In 2003, the European Space Agency (ESA) launched the Small Missions for Advanced Research in Technology-1 (SMART-1) lunar orbiter. After taking 13 months to reach the Moon using a Solar Electric Propulsion (SEP) system, the orbiter then spent the next three years studying the lunar surface. Then, on September 3rd, 2006, the mission came to an end as the spacecraft was deliberately crashed onto the lunar surface.
While the bright flash that this created was captured by observers using the Canada-France-Hawaii Telescope in Hawaii, no other spacecraft were in orbit at the time to witness it. As a result, it has been impossible for over a decade to determine precisely where SMART-1 went down. But thanks to images captured last year by NASA’s Lunar Reconnaissance Orbiter (LRO), the final resting place of SMART-1 is now known.
When it comes right down to it, the Moon is a pretty hostile environment. It’s extremely cold, covered in electrostatically-charged dust that clings to everything (and could cause respiratory problems if inhaled), and its surface is constantly bombarded by radiation and the occasional meteor. And yet, the Moon also has a lot going for it as far as establishing a human presence there is concerned.
In the coming decades, many space agencies hope to conduct crewed missions to the Moon and even establish outposts there. In fact, between NASA, the European Space Agency (ESA), Roscosmos, and the Indian and Chinese space agencies, there are no shortages of plans to construct lunar bases and settlements. These will not only establish a human presence on the Moon, but facilitate missions to Mars and deeper into space.
To put it simply, the entire surface of the Moon is covered in dust (aka. regolith) that is composed of fine particles of rough silicate. This dust was formed over the course of billions of years by constant meteorite impacts which pounded the silicate mantle into fine particles. It has remained in a rough and fine state due to the fact that the lunar surface experiences no weathering or erosion (due to the lack of an atmosphere and liquid water).
Because it is so plentiful, reaching depths of 4-5 meters (13-16.5 feet) in some places – and up to 15 meters (49 feet) in the older highland areas – regolith is considered by many space agencies to be the building material of choice for lunar settlements. As Aidan Cowley, the ESA’s science advisor and an expert when it comes to lunar soil, explained in a recent ESA press release:
“Moon bricks will be made of dust. You can create solid blocks out of it to build roads and launch pads, or habitats that protect your astronauts from the harsh lunar environment.”
In addition to taking advantage of a seemingly inexhaustible local resource, the ESA’s plans to use lunar regolith to create this base and related infrastructure demonstrates their commitment to in-situ resource utilization. Basically, bases on the Moon, Mars, and other locations in the Solar System will need to be as self-sufficient as possible to reduce reliance on Earth for regular shipments of supplies – which would both expensive and resource-exhaustive.
To test how lunar regolith would fare as a building material, ESA scientists have been using Moon dust simulants harvested right here on Earth. As Aiden explained, regolith on both Earth and the Moon are the product of volcanism and are basically basaltic material made up of silicates. “The Moon and Earth share a common geological history,” he said, “and it is not difficult to find material similar to that found on the Moon in the remnants of lava flows.”
The simulant were harvested from the region around Cologne, Germany, that were volcanically active about 45 million years ago. Using volcanic powder from these ancient lava flows, which was determined to be a good match for lunar dust, researchers from the European Astronaut Center (EAC) began using the powder (which they’ve named EAC-1) to fashioning prototypes of the bricks that would be used to created the lunar village.
Spaceship EAC, an ESA initiative designed to tackle the challenges of crewed spaceflight, is also working with EAC-1 to develop the technologies and concepts that will be needed to create a lunar outpost and for future missions to the Moon. One of their projects centers on how to use the oxygen in lunar dust (which accounts for 40% of it) to help astronauts have extended stays on the Moon.
But before the ESA can sign off on lunar dust as a building material, a number of tests still need to be conducted. These include recreating the behavior of lunar dust in a radiation environment to simulate their electrostatic behavior. For decades, scientists have known that lunar dust is electrically-charged because of the way it is constantly bombarded by solar and cosmic radiation.
This is what causes it to lift off the surface and cling to anything it touches (which the Apollo 11 astronauts noticed upon returning to the Lunar Module). As Erin Transfield – a member of ESA’s lunar dust topical team – indicated, scientists still do not fully understand lunar dust’s electrostatic nature, which could pose a problem when it comes to using it as a building material.
What’s more, the radiation-environment experiments have not produced any conclusive results yet. As a biologist who dreams of being the first woman on the Moon, Transfield indicated that more research is necessary using actual lunar dust. “This gives us one more reason to go back to the Moon,” she said. “We need pristine samples from the surface exposed to the radiation environment.”
