In his video titled “Why Exomoons Are So Important,” astrophysicist David Kipping passionately elucidates five compelling reasons behind the significance of exploring exomoons. With a career-long dedication to the subject, Kipping artfully dissects the role of exomoons in shaping our understanding of the cosmos. Delving into themes like habitability, the Rare Earth hypothesis, moon formation, and the quest for biosignatures, he underscores their profound impact on our perception of exoplanets and their potential to harbor life. Through lucid explanations and vivid analogies, Kipping invites us to recognize exomoons as more than mere satellite companions; they represent a new frontier of astronomical exploration that could revolutionize our comprehension of the universe.

In his video titled “Why Exomoons Are So Important”, astrophysicist David Kipping gives five reasons why we should search for exomoons.

Reason 1: We still didn’t detect any exomoon

In the first part of his video titled “Why Exomoons Are So Important,” astrophysicist David Kipping highlights the evolution of our understanding of exoplanets and the significance of exploring exoplanetary systems. He points out that over the past 33 years, the discovery of exoplanets has transformed our perception of the cosmos. Initially, astronomers knew of zero exoplanets, but today we’ve identified more than 5,000. This rapid progress has led to the realization that most stars have planets orbiting them.

Kipping addresses the skepticism that arises from the assumption that if we already believe in the existence of exoplanets, why bother searching for them? He parallels this with the ongoing search for exomoons, which are moons orbiting exoplanets. Although we have yet to confirm any exomoons definitively, the confidence in their existence remains high. Kipping argues that this skepticism doesn’t negate the importance of exploration; otherwise, we might also question the pursuit of other hypothetical phenomena like extraterrestrial life.

He underscores that the motivation behind exploring exoplanets and exomoons is rooted in curiosity about the diversity of other planetary systems. The discoveries made in the field of exoplanetary science have not merely confirmed their existence, but they have provided insights into the variety of planetary systems, their similarities, and their differences. This journey of curiosity has led to the identification of various types of exoplanets, such as Super-Earths, Hot Jupiters, and more, in unexpected places like binary star systems.

Kipping contends that the quest for exomoons is not solely about confirming their presence but about uncovering the unique and enriching insights they could offer. He draws a parallel to the transformative impact that exoplanet discoveries have had on astronomy and public discourse about science. Exomoons, as an entirely new type of astronomical object, hold immense potential for discovery and could yield incalculable rewards for our understanding of the universe.

In summary, Kipping’s first reason emphasizes that the pursuit of exomoons is driven by curiosity and the desire to explore the diverse and unexpected aspects of other planetary systems. The discoveries made in the realm of exoplanets underscore the value of such exploration, and the potential insights from exomoons could be groundbreaking, much like the impact of exoplanet discoveries.

Reason 2: There can be Habitable Exomoons

In the second part of his video, titled “Reason 2: Pandoras,” astrophysicist David Kipping discusses the concept of habitable exomoons and their potential significance. He starts by mentioning the familiarity of the trope of habitable moons in science fiction, with the example of Pandora from James Cameron’s “Avatar” series. He raises the question of whether this idea is purely science fiction or if it has a basis in reality.

Kipping explains that habitable exomoons could essentially be Earth-like planets with one key difference: they orbit gas giants. He emphasizes that due to their construction, these moons would likely be habitable. He addresses concerns about radiation from the gas giant, stating that while innermost moons might experience intense radiation, this effect diminishes at wider orbits. He suggests that this radiation is not a major obstacle to habitability.

Habitable exomoon
Artist’s imagination of an Earth-like “habitable exomoon” orbiting a gas giant planet in a star’s habitable zone. Image source: NASA

He goes on to discuss the advantages that exomoons might have over planets. One advantage is related to the interaction with the planetary magnetosphere. Moons can borrow the magnetic field of their host planet for protection against charged particles and cosmic radiation. As moons orbit behind their host planet, they can remain shielded by the planetary magnetosphere for a significant portion of their orbit.

Another advantage highlighted by Kipping is the potential for moons to avoid becoming tidally locked to their host stars. He explains that red dwarf stars, the most common type in the universe, often have habitable zones close to them where planets might become tidally locked. Tidal locking would result in one side of the planet always facing the star, potentially causing extreme temperature variations. Moons, however, could avoid this issue by becoming tidally locked to their planet instead, ensuring a more even distribution of radiation exposure. If a moon is tidally locked to its planet, like our moon, all of its surface gets lit by its host star as it rotates.

Kipping underscores the viability of moons as habitable worlds and mentions the intriguing possibility of subsurface ocean worlds like Europa and Enceladus, which adds complexity to the discussion.

