Introduction

In the 63 years since the commencement of the space race, how have advances in space exploration and a myriad of space missions—both successful and unsuccessful—lead us to an understanding of the origins and locations of water outside the realm of this world that we call home? We plan to study space missions throughout history, focusing on their influence and contributions towards the search for water in our solar system. By studying the space missions that have been carried out to date, we are able to identify the influence they have had on the current and future research done by scientists.

Importance of Research

The contributions made by previous missions have led to the continuing development of new technology which has helped researchers make advancements in the discovery of water in the solar system.  Water has become an important theme of exploration for astronomers as a possible and necessary resource of life and a substance with geological interest. The research currently being done also provides information on the existence of water on Earth which is suggested to have come from comets that crashed into the planet. Scientists have also found that in space, Hydrogen and Oxygen exist separately, created from the Big Bang and nuclear reactions in stars, and only meet in the cold climate of space to form water. Space exploration has led us to not only understand water within the context of our solar system but also gave clues that may help in the continued search for water elsewhere.

I. The Origins of Water in our Universe

It is well known that a water molecule is made up of two hydrogen atoms and one oxygen. What is not so well understood is where these elements come from in the first place and how they came together to give water as we now know it. Let us first start with hydrogen. It has become widely accepted that the universe as we know it began with a bang, the Big Bang. That is not to say that one cosmic event gave us the universe as we see it today, but rather that the Big Bang was the starting point for the cosmic timeline. Following the Big Bang, the universe was essentially a very hot, very dark soup of plasma composed of protons, neutrons, and electrons. It wasn’t until about 380 000 years after the big bang that the universe cooled enough to allow electrons to come together with nuclei to form neutral elements, like hydrogen.¹ Still no water. After another 400 million years of development, the stars were born–and with them–carbon-12 which burned to neon, producing oxygen-16. These stars eventually died and over the next 200 million years, this material was shot into our universe.² With this, we have the two things needed for water to form.

With the discovery of the distant quasar APM 08279+5255 and the enormous cloud of water surrounding it, it has been determined that water in our universe has been present in some form or another for at least 12 billion years.³ However, it wasn’t until about 9.3 billion years after the Big Bang that water began to make its way to our blue planet. It is proposed that 9.2 billion years after the Big Bang, our solar system began to build from clouds of recycled star material carrying with them, among other things, complex molecules like water.² Space telescopes like Hubble have looked towards the Helix Nebula and Great Orion Nebula, and found water in their ejected atmospheres, reinforcing the idea that the origins of our oceans are in the stars.⁴ Hubble has since found water elsewhere in our solar system, such as on Jupiter’s moon Europa.⁵ Most recently Hubble has found vast amounts of water vapour in the broader universe in the atmosphere of exoplanet WASP-39b.⁶ With this understanding that water exists in various forms throughout the universe and our solar system, it begs the question of how it made its way to Earth. It is suggested that the water in our oceans was delivered after Earth’s formation. We don’t have a definitive answer for how this occurred yet, but the most widely accepted hypothesis is that water was delivered in the form of ice frozen to asteroids that collided with Earth in its infancy.⁷

II. The First Time that we Found Extraterrestrial Water

On the Moon –

As the closest celestial object to Earth, the Moon has always been an important object of study for scientists. After the early moon landings through the Apollo program, many other space missions like Clementine (USAF/NASA), Lunar Prospector (NASA), SMART-1 (ESA), Kaguya (Japan), Chang’e missions (China), Chandrayaan-1 (India), Lunar Reconnaissance Orbiter (NASA), etc. were launched for further lunar exploration. In 2008, the Indian Space Research Program launched Chandrayaan-1 with the key focus to search for evidence of water on Moon, to understand the origin of the moon from mineral and chemical composition studies, and to detect the presence of atomic species in the thin atmosphere of the Moon. The mission carried technologies from various different international partners such as the USA and Bulgaria. The data found through Chandrayaan-1 shows evidence of water in the exosphere, surface, and sub-surfaces of the Moon. Through the Moon Impact Probe, south polar region of the Moon was found to host volatiles like water. The Moon Mineralogy Mapper (M3) showed the presence of water on the sunlit side using water and ice spectral signatures.⁸ In 2009, NASA crashed a part of the Kaguya Spacecraft into a crater on the south pole region of the Moon and found signatures associated with water ice and hydroxyl, a highly reactive molecule associated with water. In 2010, international scientists looked closely at collected moon rocks and found a mineral called apatite in water.⁹ This allowed scientists to reexamine Apollo samples to look for signs of water-bearing beads found from volcanic deposits.

