APOD: Moon Struck (2019 Jan 25)

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APOD: Moon Struck (2019 Jan 25)

Post by APOD Robot » Fri Jan 25, 2019 5:14 am

[img]https://apod.nasa.gov/apod/calendar/S_190125.jpg[/img] Moon Struck

Explanation: Craters produced by ancient impacts on the airless Moon have long been a familiar sight. But only since the 1990s have observers began to regularly record and study optical flashes on the lunar surface, likely explosions resulting from impacting meteoroids. Of course, the flashes are difficult to see against a bright, sunlit lunar surface. But during the January 21 total eclipse many imagers serendipitously captured a meteoroid impact flash against the dim red Moon. Found while examining images taken shortly before the total eclipse phase began, the flash is indicated in the inset above, near the Moon's darkened western limb. Estimates based on the flash duration recorded by the Moon Impact Detection and Analysis System (MIDAS) telescopes in southern Spain indicate the impactor's mass was about 10 kilograms and created a crater between seven and ten meters in diameter.

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Re: APOD: Moon Struck (2019 Jan 25)

Post by Nitpicker » Fri Jan 25, 2019 6:26 am

Great stuff.

Based on what I just read here: https://www.nasa.gov/centers/marshall/n ... rview.html, I am guessing that this meteoroid has been identified as a particular shower meteoroid, with a known velocity, as otherwise the estimate of its mass would have been given within min and max limits.

I suppose it would be too easy to assume that it was a Delta Cancrid, based on the Moon's location in Cancer. So, how does one identify the particular shower?

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Re: APOD: Moon Struck (2019 Jan 25)

Post by Ann » Fri Jan 25, 2019 9:05 am

I feel a bit stupid posting this after Nitpicker's smart comment, so I'll just say that it is fascinating to see an actual meteor impact on the Moon. It is cool, too, that it takes a lunar eclipse to actually see one - or at least it becomes so much easier to see what's going on on the lunar surface when the Moon is eclipsed.

Great APOD!

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Re: APOD: Moon Struck (2019 Jan 25)

Post by MarkBour » Fri Jan 25, 2019 9:24 am

Nitpicker wrote:
Fri Jan 25, 2019 6:26 am
Great stuff.

Based on what I just read here: https://www.nasa.gov/centers/marshall/n ... rview.html, I am guessing that this meteoroid has been identified as a particular shower meteoroid, with a known velocity, as otherwise the estimate of its mass would have been given within min and max limits.

I suppose it would be too easy to assume that it was a Delta Cancrid, based on the Moon's location in Cancer. So, how does one identify the particular shower?
This really is amazing. I had clear skies and was watching around that time. Naked eye only, and I never stared for very long without looking away for a bit. Anyway, I sure didn't see it!

The only famous shower (hitting the Earth) I can find around this time is the Quadrantids in early January. I think it would be "too easy", as you say, to think it was one of that shower. I'm curious about it, too. Perhaps we'll get an answer here.

Jose Maria Madiedo, an astronomer working on the Moon Impacts Detection and Analysis System (MIDAS) project, would know.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by gmPhil » Fri Jan 25, 2019 12:00 pm

SO what actually causes the bright "flash"? I would have guessed light reflecting off dust thrown up, but in an eclipse...?

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Re: APOD: Moon Struck (2019 Jan 25)

Post by JohnD » Fri Jan 25, 2019 12:52 pm

Really, the only reason this hits the headlines is that so may people had a camera imaging the Moon during the eclipse, and the impact happened then. Nice observation, but a known and well-studied phenomenon.

And the comment that " the flashes are difficult to see against a bright, sunlit lunar surface" is obvious to thepoint of banality. NASA has a programme to monitor lunar impacts, that looks for them during the Lunar night! See: https://www.nasa.gov/centers/marshall/n ... rview.html

AS for the flash, that NASA page says, "a large portion of the impact energy goes into heat and producing a crater; however, a small fraction goes into generating visible light, which results in a brilliant flash at the point of impact. " To date, only the flash is available to estimate the size of the impactor, and that depends on other factors - see the last paragraph of the above page.

