We’re accustomed to seeing stunning images of both the Moon and Earth floating in space. It’s the age we live in. But seeing them together is rare. Now, NASA’s Deep Space Climate Observatory (DSCOVR) has captured images of the Moon passing between itself and the Earth, in effect photo-bombing Earth.
The image was captured with the Earth Polychromatic Imaging Camera (EPIC) camera on DISCOVR, and is the second time this has been captured. EPIC is a 4 megapixel camera on board DSCOVR, and DSCOVR is in orbit about 1.6 million km (1 million miles) from Earth, between the Earth and the Sun.
“For the second time in the life of DSCOVR, the moon moved between the spacecraft and Earth,” said Adam Szabo, DSCOVR project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Cool pictures of the Moon are a bonus, though, as DSCOVR’s primary mission is to monitor the solar wind in real time for the National Oceanic and Atmospheric Administration (NOAA). It does so while inhabiting the first LaGrange point between the Earth and the Sun, where the gravitational pull of the Sun and the Earth balance each other. To do so requires a complex orbit called a Lissajous orbit, a non-recurring orbit which takes DSCOVR from an ellipse to a circle and back.
DSCOVR has other important work to do. From its vantage point, DSCOVR keeps a constantly illuminated view of the surface of the Earth as it rotates. DSCOVR provides observations of cloud height, vegetation, ozone, and aerosols in the atmosphere. This is important scientific data in monitoring and understanding Earth’s climate.
DSCOVR is a partnership between NASA, NOAA and the U.S. Air Force. As mentioned above, its primary objective is maintaining the nation’s real-time solar wind monitoring capabilities, which are critical to the accuracy and lead time of space weather alerts and forecasts from NOAA. The DSCOVR website also has daily color pictures of the Earth, for all your eye-candy needs.
We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
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Earth has a small companion that NASA is calling an almost-Moon. The small asteroid, called 2016 H03, isn’t quite a moon because it’s actually orbiting the Sun. In its orbit around the Sun, it spends about half of its time closer to the Sun than the Earth.
2016 H03 is called a “quasi-moon” or a “near-Earth companion”. It doesn’t quite qualify as a moon because of its orbit.
Paul Chodas is the manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. He had this to say about 2016 H03: “Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth.”
2016 H03’s orbit is tilted relative to Earth’s, and it passes through the plane of Earth’s orbit. Over the decades, it also performs a slow, back and forth twist. NASA describes 2016 H03’s orbit as a game of leap frog.
“The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon,” said Chodas. “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth.”
Earth’s little quasi-moon has been in its stable orbit for about a century, according to calculations, though it was only spotted on April 27th, 2016, by the Pan-STARRS 1 asteroid survey telescope in Hawaii. Pan-STARRS 1 is operated by the University of Hawaii’s Institute for Astronomy and NASA’s Planetary Defense Coordination Office. (Did you know we had a Planetary Defense Coordination Office?)
2016 H03 is small. It’s exact size has not been established, but it’s between 40 and 100 meters (120 and 300 ft.) It’s been around a century, and calculations say it will be around for centuries more.
2016 H03 is not quite unique. Earth has had other dance partners like it.
“One other asteroid — 2003 YN107 — followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come,” said Chudas.
NASA tracks thousands of NEOs and assesses their risk of collision with Earth. Though 2016 H03 is an interesting specimen because of its orbit, it poses no threat to Earth.
Over the course of the past few decades, our ongoing exploration the Solar System has revealed some surprising discoveries. For example, while we have yet to find life beyond our planet, we have discovered that the elements necessary for life (i.e organic molecules, volatile elements, and water) are a lot more plentiful than previously thought. In the 1960’s, it was theorized that water ice could exist on the Moon; and by the next decade, sample return missions and probes were confirming this.
Since that time, a great deal more water has been discovered, which has led to a debate within the scientific community as to where it all came from. Was it the result of in-situ production, or was it delivered to the surface by water-bearing comets, asteroids and meteorites? According to a recent study produced by a team of scientists from the UK, US and France, the majority of the Moon’s water appears to have come from meteorites that delivered water to Earth and the Moon billions of years ago.
