A facelift for the Moon every 81,000 years

October 12, 2016
A study estimates that asteroids and comets crashing into the moon create close to 180 new craters at least 10 metres in diameter every year

The Moon is bombarded by so much space rock that its surface gets a complete facelift every 81,000 years, according to a study released Wednesday based on NASA data.

This churn—affecting the top two centimetres (nearly an inch) of mostly loose dust—happens 100 times more frequently than previously thought, scientists reported.

The study also estimates that asteroids and comets crashing into Earth's only natural satellite create, on average, 180 new craters at least 10 metres (33 feet) in diameter every year.

The findings, published in Nature, come from "before and after" pictures taken by NASA's Lunar Reconnaissance Orbiter spacecraft, which has been mapping the Moon since 2009.

By comparing images of the same area at regular intervals, a team of scientists led by Emerson Speyerer from Arizona State University in Tempe were able to tally the number of new craters and extrapolate to the entire surface of the Moon.

"We detected 222 new impact craters and found 33 percent more craters with a diameter of at least 10 metres than predicted" by earlier models, the researchers concluded.

The scientists also found thousands of subtler disturbances on the surface, which they described as "scars" from smaller, secondary impacts that –- over thousands of years –- churned up the top layer of the Moon without creating craters.

Earth is also constantly pelted by asteroids and meteors, but is protected by a thick atmosphere.

More than 100 tonnes of dust and sand-sized particles rain down on the planet every day.

Even space rocks up to 25 metres across (80 feet) will likely explode and disintegrate in the upper layers of our atmosphere, causing little or no damage, according to NASA.

The Moon's ultra-thin atmosphere only contains about 100 molecules of gases and elements per cubic centimetre (0.6 cubic inch).

Earth's atmosphere at sea level, by contrast, is packed with about 100 billion billion molecules per cubic centimetre.

Explore further: A new, water-logged history of the Moon

More information: Emerson J. Speyerer et al. Quantifying crater production and regolith overturn on the Moon with temporal imaging, Nature (2016). DOI: 10.1038/nature19829

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24 comments

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Graeme
5 / 5 (6) Oct 12, 2016
one cubic centimeter is 0.061 cu in (not 0.6)
jonesdave
3.3 / 5 (7) Oct 12, 2016
one cubic centimeter is 0.061 cu in (not 0.6)


I'll take your word for it :) Moot point though, as no scientist is going to be using cubic inches to describe anything.
I wish NASA would stop doing this, though. Surely they realise that anybody reading their website articles is, by definition, interested in science, and is either well acquainted with the SI units used in science, or are more than capable of doing a quick search on Google to get an idea.
I've seen articles translated into American from metric, which end up looking stupid. Along the lines of:
"The Martian valley is about 1312 ft wide.", when it is obvious that the original has said ~ 400m.

Crazy.
ddaye
5 / 5 (1) Oct 13, 2016
one cubic centimeter is 0.061 cu in (not 0.6)


When I was in early grade school I decided to calculate the number of cubic inches in a cubic light-year. Short answer, it's a heap.
jonesdave
1 / 5 (3) Oct 13, 2016
one cubic centimeter is 0.061 cu in (not 0.6)


When I was in early grade school I decided to calculate the number of cubic inches in a cubic light-year. Short answer, it's a heap.


It'd be far easier to work out cubic centimetres! Rounding up: 1ly = 10^16 m = 10^18 cm. Squaring gives 10^36 cm^3. That is why metric is easier!
slash
not rated yet Oct 13, 2016
one cubic centimeter is 0.061 cu in (not 0.6)


When I was in early grade school I decided to calculate the number of cubic inches in a cubic light-year. Short answer, it's a heap.


It'd be far easier to work out cubic centimetres! Rounding up: 1ly = 10^16 m = 10^18 cm. Squaring gives 10^36 cm^3. That is why metric is easier!

Squaring doesn't give you cm^3 unless you start with cm^3/2. Try cubing.
;-p
slash
not rated yet Oct 13, 2016
More than 100 tonnes of dust and sand-sized particles rain down on the planet every day.

I wonder why they didn't translate this to lb ...
;-p
jonesdave
2 / 5 (4) Oct 13, 2016
one cubic centimeter is 0.061 cu in (not 0.6)


When I was in early grade school I decided to calculate the number of cubic inches in a cubic light-year. Short answer, it's a heap.


It'd be far easier to work out cubic centimetres! Rounding up: 1ly = 10^16 m = 10^18 cm. Squaring gives 10^36 cm^3. That is why metric is easier!