Is there no suitable telescope to identify the new craters? The flash must pinpoint it within a few hundred meters, and it's diameter would contribute to size estimate.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by neufer » Fri Jan 25, 2019 2:04 pm

JohnD wrote:
Fri Jan 25, 2019 12:52 pm

Is there no suitable telescope to identify the new craters?

The flash must pinpoint it within a few hundred meters, and it's diameter would contribute to size estimate.
https://www.syfy.com/syfywire/an-asteroid-impacted-the-moon-during-the-lunar-eclipse wrote:
An asteroid impacted the Moon during the lunar eclipse!
by Phil PlaitVerified @BadAstronomer

<<If the impact site can be found with high enough accuracy, it's possible the Lunar Reconnaissance Orbiter can get images of it! The brightness of the impact flash seen depends mostly on the mass of the impactor and the velocity at which it was traveling (see below), so if LRO can spot the crater and measure its size, that too can be tied with other physical properties of whatever hit the Moon.

These and other videos, plus images taken by people back on Earth, can help nail down the impact site location. Unfortunately, what we've seen so far is only good to a few kilometers accuracy on the impact position, so I'm making a public plea: If you have high-resolution observations taken with a telescope 25 cm or bigger, please contact planetary geologist Justin Cowart: His email is Justin (dot) cowart (at) stonybrook (dot) edu or you can find him on Twitter.

There's some uncertainty to the exact location due to various effects (like pinpointing the fireball (small gray ellipse in the image above), plus the location of the observers on Earth (larger ellipse)). The uncertainty takes the shape of an ellipse because the impact site is near the limb of the Moon as seen from Earth, and so the landscape is foreshortened there. A small uncertainty in longitude translates into a wider physical area in the east/west direction than north/south. Also as [Justin Cowart] points out, as LRO orbits the Moon it takes images with a swath about 5 km wide. If his estimates are off by even a small amount, LRO might miss it!
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Re: APOD: Moon Struck (2019 Jan 25)

Post by bls0326 » Fri Jan 25, 2019 2:16 pm

I happened to be taking a Moon pic about 4 minutes after impact. Just a point and shoot camera so no moondust cloud visible. The lighted portion of the moon in my pic (and eyeball) is at about the 11 0'clock area. The APOD pic shows the lighted area at 3 - 4 o'clock. My location is in mid-USA (N35.155, W101.839). I am seeing the Moon rising, while the Midas telescopes are seeing it setting. Is that the reason for the difference or does the telescope invert the visible image?

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Re: APOD: Moon Struck (2019 Jan 25)

Post by Chris Peterson » Fri Jan 25, 2019 2:34 pm

Nitpicker wrote:
Fri Jan 25, 2019 6:26 am
Great stuff.

Based on what I just read here: https://www.nasa.gov/centers/marshall/n ... rview.html, I am guessing that this meteoroid has been identified as a particular shower meteoroid, with a known velocity, as otherwise the estimate of its mass would have been given within min and max limits.

I suppose it would be too easy to assume that it was a Delta Cancrid, based on the Moon's location in Cancer. So, how does one identify the particular shower?
There is no method to identify any lunar impact with any shower member. Most impacts are observed during showers and are statistically likely shower members, but that's all. There are currently no significant active showers... the sporadic meteor rate is higher than the shower rate. So this was most likely sporadic, with the energy calculated directly from the intensity of the flash and the size based on an assumed impact speed based on the average. So there is certainly a wide range in possible masses, it just wasn't stated here.

(And with the Moon in Cancer, Delta Cancrids would typically impact the farside... although the actual radiant was slightly east of the Moon and this impact was near the eastern limb, so I think we might see shower impacts close to that edge, even though most would be on the farside.)
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Re: APOD: Moon Struck (2019 Jan 25)

