23 September 2016

The Eighth Continent

The northern hemisphere of the moon as viewed from the Jupiter-bound Galileo spacecraft during an Earth gravity-assist flyby. Parts of the spectrum invisible to the human eye are rendered as green and bluish tints; these provide hints to the complex, barely understood mineralogy of lunar features. Image credit: NASA
Earth's moon is for most people just a light in the sky. Many of us who have followed the course of spaceflight know that it is in fact a place we have barely explored.

I like to think of our planet's moon as its eighth continent. In terms of extent, Asia is, at 44.6 million square kilometers, the largest continent. The moon is next in order, with 37.9 million square kilometers. Africa comes in third with 30.4 million square kilometers.

Another way to look at this is, the moon has more area than North America (24.7 million square kilometers) and Europe (10.2 million square kilometers) combined. Or one could say that the moon has about the same surface area as five Australias (7.7 million square kilometers each) or three Antarcticas (14 million square kilometers each).

South America, at 17.8 million square kilometers fifth in area after Asia, the moon, Africa, and North America, has a little less area than one lunar hemisphere. When we look up at the hemisphere the moon holds forever turned toward Earth, the Nearside, we view a surface area that could comfortably encompass Brazil, Argentina, Colombia, Venezuela, Peru, Chile, Ecuador, Bolivia, Uruguay, Suriname, French Guiana, Guyana, and Paraguay, plus the nations of Central America and the Caribbean. Half a billion people call those countries home.

If there's one hemisphere we can see from Earth, it follows that there's a hemisphere we cannot see. Called the Farside, we have observed it only from lunar-orbiting spacecraft or more distantly, from interplanetary spacecraft flying through the Earth-moon system (see image at top of post). No lander, rover, or astronaut has explored there. The Farside is home to the South Pole-Aitken Basin, the largest impact basin on the moon and one of the top five largest impact basins in the entire Solar System. Its full extent and depth were not confirmed until the last years of the 20th century.

Many people - including space enthusiasts, who really should know better - look at the moon and say, "been there, done that." The fact is, we have examined up close far less than 1% of the moon's surface. All the territory that the Surveyor and Luna robot landers, Apollo astronauts, and Lunokhod robot rovers of the 1960s and 1970s explored could fit within a smallish city.

All of this unexplored territory is close at hand - on average just 385,000 kilometers away, a distance approximately equal to 10 times Earth's circumference. There exist automobiles and many ships and aircraft that have racked up more kilometers than that. If we still possessed Saturn rockets and Apollo spacecraft, in three days you could climb a ladder down to the surface of the moon. That compares favorably with the travel time to remote places on Earth, such as Antarctica or the ocean abyss.

The eighth continent. The phrase makes the moon seem more real, more like a place, more like a part of Earth. That's how it should be. Earth and moon form a unique system. When we see the Earth as everything and its moon as separate, remote, and insignificant, we are only a step removed from ancient peoples who thought the Earth was flat. It's time we stopped that nonsense and gave our eighth continent its due consideration.

18 comments:

  1. I often point out to people that the Moon and Africa are pretty close in surface area, as you point out - but there are some other comparisons which help visualise the size of our neighbours - for example, Mars has about the same surface area as all the countries of the Earth. Venus has enough surface to lay down all those countries three times over. Simple ways to bring the size of such places to life!

    ReplyDelete
    Replies
    1. Bob:

      I like to describe the moon this way because one can see the moon's disk in the sky. We have to "take on faith" to some extent that Mars and Venus have complex surfaces because they are never more than bright star-like points to our unaided eyes.

      dsfp

      Delete
  2. It's a really interesting way of looking at the Moon. I've never thought about it in that way before, thanks for the shift in perspective.
    Kerrin

    ReplyDelete
    Replies
    1. You are welcome. This post is a draft of some text I am writing for a new display where I work (USGS Astrogeology in Flagstaff, Arizona). International Observe The Moon Day is 8 October, and we are coming up fast on the first of a series of important Apollo 50th anniversaries - the Apollo 1 fire in January 2017 and the first launch of a Saturn V rocket in November 2017. So, it's an opportune time to think about the eighth continent, in my opinion.

      dsfp

      Delete
  3. I have a great pre-Apollo, sci-fi novel from 1955 called "continent in the sky" https://www.kirkusreviews.com/book-reviews/paul-berna/continent-in-the-sky/
    My mom got it in 1955, the year it was published, and it survived for decades.