Beyond establishing a human presence on the Moon and allowing for deep-space missions, the construction of the ESA’s proposed lunar village would also offer opportunities to leverage new technologies and forge partnerships between the public and private sector. For instance, the ESA has collaborated with the architectural design firm Foster + Partners to come up with the design for their lunar village, and other private companies have been recruited to help investigate other aspects of building it.
This mission, a joint effort between the ESA and Roscosmos, will involve a Russian-built lander setting down in the Moon’s South Pole-Aitken Basin, where the PROSPECT probe will deploy and drill into the surface to retrieve samples of ice. Going forward, the ESA’s long-term plans also call for a series of missions to the Moon beginning in the 2020s that would involve robot workers paving the way for human explorers to land later.
In the coming decades, the intentions of the world’s leading space agencies are clear – not only are we going back to the Moon, but we intend to stay there! To that end, considerable resources are being dedicated towards researching and developing the necessary technologies and concepts needed to make this happen. By the 2030s, we might just see astronauts (and even private citizens) coming and going from the Moon with regular frequency.
And be sure to check out this video about the EAC’s efforts to study lunar regolith, courtesy of the ESA:
To put it simply, the Earth’s Moon is a dry, airless place where nothing lives. Aside from concentrations of ice that exist in permanently-shaded craters in the polar regions, the only water on the moon is believed to exist beneath the surface. What little atmosphere there is consists of elements released from the interior (some of which are radioactive) and helium-4 and neon, which are contributed by solar wind.
However, astronomers have theorized that there may have been a time when the Moon might have been inhabitable. According to a new study by an astrophysicist and an Earth and planetary scientist, the Moon may have had two early “windows” for habitability in the past. These took place roughly 4 billion years ago (after the Moon formed) and during the peak in lunar volcanic activity (ca. 3.5 billion years ago).
For the sake of their study, Schulze-Makuch and Crawford drew on the results of several recent space missions and analyses of lunar rock and soil samples – which indicated that the Moon is not as dry as previously thought. They also drew on recent studies of the products of lunar volcanism, which indicate that the lunar interior contains more water than previously thought and that the lunar mantle may even be as comparably water-rich as Earth’s upper mantle.
From this, they concluded that conditions on the lunar surface were sufficient to support simple lifeforms during two periods in the past. The first was roughly 4 billion years ago, when the Moon began to form from a debris disk caused by an impact between a Mars-sized object (named Theia) and Earth – aka. the Giant Impact Hypothesis. The second occurred 3.5 billion years ago when the Moon was at the peak of its volcanic activity.
At both times, planetary scientists think the Moon was releasing considerable amounts of superheated volatile gasses from its interior, which would include water vapor. This outgassing could have formed pools of liquid water on the lunar surface and an atmosphere dense enough to keep it there for millions of years. The early Moon is also believed to have had its own magnetic field, which would have protected lifeforms on the surface from deadly solar radiation.
“If liquid water and a significant atmosphere were present on the early Moon for long periods of time, we think the lunar surface would have been at least transiently habitable.”
Schulze-Makuch and Crawford’s work draws on data from recent space missions and analyses of lunar rock and soil samples that show the Moon is more watery than scientists gave it credit for. These include India’s first lunar mission, Chandrayaan I, which created a high-resolution chemical and mineralogical map of the lunar surface in 2009, which confirmed the presence of water molecules in the soil.
Additionally, ongoing examinations of the lunar rocks returned by the Apollo astronauts and studies of lunar volcanic deposits have provided strong evidence that there is a large amount of water in the lunar mantle that is thought to have been deposited very early on in the Moon’s formation. As for how the life got there, that remains a bit of an open question.
Schulze-Makuch and Crawford believe that it may have originated much as it did on Earth, but that the more likely scenario is that it was brought from Earth by meteorites. Essentially, the earliest evidence for life on Earth indicates that cyanobacteria existed on our planet 3.5 to 3.8 billion years ago. This coincides with the Late Heavy Bombardment, when the Solar System was experiencing frequent and giant meteorite impacts.
So basically, it is possible that large impacts could have blasted off pieces of the Earth’s surface, which contained simple organisms like cyanobacteria. These chunks could have then reached the Moon and landed on its surface, seeding it with basic lifeforms that would have been capable of surviving in the lunar environment. As Schulze-Makuch said:
“It looks very much like the Moon was habitable at this time. There could have actually been microbes thriving in water pools on the Moon until the surface became dry and dead.”
Looking ahead, there are several missions that are scheduled to explore the lunar surface. These include India’s Chandrayaan-2, a rover and sample analysis mission, and China’s Chang’e 4 and Chang’e 5 rovers – which will explore the southern polar region and conduct a sample return mission, receptively. NASA and Roscosmos also plan to send multiple missions to the Moon in the coming years to map it’s mineralogy, water deposits, and radiation environment.