For the sake of their study, which appeared recently in Nature Communications, the international research team examined the samples of lunar rock and soil that were returned by the Apollo missions. When these samples were originally examined upon their return to Earth, it was assumed that the trace of amounts of water they contained were the result of contamination from Earth’s atmosphere since the containers in which the Moon rocks were brought home weren’t airtight. The Moon, it was widely believed, was bone dry.
However, a 2008 study revealed that the samples of volcanic glass beads contained water molecules (46 parts per million), as well as various volatile elements (chlorine, fluoride and sulfur) that could not have been the result of contamination. This was followed up by the deployment of the Lunar Reconnaissance Orbiter (LRO) and the Lunar Crater Observation and Sensing Satellite (LCROSS) in 2009, which discovered abundant supplies of water around the southern polar region,
However, that which was discovered on the surface paled in comparison the water that was discovered beneath it. Evidence of water in the interior was first revealed by the ISRO’s Chandrayaan-1 lunar orbiter – which carried the NASA’s Moon Mineralogy Mapper (M3) and delivered it to the surface. Analysis of this and other data has showed that water in the Moon’s interior is up to a million times more abundant than what’s on the surface.
The presence of so much water beneath the surface has begged the question, where did it all come from? Whereas water that exists on the Moon’s surface in lunar regolith appears to be the result of interaction with solar wind, this cannot account for the abundant sources deep underground. A previous study suggested that it came from Earth, as the leading theory for the Moon’s formation is that a large Mars-sized body impacted our nascent planet about 4.5 billion years ago, and the resulting debris formed the Moon. The similarity between water isotopes on both bodies seems to support that theory.
However, according to Dr. David A. Kring, a member of the research team that was led by Jessica Barnes from Open University, this explanation can only account for about a quarter of the water inside the moon. This, apparently, is due to the fact that most of the water would not have survived the processes involved in the formation of the Moon, and keep the same ratio of hydrogen isotopes.
Instead, Kring and his colleagues examined the possibility that water-bearing meteorites delivered water to both (hence the similar isotopes) after the Moon had formed. As Dr. Kring told Universe Today via email:
“The current study utilized analyses of lunar samples that had been collected by the Apollo astronauts, because those samples provide the best measure of the water inside the Moon. We compared those analyses with analyses of meteoritic samples from asteroids and spacecraft analyses of comets.”
By comparing the ratios of hydrogen to deuterium (aka. “heavy hydrogen”) from the Apollo samples and known comets, they determined that a combination of primitive meteorites (carbonaceous chondrite-type) were responsible for the majority of water to be found in the Moon’s interior today. In addition, they concluded that these types of comets played an important role when it comes to the origins of water in the inner Solar System.
For some time, scientists have argued that the abundance of water on Earth may be due in part to impacts from comets, trans-Neptunian objects or water-rich meteoroids. Here too, this was based on the fact that the ratio of the hydrogen isotopes (deuterium and protium) in asteroids like 67P/Churyumov-Gerasimenko revealed a similar percentage of impurities to carbon-rich chondrites that were found in the Earth’s coeans.
But how much of Earth’s water was delivered, how much was produced indigenously, and whether or not the Moon was formed with its water already there, have remained the subject of much scholarly debate. Thank to this latest study, we may now have a better idea of how and when meteorites delivered water to both bodies, thus giving us a better understanding of the origins of water in the inner Solar System.
“Some meteoritic samples of asteroids contain up to 20% water,” said Kring. “That reservoir of material – that is asteroids – are closer to the Earth-Moon system and, logically, have always been a good candidate source for the water in the Earth-Moon system. The current study shows that to be true. That water was apparently delivered 4.5 to 4.3 billion years ago.“
The existence of water on the Moon has always been a source of excitement, particularly to those who hope to see a lunar base established there someday. By knowing the source of that water, we can also come to know more about the history of the Solar System and how it came to be. It will also come in handy when it comes time to search for other sources of water, which will always be a factor when trying to establishing outposts and even colonies throughout the Solar System.
