Thursday, June 5, 2008

100 Explosions on the Moon

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:

Above: A lunar impact on Jan. 4, 2008. This is number 86 on the list
of 100 impacts recorded by the MEO team since their survey began in 2005.

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.

Above: A map of the 100 explosions observed since late 2005.
A complete list with lunar coordinates is available here.

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.

Gun Range. This is a genuine photo
showing the spray of secondary particles.

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.

Teacher's Workshop!

Teachers in the Southeast U.S. are invited to apply to attend a workshop
entitled "Paving the Way to the Moon and Beyond," held June 12 – 14, 2008
in Huntsville, Alabama. The two day workshop, sponsored by the Lunar Precursor
Robotic Program (LPRP), will focus on content that will explain the who, the what,
and the why of lunar exploration. Beginning with the Lunar Reconnaissance Orbiter
(LRO) and the Lunar Crater Observation and Sensing Satellite (LCROSS), teachers
will research mission design and scientific goals and experiments through hands
on activities. Included in the workshop will be a tour of NASA science labs and an
opportunity to talk with scientists involved in exploration related activities.
All materials will be appropriate for elementary and middle school preservice
and inservice teachers and will be aligned with national standards. Example
activities: Earth-Moon comparisons and motions, craters and lunar soils,
solar influences on the Moon. Most activities will take place at the Educator
, located at the Space and Rocket Center. Housing costs for
three nights will be provided (at the University of Alabama in Huntsville).
Stipends also will be provided. To attend, contact Mitzi Adams 256 961 7626
or mitzi dot adams @ nasa dot gov.



Kit (Keep It Trill) said...

Walter, I wondered about this post yesterday and it's still on my mind.

Considering that so many significantly-sized meteors land there instead of here, in addition to controlling our tides, could the moon be the equivalent of a lightening rod for earth by keeping us safe from meteors?

Walter said...

Kit: Yes, to some degree. Because of the its obvious gravitational influence (as you mentioned tides) the Moon does, depending on it's proximity and relation to its 27-day orbit, act as both a buffer and an attractor for space objects. This effect can be seen in the form of lunar impact craters which are the remains of collisions between an asteroid, comet, or meteorite and the Moon. These objects hit the Moon at a wide range of speeds, but average about 12 miles per second.

Kit (Keep It Trill) said...

Scientifically this is amazing to me, and from a spiritual perspective it leaves me in awe of how God thought of everything in His wonderful plan to love and protect us.

Thanks for taking the time to answer.

~ Kit

Walter said...

You are very welcome! Thanks for asking and being interested. God definitely is wise and all knowing. Nothing of this world is a random accident. Everything has a reason.