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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.”

Table of Contents

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.

Jupiter Icy Moons Explorer (JUICE)

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


1st human-made object to reach the Moon.

Luna 3 (USSR)

Oct 4, 1959

Oct 7, 1959


Captured the first photographs of the far side of the Moon.

Ranger 7 (NASA)

Jul 28, 1964

Jul 31, 1964


Captured high-resolution images of lunar surface before impact.

Luna 9 (USSR)

Jan 31, 1966

Feb 3, 1966


1st successful soft landing on the Moon. Transmitted panoramic images of the lunar surface.

Surveyor 1 (NASA)

May 30, 1966

Jan 7, 1967


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


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



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



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.

Buzz Aldrin moonwalking

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


Mission Dates

Mission Type

Mission Goals/Achievements

Venera program (Soviet Union)




Series of 16 missions to study Venus’ atmosphere, surface conditions, and geological features

Mariner 2 (NASA)


Launch: Aug 27, 1962


1st successful mission to reach another planet (Venus)

Mariner 10 (NASA)


Launch: Nov 3, 1973


1st mission to visit Mercury


End: Mar 24, 1975


Conducted three flybys of Mercury



Launch: Aug 3, 2004


1st mission to orbit Mercury


End: Apr 30, 2015


Detailed mapping and study of Mercury’s surface, composition, magnetic field, and exosphere

Magellan (NASA)


Launch: May 4, 1989


Mapped about 98% of Venus’ surface using radar


End: Oct 13, 1994


Provided detailed images and elevation data of Venus’ surface

Venus Express (ESA)


Launch: Nov 9, 2005


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)


Launch: May 20, 2010


A.k.a. the Venus Climate Orbiter


Arrival: Dec 7, 2015


Studies Venus’ atmospheric dynamics, cloud structure, and meteorology

BepiColombo (ESA/JAXA)


Launch: Oct 20, 2018


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


Launch: Nov 28, 1964


1st successful flyby of Mars


End: Dec 21, 1967


Obtained the first close-up images of Mars

Viking 1


Launch: Aug 20, 1975


1st successful landing on Mars 


End: Nov 13, 1982


Conducted experiments to search for signs of life

Mars Global Surveyor


Launch: Nov 7, 1996


Mapped the entire surface of Mars in high resolution


End: Nov 2, 2006


Studied Martian atmosphere, climate, and geology



Launch: Jun 10, 2003


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



Launch: Jul 7, 2003


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


Launch: Aug 12, 2005


Studied Martian surface, atmosphere, and climate




Detected underground ice deposits and served as a communications relay for other Mars missions



Launch: Aug 4, 2007


Confirmed the presence of water ice near the Martian pole


End: Nov 2, 2008


Analyzed Martian soil and investigated the potential habitability of Mars



Launch: Nov 26, 2011


Investigated Martian climate, geology, and potential habitability




Discovered evidence of past habitable environments and collected data on Mars’ geological history and potential for ancient life



Launch: Jul 30, 2020


Designed to explore the Jezero Crater, search for signs of past microbial life, collect samples for future return to Earth, and demonstrate new technologies




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.

Curiosity Rover

Solar missions

Mission Name and Agency

Mission Dates

Mission Type

Mission Goals/Achievements

Ulysses (ESA/NASA)

Launch: Oct 6, 1990


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


Studies the corona and the processes that heat the solar atmosphere and accelerate the solar wind




Gather data on solar wind, magnetic fields, and energetic particles near the Sun

Solar Orbiter (ESA/NASA)

Launch: Feb 9, 2020


Investigates the Sun and its heliosphere, study solar wind, magnetic fields, and solar energetic particles




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.

Mercury in front of the Sun

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


Mission Dates

Mission Type

Mission Goals/Achievements

Pioneer 10 (NASA)

Jupiter, Asteroid Belt

Launch: Mar 2, 1972


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


Conducted flybys of Jupiter and Saturn, capturing detailed images and data of their atmospheres, moons, and rings




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


Flybys of Jupiter, Saturn, Uranus, and Neptune, providing unprecedented images and data




Explored outer regions of the Solar System and provided valuable scientific insights

Galileo (NASA)


Launch: Oct 18, 1989


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


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


Flybys of Jupiter and Pluto, capturing detailed images and data of atmospheres and surfaces




Continues to explore the outer regions of the Solar System, and Kuiper Belt

Juno (NASA)


Launch: Aug 5, 2011


Investigated Jupiter’s composition, gravity, magnetic field, and atmospheric conditions




Examined Jupiter’s internal structure and provided insights into its formation and evolution

Juice (ESA)

Jupiter, Ganymede, Callisto, and Europa

Launch: April 14th, 2023


Will investigate Jupiter and its three largest icy moons, focusing on Ganymede and Europa’s potential habitability




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


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)


Proposed Mission: No earlier than 2031


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?

space probe reaching jupiter


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 H.

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 and authors self-help and children’s books.

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