More recently, water in the form of ice has been found on the Moon’s surface based on data from NASA’s Moon Mineralology Mapper (M3) which identified three signatures that prove the existence of water in the form of ice on the surface of the moon.¹⁰ Additionally, NASA’s Lunar Crater Observation and Sensing Satellite (LCORSS) has collected impact data that hints at the existence of water beneath the surface of the Moon.¹¹

On Mars –

As one of the closest planets to Earth that shows similar characteristics, Mars is being explored further to help scientists better understand our solar system and planet. On July 31st, 2008, NASA’s Phoenix Mars Lander confirmed the presence of water ice on Mars. The space mission was launched to study the history of water in the Martian arctic and search for evidence of a habitable zone. The lander touchdown on Mars’ polar region and observed the Martian ice, soil, and atmosphere by collecting soil samples containing ice. During the mission, Phoenix also documented snow falling from clouds on Mars. A sample of snow containing the mineral, Calcium carbonate, was found, giving scientists important clues about the history of liquid water on Mars. Currently, further exploration is being continued in hopes of finding better evidence to explain the history of Mars and how it became a desert wasteland.¹²

III. What has Guided our Search

As population on Earth soars and science continues to push the envelope, one of the broad themes of space exploration has been to contemplate the idea of the next frontier for humanity to conquer. For example, Mars exploration has rested on four pillars, two being the search for life and preparation for human exploration–both believed to be impossible or unfeasible without liquid water.¹³ On the other hand, some researchers are looking for data to develop and hone theories. Common to both these camps has been the search for water, either to justify its existence here or to guide them in the search for life elsewhere. Regardless of the motive, the mission is daunting. The search for anything in space is analogous to a needle in a haystack, where no matter the size of what you are looking for, the needle is infinitely small in relation to the infinitely large haystack that is space. To guide their search for water, scientists need to start somewhere. They rely on clues provided throughout history, identifying signatures common to much of the water already discovered and broadening their search in hopes that they will come across one.

The first set of signatures fit into the category of visual observations, and missions concerning Mars present perhaps the best collection of these. The easiest of these signs to visualize is the presence of polar ice caps like those found on Mars in the 1700s with early telescopes.¹⁴ With regards to liquid water, the discovery of recurring slope lines by NASA’s Mars Reconnaissance Orbiter in 2011 suggested that in the spring and summer liquid water may seep from the steep faces of some Martian slopes as seen in Figure 6.^{15 16} There is however suggestions that this may be little more than seeping sand due to the fact that the Reconnaissance Orbiter has only been able to spot them on the steepest slopes with inclines steep enough for dry particles to descend.¹⁷ Further research by the Mars Rovers is likely going to be the deciding factor in which hypothesis “holds water”.

The second set of clues guiding the search for water are a bit more intangible. Space telescopes like Hubble look to the cosmos using sophisticated tools like the Cosmic Origins Spectrograph to separate emitted light into its component colours. This allows for a compositional “fingerprint” of the object being observed.¹⁸ This method of observation has been key to the discovery of atmospheric water vapour on exoplanets such as WASP-39b.⁶ These space-based technologies continue to guide scientists through current and future space exploration.

