plans to send the first humans to Mars by the 2040s.
Solar missions
Mission Name and Agency | Mission Dates | Mission Type | Mission Goals/Achievements |
Ulysses (ESA/NASA) | Launch: Oct 6, 1990 | Flyby | Explored polar regions, studying solar wind, magnetic fields, and cosmic rays |
End: Jun 30, 2009 | Provided valuable insights into the heliosphere, discovering unexpected phenomena such as high-speed streams of solar wind from coronal holes | ||
Parker Solar Probe (NASA) | Launch: Aug 12, 2018 | Flyby | Studies the corona and the processes that heat the solar atmosphere and accelerate the solar wind |
Ongoing | Gather data on solar wind, magnetic fields, and energetic particles near the Sun | ||
Solar Orbiter (ESA/NASA) | Launch: Feb 9, 2020 | Orbiter | Investigates the Sun and its heliosphere, study solar wind, magnetic fields, and solar energetic particles |
Ongoing | Close-up, high-resolution images of the Sun’s surface and observe its polar regions |
While the below missions did not go to the Sun, they are worth noting as they are observatories dedicated to studying the Sun:
Solar Dynamics Observatory (SDO) – Launched by NASA on February 11, 2010, it was designed to study the Sun and its magnetic field, observing its atmosphere, solar flares, and coronal mass ejections in high-definition detail.
Solar and Heliospheric Observatory (SOHO) – A joint mission between NASA and ESA, the SOHO was launched on December 2, 1995. It is an ongoing mission that studies the Sun from its deep core to the outer corona and the solar wind.
Outer solar system/ deep space missions
Traveling to the outer solar system and beyond takes an enormous amount of time and increases the chance of something happening to the spacecraft along the way, meaning there have been fewer missions to the outer solar system and beyond.
Here are the past, current, and upcoming missions.
Mission Name and Agency | Destination | Mission Dates | Mission Type | Mission Goals/Achievements |
Pioneer 10 (NASA) | Jupiter, Asteroid Belt | Launch: Mar 2, 1972 | Flyby | 1st spacecraft to achieve escape velocity from the Solar System |
End: Mar 31, 1997 | 1st flyby of Jupiter and provided valuable data on its environment and magnetic field | |||
Voyager 1 (NASA) | Jupiter, Saturn | Launch: Sep 5, 1977 | Flyby | Conducted flybys of Jupiter and Saturn, capturing detailed images and data of their atmospheres, moons, and rings |
Ongoing | Reached interstellar space in 2012, becoming the first human-made object to do so | |||
Voyager 2 (NASA) | Jupiter, Saturn, Uranus, Neptune | Launch: Aug 20, 1977 | Flyby | Flybys of Jupiter, Saturn, Uranus, and Neptune, providing unprecedented images and data |
Ongoing | Explored outer regions of the Solar System and provided valuable scientific insights | |||
Galileo (NASA) | Jupiter | Launch: Oct 18, 1989 | Orbiter | Studied Jupiter’s atmosphere, magnetic field, and moons, including the first direct observation of a comet colliding with a planet (Comet Shoemaker-Levy 9) |
End: Sep 21, 2003 | Gathered crucial data on the Galilean moons (Io, Europa, Ganymede, and Callisto) | |||
Cassini-Huygens (NASA/ESA/ASI) | Saturn, Titan | Launch: Oct 15, 1997 | Orbiter | Studied Saturn’s atmosphere, rings, and moons in detail |
End: Sep 15, 2017 | The Huygens probe successfully landed on Titan providing insights into its atmosphere and surface | |||
New Horizons (NASA) | Jupiter, Pluto, Kuiper Belt | Launch: Jan 19, 2006 | Flyby | Flybys of Jupiter and Pluto, capturing detailed images and data of atmospheres and surfaces |
Ongoing | Continues to explore the outer regions of the Solar System, and Kuiper Belt | |||
Juno (NASA) | Jupiter | Launch: Aug 5, 2011 | Orbiter | Investigated Jupiter’s composition, gravity, magnetic field, and atmospheric conditions |
Ongoing | Examined Jupiter’s internal structure and provided insights into its formation and evolution | |||
Juice (ESA) | Jupiter, Ganymede, Callisto, and Europa | Launch: April 14th, 2023 | Orbiter | Will investigate Jupiter and its three largest icy moons, focusing on Ganymede and Europa’s potential habitability |
Ongoing | Will study the moons’ geology, subsurface oceans, magnetic fields, and their interactions with Jupiter’s environment | |||
Europa Clipper (NASA) | Jupiter, Europa | Planned Launch: Oct. 2024 | Orbiter | In-depth investigations of Europa, including its potential habitability and the existence of liquid water beneath its icy crust |
Investigations of Europa’s geology, ice shell thickness, subsurface ocean properties, and plumes erupting from its surface | ||||
Uranus Orbiter and Probe (NASA and ESA) | Uranus | Proposed Mission: No earlier than 2031 | Orbiter/Probe | Study Uranus, including deploying a probe into its atmosphere to gather data |
Provide comprehensive insights into the planet’s atmosphere, magnetic field, and composition |
The definition of interstellar space depends on what we count as part of our solar system. Outside the Kuiper Belt (the icy asteroid belt that extends from about 30 AU, near the orbit of Neptune, to about 50 AU from the Sun) is typically what we consider as the edge of the solar system, but the Sun still has a gravitational effect through the Oort Cloud, which Voyager 1 won’t cross out of for another 14,000 to 28,000 years.
