Friday, March 20, 2015

A Hidden Crater, Lava Tubes, and Mercurian Ice

A bit shy of eight decades ago, a pilot and navigator set off on a round-the-world flight that should have provided ample material for her next book. Instead, shortly after midnight, July 2, 1937 GMT, the modified Lockheed Model 10 Electra disappeared.

She's still famous — and now has an invisible Lunar crater named after her. Eventually, Fred Noonan may have some rock named after him, or maybe not. In a perfect world, folks in the support crew would get a tad more recognition — my opinion — but this isn't a perfect world.

What's remarkable about Earhart Crater is that it's big, on the side of Earth's moon facing our planet — and buried under billions of years' of accumulated debris. Scientists found it while sifting through gravitational data.

Other scientists found that lava tubes would be strong and safe enough to house a Lunar base, and Messenger took pictures of ice on Mercury.
  1. Lunar Construction in Lava Tubes?
  2. Ice on Mercury
  3. Earhart Crater: But First, an Aviation Mystery and Shangri-La

Getting a Grip About Celestial Spheres

I'm not one bit surprised that Messenger (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) didn't hit a solid dome, or Plato's Celestial spheres. We've learned quite a bit in the last two dozen or so centuries: and quite a bit since my youth.

I'm okay with that, even though — make that especially if — it means un-learning some of what I learned in high school.

My faith doesn't require an interest in science, but it's not threatened by facts either.

I'm a Christian, a Catholic. Among other things, that means I must read and believe the Bible. (Catechism of the Catholic Church, 101-133)

But I don't have to pretend that Job 9:6-7 is meant as a geography lesson: or that our Sun goes around Earth because Joshua 10:12-13 says so. (November 14, 2014)

Honest research cannot hurt faith.
"...God can not deny himself, nor can truth ever contradict truth...."
(Dei Filius, Vatican Council I, 248 (1870) (quoted in Catechism, 159))
Faith and reason, religion and science, aren't the same: but they they both point toward God. (Catechism, 39, 159, 282-286)

If anything, learning that the universe is larger and more ancient than we'd thought deepens admiration for the Creator: or should. My opinion.
"The question about the origins of the world and of man has been the object of many scientific studies which have splendidly enriched our knowledge of the age and dimensions of the cosmos, the development of life-forms and the appearance of man. These discoveries invite us to even greater admiration for the greatness of the Creator, prompting us to give him thanks for all his works and for the understanding and wisdom he gives to scholars and researchers"
(Catechism, 283) [emphasis mine]
We're supposed to wonder how things began and where we're headed. It's part of being human. (Catechism, 282-289, 2293)

1. Lunar Construction in Lava Tubes?

(From BBC News; used w/o permission.)
("This lava tube is in Hawaii, but the features could be even bigger on the Moon"
(BBC News))
"Lava tubes safe enough for Moon base"
Paul Rincon, BBC News (March 19, 2015)

"Natural tunnels known as lava tubes could safely house permanent bases on the Moon, scientists have said.

"The underground volcanic structures have previously been proposed as ideal sites for human settlements.

"Scientists have now assessed how stable these features might be, and found that tubes of 1km in size and bigger would be structurally sound.

"They could protect against the challenges posed by the lunar environment....

"...Unlike Earth, the Moon lacks a thick atmosphere and magnetic field to protect it against cosmic radiation. The absence of an atmospheric buffer also means that the Moon's surface receives more frequent meteorite impacts and more extremes of temperature.

"For example, the Moon's surface temperature can vary by several hundred degrees C during the course of a lunar day...."
It's not just temperature extremes. There's nothing between the Lunar surface and our star except more-or-less open space: so radiation is an issue, too. Earth's atmosphere and magnetosphere play hob with our efforts to observe the universe: but they're good for keeping us alive.

Getting back to David Blair's team, working at the Purdue University in West Lafayette, I gather that what they've done is an engineering assessment of lunar rock.

They ran data about (hypothetical) lunar lava tubes with different widths, roof shapes and roof thicknesses, through simulations — and found that we could fit downtown Philadelphia inside a subterranean (sublunarean?) dome, with room to spare. Lots of room.

Eventually, we may make our own 'lava tubes:' melting subsurface rock, using energy generated from sunlight during Luna's long day.

Next Stop: New Xanadu?

(From David Blair, via BBC News; used w/o permission.)
("Lunar lava tubes should be stable up to about 5km wide"
(BBC News))
"In Xanadu did Kubla Khan
A stately pleasure-dome decree....

