Venus: The Forgotten, Mysterious Planet
Dr.LoriS.GlazeNASA’sGoddardSpaceFlightCenter
September 27,2017
Why are we so fascinated by Venus?• Venuswasoneofthefirst
‘wanderers’ identifiedbyearlyastronomers;importantinmanyearlymythologies
• Venusisthebrightestobjectinthenightsky(otherthanthemoon)
• UniqueinthewaysheappearstojumpfromeveningtomorningskyandinhowinsyncsheiswithEarth:13Venusyears=8Earthyears
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Botticelli’s“BirthofVenus”: bornofthefoamfromtheseaafterSaturncastratedhisfatherUranusandhisbloodfelltothesea.
Venus today (at sunrise)!
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VenusiscurrentlytheMorningStar- Augustwaspinnacleofcurrentvisit- Venusrisesacouplehoursbefore
sunrise
VenusdisappearsinDecember- Notvisiblefor2monthswhileshe
passesbehindthesun
VenusastheEveningStar- VenuswillreappearinFebruaryin
theeveningsky
Venus fun facts• VenusisalmostthesamesizeasEarth(85%
Earth’sradius;91%Earth’sgravity)• Venus’“day” islongerthanits“year”
– 1“year”=225Earthdays– 1“day”=243Earthdays– Almostperfectlyspherical
• Venusrotatesbackward(retrograde)• Venushasnoseasons
– Venus’ rotationaxisisclosetovertical(relativetoorbitalplane)
• Venushasnomagneticfield9/27/17 ASU - SchoolofEarthandSpaceExploration 4
Venus shrouded in continuous cloud cover
Venus’ atmosphere: Earth’s evil twin?
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Only 10% of incident sunlight reaches the surface.Surface visibility is like Earth on a very cloudy day.
VerystronggreenhouseeffectAtmosphereis96.5%carbondioxide
LikeapressurecookerSurfacetemperature=860˚F(460˚C)meltslead!Surfacepressure=92barislikebeing~½miledeepocean!
FerociouswindsWindspeed=>250mph60xVenusrotationrateAllwest,allthetimeOnly~2mi/houratthesurface
Corrosivesulfuricacidclouds~15milesthick
Despite similar origins, sizes and masses,Venus and Earth evolved differently:
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Earth: Cool and WetVenus: Hot and Dry
When and
Why?
Dailydoseofcolor.com9/27/17 ASU - SchoolofEarthandSpaceExploration 7
> 3,500 Exoplanets have been confirmed(as of 9/20 [NASA Exoplanet Archive] – growing every day)
Hundreds of these exoplanets are in the Earth-Venus-Mars size range. But, data
are lacking to understand where these planets fit along evolutionary pathways.
Brief history of Venus exploration
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
• PioneerVenus(US;1978-1992)– Orbiter
Brief history of Venus exploration
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
• PioneerVenus(US;1978-1992)– Orbiter&probes
Brief history of Venus exploration
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
• PioneerVenus(US;1978-1992)– Orbiter&probes
• Vega(USSR/Europe;1985)– Lander&2balloons
Brief history of Venus exploration
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
• PioneerVenus(US;1978-1992)– Orbiter&probes
• Vega(USSR/Europe;1985)– Lander&2balloons
• Magellan(US;1989- 1994)– Orbitingradar
Brief history of Venus exploration
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
• PioneerVenus(US;1978-1992)– Orbiter&probes
• Vega(USSR/Europe;1985)– Lander&2balloons
• Magellan(US;1989- 1994)– Orbitingradar
• VenusExpress(ESA;2006– 2014)– Orbiter,cloudchemistry&dynamics
Brief history of Venus exploration
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• Venera(USSR;1961- 1983)– Multipleprobes/landers
• PioneerVenus(US;1978-1992)– Orbiter&probes
• Vega(USSR/Europe;1985)– Lander&2balloons
• Magellan(US;1989- 1994)– Orbitingradar
• VenusExpress(ESA;2006– 2014)– Orbiter,cloudchemistry&dynamics
• Akatsuki(JAXA;2015– ?)– Orbiter,meteorology&lightning
Brief history of Venus exploration
What we’ve learned so far...Venus & Earth have been volcanically active,
but the tectonics are very different
Earth: Plate TectonicsVenus: One “Plate”9/27/17 15ASU - SchoolofEarthandSpaceExploration
Venus does not have plate tectonics
What does the surface look like?
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Venera 13 surface image
Theonlydirectviewsoflocal-scalegeologyarefromVeneraimages,acquired>30yearsagoforfourlandingsites inthevolcanicplains
Because ofthethickcloudcover,theonlyglobal imageswehaveofVenusarefromradar– difficulttointerpret
Venus’ surface: Mystery history• 80% of the surface is volcanic
plains (basalt, from Venera)• Fewer than 1000 impact craters
– All are fresh & randomly distributed
• Average age of plains is 500 million years old – everywhere – Was this a “recent” global
resurfacing?
• “Tesserae” are high-elevation, complex ridged terrains– Noknownanaloginoursolarsystem.
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Have the surfaces of Venus and Earth always been so different?
Revealed by Magellan Radar
What are tesserae?Appeartobe“older” thantheplainsbasedonstratigraphy
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Infrared data from Venus Express[Gilmore et al., 2015]
Elemental chemistry and mineralogy could distinguish mafic versus felsic origin.
FormationofEarth’scontinentsrequiredplatetectonicsANDoceans.WhatdoesthismeanforVenus?