Squaring doesn't give you cm^3 unless you start with cm^3/2. Try cubing.
;-p


You're right. I've worked out a square ly! 7 am, not been to sleep yet! Try 10^54 cm^3.
slash
not rated yet Oct 13, 2016
I am a little confused about the math in this article:
This churn [facelift] —affecting the top two centimetres (nearly an inch) of mostly loose moon dust—happens 100 times more frequently than previously thought,

and:
"We detected 222 new impact craters and found 33 percent more craters with a diameter of at least 10 metres than predicted" by earlier models

just don't fit together in any sensible relationship I can think of. Probably I'm just not imaginative enough, but it would really help if the article offered some insight into what these numbers really mean and how they are supposed to be related.

At the very least, it would help what the number 222 new craters refers to: if it is the actual number, what percentage of the surface did they check, and what is the time frame?
FredJose
1 / 5 (7) Oct 13, 2016
The study also estimates that asteroids and comets crashing into Earth's only natural satellite create, on average, 180 new craters at least 10 metres (33 feet) in diameter every year.

Surely ANY comet crashing into the moon would have been a VERY spectacular thing to witness and record? Therefore the author(s) must be mistaken on this point unless someone can point out to me how it would be possible to have comets strike the moon without us seeing them?
from smaller, secondary impacts that –- over thousands of years –- churned up the top layer of the Moon without creating craters.

How do they come to the conclusion of "thousands of years"? The article does not enlighten us. It might just as well be a complete thumb-suck.
antialias_physorg
5 / 5 (5) Oct 13, 2016
Surely ANY comet crashing into the moon would have been a VERY spectacular thing to witness and record?

Sometimes they are spectacular (see this video)
http://www.space....deo.html

Surely ANY comet crashing into the moon would have been a VERY spectacular thing to witness and record?

Mostly the stuff that impacts is very small and not easily seen.

someone can point out to me how it would be possible to have comets strike the moon without us seeing them?

At all times 50% of the moon surface points away from Earth.

The article does not enlighten me.

There...fixed it for ya.
TheGhostofOtto1923
4.2 / 5 (5) Oct 13, 2016
Sure. We will give up feet and inches if everyone in the world agrees to speak American. Fair enough?

Re the article this is yet one more reason to live in underground colonies.
Mark Thomas
3.4 / 5 (5) Oct 13, 2016
To protect lunar bases from all the impacts and secondary impacts, essentially they will need to be bullet proof.

http://www.space....ght.html

Compared to the moon, Mars is looking better and better all the time.
antialias_physorg
5 / 5 (4) Oct 13, 2016
To protect lunar bases from all the impacts and secondary impacts, essentially they will need to be bullet proof.


With the low density of Mars' atmosphere the protection there isn't that much better. If you want to be even moderately safe for long time periods then underground is probably the only way to go (unless someone splurges on some early warning and defense systems)
Mark Thomas
1 / 5 (3) Oct 13, 2016
"With the low density of Mars' atmosphere the protection there isn't that much better."

AAP, do you have a citation for this? In any case, every serious terraforming paper and even hard science fiction story involves thickening the atmosphere of Mars to near Earth-like levels. You might try Zubrin's The Case for Mars and Kim Stanley Robinson's Red Mars, Green Mars, Blue Mars trilogy.

http://science.ho...ing2.htm
https://en.wikipe...pressure

Articles have been written about what it might take to terraform every planet in the solar system and it is clear that Mars is the best choice by far and the only one at present we have a reasonable chance of success with. It is worth pondering the gift of a 24 hour 40 minute martian day and a 25 degree tilt. The length of a day alone on the moon (and Venus) make terraforming them impractical for the time being.
antialias_physorg
5 / 5 (2) Oct 14, 2016
In any case, every serious terraforming paper and even hard science fiction story involves thickening the atmosphere of Mars to near Earth-like levels.

Sure. But I can't really see how that is going to work. If you were to thicken the atmosphere to Earth norm the CO2 level would be just about right (assuming the 'thickening' doesn't add any.) But I don't see where the oxygen - and a lot more importantly the nitrogen - is going to come from in those quantities. The 'low pressure and simply use a mask' scenarios are also not much good because even at those pressures Mars is very cold. You'll need a full body-enclosing heated suit in any case.
None of the ideas in the first link you provided are realistic short or mid term.