Post by Chris Peterson » Fri Jan 25, 2019 2:37 pm

Ann wrote:
Fri Jan 25, 2019 9:05 am
I feel a bit stupid posting this after Nitpicker's smart comment, so I'll just say that it is fascinating to see an actual meteor impact on the Moon. It is cool, too, that it takes a lunar eclipse to actually see one - or at least it becomes so much easier to see what's going on on the lunar surface when the Moon is eclipsed.
Anybody with a telescope and a cheap video camera can record quite a few of these in any year. It doesn't require a lunar eclipse, it merely requires a Moon presenting a fair bit of shadowed surface during an active shower. Eclipses tend to be poor times to look for impacts, because they rarely coincide with meteor showers.
Last edited by Chris Peterson on Fri Jan 25, 2019 3:42 pm, edited 1 time in total.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by orin stepanek » Fri Jan 25, 2019 3:39 pm

Awesome photographic catch! 8-)
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Re: APOD: Moon Struck (2019 Jan 25)

Post by neufer » Fri Jan 25, 2019 3:52 pm

https://www.nasa.gov/centers/marshall/news/lunar/overview.html wrote:

About Lunar Impact Monitoring

Mission statement: Use Earth-based observations of the dark portion of the Moon to establish the rates and sizes of large meteoroids (greater than a few ounces in mass) striking the lunar surface. Observations are taken between New and 1st Quarter Moon and between Last Quarter and New Moon, when the solar illumination is between 10 and 55 percent. These conditions yield 10-12 observing nights per month.

Observing facility: Observations are conducted at NASA Marshall Space Flight Center in Huntsville, Alabama at the Automated Lunar and Meteor Observatory (ALaMO). The facility consists of two observatory domes, a 15 meter tower with a roll-off roof, and an operations center with laboratory space. A second observatory in Chickamauga, Georgia (Walker County) was operational from September 15, 2007 to June 2011. The facility consists of a ground level building with a roll-off roof. This observatory was run remotely from Marshall Space Flight Center. A fourth 14 inch telescope was operated at New Mexico Skies Observatory from October 2011 to September 2012.

Meteor showers: It is well known that the Earth experiences meteor showers when it encounters the debris left behind by comets; so too does the Moon, though perhaps at not exactly the same time. On Earth these showers are capable of producing spectacular celestial fireworks displays, delighting the public. On the airless Moon, however, these showers are swarms of high energy projectiles, producing fireworks only when they strike the surface with tremendous force. During such times, the rate of shower meteoroids can greatly exceed that of the sporadic background rate and may pose a hazard to spacecraft. Looking for meteor shower impacts on the Moon at about the same time as they occur here on Earth will yield important data that can be fed into meteor shower forecasting models, which can then be used to predict times of greater meteoroid hazard in near-Earth space.

In designing a system to look for these impact flashes, we need to take into account two important considerations. First, we want to see as faint as possible, and secondly we want to see as much of the lunar dark side as we can. The first is important because faint flashes are generally produced by smaller meteoroids, and the smaller the meteoroid, the more there are of them. More meteoroids mean more flashes and hence better statistics on which to base improved models. We can also get more flashes by monitoring as much of the lunar surface as possible, as the number of observed hits is going to be directly proportional to the amount of area seen by our instrument. That’s why the second point is important. It turns out that a modestly-wide field optical system (one with a fast focal ratio) meets both of these criteria nicely. So we perform simultaneous observations of the Moon using two 14” telescopes.

We attach a Watec Ultimate H2 camera to each of our telescopes, and route the camera output into a Sony tape deck or Canopus video digitizer, which converts the video signal into a digital format that is stored on a hard disk. After an observing session, we look for flashes in the data. Our first impact was found by someone simply looking through a couple of hours of video. This can be quite tedious, however, and tired humans can easily miss a short impact flash, so custom computer software was developed to look for the flashes. If one is found, additional software is then used to extract detailed information on the flash -- its brightness as a function of time (light curve), where it was seen on the Moon, if it was due to a meteor shower, and so forth. Using this information, we can estimate the mass or size of the meteoroid. If it is a sporadic meteoroid, all we can do is put limits on the size, as its speed can range from 20 km/sec all the way up to 70 km/sec. If it is a shower meteoroid, then things are better because every member of a meteor shower moves with the same, known speed. This allows us to calculate a single, less uncertain size estimate..>>
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Re: APOD: Moon Struck (2019 Jan 25)

Post by BDanielMayfield » Fri Jan 25, 2019 4:18 pm

Catching the flash of one of these impacts is important for several reasons, but personally I'm more interested in the newly formed crater. I wonder how long it takes the lunar soil and rocks at the impact site to cool down to an undetectable temp? Seeing a brand new crater while it is still glowing in infrared -- now that would be something!