"...So twice five miles of fertile ground
With walls and towers were girdled round:
And there were gardens bright with sinuous rills,
Where blossomed many an incense-bearing tree;
And here were forests ancient as the hills,
Enfolding sunny spots of greenery....
(Kubla Khan, Samuel Taylor Coleridge)
Xanadu is a real place, by the way: a city on the Silk Road, and Kubla Kahn's capital before he moved his headquarters to Khanbaliq. These days we call Khanbaliq Beijing, and a thousand years from now it may have another name.

It's anyone's guess why folks from Megara settled where Kadıköy is now, instead of where Byzantium was. Still is, for that matter, except it's been renamed Constantinople, and then Istanbul. Work on the Yenikapı subway station and Marmaray tunnel uncovered pieces of what folks had built there, some 87 centuries back. I've no idea what they called it then.

Then there's Londinium, that's apparently been a port city off and on for at least ten millennia. And that's another topic. Topics. (June 6, 2014)

Getting back to Xanadu/Shangdu, Marco Polo described the place he visited on his way to Bagan and back. And I'm off-topic again.

Or maybe not so much.

I'd be very surprised if we start building cities on Earth's moon in the next few decades: or maybe centuries. We've got most of the tech we need: the holdup is economic.

With very few exceptions, like Brasilia, we build cities where folks take cargo from one sort of transportation to another: canoes to camels, trucks to container ships, maglev pods — — — no, wait. We aren't making those yet  — — — or where we make something from a natural resource that's inconvenient to move in bulk. Steubenville, Ohio, and Detroit, Michigan, are examples.

My guess is that there'll be at least one major break-bulk city on Earth's moon — in orbit, more likely — once enough folks have found reasons for living on Mars and other places. Terraforming Venus will probably take longer, and I'm losing focus again. (January 24, 2014; October 11, 2013)

On the other hand, maybe we'll never do more than visit other worlds. I don't think that's likely, though. One thing that hasn't changed in the last two million years is the human habit of finding new places to live. My guess is that it's not going to change. Not any time soon. (December 12, 2014; July 11, 2014)

(From Rick Potts, Susan Antón and Leslie Aiello; via the Smithsonian, used w/o permission.)
(One of humanity's many migrations.)

2. Ice on Mercury

(From NASA, via BBC News; used w/o permission.)
("The 27km-wide Fuller crater is among those that have now been observed in much more detail than ever before"
(BBC News))
"Best views yet of Mercury's ice-filled craters"
Paul Rincon, BBC News (March 17, 2015)

"Scientists have obtained the most detailed views yet of ice deposits inside the permanently shadowed craters at Mercury's north pole.

"The pictures were taken by Nasa's Mercury Messenger spacecraft, which has been orbiting just tens of kilometres from the planet's surface.

"This has allowed it to gather high-resolution data before the probe crashes into Mercury.

"This will end its four-year mission around the first planet from the Sun.

"You could be forgiven for wondering how a planet where temperatures soar above 400C could host water-ice.

"But some impact craters at the north pole of this scorching world are always shadowed from the Sun, turning them into cold traps.

" 'We're seeing into these craters that don't see the Sun, at higher resolution than was ever possible before,' Dr Nancy Chabot, the instrument scientist for Messenger's Mercury Dual Imaging System (MDIS), told a news conference...."
Messenger detected carbon compounds, too: organic material, probably from comets that got too close to Mercury.

No: I am not going to wander off on speculation about habitable worlds and life not-quite-as-we-know it. Maybe next week. No, wait: I did that last week. Again. (March 13, 2015; May 10, 2013)

Mercury looks a lot like Earth's moon: impact craters, smoothish plains of basaltic rock, and no atmosphere to speak of. Observing the place has been tricky, since it's so close to the sun: which is why data from the Messenger orbiter is so valuable.

Turns out, it's got a magnetic field: about one one hundredth as strong as Earth's. It's probably generated by a naturally-occurring dynamo, like Earth's, and I'll get back to that. More or less.

Mercury's Lively Past: and Present

(From NASA, via BBC News; used w/o permission.)
("A colour-coded image from MDIS shows the wide range of surface temperatures, from -223C (purple) to more than 125C (red)"
(BBC News))
"...Messenger's final, low-altitude campaign is also allowing scientists to get a closer view at other surprising phenomena on the surface.

"Early in the mission, scientists spotted strange hollows in the surface. They are found at locations all over the planet and ranged in size from tens of metres to several kilometres across, and tens of metres deep.

"David Blewett, a participating scientist on the Messenger team, said the hollows probably formed when some ingredient of rocks on Mercury was exposed to the harsh environment of the planet's surface. Sublimation (or a similar process), where solids change directly into gas, could be the mechanism.