Orbital ATK has unveiled a practical new proposal to build a near term man-tended outpost in lunar orbit that could launch by 2020 and be operational in time for a lunar link-up with NASA’s Orion crew module during its maiden mission, when American astronauts finally return to the Moon’s vicinity in 2021 – thus advancing America’s next giant leap in human exploration of deep space.
The intrepid offer by Orbital could be carried out rather quickly because it utilizes an evolved version of the company’s already proven commercial Cygnus space station resupply freighter as “the building block … in cislunar space,” said Frank DeMauro, Orbital ATK Vice President for Human Spaceflight Systems, in an exclusive interview with Universe Today. See an artist concept in the lead image.
“Our Cygnus spacecraft is the building block to become a vehicle for exploration beyond low Earth orbit,” Orbital ATK’s Frank DeMauro told Universe Today.
“We are all about supporting NASA’s Mission to Mars. We feel that getting experience in cislunar space is critical to the buildup of the capabilities to go to Mars.”
NASA’s agency wide goal is to send astronauts on a ‘Journey to Mars’ in the 2030s – and expeditions to cislunar space in the 2020s serve as the vital ‘proving ground’ to fully develop, test out and validate the robustness of crucial technologies upon which the astronauts lives will depend on later Red Planet missions lasting some 2 to 3 years.
Orbital ATK’s lunar-orbit outpost proposal was announced at an official hearing of the US House of Representatives Subcommittee on Space on Wednesday, May 18, by former NASA Astronaut and Orbital ATK President of the Space Systems Group, Frank Culbertson.
“A lunar-orbit habitat will extend America’s leadership in space to the cislunar domain,” said Orbital ATK President of the Space Systems Group, Frank Culbertson.
“A robust program to build, launch and operate this initial outpost would be built on NASA’s and our international partners’ experience gained in long-duration human space flight on the International Space Station and would make use of the agency’s new Space Launch System (SLS) and Orion deep-space transportation system.”
The idea is to assemble an initial crew-tended habitat with pressurized work and living volume for the astronauts based on a Cygnus derived vehicle, and have it pre-positioned and functioning in lunar-orbit by 2020.
As envisioned by Orbital ATK, the habitat would be visited during NASA’s first manned mission of SLS and Orion to the Moon known as Exploration Mission-2 (EM-2).
The three week long EM-2 lunar test flight could launch as early as August 2021 – if sufficient funding is available.
The goals of EM-2 and following missions could be significantly broadened via docking with a lunar outpost. And Orion mission durations could be extended to 60 days.
NASA hopes to achieve a launch cadence for Orion/SLS of perhaps once per year.
Therefore autonomy and crew tended capability has to be built in to the lunar habitat right from the start – since crew visits would account for only a fraction of its time but enable vastly expanded science and exploration capabilities.
The initial lunar habitat envisioned by Orbital ATK would be comprised of two upgraded Cygnus pressurized vehicles – provisionally dubbed as Exploration Augmentation Modules (EAM). They would be attached to a multi-port docking module very similar in concept and design to the docking Nodes already flying in orbit as integral components of the ISS.
The lunar Cygnus vehicles would be upgraded from the enhanced cargo ships currently being manufactured and launched to the ISS.
“There are additional capabilities that we can put into the Cygnus module. We can make them longer and bigger so they can carry more logistics and carry more science,” DeMauro elaborated.
A variety of supplementary subsystems would also need to be enhanced.
“We looked at what systems we would need to modify to make it a long term habitation module. Since we would not be docked to the ISS, we would need our own Environmental Control and Life Support Systems (ECLSS) out at lunar orbit to support the crew.”
“The service module would also need to be improved due to the high radiation environment and the longer time.”
“We also need to look at the thermal protection subsystem, radiation protection subsystem and power subsystems to support the vehicle for many years as opposed to the short time spent at the ISS. More power is also needed to support more science. We also need a propulsion system to get to the Moon and maintain the vehicle.”
