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Astro Bob: Moon caves may offer cozy shelter for future astronauts

Scientists have found pits on the moon with comfortable "shirt sleeve" temperatures.

Lunar pit
Researchers found that shadowed areas of this pit in the Moon's Sea of Tranquility stays consistently cool during the day and night, with a temperature around 63 degrees Fahrenheit (17 degrees Celsius). The pit — about the size of a football field and 328-feet (100-meters) deep — likely leads to a similarly temperate lava cave.
Contributed / NASA, GSFC, Arizona State University
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Caves have always been places where humans have sought shelter from the elements. For the same reason, they may prove equally useful on the moon one day.

A team of researchers led by planetary scientists at UCLA has discovered shady locations within lunar pits and caves where temperatures remain a nearly constant 63 degrees Fahrenheit day in and day out. That's in stark contrast to the average daily high and low temperatures on the moon's surface, which range from a blistering 260 degrees Fahrenheit (127 degrees Celsius) at midday to a teeth-chattering 280 degrees below zero Fahrenheit (173 degrees below zero Celsius) at night.

Two views of pit
These are two views of a pit in the Sea of Ingenuity (Mare Ingenii) taken under different lighting angles. Shadow measurements show that the pit is 230 feet (70 meters) deep and about 394 feet (120 meters) wide. It's tricky to see here, but the walls are layered, with each shelf a separate lava flow.
Contributed / NASA, GSFC, Arizona State University

Despite Earth and its satellite being the same distance from the sun, the moon has no atmosphere (or clouds) to soften the blow of sunlight or trap heat that escapes at night. Our planet's onion skin-thin envelope of air makes all the difference.

Pits were first discovered in 2009. Now, more than 200 are known based on high resolution photos taken by NASA's Lunar Reconnaissance Orbiter (LRO). Circling as low as 19 miles it can discern details as small as a foot and a half (0.5 meters) across, or about the size of a car tire.

Lava tube
This is the Thurston lave tube on the Big Island of Hawaii. The step mark or "bathtub ring" on the right wall shows the height at which molten lava flowed for some time.
Contributed / Frank Schulenburg, CC BY-SA 3.0

Pits appear to be the collapsed ceilings of lava tubes, which are also found on Earth. They form when a river of molten lava crusts over, starting from the sides and growing inward until the two meet to form a cap of cooling rock over the magmatic flow below. Ice freezes on a river the same way.


Lava tube
A small opening or "skylight" in a lava tube on the Big Island of Hawaii serves an entrance to the sights below.
Contributed / dronepicr, CC BY-SA 2.0

Once the lava flow drains away or is diverted, it leaves a long, hollow tube behind. Later, sections of the roof collapse, exposing the cavern below. The openings are known as "skylights" in volcano-speak.

Much lava flowed beneath and across the moon during its early history. The gray patches called the lunar seas that outline the face of the man-in-the-moon are now-hardened lava flows that rose up from mantle and flooded the enormous basins plowed out by asteroid impacts some 3 billion years ago.

Lunar pits and the caves to which they may lead would make make far more comfortable and stable living quarters for astronauts compared to toughing it out on the moon's surface. Two of the most prominent pits have visible overhangs that clearly lead to caves or voids, and there's strong evidence that the overhang of another may also lead to a large cave.

Marius pit
Variations in lighting reveal the structure of this fascinating pit in the Marius Hills. The center panel, with the Sun high above, gives a great view of the floor. The pit is about 112 feet (34 meters) deep and 295 feet (90 meters) wide.
Contributed / NASA, GSFC, Arizona State University

Tyler Horvath, a doctoral student in planetary science at UCLA, led the study, which was published in this recent (free) paper published in the journal Geophysical Research Letters. He and the team used data gathered by the LRO's Diviner Lunar Radiometer Experiment — a thermal camera that measures lunar surface temperatures — to chart the temperature of the Sea of Tranquility pit over time.

That led to its discovery as a potentially habitable shelter. Like caves on Earth, those on the moon are surrounded by dirt and rock which act as natural insulators to maintain stable temperatures. Of course, you'd still have to wear a spacesuit because there's no air to breathe, but at least you'd be well-protected from solar radiation, cosmic rays and extreme temperatures.

5-day moon
On Wednesday, Aug. 3, the moon will be a thick five-day-old crescent low in the southwestern sky at dusk. With binoculars you can make out several patchy, gray lunar "seas" and some of the larger craters. The Sea of Tranquility is the large, smooth, gray region along the day-night boundary just above a line running through the center of the moon.
Contributed / Bob King

Imagine walking into one of these caves. What rare mineral formations (lunar stalactites!) await the first astronaut to rappel down to the pit's floor and swing a flashlight around for a look.

I suppose the only question would be how to get in and out of one of these pits safely. But given that our ancestors figured that one out, I trust we'll do the same when the time comes.

Read more from Astro Bob
The smallest, swiftest planet puts on a fine show the next couple weeks.

"Astro" Bob King is a freelance writer for the Duluth News Tribune.

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at nightsky55@gmail.com.
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