Some of these missions may be able to obtain samples from volcanic deposits that correspond to the period of heightened volcanic activity that took place 3.5 billion years ago for signs of water and biomarkers. In the meantime, experiments could be conducted on Earth or aboard the ISS to simulate lunar environments to see if microorganisms could survive under the conditions that are predicted to have existed at these times.
If successful, these sample return missions and experiments could indicate that the Moon itself was once a habitable environment. And, with the right kind of geoengineering (aka. terraforming), maybe it could be habitable again someday!
For decades, scientists have pondered how Earth acquired its only satellite, the Moon. Whereas some have argued that it formed from material lost by Earth due to centrifugal force, or was captured by Earth’s gravity, the most widely accepted theory is that the Moon formed roughly 4.5 billion years ago when a Mars-sized object (named Theia) collided with a proto-Earth (aka. the Giant Impact Hypothesis).
However, since the proto-Earth experienced many giant-impacts, several moons are expected to have formed in orbit around it over time. The question thus arises, what happened to these moons? Raising this very question, a team an international team of scientist conducted a study in which they suggest that these “moonlets” could have eventually crashed back into Earth, leaving only the one we see today.
For the sake of their study, Dr. Malamud and his colleagues – Prof. Hagai B. Perets, Dr. Christoph Schafer and Mr. Christoph Burger (a PhD student) – considered what would happen if Earth, in its earliest form, had experienced multiple giant impacts that predated the collision with Theia. Each of these impacts would have had the potential to form a sub-Lunar mass “moonlet” that would have interacted gravitationally with the proto-Earth, as well as any possible previously-formed moonlets.
Ultimately, this would have resulted in moonlet-moonlet mergers, the moonlets being ejected from Earth’s orbit, or the moonlets falling to Earth. In the end, Dr. Malamud and his colleagues chose to investigate this latter possibility, as it has not been previously explored by scientists. What’s more, this possibility could have a drastic impact on Earth’s geological history and evolution. As Malamud indicated to Universe Today via email:
“In the current understanding of planet formation the late stages of terrestrial planet growth were through many giant collisions between planetary embryos. Such collisions form significant debris disks, which in turn can become moons. As we suggested and emphasized in this and our previous papers, given the rates of such collisions and the evolution of the moons – the existence of multiple moons and their mutual interactions will lead to moonfalls. It is an inherent, inescapable part of the current planet formation theory.”
However, because Earth is a geologically active planet, and because its thick atmosphere leads to natural weathering and erosion, the surface changes drastically with time. As such, it is always difficult to determine the effects of events that happened during the earliest periods of Earth – i.e. the Hadean Eon, which began 4.6 billion years ago with the formation of the Earth and ended 4 billion years ago.
To test whether or not multiple impacts could have taken place during this Eon, resulting in moonlets that eventually fell to Earth, the team conducted a series of smooth particle hydrodynamical (SPH) simulations. They also considered a range of moonlet masses, collision impact-angles and initial proto-Earth rotation rates. Basically, if moonlets did fall to Earth in the past, it would have altered the rotation rate of the proto-Earth, resulting in its current sidereal rotation period of 23 hours, 56 minutes, and 4.1 seconds.
In the end, they found evidence that while direct impacts from large objects were not likely that a number of grazing tidal-collisions could have taken place. These would have caused material and debris to be thrown up into the atmosphere that would have formed small moonlets that would have then interacted with each other. As Malamud explained:
“Our results however do show that in the case of a moonfall, the distribution of the material from the moonfall is not even on the Earth, and therefore such collisions can give rise to asymmetries and composition inhomogeneities. As we discuss in the paper, there are actually possible evidence for the latter – moonfalls can potentially explain the isotopic heterogeneities in highly siderophile elements in terrestrial rocks. In principle a moon collisions may also produce a large scale structure on the Earth, and we speculated that such an effect could have contributed to the formation of Earth’s earliest super-continent. This aspect, however, is more speculative, and it is difficult to directly confirm, given the geological evolution of the Earth since those early times.”
This study effectively extends the current and widely-popular Giant Impact Hypothesis. In accordance with this theory, the Moon formed during the first 10 to 100 million years of the Solar System, when the terrestrial planets were still forming. During the final stages of this period, these planets (Mercury, Venus, Earth and Mars) are believed to have grown mainly through impacts with large planetary embryos.
Since that time, the Moon is believed to have evolved due to mutual Earth and Moon tides, migrating outwards to its current location, where it has been ever since. However, this paradigm does not consider impacts that took place before the arrival of Theia and the formation of Earth’s only satellite. As a result, Dr. Malamud and his colleagues assert that it is disconnected from the wider picture of terrestrial planet formation.