“All that work is getting looked at now – to determine what we need to modify and upgrade and how we would do all that work,” DaMauro told me.
The habitat components would be launched to the Moon on a commercial launch vehicle.
High on the list of candidate launchers would be the United Launch Alliance Atlas V rocket which recently already successfully delivered two Cygnus cargo ships to the ISS in Dec. 2015 and March 2016.
Other potential boosters include the ULA Delta IV and even ESA’s Ariane V as a way to potentially include international participation.
The habitat components could be manufactured and launched about three years after getting a ‘Go Ahead’ contract from NASA.
Orbital ATK already has an established production line flowing to manufacture a steady stream of Cygnus cargo freighters to fulfill their NASA commercial resupply contract with NASA for the ISS – accumulating know how and cost reduction efficiencies.
“Since many aspects of operations in deep space are as yet untested, confidence must be developed through repeated flights to, and relatively long-duration missions in, cislunar space,” says Culbertson.
“Orbital ATK continues to operate our Cygnus cargo logistics vehicle as a flagship product, so we are ready to quickly and affordably implement an initial Cygnus-derived habitat in cislunar space within three years of a go-ahead.”
Over time, the outpost could be expanded with additional habitat and research modules delivered by Orion/SLS, commercial or international rockets. Perhaps even Bigelow expandable commercial modules could be added later.
Cygnus is suitable for wide ranging science experiments and gear. It could also launch cubesats – like the current Cygnus berthed at the ISS is equipped with a cubesat deployer.
Potential lunar landers developed by international partners could dock at the cislunar habitats open docking ports in between surface science forays.
“We are doing science now on Cygnus and we would expect to carry along science experiments on the new Cygnus vehicle. The vehicle is very attractive to science experiments,” DeMauro explained.
“There really is no limit to what the outpost could become.”
“What we put out is very exciting,” DeMauro noted.
“As a company we are looking forward to working in this arena. Our suggested plans are in line with where NASA wants to go. And we think we are the right company to play a big part in that!”
By incorporating commercial companies and leveraging the considerable technology development lessons learned from Cygnus, NASA should realize significant cost savings in implementing its human exploration strategy. Although Orbital ATK is not divulging a cost estimate for the lunar habitat at this time, the cost savings from a commercial partner should be considerable. And the 3 year time frame to launch is very attractive.
Orion is designed to send astronauts deeper into space than ever before, including missions to the Moon, asteroids and the Red Planet. Cygnus derived modules and/or other augmenting hardware components will be required to carry out any round trip human missions to the Martian surface.
NASA is now building the next Orion capsule at the Kennedy Space Center. It will launch unpiloted atop the first SLS rocket in late 2018 on the EM-1 mission.
Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.
A crowning achievement of the Cassini mission to Saturn is the discovery of water vapor jets spraying out from Enceladus‘ southern pole. First witnessed by the spacecraft in 2005, these icy geysers propelled the little 515-kilometer-wide moon into the scientific spotlight and literally rewrote the mission’s objectives. After 22 flybys of Enceladus during its nearly twelve years in orbit around Saturn, Cassini has gathered enough data to determine that there is a global subsurface ocean of salty liquid water beneath Enceladus’ frozen crust—an ocean that gets sprayed into space from long “tiger stripe” fissures running across the moon’s southern pole. Now, new research has shown that at least some of the vapor jets get a boost in activity when Enceladus is farther from Saturn.
By measuring the changes in brightness of a distant background star as Enceladus’ plumes passed in front of it in March 2016, Cassini observed a significant increase in the amount of icy particles being ejected by one particular jet source.
Named “Baghdad 1,” the jet went from contributing 2% of the total vapor content of the entire plume area to 8% when Enceladus was at the farthest point in its slightly-eccentric orbit around Saturn. This small yet significant discovery indicates that, although Enceladus’ plumes are reacting to morphological changes to the moon’s crust due to tidal flexing, it’s select small-scale jets that are exhibiting the most variation in output (rather than a simple, general increase in outgassing across the full plumes.)
