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the mystery of the lunar ionosphere

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presented by science at nasa

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how can a world with no air have an

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ionosphere

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somehow the moon has done it

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lunar researchers have been struggling

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with this mystery for years and they may

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have finally found a solution

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but first what is an ionosphere

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every terrestrial planet with an

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atmosphere has one high above the

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planet's rocky surface where the

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atmosphere meets the vacuum of space

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ultraviolet rays from the sun break

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apart atoms of air

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this creates a layer of ionized gas an

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ionosphere

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impact on communications and navigation

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for instance it reflects radio waves

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allowing shortwave radio operators to

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bounce transmissions over the horizon

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for long-range communication

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the ionosphere also bends and scatters

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signals from gps satellites sometimes

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causing your gps tracker to misread your

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position

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the first convincing evidence for an

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ionosphere around the moon came in the

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1970s from the soviet probes luna 19 and

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22. circling the moon at close range the

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orbiter sensed a layer of charged gas

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tens of kilometers above the lunar

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surface containing as many as 1 000

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electrons per cubic centimeter a

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thousand times more than any theory

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could explain

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the idea of an airless moon having an

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ionosphere didn't make much sense but

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the evidence seemed compelling

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in fact the moon isn't quite as airless

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as most people think

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small amounts of gas created by

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radioactive decay seep out of the lunar

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interior

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meteoroids and the solar wind also blast

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atoms off the moon's surface

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the resulting shroud of gas is so thin

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however that many researchers refused to

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call it an atmosphere preferring instead

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the term exosphere

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the density of the lunar exosphere is

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about a hundred million billion times

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less than that of air on earth

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not nearly enough to support the kind of

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ionosphere the luna probes saw

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for 40 years the moon's ionosphere

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remained a mystery until tim stubbs of

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the goddard space flight center

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published a solution in 2011.

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the answer he proposes is moon dust

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stubbs a 30-something scientist who

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wasn't even born when the moon's

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ionosphere was discovered read the

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accounts of apollo 15 astronauts who

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reported seeing a strange glow over the

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moon's horizon

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many researchers believe the astronauts

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were seeing dust

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the moon is an extremely dusty place

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naturally surrounded by a swarm of

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particles think pig pen in the charlie

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brown comics

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when these floating dust grains catch

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the light of the rising or setting sun

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they create a glow along the horizon

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stubs and colleagues realized that dust

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could be the key

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uv rays from the sun hit the floating

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grains and ionized them

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according to their calculations this

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process can produce enough charge

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that is positively charged grains

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surrounded by negatively charged

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electrons to create the moon's

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ionosphere

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gas is new to planetary science no one

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knows how it will behave at different

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times of night and day or how it might

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affect communications and navigation on

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the moon

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with nasa's artemis probes orbiting the

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moon now and the lady spacecraft

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scheduled to launch in 2013 to study the

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moon's exosphere more information should