By taking into account potential collisions that predate the formation of the Moon, they claim, scientist could have a more complete picture of how both the Earth and the Moon evolved over time. These findings could also have implications when it comes to the study of other Solar planets and moons. As Dr. Malamud indicated, there is already compelling evidence that large-scale collisions affected the evolution of planets and moons.
“On other planets we do see evidence for very large impacts that produced a planet scale topographic features, such as the so-called Mars dichotomy and possibly the dichotomy of Charon’s surface,” he said. “These had to arise from large scale impacts, but small enough as to make sub-global planet features. Moonfalls are natural progenitors of such impacts, but one cannot exclude some other large impacts by asteroids which could produce similar effects.”
There’s also the possibility of such collisions happening in the distant future. According to current estimates of its migration, Mars’ moon Phobos will eventually crash into the surface of the planet. While small compared to the impacts that would have created moonlets and the Moon around Earth, this eventual collision is direct evidence that moonfalls took place in the past and will again in the future.
In short, the history of the early Solar System was violent and cataclysmic, with a great deal of creation resulting from powerful collisions. By having a more complete picture of how these impact events affected the evolution of the terrestrial planets, we may gain new insight into how life-bearing planets formed. This, in turn, could help us track down such planets in extra-solar systems.
It’s been over forty years since the Apollo Program wrapped up and the last crewed mission to the Moon took place. But in the coming years and decades, multiple space agencies plan to conduct crewed missions to the lunar surface. These includes NASA’s desire to return to the Moon, the ESA’s proposal to create an international Moon village, and the Chinese and Russian plans to send their first astronauts to the Moon.
For this reason, a great deal of research has been dedicated to what the health effects of long-duration missions to the Moon may be – particularly the effects a lower gravity environment would have on the human body. But in a recent study, a team of pharmacologists, geneticists and geoscientists consider how being exposed to lunar dust could have a serious effect on future astronauts’ lungs.
Because it has no atmosphere, the Moon’s surface has been pounded by meteors and micrometeroes for billions of years, which have created a fine layer of surface dust known as regolith. In addition, the Moon’s surface is constantly being bombarded by charged particles from the Sun, which cause the lunar soil to become electrostatically charged and stick to clothing.
Indications that lunar dust could cause health problems first emerged during the Apollo missions. After visiting the Moon, astronauts brought lunar soil back with them into the command module as it clung to their spacesuits. After inhaling the dust, Apollo 17 astronaut Harrison Schmitt described having symptoms akin to hay fever, which including sneezing, watery eyes and a sore throat.
While the symptoms were short-lived, researchers wanted to know what the long-term effects of lunar dust could be. There have also been indications that exposure to lunar dust could be harmful based on research that has shown how breathing dust from volcanic eruptions, dust storms and coal mines can cause bronchitis, wheezing, eye irritation and scarring of lung tissue.
Previous research has also shown that dust can cause damage to cells’ DNA, which can cause mutations and eventually lead to cancer. For these reasons, Caston and her colleagues were well-motivated to see what harmful effects lunar soil could have on the human body. For the sake of their study, the team exposed human lung cells and mouse brain cells to samples of simulated lunar soil.
These simulants were created by using dust samples from Earth that resemble soil found on the Moon’s lunar highlands and volcanic plains, which were then ground to a fine powder. What they found was that up to 90% of human lung cells and mouse neurons died when exposed to the dust samples. The simulants also caused significant DNA damage to mouse neurons, and the human lung cells were so effectively damaged that it was impossible to measure any damage to the cells’ DNA.
The results show that breathing lunar dust (even in minute quantities) could pose a serious health hazard to astronauts traveling to any airless bodies in the future. This includes not only the Moon, but also Mars and other terrestrial bodies like Mercury. Until now, this health hazard has been largely overlooked by space agencies seeking to understand the long-term health risks of space travel.
“There are risks to extraterrestrial exploration, both lunar and beyond, more than just the immediate risks of space itself,” said Rachel Caston. According to Bruce Demple, a biochemist at Stony Brook University School of Medicine and senior author of the new study, their results (coupled with the experience of the Apollo astronauts) indicate that prolonged exposure to lunar dust could impair airway and lung function.
What’s worse, he also indicated that if the dust induces inflammation in the lungs, it could increase the risk of more serious diseases like cancer. “If there are trips back to the Moon that involve stays of weeks, months or even longer, it probably won’t be possible to eliminate that risk completely,” he said.
