APOD: Lunar Craters Langrenus and Petavius (2019 Nov 11)

[APOD Robot]

Lunar Craters Langrenus and Petavius

Explanation: The history of the Moon is partly written in its craters. Pictured here is a lunar panorama taken from Earth featuring the large craters Langrenus, toward the left, and Petavius, toward the right. The craters formed in separate impacts. Langrenus spans about 130 km, has a terraced rim, and sports a central peak rising about 3 km. Petavius is slightly larger with a 180 km diameter and has a distinctive fracture that runs out from its center. Although it is known that Petravius crater is about 3.9 billion years old, the origin of its large fracture is unknown. The craters are best visible a few days after a new Moon, when shadows most greatly accentuate vertical walls and hills. The featured image is a composite of the best of thousands of high-resolution, infrared, video images taken through a small telescope. Although mountains on Earth will likely erode into soil over a billion years, lunar craters Langrenus and Petavius will likely survive many billions more years, possibly until the Sun expands and engulfs both the Earth and Moon.

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[wolfie138]

Why is there so little rubble around all these craters? the amount of stuff kicked up from 180km's worth of crater, i'd have thought there'd be mountains of the stuff. I guess some gets kicked into space and some is just vaporised, but still.

[JohnD]

Wolfie,
I think you need to change your perspective on these craters. They are not the result of high explosive, that will throw rocks about, they are cosmic impact craters, the result of rocks coming in at a minimum of tens of kilometers PER SECOND. See: https://www.lpi.usra.edu/exploration/tr ... Mechanics/

Likewise, the energy of such an impact is enormous, estimated to be in tens of kilotons of TNT. Much rock will be vapourised, and the formation of the final crater is a dynamic process. See: https://www.lpi.usra.edu/exploration/tr ... cratering/

But some craters do leave a mark on the surrounding terrain (Lunain?) Many Lunar craters have "rays", as do Martian ones. See: http://www.astronomy.com/news/2018/08/crater-rays

JOhn

[orin stepanek]

The starkness of Luna says; why would you want to come here ? But
adventure, and knowledge, brings man to many foreboding places!
Gotta love it!

[neufer]

Click to play embedded YouTube video.

---

[sillyworm 2]

Got a kick (hee hee) out of reading the engulf link.Can you imagine actually planning to nudge Earth to an outer orbit?

[SpaceCadet]

Wolfie,
I think you need to change your perspective on these craters. They are not the result of high explosive, that will throw rocks about, they are cosmic impact craters, the result of rocks coming in at a minimum of tens of kilometers PER SECOND. See: https://www.lpi.usra.edu/exploration/tr ... Mechanics/

Likewise, the energy of such an impact is enormous, estimated to be in tens of kilotons of TNT. Much rock will be vapourised, and the formation of the final crater is a dynamic process. See: https://www.lpi.usra.edu/exploration/tr ... cratering/

But some craters do leave a mark on the surrounding terrain (Lunain?) Many Lunar craters have "rays", as do Martian ones. See: http://www.astronomy.com/news/2018/08/crater-rays

JOhn

But wouldn't the force of the explosion leave scorch marks and discoloration on whatever remains?

[TheOtherBruce]

Why is there so little rubble around all these craters? the amount of stuff kicked up from 180km's worth of crater, i'd have thought there'd be mountains of the stuff. I guess some gets kicked into space and some is just vaporised, but still.

I watched a documentary recently about asteroid impacts; part of it showed a gas gun (built for NASA as part of the Apollo program, IIRC) used to simulate big rocks hitting solid ground. Whatever impact angle was used, the result was a roundish crater and debris going flying for a very long distance. Look at Tycho (one of the brightest ray systems on the lunar nearside), it's spread over most of a hemisphere — considering how many craters we can see, it would be impossible to recognise any random chunk of debris as coming from any particular crater.

There's always some larger rubble close to the crater, though; that's what forms the crater rim. Look through the APOD archives (less than a year ago, I think) and you'll find an animated simulation of what the Chicxulub crater looked like in the first few minutes after impact. (Yes, that's how little time it took for the crater to form.)

[neufer]

But wouldn't the force of the explosion leave scorch marks and discoloration on whatever remains?

• Black carbon scorch marks

<<The Moon has an exceptionally low albedo, giving it a reflectance that is slightly brighter than that of worn asphalt.

High-reflectance ejecta created a starburst pattern originating from an unnamed ~270 m diameter crater. [NASA/GSFC/Arizona State University].

---

<<Small, Copernican-aged craters abound on the Moon and their ejecta blankets often look like miniature starbursts. For young craters like this one, located on the farside at 25.876°S, 136.081°E, the ejecta is high-reflectance because it was recently exposed by the impact process and is thus really fresh material.

When we observe the ejecta blanket in detail, there are variations in reflectance within the ejecta and it looks as though the ejecta swept out from the crater in sheets. During the impact event, material is ejected from the growing crater and is emplaced over a short period of time. However, the emplacement is not instantaneous and the ejecta is expelled from the growing crater at different speeds and angles depending on where within the impact cavity it originates. Some of the target rock is melted and is also sprayed out of the crater with the pulverized target material. The bright and dark fingers of ejecta seen in the opening image may represent granular and melt materials, respectively. Furthermore, the ejecta farthest away from the crater is thinner and less continuous than the ejecta closest to the crater. At the distal margins of the ejecta blanket, contrasts may simply be due to original mature material showing through between fingers of ejected fresh material. Over geologic time, the starburst pattern of ejecta will gradually disappear as the material matures, and eventually no ejecta blanket will be visible in the NAC images at all.>>

Young bright Tycho debris rays

---

<<Tycho is a prominent lunar impact crater located in the southern lunar highlands. Tycho is a relatively young crater, with an estimated age of 108 million years (Ma), based on analysis of samples of the crater ray recovered during the Apollo 17 mission. The crater is sharply defined, unlike older craters that have been degraded by subsequent impacts. The interior has a high albedo that is prominent when the Sun is overhead, and the crater is surrounded by a distinctive ray system forming long spokes that reach as long as 1,500 kilometers. Sections of these rays can be observed even when Tycho is illuminated only by earthlight. The surface around Tycho is replete with craters of various sizes, many overlapping still older craters. Some of the smaller craters are secondary craters formed from larger chunks of ejecta from Tycho. It is one of the Moon's brightest craters, with a diameter of 85 km and a depth of 4,800 m.

