Two New Man-made Craters Grace The Moon

The lunar craters Archimedes (top) and Eratosthenes and the Apennine Mountains. All these features will be visible in the northern half of the moon tonight March 20.

I’m a happy cheerleader for the moon. I think it’s because I’ve stared at countless faint galaxies and spent hours eking out planetary details through choppy air. So last night, when I turned the telescope at the first quarter moon, it felt as though I’d arrived in the garden of plenty.

Craters everywhere, rugged mountains poking from the beige cream of the lunar seas and beautiful shadows stretching like figures in a Dali painting across a landscape at once familiar and yet totally alien.

There’s so much to enjoy even in small scopes at low power. A magnification of 50-75x is sufficient to see most of the features in the photo at right.

This Lunar Reconnaissance Orbiter image shows the impact site of GRAIL A (Ebb spacecraft) before and after the spacecraft’s descent to the lunar surface. The crater is about 13 to 20 feet across. Credit: NASA/GSFC/ASU

I’d love to feast my eyes on the two freshly-minted, man-made craters punched into a mountainside near the moon’s north pole. On Dec. 17, 2012, the twin GRAIL probes, nicknamed Flow and Ebb, were intentionally crashed there after wrapping up a successful mission mapping the moon’s gravity field and interior.

Animation showing the final flight path for NASA’s twin Gravity Recovery and Interior Laboratory (GRAIL) mission spacecraft as they headed for crash landings

Why smack the moon? It was NASA’s plan to squeeze one last bit of science out of the mission. The Lunar Reconnaissance Orbiter (LRO), which orbits the moon and takes closeup photos of it surface, was placed into position to study the last whiffs of the dust plumes kicked up by the two washing-machine-sized probes. Each weighed 440 lbs. (200 kg) and were traveling at 3,800 mph (6,100 km/h) when they struck the mountain.

The twin GRAIL space probes orbited in tandem about the moon. Subtle changes in the gravity exerted on each during orbit caused the distance between them to vary. By measuring the distance variations, astronomers mapped the moon’s gravity field. Credit: NASA

Later, the LRO’s camera zoomed in for a look at the two craters resulting from the crashes and pinpointed them both despite their tiny size – only 13-20 feet (4-6 meters) in diameter. Named Ebb and Flow (of course!), they’re surrounded by faint, dark ejecta or rock sprays gouged from the crust during impact.

Rays of brighter dust and rock surroud younger craters on the moon. With time, the dust darkens in sunlight. At bottom are craters Aristarchus (left) and Kepler. Copernicus is at top.

Radiation in sunlight darkens lunar dust. Fresh lunar craters are typically surrounded by bright ejecta rays created since the impact exposes dust and rock beneath the surface that’s been shielded from sunlight. Ebb and Flow are ringed in darker material; scientists suspect spacecraft material has mixed with the ejecta adding yet another “we were here” signpost to the scene.

I’ll return to observing the moon the next clear night. Maybe I’ll get even luckier than I did on Tuesday. Along the edge of its unlit half, a bright star in Gemini hovered briefly before suddenly disappearing behind the moon. These little “coverups” occur regularly as the moon rolls along its orbit, hiding and then “releasing” this star and that. On good nights, lunar observers are like that star, completely absorbed by our nearest cosmic neighbor.

8 Responses

  1. Edward M. Boll

    The Moon did not interfere with the better view of Panstaars tonight. Just before 9 PM tonight on the 20th around 5 degrees elevation the comet was fainter than last night but the tail of around 2 degrees in 20 power binoculars was quite prominent, around half a degrees wide, pointing nearly straight up. I would put at least 1 degree of comet length in the magnitude 4-5 range guessing the head at 2.9 magnitude.

    1. astrobob

      I’m glad to see you’re also getting a 2 degree tail. A few folks on the comet list are either being very conservative or not waiting until the sky is dark enough. I carefully measured the length at the same time you did (last night) and found the same.

  2. Edward M. Boll

    Comet Lemmon is near perihelion. The best that it did was possibly magnitude 4.5 or 4.6. It is heading away from Earth now and the last observation I saw recorded was 5.0. So it may be already fading. If it fades like it brightened it may be brighter than magnitude 6 at the end of April. If it fades at a normal rate it will be dimmer than 6 by the end of April. It should be rising in a fairly dark sky for us by then.

    1. astrobob

      We’ll have two decent comets in the a.m. sky in late April – PANSTARRS will be circumpolar and Lemmon will make its appearance.

    1. astrobob

      Thanks Lynn – an interesting article. Just a small correction. The map shows that the universe rather than the Earth is a little older than we thought.

  3. Edward M. Boll

    After a month of clouds Panstaars was back for a third time in a rtow. That is the number of days I saw McNaught in Jan. of 07. My 16 year old son found it without my help. I could not see it with the naked eye. The tail is pointing up at slight angle, still more than a degree long at around magnitude 5 or 6 still wide and fuzzy. I had a hard time seeing the head at first. I estimate the head at around magnitude 3.3.

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