Ergo, any attempts to mitigate the risks of mounting crewed missions to the Moon, Mars, and beyond will have to take into account exposure to not only low-gravity and radiation, but also electrostatically charged soil. Aside from limiting the duration of missions and the number of EVAs, certain protective counter-measures may need to be incorporated into any plans for long-duration missions.
One possibility is to have astronauts cycle through an airlock that would also spray their suits with water or a compound designed to neutralize the charge, thus washing them clean of dust before they enter the main habitat. Otherwise, astronauts working in the International Lunar Village (or any other off-world habitat for that matter) may have to wear breathing masks the entire time they are not in a spacesuit.
For some time, scientists have known that the Moon and Mars have some fascinating similarities to Earth. In addition to being similar in composition, there is ample evidence that both bodies had active geological pasts. This includes stable lava tubes which are very similar to those that exist here on Earth. And in the future, these tubes could be an ideal location for outposts and colonies.
However, before we can begin choosing where to settle, these locations need to be mapped out to determining which would be suitable for human habitation. Luckily, a team of speleologists (cave specialists), geologists and ESA astronauts recently created the largest 3D image of a lava tube ever created. As part of the ESA’s PANGAEA program, this technology could one day help scientists map out cave systems on the Moon and Mars.
The lava tube in question was the La Cueva de Los Verdes, a famous tourist destination in Lanzarote, Spain. In addition to ESA astronaut Matthias Mauer, the team consisted of Tommaso Santagata (a speleologist from the University of Padova and the co-founder of the Virtual Geographic Agency), Umberto Del Vecchio and Marta Lazzaroni – a geologists and a masters student from the University of Padova, respectively.
For five days in November 2017, this campaign mobilized 50 people, four space agencies and 18 organizations in five different locations. The La Cueva de los Verdes lava tube was of particular importance since it is one of the world’s largest volcanic cave complexes, measuring roughly 8 km in length. Some of these caves are even large enough to accommodate residential streets and houses.
During the campaign, Mauer, Santagata, Vecchio and Lazzaroni relied on two instruments to map the lava tube in detail. These included the Pegasus Backpack, a wearable mapping solution that collects geometric data without a satellite ad synchronizes images collected by five cameras and two 3D imaging laser profilers, and the Leica BLK360 – the smallest and lightest imaging scanner on the market.
In less than three hours, the team managed to map all the contours of the lava tube. And while the results of the campaign continue to be analyzed, the team chose to use the data they obtained to produce a 3D visual of all the twists and turns of the lava tube. The scan that resulted covers a 1.3 km section of the cave system with an unprecedented resolution of a few centimeters.
Santagata and the Virtual Geography Agency also turned their 3D visual into a lovely video titled “Lave tube fly-through”, which beautifully illustrates the winding and organic nature of the lava tube system. This video was posted to the ESA’s twitter feed on Tuesday, March 13th (shown above). This video, like the scans that preceded it, represent a breakthrough in geological mapping and astronaut training.
While lava tubes have been mapped since the 1970s, a clear view of this subterranean passage has remained elusive until now. Beyond being the first, the scans the team conducted could also help scientists to study the origins of the cave system, its peculiar formations, and assist local institutions in protecting the subterranean environment. As intended, the scans could also assist future space exploration and colonization efforts.
For instance, the 8 km lava tube has both dry and water-filled sections. In the six-kilometer dry section, the lava tube has natural openings (jameos), that are aligned along the top of the cave pathway. These formations are very similar to “skylights” that have been observed on the Moon and Mars, which are holes in the surface that open into stable lava tubes.
Such structures are considered to be a good place for building outposts and colonies since they are naturally shielded from radiation and micrometeorites. Lava tubes also have a constant temperature, therefore offering protection against environmental extremes, and could provide access to underground sources of water ice. Some sections could also be sealed off and pressurized to create a colony.
As such, exploring such environments here on Earth is a good way to train astronauts to explore them on other bodies. As all astronauts know, mapping an environment is the first step in exploration, especially when you are looking for a place to establish a base camp. And in time, this information can be used to establish more permanent settlements, giving rise to eventual colonization.
The OSIRIS-REx mission is an historic one, since it will be the first US spacecraft to conduct a sample-return mission with an asteroid. In the meantime, as the probe has makes its way further into space, it has been providing some truly breathtaking images of the journey. Consider the recently-released composite image of the Earth-Moon system, which NASA created using images that were taken by the probe on October 2nd, 2017.
The images were all taken by the probe’s MapCam instrument, a medium-range camera designed to capture images of outgassing around Bennu and help map its surface in color. On this occasion, it snapped three beautiful pictures of Earth and the Moon. These images were all taken when the spacecraft was at a distance of approximately 5 million km (3 million mi) from Earth – about 13 times the distance between the Earth and the Moon.
