Spot The Apollo 17 Landing Site And Learn Why Hubble Can’t See The Landers

In December 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon in the Taurus-Littrow valley. This photo was taken by Cernan as he and Schmitt roamed the valley floor and shows Schmitt on the left with the lunar rover at the edge of Shorty Crater. Just below the crumbling rock to the upper right of the rover, Schmitt discovered orange lunar soil (visible in the photo). Other orange patches are seen on the crater’s wall at far right. The Apollo 17 crew returned with 242.5 pounds (110 kg) of rock and soil samples. All lunar samples from the Apollo missions are curated at the Lunar Sample Laboratory Facility at Johnson Space Center in Houston. Scientists can request samples for research. Apollo 17 crew / NASA

45 years ago next month, Apollo 17 astronauts Gene Cernan and Harrison Schmitt took three separate hikes and car rides on the lunar surface in the Taurus-Littrow Valley, a low spot tucked between the mountains that rim the southeastern “shore” of the Sea of Serenity. You can take a pair of binoculars, or better, a telescope and look at the spot tonight.

The Apollo 17 astronauts discovered and brought back samples of the orange soil (foreground) found at Shorty Crater. The orange material turned out to be tiny spheres of volcanic glass shot up from beneath the surface in “fire fountains” as part of an explosive volcanic eruption here 3.64 billion years ago. NASA

All that’s visible with earthbound telescopes is a location; the Apollo descent stage, rover and astronauts footpaths are below the limit of resolution even with the Hubble Space Telescope. People argue with me about that. They’ll point out rightly that Hubble can see see millions of galaxies, so why can’t we see the Apollo leftovers? Hubble’s highest resolution camera can resolve (picture) objects down to 0.03 arc seconds. One arc second is 1/60th of an arc minute and one arc minute is 1/30th the diameter of a full moon, so you see that 0.03 subtends a VERY tiny angle.

The Apollo 11 Lunar Module Eagle photographed in lunar orbit from the Command and Service Module Columbia in July 1969. Inside the module were Commander Neil A. Armstrong and Lunar Module Pilot Buzz Aldrin. NASA

The biggest piece of hardware left on the lunar surface by the Apollo lunar landings was the descent stage, which measured 4.37 yards (4 m) across. At the moon’s distance, 4.37 yards is only 0.002 arc seconds wide, an order of magnitude and then some below Hubble’s limit. The only way we’ve been able to see the Apollo sites up close is through the eyes of NASA’s Lunar Reconnaissance Orbiter (LRO). Its orbit can be lowered to about 22 miles (35 km), close enough to take low res images of footpaths, the rovers, the descent stages and even a couple of the remaining flags.

At the Apollo 17 site, photographed by the LRO, the tracks laid down by the lunar rover are clearly visible, along with the last foot trails left on the moon. The images also show where the astronauts placed some of the scientific instruments that provided the first insight into the moon’s environment and interior. NASA

Hubble can spot individual stars in relatively distant galaxies millions of light years away, stars that are way below the telescope’s resolution limit. How is that be possible? Easy. The star’s a brilliant point of light shining in the blackness of space. Hubble can’t see any details of the star, but the contrast makes it easy to see the thing itself.

The moon will be a thick crescent tonight. Use this map to spot the Apollo 17 landing site location along the eastern side of the Sea of Serenity near the prominent craters Posidonius and Plinius. I’ve also labeled a wonderful trio of craters in the moon’s southern hemisphere. Virtual Moon Atlas

The descent stage takes up only 0.15% of a pixel in a photograph. To fill just one pixel, the limit in terms of being able to say, “yes, it’s there,” we’d need to put a telescope with a 1,575-inch mirror (40-meter) into orbit. Hubble’s mirror measures just 94-inches (2.38-meters) across. No can do.

But I digress.

Have a telescope? This closeup view better pinpoints the narrow, dark Taurus-Littrow Valley and landing site. Virtual Moon Atlas

If you’re blessed with a clear sky tonight, the fat crescent moon will catch your eye in the southwestern sky. At six different places, our fellow humans have kicked up dust up on that rocky orb.

Vice President Mike Pence delivers opening remarks during the National Space Council’s first meeting, Thursday, Oct. 5, 2017. The Trump administration wants NASA to return to the moon. NASA/Joel Kowsky

Cernan and Schmitt were the last people to leave their footprins. Indeed, it’s hard to believe so many years have passed since humankind launched a manned lunar mission. That may soon change but not without swallowing a bitter pill for some. The past administration made a manned mission to Mars a priority; the current administration instead wants NASA to focus on returning to the moon and establishing a permanent base there.

Although my heart belongs to Mars, refocusing on the moon has key advantages: it’s easier, faster and safer. Putting the moon first would delay a mission to Mars by 10 or 20 years. Supporters counter by offering that the experience gained there would be invaluable in making a trip to Mars and setting up a base there.

What do you think?


6 Responses

    1. astrobob

      I wish it were that simple. Politics has always been a part of NASA funding not to mention the competing interests of scientists in the agency.

  1. Troy

    There’s actually a lot left to do on the moon. The poles and far side remain unexplored. It would be better if India and China duked it out for the moon.
    Rather than Mars, a Near Earth Asteroid would make a great target. I already have the music picked out for NASA to play for their wake up call, “It’s a small world after all”. (But seriously NEOs have the most potential for profit and problems.)

    1. astrobob

      Absolutely, Troy. Imagine if we only visited six small locales on Earth. That would only give us a gross idea of the planet’s qualities and life. A polar base on the moon’s a great idea because you’d get nearly continuous sunlight. With the new administration’s priorities, I’m going to miss that asteroid initiative.

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