Lunar Trailblazer and the Decadal Survey

NASA is a government agency with thousands of employees, conducting groundbreaking research and carrying out the nation’s priorities in space. To stay focused on furthering the top science priorities, NASA seeks advice from the National Academies of Sciences, Engineering, and Medicine in a decadal survey. Every ten years, the survey broadly engages the scientific community to summarize the discoveries of the last decade and then outlines the planetary science field’s most important scientific questions and needed activities. The 2022 decadal survey covers the scientific goals from 2023 to 2032 and identifies twelve organizing scientific questions that cover everything from looking for extraterrestrial life to understanding the origin story of our solar system.

The Lunar Trailblazer mission will collect data on the form, abundance, and distribution of water on the Earth’s Moon. It will also collect data on the Moon’s surface temperature and the composition of regolith and rocks. These high-resolution measurements from lunar orbit enable Lunar Trailblazer to contribute to answering many of the scientific questions outlined in the Decadal Survey.

Decadal Survey Questions

Water Questions

What role does the space environment play in forming and liberating the volatiles contained within surface-bounded exospheres like that at the Moon and Mercury?

How can an airless body like the Moon have water on the surface, even in the vacuum of space? The Moon’s water cycle is very different from our own here on Earth. There is no liquid water. Instead, water (H2O) can exist as molecules of water trapped in cold traps, as well as water ice in permanently shadowed regions. There is also hydroxyl (OH), which may be bound to silicate minerals and can be trapped in tiny amounts in rock as molten materials solidify. Hydroxyl can also form on the Moon due to the interaction between hydrogen (H) from the solar wind and oxygen (O) from silicate minerals on the Moon’s surface. More information on what we know so far about the forms of water and processes that produce them on the Moon can be found here.

What we don’t know includes how temperature, soil age, and rock type determine how much OH or H2O are present. Does solar wind interact differently with different rock and soil compositions? Do temperature changes trap and release volatiles over the course of a lunar day in cycles? Do micrometeorite impacts remove water or add water? Determining the form, abundance, and distribution of different types of water – Lunar Trailblazer’s primary objective – will give scientists information on how water formed on the Moon and how the space environment influences water cycles. Lunar Trailblazer’s infrared sensors will take measurements of water in different forms at multiple times during the lunar day, thereby providing the most accurate data on the nature of the Moon’s water.

Water availability: what controls the amount of available water on a body over time? What sets initial limits on planetary liquid water and water inventories?

Water is of very high interest for the planetary science community because water is essential for life as we know it and is also a key resource for lunar exploration. Water is what sustains life on our planet, so it is important to know how Earth became water-rich while other planets did not. Learning how the Moon got its water will help us do just that. Lunar Trailblazer measures water trapped in volcanic rocks at the lunar surface, which provides an indirect clue as to how much water might be trapped inside the rocks of the Moon’s mantle. The Moon was originally thought to be “bone-dry” because it formed from rocks melted by a giant impact, but recent data from the Apollo samples showed that the Moon’s mantle contains water.

The Moon’s permanently shadowed regions are so cold that they can keep water stable on the Moon's surface for billions of years. If we study the ancient water that exists in these cold traps, then we can learn more about how the Earth became a water-rich planet. Did lunar water come from comets/asteroids, solar wind, and/or volcanism? How much is there? Are there volatiles other than water trapped also that provide a clue as to the water’s origin? Lunar Trailblazer will provide clues that will help us answer such questions.

How have surface characteristics and compositions of solid bodies been modified by, and recorded, external processes? Where and how do volatile deposition, sublimation, transport, redeposition and loss take place, now and in the past?

The Moon is iconic for its large and abundant impact craters. These impacts were instrumental in delivering, redistributing, and sublimating volatiles (including water) on the Moon’s surface. Some impact craters near the poles may become cold traps due to the sunlight not being able to reach the bottom of these craters. The water that exists at the bottom of these cold traps can be billions of years old. As a result, these craters may serve as a record of past and present bombardment and associated volatiles. This can also lead to insights to where volatiles were delivered from to the Earth-Moon system as a whole, including organics to Earth. Lunar Trailblazer’s infrared sensors will be able to detect the composition of volatiles in the Moon’s permanently shadowed regions, which provide clues on the origin, time of delivery, and distribution of these volatiles. These sensors can evaluate differences in composition of volatiles in the lunar regolith. These differences in composition give insight into how volatiles can be produced.

Credit: NASA/GSFC/Arizona State University
This is an image of the Cabeus Crater that is located in the Moon’s southern pole. The image was taken by the Lunar Reconnaissance Orbiter Camera (LROC). This crater has regions of permanent shadow. These permanently shadowed regions are so cold that they keep water on the Moon’s surface for billions of years.

Composition and History Questions

How have the interiors of solid bodies evolved? What are the chemical and physical consequences of cooling and solidification on solid body crusts?

One aspect of planetary science the 2022 Decadal Survey emphasizes is the origin and history of rocky planetary bodies in our solar system. The current theory of the origin of the Moon is that a Mars-sized body collided with the early Earth, thus launching extremely hot debris into space. The debris first coalesced into a disk and then eventually into a molten sphere of magma that would become the Moon. As the magma cooled, different minerals formed. These minerals either sank or floated depending on their density, forming a layered interior. Some parts of this interior trapped radioactive elements, whose decay provided heat that kept portions molten longer or changed the minerals formed at different depths. After solidification of a primary crust, a secondary crust formed as volcanic eruptions – some relatively quiet and others explosive – shaped the lunar surface. Understanding how the Moon formed and its internal structure will help scientists understand how rocky planets form and evolve in general. The insights we gain from our own solar system might be used as a template to understand other solar systems.

To study the Moon’s internal structure without collecting samples, Lunar Trailblazer’s Lunar Thermal Mapper (LTM) and High-resolution Volatiles and Minerals Moon Mapper (HVM3) will be able to detect minerals and signs of volcanism that will tell us about the elusive interior of the Moon and the history of how volcanic activity shaped the surface. One of the best places to study the Moon’s mantle is across the well-exposed interior of the 2500 km South Pole-Aitken (SPA) basin on the lunar farside. Unlike basins on the lunar nearside (where we have Apollo samples), SPA interior has not been covered by extensive mare basalt. Trailblazer has targets selected to explore the exposed diverse compositions in detail. Lunar Trailblazer’s instruments will also map some of the Moon’s most curious volcanic rocks, high-silica compositions, and rocks enriched in a mineral called spinel. Where did magmas feeding ancient volcanoes originate? Were there different styles of eruptions in areas with high concentrations of radioactive elements? Were the Moon’s explosive volcanic eruptions driven by volatiles like water? Lunar Trailblazer will provide data that will help us answer such questions.

Missions of the Decade

Small Innovative Missions for Planetary Exploration (SIMPLEx) like Lunar Trailblazer accomplish Decadal Survey goals despite being the smallest mission class. SIMPLEx is a program for higher risk, low-cost spacecraft, including those that ride-along into space aboard rockets with another mission. This allows for more scientific exploration and a higher data return for each rocket that leaves Earth. Lunar Trailblazer will be one of the first SIMPLEx missions for planetary science. Although Lunar Trailblazer is a small satellite, the information it will give us on our solar system addresses some of the most important planetary science questions identified for NASA by the National Academies.

By Maya Porcelli
Maya Porcelli is a Pasadena City College student and Caltech intern working on science communication for the Lunar Trailblazer mission.


National Academies of Sciences, Engineering, and Medicine. 2022. Origins, Worlds, Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032. Washington, DC: The National Academies Press.

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