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Re: APOD: Moon Struck (2019 Jan 25)

Post by JohnD » Fri Jan 25, 2019 4:40 pm

For an impact in Lunar night time, the crater will radiate to the Cosmos at 3K, just above absolute zero, and conduct to the parent rock at -35C (238K) a metre down. I'm too lazy to calculate how quickly it will cool down, but in the Lunar day time, the surface may be at more than 280C (553K) on the equator at Lunar noon, so much less contrast to detect, and then cool to less than -180C (93K) in the Lunar night. So I if the entire surface cools that quickly, a little patch will cool even quicker!

You want a go, BDaniel? Start here? https://agupubs.onlinelibrary.wiley.com ... i032p06553 Thermal conductivity of Apollo 11 rock No. 10046 was 2.5(±0.5) × 10−6 cal/sec cm deg

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Re: APOD: Moon Struck (2019 Jan 25)

Post by MarkBour » Fri Jan 25, 2019 5:21 pm

BDanielMayfield wrote:
Fri Jan 25, 2019 4:18 pm
Catching the flash of one of these impacts is important for several reasons, but personally I'm more interested in the newly formed crater. I wonder how long it takes the lunar soil and rocks at the impact site to cool down to an undetectable temp? Seeing a brand new crater while it is still glowing in infrared -- now that would be something!

Bruce
I agree, that would be awesome. It would be pretty exciting for an astronaut living on the Moon to see one nearby, assuming the crater did not coincide with her spacesuit or moonbase wall. :-(

How long the crater would show itself with a heat signature is a great question, Bruce. I appreciate the answer and link that JohnD gave!
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Re: APOD: Moon Struck (2019 Jan 25)

Post by neufer » Fri Jan 25, 2019 6:20 pm

JohnD wrote:
Fri Jan 25, 2019 4:40 pm

For an impact in Lunar night time, the crater will radiate to the Cosmos at 3K, just above absolute zero.
  • The infrared radiation from the Earth for the near side Moon
    exceeds the the cosmic background radiation by a factor of about a million.

    The minimum near side equatorial lunar surface temperature of 100 K
    is in rough thermal equilibrium with the radiation it receives from the Earth (in infrared plus visible).
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Re: APOD: Moon Struck (2019 Jan 25)

Post by JohnD » Fri Jan 25, 2019 6:39 pm

But, neufer, the disc of the Earth will occupy a part of the Moon's sky only a slightly larger than the Moon as we see it. Vide the Apollo Earthrise pics. So at best, the Earth will be about as warming as the full Moon is at night.

Ok, so the lowest temperature that the Moon's surface gets to is 100K. That's -193C, and if I may say so bl&&dy cold! We already have materials that superconduct if hotter than that!
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Re: APOD: Moon Struck (2019 Jan 25)

Post by Chris Peterson » Fri Jan 25, 2019 7:04 pm

JohnD wrote:
Fri Jan 25, 2019 6:39 pm
But, neufer, the disc of the Earth will occupy a part of the Moon's sky only a slightly larger than the Moon as we see it. Vide the Apollo Earthrise pics. So at best, the Earth will be about as warming as the full Moon is at night.
It doesn't matter what part of the sky it occupies. What matters is that it radiates electromagnetic energy from a certain distance, and that energy heats the surface of the Moon. The comparison between the Earth and Moon here is complex. The Moon is likely to be more warming on the Earth than vice versa, depending on its phase. The Earth's radiation doesn't change much between its night and day sides; the Moon's changes radically.
Ok, so the lowest temperature that the Moon's surface gets to is 100K. That's -193C, and if I may say so bl&&dy cold!
100 K is -173° C. Not quite as cold as you suggest ;-)
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Re: APOD: Moon Struck (2019 Jan 25)

Post by neufer » Fri Jan 25, 2019 8:08 pm

JohnD wrote:
Fri Jan 25, 2019 6:39 pm

But, neufer, the disc of the Earth will occupy a part of the Moon's sky only a slightly larger than the Moon as we see it. Vide the Apollo Earthrise pics. So at best, the Earth will be about as warming as the full Moon is at night.
The disc of the Earth will occupy a part of the Moon's sky about 16 times larger than the Moon's disc as we see it.
And the Earth's albedo is about 2.5 times that of the Moon...so a factor of about 40.