    ReplyDelete
    Replies
    1. Fascinating! The review says it was translated from French. Too bad about not including women or girls, but that's the 1950s for you!

      dsfp

      Delete
  4. If NASA, as actually proposed, had made provisions for the LRVs to be teleoperated and hence continue the exploration of the Moon after the departure of the Apollo astromauts, a bit more of the lunar surface would have been explored. What a waste.

    ReplyDelete
    Replies
    1. I think the teleoperated LRVs might have been overly ambitious if the aim was to drive from one Apollo site to another. But if the aim was simply to continue exploring after the Apollo astronauts stopped visiting the moon, they'd have been pretty nifty. The video from the LRV remote-controlled camera captured some of that "I'm on the moon and no one else is here" feeling.

      dsfp

      Delete
    2. There were two Lunokhods doing pretty much that job, one of them being not too far from the Apollo 15 landing site. Still it would have been a nice idea. Were early 1970s technology up to the task?

      Delete
    3. Lunokhod 2 is north of the Apollo 17 site in Le Monnier crater, but Lunokhod 1 is all the way across Mare Imbrium from Apollo 15.

      dsfp

      Delete
  5. The Jules Verne classic From the Earth to the Moon had some of the US Naval officers waiting to retrieve the Columbiad when it splashed down (how prophetic can you get) talking about sending troops to the Moon on the next flight to subdue the natives there and make Earth's satellite the 36th state! No PC in 1865, I guess.

    ReplyDelete
    Replies
    1. I have a copy of FROM THE EARTH TO THE MOON with historical and cultural annotations. It's fascinating to get the 19th-century background. 1865 had its own version of PC that most of us today - even those who deride political correctness - would find repugnant, I suspect. We grow and change and hopefully learn to get along.

      dsfp

      Delete
  6. The moon has always held a special place for me because Apollo 11 launched on my birthday. I mean what a birthday candle, Saturn V!

    ReplyDelete
    Replies
    1. That's pretty neat. I was seven when Apollo 11 landed. I remember watching the landing and moonwalk on my parents' old console TV in the family room downstairs. I ran outside a couple of times during descent to tell my dad and passers-by to get to a TV. My little brother fell asleep even before the moonwalk started - it was well past our bedtimes. I think I fell asleep during Nixon's phone call.

      dsfp

      Delete
  7. It's right there in plain sight and easy to communicate from, which means that the surface of the moon is more well-mapped than the deep ocean, which is 2 1/2 times larger. I don't think it would be hard to find a 747 jetliner on the moon, but MH370 is still lost somewhere in the Indian Ocean after years of searching. I don't know which is the more challenging environment to work in, the vacuum and abrasive dust on the Lunar surface, or the unimaginable pressure, corrosive salt water and mud of the ocean bottom, not to mention that the darkness is eternal and opaque, not simply two weeks of starry night.

    ReplyDelete
    Replies
    1. They've been finding pieces of MH370 for a while, but you're right, most of the plane is deep down, probably not in its original shape (broken up) and thus hard to locate using sonar. A 747 (or equivalent-size lunar outpost) would stand out like crazy on the moon in LROC images, unless most of it were buried for radiation protection, but I suspect that the disturbed ground would show up plainly (it does in Apollo site images) and various exposed bits (solar arrays, big antennas, radiators) would be geometrical and thus pretty obvious.

      The lunar environment is probably about as harsh as the deep-ocean, I suspect, though the problems are completely different (as you indicate). Of course, it depends to some degree on where one puts the base. Putting it atop a permanently lit (or nearly) near-polar crater rim would mostly smooth out the temperature swings, for example. Radiation and micrometeoroids could be dealt with through habitat burial, though burying would mean throwing that insidious, hard, intensely scratchy dust around even if one had in hand an excavator that bagged the dust. I suspect that the dust will be on of the greatest challenges, though Mars dust will be worse - moon dust doesn't fill the sky!

      dsfp

      Delete
  8. Even more mysterious than the far side is the cold traps. Crater floors that haven't felt sunlight in eons and with temperatures colder than Pluto. Some of the strangest spots in the solar system in our back yard.

    ReplyDelete
    Replies
    1. That's a very good point. Would you happen to know what percentage of the moon's surface area is permanently dark?

      An earlier version of this got into the cold traps in the context of mining propellants, but I thought it muddled the main idea, which is that the moon has a lot of turf for us to explore and we've looked at only a tiny area up close.

      I wonder if we'll be able to build digging and hauling equipment that can function in the cold traps?

      dsfp

      Delete

I like hearing from my readers. No rules except the obvious ones - please keep it civil and on topic.