Australian Sky & Telescope — January 01, 2018

10 AUSTRALIAN SKY & TELESCOPE January 2018

been a brownish yellowish haze, due to the

sulfur concentration.”

This new vision of Earth’s natural

satellite comes from an improved analysis

ofgasestrappedintheMoonrocks

gatheredduringtheApollomission,as

well as detailed measurements of

lunarfeaturesobtainedbyrecent

orbiter missions.

Researchers estimate

that,atitspeak,thelunar

atmospherewasupto1½

timesasthickasthatof

present-day Mars, which

has a surface pressure of

0.01 bar — equivalent

to 1% of Earth’s

atmospheric pressure

at sea level.

■JAVIER BARBUZANO

ANCIENT MOON HAD VOLCANO-GENERATED ATMOSPHERE

ABOUT 3½ BILLIONyears ago, active

volcanoesontheMoonmighthave

releasedenoughgastoformatransient,

sulfuric atmosphere.

Intense eruptions that produced the

Moon’s dark volcanic plains, ormaria,

mighthavereleasedenoughgastoforma

thinatmosphere,anewstudypublished

intheNovember15thEarth and Planetary

Science Lettersshows.This atmosphere

mayhavesurvivedformillionsofyears

before being lost to space.

“The terrain would have looked like

aseaofglowingmoltenrock,with

patchesofdarker,coolingrocksforming

afracturedcrustontopoflavaexposed

tothedevelopingatmosphere,”says

lead author Debra Needham (NASA

MarshallSpaceFlightCenter).“The

atmosphere would most likely have

Pulsations in the Pleiades

THE EXOPLANET-HUNTINGKepler

spacecraft long monitored hundreds

ofthousandsofdistantstarswithan

exquisite sensitivity that — ironically

—putthebrighteststarsoutofits

reach. But not anymore: Publishing

intheNovemberissueofThe Monthly

NoticesoftheRoyalAstronomical

Society, Timothy White (Aarhus

University,Denmark)andcolleagues

describe an innovative new technique

known ashalo photometryon Kepler

observations of the brilliant ‘Seven

Sisters’ of the Pleiades.

CCD cameras capture photons in

‘wells,’ each of which corresponds to

asinglepixelintheresultingimage.

Butabrightsourcecancauseawellto

overflow, saturating the central pixel(s)

andcreatinga‘bleedtrail’.Whiteand

colleagues instead measured brightness

using photons recorded in the

unsaturatedpixelsaroundthecentral

one(s)andshowedthatthishaloisa

reliablemeasureofstellarbrightness.

Thesevenbrighteststarsofthe

Pleiadesareblue-giantstarsbrighter

and more massive than the Sun,

nearing the end of their short lives.

Asexpectedforthistypeofstar,the

newobservationsrevealthattheyall

pulsate,slowlyvaryinginbrightness

bylessthan1%.Theirlightcurves

are shown at right.

Amongthem,Maia(20Tauri)is

unusual.Ithasaslowrotationand

calmatmosphere,bothofwhich

allow unusual concentrations of

heavyelementstocirculatenear

itssurface.Keplerobservations

reveal that Maia varies over

an exceptionally long period,

brightening and fading with a

period of 10 days. The cause, the

authorsargue,ismostlikelyalarge,

chemically enriched spot on its

surface. If the spot is fixed, then it

probablyhassomerelationtothe

star’s magnetic field, but more data

areneededtolearnhowandwhy

thesechemicalspotsexist.

■MONICA YOUNG Days observed

Relative brightness

100

0.

30 50

Pleione

1.

1.

Taygeta

0.

1.

1.

Merope

0.

1.

1.

Maia

0.

1.

1.

Atlas

0.

1.

1.

Electra

1.

1.

0.

Alcyone

1.

1.

0.

NEWS NOTES

Artist’s concept of the

ancient Moon’s volcano-

produced atmosphere