As part of the OSIRIS-REx Camera Suite (OCAMS), which is operated by researchers at the University of Arizona, the CapCam has four color filters. To produce the image, three of them (b, v and w) were used as a blue, green and red filters and then stacked on top of each other. The Earth and Moon were each color-corrected, and the Moon was brightened to make it more easily visible.
A second image of planet Earth (shown above), was taken on September 22nd, 2017, by one of the probe’s navigational cameras (NavCam 1). As the name suggests, this instrument is intended to help OSIRIS-REx orient itself while making its journey to Bennu and while it studies the asteroid. This is done by tracking starfields in space (while in transit) and landmarks on Bennu’s surface once it has arrived.
The image was taken when OSIRIS-REx was at a distance of 110,000 km (69,000 mi) from Earth. This was just after the probe had completed an Earth gravity-assist maneuver, where it used Earth’s gravitational force to slingshot around its equator and pick up more speed. The original image (shown below) was rotated so that the North Pole would be pointed up and the entire image was enlarged to provide more detail.
As you can see in the altered image, North America is visible on the upper right portion, while Hurricane Maria and the remnants of Hurricane Jose are visible in the far upper-right. The acquisition of these images was the result of painstaking calculations and planning, which were performed in advance by engineers and navigation specialists on the mission team using software called Systems Tool Kit (STK).
These plans were developed to ensure that the probe would be able to snap pictures with precise timing, which were then uploaded to the spacecraft’s computer weeks ahead of time. Within hours of the probe executing its gravity-assist maneuver, crews on the ground were treated to the first images from the spacecraft’s navigational cameras, which confirmed that the probe was following the right path.
The probe is scheduled to reach Bennu in December of 2018, with approach operations commencing this coming August. Bennu is also expected to make a close pass with Earth several centuries from now, and could even collide with us by then. But for the time being, it represents a major opportunity to study the history and evolution of the Solar System, since it is essentially a remnant left over from its formation.
By studying this asteroid up close, and bringing samples back to Earth for further study, the OSRIS-REx mission could help us understand how life began on Earth and where the Solar System as a whole is headed. But in the meantime, the probe has been able to provide us with some beautiful snapshots of Earth, which serve to remind us all of certain things.
Much like Voyager 1‘s “Pale Blue Dot” photo, seeing Earth from space helps to drive home the fact that life is rare and precious. It also reminds us that we, as a species, are all in this together and completely and utterly dependent on our planet and its ecosystems. Once in awhile, we need to be reminded of these things. Otherwise, we might do some stupid – like ruin it!
Finding planets beyond our Solar System is already tough, laborious work. But when it comes to confirmed exoplanets, an even more challenging task is determining whether or not these worlds have their own satellites – aka. “exomoons”. Nevertheless, much like the study of exoplanets themselves, the study of exomoons presents some incredible opportunities to learn more about our Universe.
Of all possible candidates, the most recent (and arguably, most likely) one was announced back in July 2017. This moon, known as Kepler-1625 b-i, orbits a gas giant roughly 4,000 light years from Earth. But according to a new study, this exomoon may actually be a Neptune-sized gas giant itself. If true, this will constitute the first instance where a gas giant has been found orbiting another gas giant.
Within the Solar System, moons tell us much about their host planet’s formation and evolution. In the same way, the study of exomoons is likely to provide insight into extra-solar planetary systems. As Dr. Heller explained to Universe Today via email, these studies could also shed light on whether or not these systems have habitable planets:
“Moons have proven to be extremely helpful to study the formation and evolution of the planets in the solar system. The Earth’s Moon, for example, was key to set the initial astrophysical conditions, such as the total mass of the Earth and the Earth’s primordial spin state, for what has become our habitable environment. As another example, the Galilean moons around Jupiter have been used to study the conditions of the primordial accretion disk around Jupiter from which the planet pulled its mass 4.5 billion years ago. This accretion disk has long gone, but the moons that formed within the disk are still there. And so we can use the moons, in particular their contemporary composition and water contents, to study planet formation in the far past.”
When it comes to the Kepler-1625 star system, previous studies were able to produce estimates of the radii of both Kepler-1625 b and its possible moon, based on three observed transits it made in front of its star. The light curves produced by these three observed transits are what led to the theory that Kepler-1625 had a Neptune-size exomoon orbiting it, and at a distance of about 20 times the planet’s radius.
But as Dr. Heller indicated in his study, radial velocity measurements of the host star (Kepler-1625) were not considered, which would have produced mass estimates for both bodies. To address this, Dr. Heller considered various mass regimes in addition to the planet and moon’s apparent sizes based on their observed signatures. Beyond that, he also attempted to place the planet and moon into the context of moon formation in the Solar System.
