100 Explosions on the Moon

100 Explosions on the Moon
A map of the 100 explosions observed since late 2005.

Not so long ago, anyone claiming to see flashes of light on the Moon would be viewed with deep suspicion by professional astronomers. Such reports were filed under "L" ... for lunatic.

Not anymore. Over the past two and a half years, NASA astronomers have observed the Moon flashing at them not just once but one hundred times.

"They're explosions caused by meteoroids hitting the Moon," explains Bill Cooke, head of NASA's Meteoroid Environment Office at the Marshall Space Flight Center (MSFC). "A typical blast is about as powerful as a few hundred pounds of TNT and can be photographed easily using a backyard telescope."

As an example, he offers this video of an impact near crater Gauss on January 4, 2008.

The impactor was a tiny fragment of extinct comet 2003 EH1. Every year in early January, the Earth-Moon system passes through a stream of debris from that comet, producing the well-known Quadrantid meteor shower. Here on Earth, Quadrantids disintegrate as flashes of light in the atmosphere; on the airless Moon they hit the ground and explode.

"We started our monitoring program in late 2005 after NASA announced plans to return astronauts to the Moon," says team leader Rob Suggs of the MSFC. If people were going to be walking around up there, "it seemed like a good idea to measure how often the Moon was getting hit."

"Almost immediately, we detected a flash."

That first detection—"I'll never forget it," he says--came on Nov. 7, 2005, when a piece of Comet Encke about the size of a baseball hit Mare Imbrium. The resulting explosion produced a 7th magnitude flash, too dim for the naked eye but an easy target for the team's 10-inch telescope.

A common question, says Cooke, is "how can something explode on the Moon? There's no oxygen up there."

These explosions don't require oxygen or combustion. Meteoroids hit the moon with tremendous kinetic energy, traveling 30,000 mph or faster. "At that speed, even a pebble can blast a crater several feet wide. The impact heats up rocks and soil on the lunar surface hot enough to glow like molten lava--hence the flash."

During meteor showers such as the Quadrantids or Perseids, when the Moon passes through dense streams of cometary debris, the rate of lunar flashes can go as high as one per hour. Impacts subside when the Moon exits the stream, but curiously the rate never goes to zero.

"Even when no meteor shower is active, we still see flashes," says Cooke.

These "off-shower" impacts come from a vast swarm of natural space junk littering the inner solar system. Bits of stray comet dust and chips off old asteroids pepper the Moon in small but ultimately significant numbers. Earth gets hit, too, which is why on any given night you can stand under a dark sky and see a few meteors per hour glide overhead—no meteor shower required. Over the course of a year, these random or "sporadic" impacts outnumber impacts from organized meteor showers by a ratio of approximately 2:1.

"That's an important finding," says Suggs. "It means there's no time of year when the Moon is impact-free."

Fortunately, says Cooke, astronauts are in little danger. "The odds of a direct hit are negligible. If, however, we start building big lunar outposts with lots of surface area, we'll have to carefully consider these statistics and bear in mind the odds of a structure getting hit."

Secondary impacts are the greater concern. When meteoroids strike the Moon, debris goes flying in all directions. A single meteoroid produces a spray consisting of thousands of "secondary" particles all traveling at bullet-like velocities. This could be a problem because, while the odds of a direct hit are low, the odds of a secondary hit may be significantly greater. "Secondary particles smaller than a millimeter could pierce a spacesuit," notes Cooke.

At present, no one knows how far and wide secondary particles travel. To get a handle on the problem, Cooke, Suggs and colleagues are shooting artificial meteoroids at simulated moon dust and measuring the spray. This work is being done at the Vertical Gun Range at NASA's Ames Research Center in Mountain View, CA.

Meanwhile, back at the observatory, the team has upgraded their original 10-inch (25 cm) telescope to a pair of telescopes, one 14-inch (36 cm) and one 20-inch (51 cm), located at the Marshall Space Flight Center in Alabama. They've also established a new observing site in Georgia with a 14-inch telescope. Multiple telescopes allow double- and triple-checking of faint flashes and improve the statistical underpinnings of the survey.

"The Moon is still flashing," says Suggs. Indeed, during the writing of this story, three more impacts were detected.

New title: 103 Explosions on the Moon.

Source: Science@NASA, by Dr. Tony Phillips

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May 21, 2008
Sounds like a lunar base will be a lunar bunker.
Presumably it should able to withstand at least a 1000lb bomb. I recommed they install large screen tv's to act like windows. It would make it more homely and help folks feel connected with above lunar ground activity. Then again perhaps they would rather watch Oprah.

May 21, 2008
Since most activities on the moon are going to require digging, we may as well build moon bases in mine shafts anyway. That's where we're going to find the minerals needed for construction, manufacturing, oxygen production etc.

