Looking For A Good Freezer? Try Shackleton Crater

Mercury and the crescent moon low in the western sky 40 minutes after sunset and about 6 degrees apart. Created with Stellarium

Let’s start with a quick reminder that the thin crescent moon will be low in the western sky during twilight this evening. Look several degrees (two or three fingers held at arm’s length) to its upper right to spot the planet Mercury. Since I’m writing much later than usual, I hope you’ll still have time to catch sight of them both.

Through a telescope at magnifications of 50x and higher, Mercury will look like a very tiny half moon.

Shackleton Crater, named after Antarctic explorer Ernest Shackleton is located at the lunar south pole. Because the moon’s axis is only slightly tilted, the crater’s floor is in perpetual shade. The average temperature there is 300 below zero F. Credit: NASA

The floor of the crater Shackleton, located in the chill shade of moon’s south pole, appears to harbor 22 percent ice among its rocks. That’s the story according to data from NASA’s Lunar Reconnaissance Orbiter (LRO). The craft shot laser beams into the 3-plus billion year-old dusty dark crater interior and measured the brightness of the light reflected back. The results showed that parts of the floor and walls are brighter than those of nearby craters, consistent with the presence of water ice.

Elevation (left) and shaded relief (right) image of the 12.5 mile-diameter crater Shackleton. The structure of the crater’s interior was revealed by a digital elevation model constructed from over 5 million laser elevation measurements made by the LRO. Credit: NASA/Zuber, M.T. et al., Nature, 2012

Shackleton might be one of the solar system’s best places to keep ice cream from melting. Because the tilt of the moon’s axis is a scant 5 degrees compared to Earth’s more generous 23.5 degrees, sunlight only grazes the rims of craters at the north and south poles. Their interiors remain in near-permanent shadow, making them ideal environments for preserving water and other ices that may have been delivered by long-ago comets.

Earth was bombarded by comets, too. That water has long since become one with the rivers, oceans and what pours from your faucet. To read more about Shackleton’s bounty of ice, click HERE.

13 Responses

  1. Tim Fleming

    Hi Bob,
    On my nightly walk with our dog, I saw two interesting sites. One was an tremendously bright and long-lasting iridium flare. It was moving southeast, nearly overhead. I first noticed a bright light in the bowl of the Big Dipper and it headed southeast. I could not find an iridium flare that matched at Heaven’s Above. Are these type of flares more frequent than listed?

    The second interesting site was a weak looking iridium-flare like flash that pulsated – meaning flash out flash out. It kept on a straight line moving south – I first spotted it between Saturn and Spica. My educated guess was a rotating satellite. The pulses being the rotation frequency of the atenna. Have you seen anything similar.

    Thanks for your efforts on your column.

    Best wishes,

    1. astrobob

      Hi Tim,
      Are you sure the first satellite was an Iridium? Iridium satellites are generally only visible for very short amount of time immediately before and immediately after flaring. It could have been a random bright flare from a non-Iridium. Heavens Above should list all flares for your location though I suppose it’s possible they can be wrong. The second flashing satellite was probably an old tumbling rocket stage.
      Here’s a good article on tumbling satellites: http://www.satobs.org/tumble/tumbleintro.html
      To find out which satellite you saw, try clicking on the “Daily predictions for all satellites brighter than magnitude:3.5” at Heavens Above. You can print out the list and check your next satellite observation against it.

      1. lorie

        Bob I have a question. I was taking a walk at 12:12am 06/21/12 and to my left I saw a bright yellowish white light in the sky it stayed there for several minutes, I went in side grabbed my camera, took a picture and then it was gone. It looked like images you see of the north start on TV or in a picture beacuse you could see the beem looking things to the side because it was so brigt. I saw it when i was at Latitude: 42.244714 Longitude: -88.823932 in the south west sky. so if I was standing at the latitude and longitude i listed I would be looking up towards the west or south west. Any idea what it could be?

        1. astrobob

          Hi Lorie,
          I’m not sure what you saw. There were no space station passes for you at that time, no Iridium flares and no particularly bright satellites. Mars is in the western sky around midnight. Sometimes approaching airplanes look like steady lights in the sky for a few minutes before they get close enough to show movement and disappear off in another direction.

    2. astrobob

      Hi again Tim,
      Now I’m thinking you may have seen the space station. Can you tell me the time of your observation and your location?

  2. Priscilla

    Hey, Bob-

    I was at Brighton Beach last night at about 10:30pm and saw a bright light traveling across the sky almost directly overhead, from West to East……

    Space station?

    1. astrobob

      Hi Priscilla,
      The space station made only a moderately high pass in the southwest-south around 10:45 p.m. last night. We did get a fairly bright pass of the Chinese Long March rocket body (CZ-4B R/B) at 10:35 p.m. It passed directly overhead traveling from south to north. I’m guessing that’s what you saw.

  3. Timothy Fleming

    Hi Bob,
    I live about 20 west of St. Louis and I was out last night 10:30 to 11:00. My walks have gotten longer as I stop periodically in a dark spot to view the stars. The first object was so bright and lasted so long – but it was definitely a satellite as it darkened upon hitting the earth’s shadow.

    I spent the first part of dusk watching bats in the backyard. I am a cancer researcher at a local university. If you ever need any info on cancer/cancer genetics, I would be happy to help you out.

    Thanks so much for sparking my interest in the night sky. I have used learning the stars and constellations as a “brain exercise” as I enter the senior period of my life.

    Best regards,

    1. astrobob

      Thanks for writing back. Glad to know you’re getting acquainted with the stars, both manmade and natural.

  4. Hi Bob, I just saw some of your amazing photos of the flood..you must be exhausted. I see you also got a view from the air..and the harbor all muddy what a shot.
    I hope you and your family are all safe:)

    1. astrobob

      Hi Far Side,
      It’s been a long time. Yes, we did OK. A little leakiness in the basement was all. The unrelenting rain and thunder were a bit much. Still, it was nature at its finest. I hope you’re doing well. Far Guy OK?

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