To summarize, Kipping’s second reason centers around the potential habitability of exomoons. He emphasizes that exomoons could indeed be habitable, challenging the notion that only exoplanets can host life. He argues that assessing the frequency of habitable worlds around other stars should consider the contribution of exomoons, as they could significantly impact mission design and engineering considerations. Kipping suggests that habitable moons might even be the most common type of living world in the universe.

Reason 3: Rare Earth Hypothesis

In the third segment of his video titled “Reason 3: Rare Earth Hypothesis,” astrophysicist David Kipping discusses the Rare Earth hypothesis and its relation to exomoons. He starts by mentioning that the Rare Earth hypothesis, previously discussed in detail in another video, proposes that Earth’s conditions for supporting civilization might be exceptionally unique. He highlights that the moon plays a key role in this hypothesis.

Kipping introduces the peculiarity of Earth’s moon, stating that it’s 1.2% the mass of our planet, which is an unusually high mass ratio for any planet in the solar system. He notes that the moon’s large mass is believed to be crucial for three primary reasons:

  • Stabilizing Earth’s Obliquity: The moon’s presence stabilizes Earth’s axial tilt (obliquity) against the gravitational influences of planets like Jupiter. This stabilization leads to a consistent and stable climate, which is essential for the development and maintenance of complex life.
  • Formation and Impact: The moon is thought to have formed through a giant impact, which might have removed much of Earth’s original lithosphere. This impact prevented the lithosphere from becoming so thick that it would inhibit plate tectonics. Without plate tectonics, important processes like the carbon cycle would be disrupted, posing challenges for life as we know it.
  • Tidal Effects and Birth of Life: The moon’s formation, occurring relatively close to Earth, would have generated enormous tides and rock pools on the planet’s surface. These tides and pools might have provided conducive environments for the emergence of life.

Kipping acknowledges that these arguments are speculative, contributing to the controversy surrounding the Rare Earth hypothesis. However, he emphasizes that the moon has undoubtedly played a significant role in Earth’s formation and development.

He concludes by asserting that when astronomers eventually detect the first Earth-like exoplanet, one of the primary inquiries will likely be whether it possesses an exomoon. This question stems from the understanding that if moons indeed have played a pivotal role in Earth’s habitability, then the presence of similar exomoons could be a crucial factor in determining the potential habitability of exoplanets.

In summary, Kipping’s third reason emphasizes the connection between exomoons and the Rare Earth Hypothesis, suggesting that the presence and characteristics of moons could be vital in assessing the habitability of exoplanets, particularly in relation to the stability of climate, geological processes, and the emergence of life.

Reason 4: Exomoons can increase our knowledge about the Formation of Moons

In the fourth portion of his video titled “Reason 4: How Moons Form,” astrophysicist David Kipping delves into the importance of studying moons to gain insight into their formation processes. He opens by comparing our previous assumptions about planet formation to the paradigm shift brought about by the discovery of exoplanets. This unexpected diversity in exoplanets and their formation challenged our existing models.

Kipping explains that just as exoplanets shattered our initial understanding of planet formation, exomoons hold the potential to do the same for our knowledge of moon formation. He highlights the complexity of the formation processes and notes that while we have some explanations for moon formation, they might not be comprehensive.

He brings up the example of moons that co-form around gas giants and notes that current theories suggest these moons would be relatively small, not exceeding 1/10,000th the mass of the host planet. However, he raises the question of whether this size ratio holds true in all cases or if there might be exceptions elsewhere in the universe.

Kipping then turns to “weird” cases like our own moon, which is thought to have formed through a giant impact. This prompts the question of how frequently such events occur during planetary formation. He wonders if this is an unusual occurrence or a common outcome in planetary system development. With only Earth’s moon as a reference point, it’s impossible to draw definitive conclusions.

He concludes by emphasizing that to truly understand the origins of our own solar system and its uniqueness, we need a broader dataset. To achieve this understanding, Kipping asserts that discovering and studying other moons is crucial. Just as exoplanets expanded our understanding of planet formation, exomoons could significantly contribute to our knowledge of moon formation processes.

In summary, Kipping’s fourth reason underscores the importance of studying exomoons to gain insights into the diverse processes behind moon formation. He highlights the limitations of our current understanding and the need for a more extensive dataset to unravel the complexities of moon origins and their role in shaping planetary systems.

Reason 5: Biosignatures

In the fifth and final segment of his video titled “Reason 5: Some Inconvenient Truths about Biosignatures,” astrophysicist David Kipping presents a compelling argument regarding the role of exomoons in the search for life beyond Earth. He introduces a pivotal 2014 paper by Hanno Rein and colleagues, which he considers one of the most significant exoplanet papers in recent times.