May 21, 2008
or we could have president bush build us a magical force fieldificator to protect us from the bad moon rocks!

May 21, 2008
We need to have some more geophones on the moon to listen for the sound of the impacts. It would be interesting to see if there is a correlation. This observation program would miss impacts on the far side of the moon, the far side of the earth and possibly the sunlit face, and probably does not work in daylight. So maybe it observes one sixteenth of the explosions.

May 21, 2008
Each of us is far, far more likely to be hit by a bolt of lightning than an astronaut would be to be hit by a cosmic pebble on the moon. They need to get real and get us up there. All this fumbling with nonsense to get grants just slows down the real science.
An astronaut on the moon with the same telescope aimed at Earth would see several magnitude more "flashes." But I've got no plans to move into an abandoned coal mine. And niether do any of you.
Build the ships and go. This new Lunar program is looking more and more like a bad joke. And a waste of money.
I love space science and space travel. But this is truly ridiculous. Too much dust. Dangerous meteors. Next it'll be the sunburn risk.
Let's go already!

May 21, 2008
Apparently Mayday missed the comment about secondary impacts. What part of "a spray consisting of thousands of "secondary" particles all traveling at bullet-like velocities" sounded safe to you?

May 21, 2008
Just started noticing them in 2005? Um...

May 21, 2008
Good going, Mayday. Let's throw all caution to the wind and place real human beings in potential danger just to satisfy your impatience. I bet if it was your life in danger you'd be all for the safety measures and extra bit of time and money spent researching how to ensure people don't die while they're up there working for the benefit of all mankind.

You're just one person, and like many of us, you could be dead by the time we reap the real benefits of a major lunar outpost. Why put so much at stake just so you can see something before your time is up? This isn't about "right now", it's about what it will end up doing for us all.

May 22, 2008
You're right, my bad. I guess 50-odd years between moon landings is the prudent path. I'll just chill and watch you all come up with that "safe" moon mission. It'll be fun. No hurry. Really.

But I do like the offer of going myself. Even if the latest "science" has declared it just a teesy-weensy bit unsafe. I'll go. Cripes! Where do I check-in for the physical?

But has it occured to you that all the astronauts that have ever left Earth's cozy atmosphere have been exposed to the same killer meteors? Are you suggesting that we shut the whole thing down until we can figure a way to sweep space clean of danger.
Please stop and think. Demanding(or even suggesting) that space travel be made as safe as your living room sofa is a serious uphill battle. Me thinks you may have ingested a little too much Star Trek as a child.

So here's the question: If we could reassemble an exact duplicate of the Apollo 12 vehicle(and obviously all the ground support gear and staff), would you go?

I would, in a heartbeat.
But I'll need two more takers.

May 22, 2008
On yourself Mayday!! I would love to come but I'm not a big fan of travelling and get bored too easily. Risk wouldn't be an issue as I'm not scared of my mortallity. Maybe once you've developed a skate park and teleport system I'll pay you a visit :-)

May 22, 2008
We can't properly learn without doing.

Sign me up, I'll go to the moon.


May 22, 2008
Actually mayday is right. There is no way to mitigate all the risks and at some point you just have to buy off on them.
We cannot transport heavy machinery to dig bunkers, the best we may do is use lots of kevlar.
And yes there are astronauts who would volunteer for one way trips to mars - of course NASA will not let them.

May 22, 2008
If space is shooting at us, I say we start shooting back!

Just a thought.

May 22, 2008
But seriously. Now this has got me thinkin'. Apollo hardware. Technically simple. Low cost(relative to what NASA is planning). Proven system. Never failed. No fatalities(in flight). Highly successful(even when it didn't work right, it still made a great movie). Why not just do it again?

Okay, throw in some kevlar underwear. But that's it.

Or can someone think of another example from history where a perfectly proven and successful system, by any measure, was shelved for something so dubious, delay-ridden and demonically money-sucking?


May 24, 2008
The threat by these meteoroids is negligible.

Imagine: On the area of northern America, people shoot 100 times in the air in 2 years. Would you be afraid of being hit by a falling bullet?

Even if building "big structures": would you be afraid of you greenhouse being hit?

Neglect this threat, make the effort on more serious ones.

May 27, 2008
kevlar underwear huh? let's send the mormons up in their 'magic' underwear.

May 27, 2008
We haven't been to the moon in 50 years because it's not worth it. We've already discovered what we could on the first trip and by observing it from here. The next step is a lunar base -- not another trip, which would just waste tax dollars and time. And the meteorites pose a threat to a base, not to a trip. Why not just do it again?
Because it's a waste of resources.

Jun 01, 2008
You are probably in more danger every time you get in your car. Really.

Jun 30, 2008
Correction Thales-
It's actually a race against time. There are VAST resources on the moon.

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