“How do the tiger stripe fissures respond to the push and pull of tidal forces as Enceladus goes around its orbit to explain this difference? We now have new clues!” said Candice Hansen, senior scientist at the Planetary Science Institute and lead planner of the study. “It may be that the individual jet sources along the tiger stripes have a particular shape or width that responds most strongly to the tidal forcing each orbit to boost more ice grains at this orbital longitude.”
The confirmation that Enceladus shows an increase in overall plume output at farther points from Saturn was first made in 2013.
Whether this new finding means that the internal structure of the fissures is different than what scientists have suspected or some other process is at work either within Enceladus or in its orbit around Saturn still remains to be determined.
“Since we can only see what’s going on above the surface, at the end of the day, it’s up to the modelers to take this data and figure out what’s going on underground,” said Hansen.
Here on Earth, we’re always concerned with the weather.
“OK Google, am I going to need an umbrella tomorrow?”
[Google] No, rain is not expected tomorrow in Curtney. The forecast is 20 degrees and partly cloudy.
Uh, it’s pronounced “Courtenay”.
Fine, what if I lived on the Moon? OK Google, am I going to need an umbrella tomorrow on the Moon?
[Google] …
Let’s take Google’s silence for uncertainty.
The names of geological features on the Moon sure evoke mental images of weather. There’s the Ocean of Storms, also known as Oceanus Procellarum, or the Ocean of Clouds – aka Mare Nubium. In fact, most of the regions of the Moon are named after oceans. That’s got to count for something, right?
They got these names because the early astronomers thought they were seeing actual oceans on the Moon. They imagined vast seas, where heroic 6-legged creepy bug people plied the icy waves seeking fame, fortune and lunar plunder. I don’t know, like gold cheese or something. Seriously, they were making a lot of this stuff up until telescopes were invented.
But when the NASA astronauts finally set foot on the Moon, they knew they wouldn’t need to pack their snorkeling gear because there weren’t any oceans on the Moon, or really any atmosphere. The Moon is almost as dead and lifeless as space itself.
The storms we see battering the astronauts on every Mars science fiction story just can’t happen on the Moon because there’s no air there.
There’s an ongoing lethal radiation solar wind blowing from the Sun and deep space, but nothing that you’d be able to windsurf too.
So why isn’t there an atmosphere on the Moon? It all comes down to gravity. The Moon has about 1% of the mass of the Earth, which means that it doesn’t have enough gravity to hold onto any gas atmosphere. Anything that it did have would have been blown away by the solar wind billions of years ago.
We did a whole episode on what it would take to terraform the Moon, and it turns out you’d need to constantly replenish the atmosphere.
In fact, this is one of the reasons why the Martian atmosphere is so thin. It was probably thicker in the past, but the solar winds stripped off all the lighter atmosphere long ago. Now it’s just 1% the thickness of the Earth’s atmosphere.
Now, I’ve said that the Moon has almost no atmosphere. But almost no means partly yes. There is in fact an incredibly thin atmosphere surrounding the Moon which measures about a hundred trillionth the thickness of the Earth’s atmosphere.
There are a few sources of this atmosphere. First there’s volcanic outgassing that comes from the Moon. this contributes a little helium and radon. Then there’s the constant micrometeorite bombardment that kicks up pulverized lunar regolith.
But perhaps the strangest atmospheric feature is a storm that does rage across the surface of the Moon right at the terminator, the exact line between the Moon’s day side and its night side. It turns out the day side of the Moon is positively charged, and the night side is negatively charged.
As the terminator moves, the polarity of the dust flips and it drives it sideways. In fact, the astronauts who walked on the Moon actually reported seeing this. They saw bands or twilight rays in the sky around lunar sunrise/sunset.
Without a thick atmosphere, the surface of the Moon just doesn’t have any appreciable weather and definitely doesn’t have storms like we have on Earth. Mark Watney will need some other reason than weather to be stuck behind on the Moon.
