Crashing comets may explain mysterious lunar swirls

June 1, 2015 by Kevin Stacey
Source of mysterious lunar swirls. New research suggests that comet collisions could explain the formation of lunar swirls like these at Mare Marginis on the Moon’s far side. Credit: NASA/Lunar Reconnaissance Orbiter

Brown University researchers have produced new evidence that lunar swirls—wispy bright regions scattered on the moon's surface—were created by several comet collisions over the last 100 million years.

In a paper published in the journal Icarus, the researchers use state-of-the-art computer models to simulate the dynamics of comet impacts on the lunar soil. The simulations suggest that such impacts can account for many of the features in the mysterious swirls.

'We think this makes a pretty strong case that the swirls represent remnants of cometary collisions,' said Peter Schultz, a planetary geoscientist at Brown University. Schultz co-wrote the paper with his former graduate student, Megan Bruck-Syal, who is now a researcher at the Lawrence Livermore National Laboratory.

Lunar swirls have been the source of debate for years. The twisting, swirling streaks of bright soil stretch, in some cases, for thousands of miles across the . Most are found on the unseen far side of the moon, but one famous swirl called Reiner Gamma can be seen by telescope on the southwestern corner of the moon's near side. 'It was my favorite object to look at when I was an amateur astronomer,' Schultz said.

At first glance, the swirls do not appear to be related to large impact craters or any other topography. 'They simply look as if someone had finger-painted the surface,' Schultz said. 'There has been an intense debate about what causes these features.'

In the 1970s, scientists discovered that many of the swirls were associated with anomalies of the moon's crustal magnetic field. That revelation led to one hypothesis for how the swirls may have formed. Rocks below the surface in those spots might contain remanent magnetism from early in the moon's history, when its magnetic field was much stronger than it is now. It had been proposed that those strong, locally trapped magnetic fields deflect the onslaught of the solar wind, which was thought to slowly darken the moon's surface. The swirls would remain brighter than the surrounding soil because of those magnetic shields.

But Schultz had a different idea for how the swirls may form—one that has its roots in watching the lunar modules land on the moon during the Apollo program.

'You could see that the whole area around the lunar modules was smooth and bright because of the gas from the engines scoured the surface,' Schultz said. 'That was part of what got me started thinking comet impacts could cause the swirls.'

Comets carry their own gaseous atmosphere called a coma. Schultz thought that when small comets slam into the moon's surface—as they occasionally do—the coma may scour away loose soil from the surface, not unlike the gas from the lunar modules. That scouring may produce the bright swirls.

A closer look at the Reiner Gamma. Credit: NASA/Lunar Reconnaissance Orbiter

Schultz first published a paper outlining the idea in the journal Nature in 1980. That paper focused on how the scouring of the delicate upper layer of lunar soils could produce brightness consistent with the swirls. The structure of the grains in the upper layer (termed the 'fairy castle structure' because of the way grains stick together) scatters the sun's rays, causing a dimmer and darker appearance. When this structure is stripped away, the remaining smoothed surface would be brighter than unaffected areas, especially when the sun's rays strike it at certain angles. For Reiner Gamma on the lunar nearside, those areas appear brightest during the crescent moon just before sunrise.

As computer simulations of impact dynamics have gotten better, Schultz and Bruck-Syal decided it might be time to take a second look at whether comet impacts could produce that kind of scouring. Their new simulations showed that the impact of a comet coma plus its icy core would indeed have the effect of blowing away the smallest grains that sit atop the . The simulations showed that the scoured area would stretch for perhaps thousands of kilometers from the impact point, consistent with the swirling streaks that extend across the moon's surface. Eddies and vortices created by the gaseous impact would explain the swirls' twisty, sinuous appearance.

The comet impact hypothesis could also explain the presence of magnetic anomalies near the swirls. The simulations showed that a comet impact would melt some of the tiny particles near the surface. When small, iron-rich particles are melted and then cooled, they record the presence of any magnetic field that may be present at the time. 'Comets carry with them a magnetic field created by streaming charged particles that interact with the solar wind,' Schultz said. 'As the gas collides with the lunar surface, the cometary becomes amplified and recorded in the small particles when they cool.'

Taken together, the results offer a more complete picture of how the swirls form, the researchers say.

'This is the first time anyone has looked at this using modern computational techniques,' Schultz said. 'Everything we see in simulations of is consistent with the swirls as we see them on the moon. We think this process provides a consistent explanation, but may need new missions to finally resolve the debate.'