From the 1950s through the 1990s, NASA aerodynamicist Dean Chapman and others advanced the lunar origin theory of tektites. Chapman used complex orbital computer models and extensive wind tunnel tests to support the theory that the so-called Australasian tektites originated from the Rosse ejecta ray of Tycho. Until the Rosse ray is sampled, a lunar origin for these tektites cannot be ruled out.>>

[BDanielMayfield]

Can you imagine actually planning to nudge Earth to an outer orbit?

Yes, indeed I can. Many determined people are working very hard to save this or that endangered species, or entire ecosystems that are threatened. But the whole Earth as a habitable world will also ultimately be cooked unless it's orbit is altered due to the gradual swelling of the Sun. Of course this would be a far future project once space tech has matured, but if Earth viability can be maintained for multi billions of extra years, why shouldn't it be saved for as long as possible?

Bruce

[neufer]

Can you imagine actually planning to nudge Earth to an outer orbit?

Yes, indeed I can.

Many determined people are working very hard to save this or that endangered species, or entire ecosystems that are threatened. But the whole Earth as a habitable world will also ultimately be cooked unless it's orbit is altered due to the gradual swelling of the Sun. Of course this would be a far future project once space tech has matured, but if Earth viability can be maintained for multi billions of extra years, why shouldn't it be saved for as long as possible?

• But, can you imagine actually nudging the Trump Administration back into the Paris climate agreement

Click to play embedded YouTube video.

<<Trump rejects the scientific consensus on climate change, repeatedly contending that global warming is a "hoax." He has said that "the concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive." Trump criticized President Obama's description of climate change as "the greatest threat to future generations" for being "naive" and "one of the dumbest statements I've ever heard."

In May 2016, during his presidential campaign, Trump issued an energy plan focused on promoting fossil fuels and weakening environmental regulation.Trump promised to "rescind" in his first 100 days in office a variety of Environmental Protection Agency regulations established during the Obama administration to limit carbon emissions from coal-fired power plants, which contribute to a warming global climate.

Trump has said "we're practically not allowed to use coal any more." Trump has criticized the Obama administration's coal policies, describing the administration's moves to phase out the use of coal-fired power plants are "stupid." Trump has criticized the Obama administration for prohibiting "coal production on federal land" and states that it seeks to adopt "draconian climate rules that, unless stopped, would effectively bypass Congress to impose job-killing cap-and-trade."

According to FactCheck.org, over at least a five-year period, Trump has on several occasions made incorrect claims about the use of hair spray and its role in ozone depletion. At a rally in May 2016, "Trump implied that the regulations on hairspray and coal mining are both unwarranted" and incorrectly asserted that hairspray use in a "sealed" apartment prevents the spray's ozone-depleting substances from reaching the atmosphere.

In June 2019, the Trump White House tried to prevent a State Department intelligence analyst from testifying to Congress about "possibly catastrophic" effects of human-caused climate change, and prevented his written testimony containing science from NASA and NOAA from being included in the official Congressional Record because it was not consistent with administration positions.

In August 2019, Trump described America's coal production as "clean, beautiful", despite coal being a particularly polluting energy source. Although "clean coal" is a specific jargon used by the coal industry for certain technologies, Trump instead generally describes that coal itself is "clean".>>

[BDanielMayfield]

Can you imagine actually planning to nudge Earth to an outer orbit?

Yes, indeed I can.

Many determined people are working very hard to save this or that endangered species, or entire ecosystems that are threatened. But the whole Earth as a habitable world will also ultimately be cooked unless it's orbit is altered due to the gradual swelling of the Sun. Of course this would be a far future project once space tech has matured, but if Earth viability can be maintained for multi billions of extra years, why shouldn't it be saved for as long as possible?

• But, can you imagine actually nudging the Trump Administration back into the Paris climate agreement

No. But note that I spoke of MATURE tech to nudge the Earth. Society needs to mature as well. The opposite seems to be taking place.

[Boomer12k]

Very nice, crisp shot... love the detail in the enlarged image on magnification... awesome...

:---[===] *

[JohnD]

But wouldn't the force of the explosion leave scorch marks and discoloration on whatever remains?

Most of the large Moon craters were formed in the Late Heavy Bombardment, about 4 billion years ago. Since then the constant flux of micro meteorites has worn at the lunar surface, forming the regolith and evening out any local colours. Think how excited Harrison Schmidt was to find a rock that was very slightly pink on the Apollo 17 mssion, when everything else about them was grey.

This short video, from NASA's 'crater gun' shows just how far and high the debris is thrown.
https://www.youtube.com/watch?v=nbkkMKkjx6k

But see for yourself! Nasa also published this demonstration that you can try in the kitchen!
Flour for bedrock, cocoa for regolith and hudreds'n'thousands (sprinkles)for rocks. Try it!
Obviously, the impact doesn't vapourise the impactor, but its does demonstrate 'rays'.
https://www.youtube.com/watch?v=HTukFx17Ryg

John

[dwhightowe]

Beautiful picture but digital sharpening in post-processing is evident.