The first step, accroding to Dr. Heller, was to conduct estimates of the possible mass of the exomoon candidate and its host planet based on the properties that were shown in the transit lightcurves observed by Kepler.
“A dynamical interpretation of the data suggests that the host planet is a roughly Jupiter-sized (“size” in terms of radius) brown dwarf with a mass of almost 18 Jupiter masses,” he said. “The uncertainties, however, are very large mostly due to the noisiness of the Kepler data and due to the low number of transits (three). In fact, the host object could be a Jupiter-like planet or even be a moderate-sized brown dwarf of up to 37 Jupiter masses. The mass of the moon candidate ranges somewhere between a super-Earth of a few Earth masses and Neptune’s mass.”
Next, Dr. Heller compared the relative mass of the exomoon candidate and Kepler-1625 b and compared this value to various planets and moons of the Solar System. This step was necessary because the moons of the Solar System show two distinct populations, based the mass of the planets compared to their moon-to-planet mass ratios. These comparisons indicate that a moon’s mass is closely related to how it formed.
For instance, moons that formed through impacts – such as Earth’s Moon, and Pluto’s moon Charon – are relatively heavy, whereas moons that formed from a planet’s accretion disk are relatively light. While Jupiter’s moon Ganymede is the most massive moon in the Solar System, it is rather diminutive and tiny compared to Jupiter itself – the largest and most massive body in the Solar System.
In the end, the results Dr. Heller obtained proved to be rather interesting. Basically, they indicated that Kepler-1625 b-i cannot be definitively placed in either of these families (heavy, impact moons vs. lighter, accretion moons). As Dr. Heller explained:
“[T]]he most reasonable scenarios suggest that the moon candidate is more of the heavy kind, which suggests it should have formed through an impact. However, this exomoon, if real, is most likely gaseous. The solar system moons are all rocky/icy bodies without a significant gas envelope (Titan has a thick atmosphere but its mass is negligible). So how would a gas giant moon have formed through an impact? I don’t know. I don’t know if anybody knows.
“Alternatively, in a third scenario, Kepler-1625 b-i could have formed through capture, but this implies a very unlikely progenitor planetary binary system, from which it was pulled into a bound orbit around Kepler-1625 b, while its former planetary companion was ejected from the system.”
What was equally interesting were the mass estimates for Keple-1625 b, which Dr. Heller averaged to be 19 Jupiter masses, but could be as high as 112 Jupiter Masses. This means that the host planet could be anything from a gas giant that is just slightly larger than Saturn to a Brown Dwarf or even a Very-Low-Mass-Star (VLMS). So rather than a gas giant moon orbiting a gas giant, we could be dealing with a gas giant moon orbiting a small star, which together orbit a larger star!
It’s the stuff science fiction is made of! And while this study cannot provide exact mass constraints on Keplder-1625 b and its possible moon, its significance cannot be denied. Beyond providing astrophysicists with the first possible example of a gas giant moon, this study is of immense significance as far as the study of exoplanet systems is concerned. If and when Kepler-1625 b-i is confirmed, it will tell us much about the conditions under which its host formed.
In the meantime, more observations are needed to confirm or rule out the existence of this moon. Fortunately, these observations will be taking place in the very near future. When Kepler-1625 b makes it next transit – on October 29th, 2017 – the Hubble Space Telescope will be watching! Based on the light curves it observes coming from the star, scientist should be able to get a better idea of whether or not this mysterious moon is real and what it looks like.
“If the moon turns out to be a ghost in the data, then most of this study would not be applicable to the Kepler-1625 system,” said Dr. Heller. “The paper would nevertheless present an example study of how to classify future exomoons and how to put them into the context of the solar system. Alternatively, if Kepler-1625 b-i turns out to be a genuine exomoon, then my study suggests that we have found a new kind of moon that has a very different formation history than the moons we know as of today. Certainly an exquisite riddle for astrophysicists to solve.”
The study of exoplanet systems is like pealing an onion, albeit in a dark room with the lights turned off. With every successive layer scientists peel back, the more mysteries they find. And with the deployment of next-generation telescopes in the near future, we are bound to learn a great deal more!
Long before the Apollo missions reached the Moon, Earth’s only satellites has been the focal point of intense interest and research. But thanks to the samples of lunar rock that were returned to Earth by the Apollo astronauts, scientists have been able to conduct numerous studies to learn more about the Moon’s formation and history. A key research goal has been determining how much volatile elements the Moon possesses.