Explore further: Lunar Reconnaissance Orbiter: Reiner Gamma Region of Interest

More information: Icarus, www.sciencedirect.com/science/article/pii/S0019103515002079

Related Stories

'Deflector Shields' protect the Lunar Surface

July 19, 2012

(Phys.org) -- Scientists from RAL Space at the Rutherford Appleton Laboratory have solved a lunar mystery and their results might lead the way to determining if the same mechanism could be artificially manipulated to create ...

Moon's molten, churning core likely once generated a dynamo

December 4, 2014

When the Apollo astronauts returned to Earth, they brought with them some souvenirs: rocks, pebbles, and dust from the moon's surface. These lunar samples have since been analyzed for clues to the moon's past. One outstanding ...

Comet dust—planet Mercury's 'invisible paint'

March 30, 2015

A team of scientists has a new explanation for the planet Mercury's dark, barely reflective surface. In a paper published in Nature Geoscience, the researchers suggest that a steady dusting of carbon from passing comets has ...

Recommended for you

Spitzer Space Telescope begins 'Beyond' phase

August 26, 2016

Celebrating the spacecraft's ability to push the boundaries of space science and technology, NASA's Spitzer Space Telescope team has dubbed the next phase of its journey "Beyond."

NASA's Juno to soar closest to Jupiter this Saturday

August 26, 2016

This Saturday at 5:51 a.m. PDT, (8:51 a.m. EDT, 12:51 UTC) NASA's Juno spacecraft will get closer to the cloud tops of Jupiter than at any other time during its prime mission. At the moment of closest approach, Juno will ...

Rosetta captures comet outburst

August 25, 2016

In unprecedented observations made earlier this year, Rosetta unexpectedly captured a dramatic comet outburst that may have been triggered by a landslide.

5 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

cantdrive85
1.8 / 5 (5) Jun 01, 2015
Of course there is no mention of the possibility of a plasma discharge causing the "swirling" material. It's an obvious consideration being the these types of discharge actually "swirl". What are mysteries for standard theorists are expected phenomena for scientists who actually understand real plasma physics.
rossim22
2.6 / 5 (5) Jun 01, 2015
So, because the bright swirls are reminiscent of a magnetic field influence, this becomes evidence of cometary impact? If the surface was altered by electrical processes, as conveyed in crater formations, then we'd expect to find surface anomalies associated with magnetic patterns.
Captain Stumpy
3.7 / 5 (3) Jun 02, 2015
there is no mention of the possibility of a plasma discharge
@cd
there is not enough evidence to support the conclusions

and your comment regarding the knowledge of plasma physics is an old, tired one that has been repeatedly debunked
so it only exists in your head because of your faith in eu pseudoscience (actually, in this case it is considered science fiction)
just because you keep repeating the lie doesn't make it true

another point
your idiot plasma theory has already been discussed (read the 6th paragraph, sparky)
the problem was that there is BETTER evidence suggesting that there is another cause, as noted in the next few paragraphs
the comet hypothesis also explains the magnetic anomalies too

and lets not discount the fact that comets strike the moon, like you are trying to do
like you did with meteor craters

you are a conspiracy theorist making stuff up and trying to fit the evidence to your faith

real Science follows the evidence
Stevepidge
1 / 5 (2) Jun 02, 2015

there is not enough evidence to support the conclusions

and your comment regarding the knowledge of plasma physics is an old, tired one that has been repeatedly debunked
so it only exists in your head because of your faith in eu pseudoscience (actually, in this case it is considered science fiction)
just because you keep repeating the lie doesn't make it true

another point
your idiot plasma theory has already been discussed (read the 6th paragraph, sparky)
the problem was that there is BETTER evidence suggesting that there is another cause, as noted in the next few paragraphs
the comet hypothesis also explains the magnetic anomalies too

and lets not discount the fact that comets strike the moon, like you are trying to do
like you did with meteor craters

you are a conspiracy theorist making stuff up and trying to fit the evidence to your faith

real Science follows the evidence


Your science follows grants and funding, you really need to get a grip.
Captain Stumpy
3.7 / 5 (3) Jun 02, 2015
Your science follows grants and funding, you really need to get a grip
@stevepig
personal conjecture without evidence
considering the advances made just since 1970, your comment is proven to be a politically, religious and conspiratorial based delusion because of your fears and inability to accept reality over your religion

http://www.ploson...tion=PDF

perhaps you should consider getting an education
try here: http://ocw.mit.edu/index.htm

you might learn something

its free

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.