However, most of the Earth's heating comes from it's infrared radiation (even at Full Earth).
Chris Peterson wrote:
Fri Jan 25, 2019 7:04 pm
JohnD wrote:
Fri Jan 25, 2019 6:39 pm

Ok, so the lowest temperature that the Moon's surface gets to is 100K. That's -193C, and if I may say so bl&&dy cold!
100 K is -173° C. Not quite as cold as you suggest ;-)
The minimum near side equatorial lunar temperature is 100 K.

However, there are parts of the Moon that hardly ever (directly) observe either the Sun or the Earth.
(Presumably, these are primarily in radiative equilibrium with star light.)
https://en.wikipedia.org/wiki/Moon wrote:
<<The Moon's axial tilt with respect to the ecliptic is only 1.5424°, much less than the 23.44° of Earth. From images taken by Clementine in 1994, it appears that four mountainous regions on the rim of Peary Crater at the Moon's north pole may remain illuminated for the entire lunar day, creating peaks of eternal light. No such regions exist at the south pole. Similarly, there are places that remain in permanent shadow at the bottoms of many polar craters, and these "craters of eternal darkness" are extremely cold: Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C) and just 26 K (−247 °C) close to the winter solstice in north polar Hermite Crater. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto.>>
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Re: APOD: Moon Struck (2019 Jan 25)

Post by MarkBour » Sat Jan 26, 2019 12:02 am

As deep as the rest of this discussion is getting, I'm guessing that an impact crater will start out quite hot and partially molten, though perhaps in some cases not all that much (if most of the material vaporizes). Then it would begin to equiliibrate with its surrounding lunar regolith while radiating some heat into space. I would think this would follow a Newtonian cooling curve. Of course the constant for the equation is the big question. I would have guessed that you could tell the crater was hot for days. It was a wild guess. I did find one rather different article that might help. It gives hope that one could detect heat in this brand-new crater for a lot longer than my guess.
https://pubs.usgs.gov/of/1997/of97-724/lavacool.html
Nature of the Lava Cooling

Rock is a poor conductor of heat, so that a lava slab 10 m thick is known to be hot for years, if it is [solidly] intact and not fractured, even if its surface is continually cooled by water. Generally, however, lava is fractured; joints are formed during the abrupt cooling that has taken place.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by Chris Peterson » Sat Jan 26, 2019 12:13 am

MarkBour wrote:
Sat Jan 26, 2019 12:02 am
As deep as the rest of this discussion is getting, I'm guessing that an impact crater will start out quite hot and partially molten, though perhaps in some cases not all that much (if most of the material vaporizes). Then it would begin to equiliibrate with its surrounding lunar regolith while radiating some heat into space. I would think this would follow a Newtonian cooling curve. Of course the constant for the equation is the big question. I would have guessed that you could tell the crater was hot for days. It was a wild guess. I did find one rather different article that might help. It gives hope that one could detect heat in this brand-new crater for a lot longer than my guess.
https://pubs.usgs.gov/of/1997/of97-724/lavacool.html
Nature of the Lava Cooling

Rock is a poor conductor of heat, so that a lava slab 10 m thick is known to be hot for years, if it is [solidly] intact and not fractured, even if its surface is continually cooled by water. Generally, however, lava is fractured; joints are formed during the abrupt cooling that has taken place.
In fact, I think there is virtually no molten material left in a crater at all. The molten material is vaporized and ejected. I think the crater is cool and the underlying rock is not much changed from its original temperature.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by neufer » Sat Jan 26, 2019 1:18 am