Intrinsic to this is determining how much water the Moon possesses, and whether it has a “wet” interior. If the Moon does have abundant sources of water, it will make establishing outposts there someday much more feasible. However, according to a new study by an international team of researchers, the interior of the Moon is likely very dry, which they concluded after studying a series of “rusty” lunar rock samples collected by the Apollo 16 mission.
Determining how rich the Moon is in terms of volatile elements and compounds – such as zinc, potassium, chlorine, and water – is important because it provides insight into how the Moon and Earth formed and evolved. The most-widely accepted theory is that Moon is the result of “catastrophic formation”, where a Mars-sized object (named Theia) collided with Earth about 4.5 billion years ago.
The debris kicked up by this impact eventually coalesced to form the Moon, which then moved away from Earth to assume its current orbit. In accordance with this theory, the Moon’s surface would have been an ocean of magma during its early history. As a result, volatile elements and compounds within the Moon’s mantle would have been depleted, much in the same way that the Earth’s upper mantle is depleted of these elements.
“It’s been a big question whether the moon is wet or dry. It might seem like a trivial thing, but this is actually quite important. If the moon is dry – like we’ve thought for about the last 45 years, since the Apollo missions – it would be consistent with the formation of the Moon in some sort of cataclysmic impact event that formed it.”
For the sake of their study, the team examined a lunar rock named “Rusty Rock 66095” to determine the volatile content of the Moon’s interior. These rocks have mystified scientists since they were first brought back by the Apollo 16 mission in 1972. Water is an essential ingredient to rust, which led scientists to conclude that the Moon must have an indigenous source of water – something which seemed unlikely, given the Moon’s extremely tenuous atmosphere.
Using a new chemical analysis, Day and his colleagues determined the levels of istopically light zinc (Zn66) and heavy chlorine (Cl37), as well as the levels of heavy metals (uranium and lead) in the rock. Zinc was the key element here, since it is a volatile element that would have behaved somewhat like water under the extremely hot conditions that were present during the Moon’s formation.
Ultimately, the supply of volatiles and heavy metals in the sample support the theory that volatile enrichment of the lunar surface occurred as a result of vapor condensation. In other words, when the Moon’s surface was still an ocean of hot magma, its volatiles evaporated and escaped from the interior. Some of these then condensed and were deposited back on the surface as it cooled and solidified.
This would explain the volatile-rich nature of some rocks on the lunar surface, as well as the levels of light zinc in both the Rusty Rock samples and the previously-studied volcanic glass beads. Basically, both were enriched by water and other volatiles thanks to extreme outgassing from the Moon’s interior. However, these same conditions meant that most of the water in the Moon’s mantle would have evaporated and been lost to space.
This represents something of a paradox, in that it shows how rocks that contain water were formed in a very dry, interior part of the Moon. However, as Day indicated, it offers a sound explanation for an enduring lunar mystery:
“I think the Rusty Rock was seen for a long time as kind of this weird curiosity, but in reality, it’s telling us something very important about the interior of the moon. These rocks are the gifts that keep on giving because every time you use a new technique, these old rocks that were collected by Buzz Aldrin, Neil Armstrong, Charlie Duke, John Young, and the Apollo astronaut pioneers, you get these wonderful insights.”
These results contradict other studies that suggest the Moon’s interior is wet, one of which was recently conducted by researchers at Brown University. By combining data provided by Chandrayaan-1 and the Lunar Reconnaissance Orbiter (LRO) with new thermal profiles, the Brown research team concluded that lots of water exists within volcanic deposits on the Moon’s surface, which could also mean there are vast quantities of water in the Moon’s interior.
To these, Day emphasized that while these studies present evidence that water exists on the lunar surface, they have yet to offer a solid explanation for what mechanisms deposited it on the surface. Day and his colleague’s study also flies in the face of other recent studies, which claim that the Moon’s water came from an external source – either by comets which deposited it, or from Earth during the formation of the Earth-Moon system.
Those who believe that lunar water was deposited by comets cite the similarities between the ratios of hydrogen to deuterium (aka. “heavy hydrogen”) in both the Apollo lunar rock samples and known comets. Those who believe the Moon’s water came from Earth, on the other hand, point to the similarity between water isotopes on both the Moon and Earth.
In the end, future research is needed to confirm where all of the Moon’s water came from, and whether or not it exists within the Moon’s interior. Towards this end, one of Day’s PhD students – Carrie McIntosh – is conducting her own research into the lunar glass beads and the composition of the deposits. These and other research studies ought to settle the debate soon enough!
And not a moment too soon, considering that multiple space agencies hope to build a lunar outpost in the upcoming decades. If they hope to have a steady supply of water for creating hydrazene (rocket fuel) and growing plants, they’ll need to know if and where it can be found!