We always see the same side of the Moon. It’s always up there, staring down at us with its terrifying visage. Or maybe it’s a creepy rabbit? Anyway, it’s always showing us the same face, and never any other part.
This is because the Moon is tidally locked to the Earth; the same fate that affects every single large moon orbiting a planet. The Moon is locked to the Earth, the Jovian moons are locked to Jupiter, Titan is locked to Saturn, etc.
As the Moon orbits the Earth, it slowly rotates to keep the same hemisphere facing us. Its day is as long as its year. And standing on the surface of the Moon, you’d see the Earth in roughly the same spot in the sky. Forever and ever.
We see this all across the Solar System.
But there’s one place where this tidal locking goes to the next level: the dwarf planet Pluto and its large moon Charon are tidally locked to each other. In other words, the same hemisphere of Pluto always faces Charon and vice versa.
It take Pluto about 6 and a half days for the Sun to return to the same point in the sky, which is the same time it takes Charon to complete an orbit, which is the same time it takes the Sun to pass through the sky on Charon.
Since Pluto eventually locked to its moon, can the same thing happen here on Earth. Will we eventually lock with the Moon?
Before we answer this question, let’s explain what’s going on here. Although the Earth and the Moon are spheres, they actually have a little variation. The gravity pulling on each world creates love handle tidal bulges on each world.
And these bulges act like a brake, slowing down the rotation of the world. Because the Earth has 81 times the mass of the Moon, it was the dominant force in this interaction.
In the early Solar System, both the Earth and the Moon rotated independently. But the Earth’s gravity grabbed onto those love handles and slowed down the rotation of the Moon. To compensate for the loss of momentum in the system, the Moon drifted away from the Earth to its current position, about 370,000 kilometers away.
But Moon has the same impact on the Earth. The same tidal forces that cause the tides on Earth are slowing down the Earth’s rotation bit by bit. And the Moon is continuing to drift away a few centimeters a year to compensate.
It’s hard to estimate exactly when, but over the course of tens of billions of years, the Earth will become locked to the Moon, just like Pluto and Charon.
Of course, this will be long after the Sun has died as a red giant. And there’s no way to know what kind of mayhem that’ll cause to the Earth-Moon system. Other planets in the Solar System may shift around, and maybe even eject the Earth into space, taking the Moon with it.
What about the Sun? Is it possible for the Earth to eventually lock gravitationally to the Sun?
Astronomers have found extrasolar planets orbiting other stars which are tidally locked. But they’re extremely close, well within the orbit of Mercury.
Here in our Solar System, we’re just too far away from the Sun for the Earth to lock to it. The gravitational influence of the other planets like Venus, Mars and Jupiter perturb our orbit and keep us from ever locking. Without any other planets in the Solar System, though, and with a Sun that would last forever, it would be an inevitability.
It is theoretically possible that the Earth will tidally lock to the Moon in about 50 billion years or so. Assuming the Earth and Moon weren’t consumed during the Sun’s red giant phase. I guess we’ll have to wait and see.
We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we’ve started a new system. Instead of adding all of the stories to the spreadsheet each week, we are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.
Welcome back to our ongoing series, “The Definitive Guide To Terraforming”! We continue with a look at the Moon, discussing how it could one day be made suitable for human habitation.
Ever since the beginning of the Space Age, scientists and futurists have explored the idea of transforming other worlds to meet human needs. Known as terraforming, this process calls for the use of environmental engineering techniques to alter a planet or moon’s temperature, atmosphere, topography or ecology (or all of the above) in order to make it more “Earth-like”. As Earth’s closest celestial body, the Moon has long been considered a potential site.
All told, colonizing and/or terraforming the Moon would be comparatively easy compared to other bodies. Due to its proximity, the time it would take to transport people and equipment to and from the surface would be significantly reduced, as would the costs of doing so. In addition, it’s proximity means that extracted resources and products manufactured on the Moon could be shuttled to Earth in much less time, and a tourist industry would also be feasible.