Kipping highlights the challenge of building a space telescope capable of directly imaging distant Earth-like exoplanets, a project often referred to as the Habitable Worlds Observatory. This telescope would aim to capture light from these exoplanets and analyze their spectral characteristics for signs of biogenic molecules like oxygen and methane, often considered strong indicators of life.

He discusses the concept of chemical disequilibrium in pairs of molecules, such as oxygen and methane, where their coexistence could indicate an active process producing these molecules. However, Kipping introduces a thought-provoking scenario involving an ocean planet without life but with a methane-rich moon. If both the planet and moon were too close to each other for the telescope to resolve individually, they would appear as a single blended signal in the telescope’s observation.

This blending of signals could lead to a misinterpretation. Kipping presents a scenario in which scientists analyze the combined light and detect both oxygen and methane, seemingly confirming the presence of life. However, the oxygen could have been produced through non-biological processes, and the methane might have originated from the moon, unrelated to the planet’s conditions. This “trick” by the universe, as Kipping puts it, highlights the complexities introduced by exomoons in the search for biosignatures.

He concludes by stressing the importance of understanding exomoons in order to avoid such misinterpretations and to conduct accurate assessments of potential habitability and signs of life on exoplanets. Kipping emphasizes the necessity of a systematic effort to study exomoons, including their occurrence rates, sizes, and associations with different types of planets.

In summary, Kipping’s fifth reason underscores the critical role of exomoons in refining the search for life beyond Earth. He highlights the potential challenges introduced by exomoons in interpreting biosignatures and emphasizes the need for comprehensive studies of exomoons to enhance the accuracy of our understanding of habitability and potential life on exoplanets.


In the concluding remarks of his video titled “Why Exomoons Are So Important,” astrophysicist David Kipping addresses his personal connection to the topic and explains why he believes exomoons are a critical area of study within the field of exoplanet research.

Kipping acknowledges that some viewers might perceive his passion for exomoons as biased, given his deep involvement in the subject. However, he emphasizes his intent in the video was to lay out the reasons why exomoons are of utmost importance and how they contribute to the broader goals of exoplanet research.

He references a recent proposal he made for exomoon research using the James Webb Space Telescope (JWST), which unfortunately was not approved. Previously, David Kipping’s request to use the James Webb Space Telescope (JWST) to search for exomoons was denied. Kipping and his team proposed to utilize the JWST to investigate two distinct planets in hopes of detecting exomoons. One planet was similar to Earth – a rocky planet, while the other resembled Jupiter – a massive gas giant.

Kipping and his team believed both planets had a high likelihood of hosting moons that have persisted until the present day and that the JWST could detect them. Despite the rarity of such planets, even among the thousands known, and their supporting models showing the probable existence and survival of these moons over billions of years, their proposal was not approved, and they did not receive the telescope time they sought.

He notes the limited lifespan of JWST due to factors like fuel depletion and potential technical issues. Despite these challenges, Kipping believes that JWST has the potential to provide answers regarding exomoons, and he stresses the urgency of conducting experiments and observations before this valuable resource diminishes.

He expresses his conviction that not attempting to explore exomoons would be a regrettable decision, potentially depriving us of valuable insights into the cosmos. Kipping emphasizes that exomoons matter in a profound way that might not be immediately apparent to everyone.

In closing, he invites viewers to join him in advocating for the exploration of exomoons, suggesting that by working together, we can create new opportunities for understanding the universe through this unique and captivating avenue of research.

About David Kipping

David Kipping explains why we should look for exomoons
David Kipping is an Assistant Professor of Astronomy at Columbia University.

Born in either late 1983 or 1984, David Mathew Kipping is a distinguished astronomer and an assistant professor at Columbia University. His expertise lies in the realm of exoplanets and exomoons, and he leads the Cool Worlds Laboratory within Columbia University’s Astronomy Department.

In 2011, he successfully defended his Ph.D. thesis titled “The Transits of Extrasolar Planets with Moons” at University College London.

While Kipping is renowned for his contributions to exoplanet research, his scholarly pursuits encompass the study of transiting exoplanets, the evolution of detection and characterization methodologies, exoplanet atmospheres, Bayesian inference, and population statistics.

Kipping was the principal investigator of The Hunt for Exomoons with Kepler (HEK) project (after discovering more than 2600 exoplanets, the Kepler Space Telescope was retired on November 15, 2018).

Passionate about disseminating knowledge, Kipping manages a YouTube channel named “Cool Worlds,” where he delves into his team’s findings and associated scientific topics.


  • Header image: “Red planet with rusty dunes, bright sunlight, and an exomoon in the sky.” on Deposit Photos
M. Özgür Nevres

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