"Together with other evidence, these paint a picture of a dynamic world, not the dead relic Mercury was thought to be decades ago...."
(Paul Rincon, BBC News))
Mercury's apparently had a lively past, too. This little world has one of the Solar System's largest known impact features, the Caloris Basin: and "Chaotic/Weird Terrain" that's exactly on the other side of Mercury.

Mercury's Weird Terrain may be where debris from the Caloris impact hit — or what happens when seismic waves get focused by a planet's core.

Something like that may have caused a million-year-long nation-size volcanic event that probably helped kill off about nine tenths of life on Earth. There are worse things than carelessly discarded six-pack rings, and that's yet another topic. (June 27, 2014; November 29, 2013)

Those Mercurian hollows are crater-free — which means they're very young, no more than a few multiples of 10,000,000 years old. On a geologic time scale, that's young.

Another Mercurian oddity is the size of its core, relative to the planet. The thing's huge.

Or maybe Mercury's mantle is really small.

Messenger's deputy principal investigator, Larry Nittler, says a very plausible explanation is that something big hit Mercury, back when the Solar planets were playing bumper cars. (March 13, 2015)

That sort of impact could have knocked most of Mercury's original mantle off the planet — but we'll need more data before that's more than a plausible and interesting idea.

3. Earhart Crater: But First, an Aviation Mystery and Shangri-La

(From Getty Images, via BBC News; used w/o permission.)
("Amelia Earhart set a number of flying records before her disappearance in 1937"
(BBC News))
"New lunar crater named after aviation pioneer Earhart"
Paul Rincon, BBC News (March 17, 2015)

"Scientists have discovered a large crater on the Earth-facing side of the Moon - the first detection of its kind in at least a century.

"The previously unknown structure has been named after aviation pioneer Amelia Earhart - the first woman to fly solo across the Atlantic.

"The 200km-wide buried crater was found in data from Nasa's Grail spacecraft, which mapped the Moon's gravity field.

"The results were presented at a major scientific meeting in Texas.

"The discovery was the outcome of work by Rohan Sood, Loic Chappaz and Prof H Jay Melosh at Purdue University, where Earhart was a member of the academic faculty from 1935 until her death in 1937...."
Amelia Earhart is a fairly high-profile cultural icon, which probably explains why BBC News put her photo at the top of this article.

These days, she's chiefly known for dropping out of site somewhere in the Pacific. She was an aviation pioneer, author, Charles Lindbergh lookalike, and promoter of an 'active living' clothing line.

Colorful explanations for her disappearance include claims that she was a spy for FDR, Tokyo Rose, and that she assumed another identity.

My guess is that she ran out of gas, had engine trouble, or encountered some other inconvenience, over Earth's largest expanse of water: then died, taking a navigator with her.

It's possible that radio signals which may or may not have come from Erhart's (damaged?) radio, picked up at Howland Island, show that she landed on Nikumaroro, a patch of land called Gardner Island by Westerners in those days.

Interestingly, that's in very roughly the same area as Malden Island, where someone built stone structures — a few centuries back, most likely. Who knows? Maybe Earhart accidentally triggered a gate to Shangri-La, and has been contemplating the whichness of what ever since.

No, I don't think so: and Shangrli-La, the real one, is an administrative center for China's Dêqên Tibetan Autonomous Prefecture. I haven't found an authenticated source for "the iron bird flies and horses run on wheels...," and that's still another set of topics.

Buried for Billions of Years

(From BBC News, used w/o permission.)
("The crater had been heavily altered by a later impact, rendering it unrecognisable"
(BBC News))
"...'The crater probably pre-dates the big Serenitatis basin, which is just south of it. The Serenitatis ejecta covered it up, probably destroying the southern part of the crater rim and greatly modifying it,' Prof Melosh said....

"...The Serenitatis Basin is thought to have been created by a giant impact about 3.9 billion years ago. So Earhart, which lies partially buried under the debris, must be at least that age, but how much older is not known at this stage.

"Grail measured variations in the acceleration of gravity, which can provide a window into the Moon's internal structure...."
(Paul Rincon, BBC News)
Now, about Erhart Crater. It's buried under the Serenitatis Basin, so it's at least 3,900,000,000 years old. Traces of the 200-kilometer-wide crater are (barely) visible, now that we know what to look for.

Scientists found it by taking data about minute differences in Lunar gravity, using math to remove effects from surface features we know about — and what was left was best explained by a previously-unknown crater.

There have probably been dozens more craters like Erhart: but traces of them were wiped away by later impacts. For now, anyway.

A century from now, we may have more data, and better tools, than we do today. I'd be a bit surprised if we didn't: and disappointed. It's nice, knowing that there's more to learn.

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