IV. Life Looking for Life

In our search for life, we start by looking at our one and only example, Earth. We look for other places that are similar to our own. This has lead to the idea of the Habitable Zone. The habitable zone is the place for a planet that is not too far and too cold from its local star and is also not too close to be too hot. The habitable zone is defined as the particular zone or range of distance around a star in which we may find liquid water pooling on a planet’s surface.¹⁹ An example of a planet in the habitable zone is the planet Kepler-452b which is 1.6 times larger than Earth and is in the habitable zone of a sun-like star.²⁰

Why do we associate the search for water with the search for life? The reason for this is that when using Earth as an example, we see that “almost everywhere there is water, there is life [, and w]hether the water is boiling hot or frozen, some sort of creature seems to thrive in it.”²¹ We ask the question if it is like that here, are other planets the same?²¹ To the best of our knowledge, water is required for life. Without water, there is no life. It transports materials and molecular machinery to the places in the living organism that are required to allow for the chemical reactions essential for life. Water also carries nutrients and removes any waste. Without it, life as we know it, would quickly die.²²

V. What are we Finding?

Over time, we have continued to find a number of places with water, not all of it is liquid. Notably, the moons of other planets have been found to hold water. Through NASA’s Cassini’s numerous gravity measurements of Saturn’s moon, Titan, it has been shown that beneath its surface was hidden liquid water and ammonia ocean.²³ Just like Titan, Jupiter’s moon Europa has a water-ice surface. It is thought that a 60-150 km deep ocean of salty water lies below a layer of ice that is probably between 15 and 25 kilometers thick. From 1995 to 2003, NASA’s Galileo spacecraft made numerous flybys of Europa while exploring the Jupiter system. In these flybys, it found pit and domes–suggesting that Europa’s surface ice may be slowly turning over due to convection caused by the heat below. Hubble, in 2013, found evidence of water plumes erupting off Europa’s surface as well.²⁴ Using the imaging spectrograph provided by Hubble, faint ultraviolet light was seen in an aurora that Jupiter’s magnetic field powered near Europa’s southern pole.²⁵ This was a sign that there are products of water molecules that are “being broken apart by electrons along magnetic field lines.”²⁵ Later, while using Hubble, scientists observed Europa passing in front of Jupiter. Over a 15 month time, this passing was viewed 10 times. In these 10 times, there were 3 occasions where plumes could be seen erupting from Europa.²⁶

Furthermore, beneath the ice crust of Saturn’s moon, Enceladus is a global ocean according to research using data from NASA’s Cassini mission. Cassini’s data was previously analyzed and the Enceladus was suggested to have a sea or body of water shaped like a lens and beneath Enceladus’ South polar region. Although now, with the gravity data collected during Cassini’s several close passes over the south polar region, it has lead to support the possibility that the sea is global. This was confirmed by results derived from analyzing over seven years of images taken by Cassini. In these images, a tiny wobble called a libration was found as it orbits Saturn. This information was then plugged into different models of how Enceladus’ interior might be arranged.²⁷

VI. Who is Funding this and what is next?

Governments are often times the biggest investors in space exploration missions. Global expenditures have grown over the years in leading countries investing more and more. By 2027, it is estimated that global space budgets will grow over $20 billion. Recently, private sectors such as start-ups to large companies are also increasingly seeking to leverage partnerships with space agencies. Today, transportation is the largest expenditure area reaching nearly $7.7 billion supported by multiple countries to support the development of next-generation crew and cargo vehicles. Moon exploration is said to experience sustained growth and will budget around $2.8 billion by 2027 to support government missions and partnership programs. Mars exploration budgets reach $1.4 billion in 2017 and are expected to reach $1.8 billion.²⁸ Mostly all early planet related exploration missions have been dedicated to Mars. The increase in budgets for all space missions is mainly due to the future missions and technology being developed, like ExoMars Rover and Mars 2020, are set to travel across the Martian surface to search for signs of extraterrestrial life by collecting samples of water ice and soil and analyzing them with next-generation instruments.²⁹

Conclusion

Water has continued to be an important theme of space exploration for astronomers as a possible and necessary resource of life. Through our knowledge of water and how it is composed here on Earth, it can aid scientists in understanding where water may be within the universe.  Throughout space exploration, we have found water in a number of places within the solar system, while not always in liquid form, many of the different forms of water have been ice, leading scientists to believe that it may have been liquid at one point in time. Within the 63 years since the commencement of the space race, there have been numerous advances in space exploration and a myriad space missions, leading us to a greater understanding of the origins and locations of water outside of our home planet, Earth.

 

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