However, interstellar space is officially defined as past the heliopause, which is where the impact of solar wind greatly diminishes and although it varies, is generally considered to be 120-150AU from the sun.
All in all, we’ve had 5 missions that have either left the solar system (past Neptune or the Kuiper Belt) or are on a trajectory to do so:
- Pioneer 10: We received its last signal on January 23, 2003 from a distance of 7.6 billion miles (12.23 billion km). It continues traveling at 230 million miles (370 million km) a year in the direction of the red giant Aldebaran in the constellation Taurus, making it approximately 132 AU away.
- Pioneer 11: We received its last engineering data in November 1995. In late May 2023, it is about 109 AU away.
- Voyager 1: In August 2012, Voyager 1 entered interstellar space, making it the first human-made object to travel so far into space. As of late May 2023, it is 14.8 billion miles (23.81 billion km or 159.2 AU) away.
- Voyager 2: In December 2018 Voyager 2 entered interstellar space and even successfully fired its trajectory correction maneuver thrusters in July 2019. As of late May 2023, it is 12.35 billion miles (19.88 billion km or 132.9 AU) away.
- New Horizons: still within the solar system as it is studying objects in Kuiper Belt as well as assisting in various solar system studies as well as observations for NASA’s Heliophysics and Astrophysics Divisions. It is deep in the Kuiper Belt, speeding away from the Earth and Sun at a rate of about 300 million miles per year with its current location as of late May 2023 at 55.37 AU from Earth.
While not a probe out in deep space, the Interstellar Boundary Explorer (IBEX) is a small satellite the size of a bus tire observing the solar system boundary from orbit around Earth. Instead of collecting light, its instruments collect particles called energetic neutral atoms (ENAs)—high-energy particles produced at the very edge of the heliosphere, the heliopause which travel all the way back to Earth. IBEX has already created the first all-sky map of the heliosphere, helping us better understand the boundary of our solar system.
Although historically, interstellar missions have been deprioritized over exploration of the solar system, that has changed recently. NASA’s Interstellar Probe proposal would be designed as a successor to the Voyager missions and launch in the 2030s to reach the heliopause in 15 years and eventually travel a distance of more than 300 astronomical units (AU) within 50 years, potentially extending to 1,000 AU in nearly 150 years.
The Chinese National Space Administration’s Interstellar Express would first study targets such as Jupiter, Neptune, and Kuiper Belt objects before heading on to the heliopause and interstellar space. Press regarding the Interstellar Express mission proposed a launch date as early as 2024, but the most recent was only published in 2022 so it is unclear on if that mission is still scheduled for launch next year. Both missions would focus on providing consistent scientific data and observations throughout the journey in interstellar space, with particular attention to the heliopause.
Private companies have also been focusing on interstellar space such as the Breakthrough Starshot Initiative’s solar sail research with an ultimate goal of sending a tiny probe the size of a microchip to the nearest star, Proxima Centauri, 4 light-years away.
Instead of taking 50,000 to 80,000 years like our current space technology, the solar sail could make it in 20. However, this technology is still in its nascent stages (primarily still a concept with simulations and tests on the materials in very small sizes) and likely won’t be setting sail any time soon.
In general, we still struggle with the viability of interstellar space travel, especially if the mission will be crewed. Even sending someone out to Jupiter or Saturn will take 8-12 years one-way. Even sending probes out that far creates continuous worry about anything that could go wrong on the long voyage, potentially jeopardizing the mission.
If we send the spacecraft into hibernation to conserve power, we go months and even years with limited data. Interstellar space travel also comes under fire when we consider the rapid expansion of the universe and the fact that 94% of the universe’s galaxies are permanently beyond our reach. Will even travel to our nearest stars be continually out of reach for humans of the next several generations?
Conclusion
So how much of it have we explored? It’s hard to put a number on it, but we have explored each of the planets (plus dwarf planets Pluto and Ceres) at close range as well as numerous asteroids and comets. Many planets have been the target of multiple missions.
In the past 70 years, we have made great leaps in our exploration of space through probes and manned missions in addition to observatories. While we have focused more on probes for space exploration beyond Earth orbit, that is changing as we are planning to send humans back to the moon’s surface in the next two years and then on to Mars by the 2040s.
It’s an exciting time for space exploration and while we have still studied so little of it in close proximity, our knowledge is continuing to grow and our innovation is continually bringing these locations a little closer.
Sarah Hoffschwelle is a freelance writer who covers a combination of topics including astronomy, general science and STEM, self-development, art, and societal commentary. In the past, Sarah worked in educational nonprofits providing free-choice learning experiences for audiences ages 2-99. As a lifelong space nerd, she loves sharing the universe with others through her words. She currently writes on Medium at https://medium.com/@sarah-marie and authors self-help and children’s books.
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