MarkBour wrote:
Sat Jan 26, 2019 12:02 am

As deep as the rest of this discussion is getting, I'm guessing that an impact crater will start out quite hot and partially molten, though perhaps in some cases not all that much (if most of the material vaporizes). Then it would begin to equiliibrate with its surrounding lunar regolith while radiating some heat into space. I would think this would follow a Newtonian cooling curve. Of course the constant for the equation is the big question. I would have guessed that you could tell the crater was hot for days. It was a wild guess. I did find one rather different article that might help. It gives hope that one could detect heat in this brand-new crater for a lot longer than my guess.
https://pubs.usgs.gov/of/1997/of97-724/lavacool.html
Nature of the Lava Cooling

Rock is a poor conductor of heat, so that a lava slab 10 m thick is known to be hot for years, if it is [solidly] intact and not fractured, even if its surface is continually cooled by water. Generally, however, lava is fractured; joints are formed during the abrupt cooling that has taken place.
  • That cuts both ways.
Rock being a poor conductor also means that the hot (partially molten) rock will quickly radiate off from its top surface thereby covering these hot pieces with a thin poorly conducting cool layer that will rapidly make them very hard to see in the IR.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by Chris Peterson » Sat Jan 26, 2019 1:23 am

neufer wrote:
Sat Jan 26, 2019 1:18 am
MarkBour wrote:
Sat Jan 26, 2019 12:02 am

As deep as the rest of this discussion is getting, I'm guessing that an impact crater will start out quite hot and partially molten, though perhaps in some cases not all that much (if most of the material vaporizes). Then it would begin to equiliibrate with its surrounding lunar regolith while radiating some heat into space. I would think this would follow a Newtonian cooling curve. Of course the constant for the equation is the big question. I would have guessed that you could tell the crater was hot for days. It was a wild guess. I did find one rather different article that might help. It gives hope that one could detect heat in this brand-new crater for a lot longer than my guess.
https://pubs.usgs.gov/of/1997/of97-724/lavacool.html
Nature of the Lava Cooling

Rock is a poor conductor of heat, so that a lava slab 10 m thick is known to be hot for years, if it is [solidly] intact and not fractured, even if its surface is continually cooled by water. Generally, however, lava is fractured; joints are formed during the abrupt cooling that has taken place.
  • That cuts both ways.
Rock being a poor conductor also means that the hot (partially molten) rock will quickly radiate off from its top surface thereby covering these hot pieces with a thin poorly conducting cool layer that will rapidly make them very hard to see in the IR.
Yes... but this presumes there is any hot rock at the bottom of the hole in the first place. I think that the the molten material is immediately ejected, and there is a shockwave which propagates somewhat deeper at supersonic speed, breaking up and flinging out big chunks, and what's left after a second or two is a hole with the bottom about the same temperature as the rock at that depth was already at.

It's also worth noting that radiation is the least efficient way of cooling something off, so I don't know that most materials will cool all that quickly on the Moon, at least not compared with the Earth.
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Re: APOD: Moon Struck (2019 Jan 25)

Post by Nitpicker » Sat Jan 26, 2019 3:19 am

Thanks Chris. It looks a lot like the meteor in the Matterhorn APOD from yesterday, might be a Delta Cancrid. However, it seems that the orbit of this shower is not known and hence also its velocity. So whether or not the "moon struck" meteoroid might also have been a Delta Cancrid is something of a moot point. If it was, I suppose it must have struck at a very shallow angle.

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Re: APOD: Moon Struck (2019 Jan 25)

Post by alter-ego » Sat Jan 26, 2019 4:14 am

Nitpicker wrote:
Sat Jan 26, 2019 3:19 am
Thanks Chris. It looks a lot like the meteor in the Matterhorn APOD from yesterday, might be a Delta Cancrid. However, it seems that the orbit of this shower is not known and hence also its velocity. So whether or not the "moon struck" meteoroid might also have been a Delta Cancrid is something of a moot point. If it was, I suppose it must have struck at a very shallow angle.
At the impact time and coordinates, the δ-Cancrid radiant was 16° below the site's horizon, so this shower is likely not a candidate source.
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