Density of Mars' atmosphere is 1% of Earth atmosphere. I'm not entirely sure people appreciate what a HUGE volume of gas is missing (and whether the low gravity of Mars would keep ahold of it without constant replenishment)
TheGhostofOtto1923
3 / 5 (4) Oct 14, 2016
But I can't really see how that is going to work. If you were to thicken the atmosphere to Earth norm the CO2 level would be just about right (assuming the 'thickening' doesn't add any.) But I don't see where the oxygen - and a lot more importantly the nitrogen - is going to come from in those quantities
Plenty of non-scifi sources for terraforming. Wiki is a place to start.
https://en.wikipe..._of_Mars

There is also plenty of oxygen and nitrogen on mars. Comets and asteroids can also be dumped on the surface if needed, and N2 can be mined in titans atmosphere.

Again I know the scale is a hard thing for you to grasp but the scale of global transportation today would have been equally hard for someone from the 16th century to imagine.

Robotics will make this easy. And do consider that AGWites already understand that we are affecting our own atmosphere at similar scales, without even trying.
Mark Thomas
1 / 5 (3) Oct 14, 2016
AAP, please don't get me wrong, I did not mean to imply this would be easy, because it won't. My point is simply bringing volatiles to Mars can greatly accelerate the terraforming process. If the comet the article mentioned had hit Mars, presumably there would have been a similar effect there. Importantly, some authors have concluded that a dozen or so large comets would be enough to tip the equilibrium on Mars to a condition part-way to what we want. Before we reach the holy grail of a human-breathable atmosphere on Mars, the atmosphere can be thickened enough to pass the Armstrong limit (Harry, not Neil) and the minimum necessary for hardy plants. This will make the environment more forgiving for colonists.
Mark Thomas
1 / 5 (3) Oct 14, 2016
"But I don't see where the oxygen - and a lot more importantly the nitrogen - is going to come from in those quantities."

For argument's sake, lets say this is actually the right question, meaning, Mars currently lacks certain volatiles, especially nitrogen, but also molecular oxygen, which are important for terraforming. Is there any place in the solar system where we could find large quantities of potentially movable nitrogen and oxygen? Does comet P67 tell us anything about nitrogen ice and oxygen ice in the solar system? I suggest that like a fish in the sea, if you find one, you can bet there is more.
TheGhostofOtto1923
3.4 / 5 (5) Oct 15, 2016
"The team found evidence for nitrates in scooped samples of windblown sand and dust at the "Rocknest" site, and in samples drilled from mudstone at the "John Klein" and "Cumberland" drill sites in Yellowknife Bay. Since the Rocknest sample is a combination of dust blown in from distant regions on Mars and more locally sourced materials, the nitrates are likely to be widespread across Mars, according to Stern. The results support the equivalent of up to 1,100 parts per million nitrates in the Martian soil from the drill sites."
Mark Thomas
1 / 5 (2) Oct 15, 2016
TheGhostofOtto1923, local Martian resources are certainly a possibility and may still turn out to be the best option for terraforming. But even if Mars is missing something like nitrogen, there is at least a possibility we will be able to bring it to Mars. While a monumental task, there are no known showstoppers to terraforming Mars. The only way to fully answer the question of how best to terraform Mars is to boldly go where no one has gone before.
TheGhostofOtto1923
4.2 / 5 (5) Oct 15, 2016
But even if Mars is missing something like nitrogen, there is at least a possibility we will be able to bring it to Mars
Right. From titan like I said. According to Kim Stanley Robinson.
Solon
1 / 5 (2) Oct 16, 2016
@antialias_physorg
"Sometimes they are spectacular (see this video)"

Without functioning seismometers on the Moon it is not possible to tell if these are electrical discharges and not impacts. the seismometers installed during the Apollo missions were turned off in 1977, and apparently, even with the gain turned up, the Moon was seismically silent, as reported by Adrian Berry, in a 1995 article in the Daily Telegraph. He was also a columnist for Astronomy Now magazine. A discharge would produce more of a 'sucking' force, removing surface material, than an impact, explaining a seismically silent Moon.
SCVGoodToGo
2.3 / 5 (3) Oct 18, 2016
@ Otto

Sorry those were supposed to be 5's.
jonesdave
3.7 / 5 (3) Oct 18, 2016
Without functioning seismometers on the Moon it is not possible to tell if these are electrical discharges and not impacts...


Lol. Yes we can tell. How do you think an electric discharge shows up on the EM spectrum? Given that your education of such matters seems to come from a laughable source, let me explain: IT WOULD BE BLEEDING OBVIOUS. Is that sufficient? Probably not, for someone who thinks the Sun is invisible in visible wavelengths! Still, keep trolling away, yes? You never know - someone with an IQ less than 50 might actually see your post, and take it seriously.
Jesus, where do they find these people?

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