Aretheyadifferentkindofrock?Maybemoresilica-rich,likeEarth’scontinents?
VenusExpressseemstoindicateyes
Planets in our Solar System
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Core
Crust
Atmosphere
Mer
cury
, Plu
to, M
ars
& st
uff
Graphic borrowed from Kevin Zahnle
Venu
s &
Earth
Neptune& Uranus
Jupiter & SaturnDid Venus and Earth start out the same?
Origin of Venus’ atmosphere• Neonandargon:ConsistentwithEarthandVenusbeingmadefromsamestuff
• Krypton:Storyfallsapart!– PioneerandVeneradiscrepantbyafactorof15
• Xenon:Nomeasurementsofanykind!!– CriticaltounderstandifVenus’originwasdifferentfromEarth,setting itoffonauniquepath
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Figure after Baines et al. [2013]
Noble Gas Inventories
How recently was Venus an ocean world?Deuterium/Hydrogen enables transformational understanding of oceans on Venus
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Venus today Venus 4Ga? 1Ga?ASU - SchoolofEarthandSpaceExploration
Need new water measurements!
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Off the chart!
If we can get a better measurement of the water today, we can use models to determine when Venus lost its water to space.
AmountofwaterlossinVenus’atmosphereisstillcontroversial
Pioneermeasurementwasmadeafterinletwascloggedwithsulfuricaciddroplet(only1msmt)
VenusExpressmeasurementsabovetheclouds(~70km)areasmuchas3xgreaterthanthosefromPioneer
What ‘drives’ the Venus atmosphere?
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If we can learn how to model Venus’ atmosphere, we can better predict Earth’s future.
VIRTIS 5 µm - infrared
VMC 0.365 µm - ultraviolet
Venus’ south polar vortex, as viewed by two instruments on Venus Express
VenusExpressobservedclouddynamics
Modelscannotexplainwhycloudsmovesofast
Wedon’tunderstandhowthesun’sinteractionwithcloudparticles(aerosols)affectsthechemistryanddynamicsoftheatmosphere
50%ofincidentUVlightisabsorbed– bywhat??
75% of the atmosphere is unexplored!• Veryfewmeasurements below30km• Chemicalprocessescompletelyunconstrained inthelowest15kmoftheVenusatmosphere
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Guesses based on models
Earth for
scale
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How do the surface and atmosphere interact?
ProposedbyBruceFegley
Understanding the role of trace gases on Venus helps put limits on natural climate drivers.
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Whatroledotracegasesplay?– SO2,H2O,OCS,H2S
Howarethesulfuricacidcloudsmaintained?
Canchemicalweatheringofthesurfaceprovidethesulfur?
Isanactivevolcanicsourcerequiredtosupplysulfur?
Is Venus still volcanically active?
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If so, could we tell?
Artist’s rendition of active volcanoes on Venus
Venus’interiorshouldstillbehot(likeEarth)
– Because VenusandEarthareaboutthesamesize
Earthlosesmostofitsheatatplateboundaries
HowdoesVenusloseheat?– “Heatpipe”volcanoes?– Periodic“overturn”events?– Canthesetypesofeventsbethesourceofsulfur?
Evidence for “current” volcanism?
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Pioneer Venus Orbiter/Ground-Based
Venus Express What caused “spikes” in sulfur dioxide?
Ø Pioneer Venus (1978) and Venus Express (2007) both saw spikes
Ø Seen at the cloud tops - 43 miles high (70 km)
Models can predict how much water and sulfur we should be looking for and where.
Sulfur dioxide at the cloud tops
What can provide “pulse” of SO2?
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OnEarth,thelargestplumesriseto20-25miles altitude (35-40km- 4xhigherthancommercialaircraftfly)
OnVenus,verydifficulttodriveaplumetocloudtopaltitudes becausethelowestatmosphere issohotanddense
Otherhypotheses:– Periodicoverturnevent intheclouds?
– Meteorite disturbance?
Largeexplosivevolcaniceruption?
Other possible evidence?
VenusExpressobservedunusualanomaliesinsurfacereflectancenearvolcanoes
9/27/17 ASU - SchoolofEarthandSpaceExploration 29Ganiki Chasma [Shalygin et al., 2015]
Idunn Mons [Smrekar et al., 2010]
“younger” surfacesatpotentially activevolcanoes
Anomalies thatcomeandgoinplausiblyvolcanicallyactiveareas
NASA’s “Discovery”
Program• TheDiscoveryprogramsupportssmall($500M)missions:
– DAWN,GRAIL,MESSENGER,MarsPathfinder,Kepler,InSight….
• NASAholdsacompetitioneveryfewyearsforplanetarymissionconcepts– 28conceptssubmitted in2015competition– Fiveselected for9monthstudy: 2Venus(includingDAVINCI)+3asteroid– LucyandPsyche(bothasteroidmissions) selected tofly
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Probemissionfocusedon:Ø NoblegasesØ Compositionoftheatmospherebelow12kmwhere2/3ofatmosphericmassresides(unexplored)
Ø AtmosphereinteractionwiththesurfaceØ Tesseramorphology
NASAsupports~2medium($1B)missionsperdecade(3sofar):v NewHorizonsencountered PlutoinJuly2015v Juno iscurrentlyinorbitatJupiterv OSIRIS-REx isen routetoBennu tocollectsample; arrivesAugust2018
Venusisoneof6targetsallowedinthecurrentcompetition(28April2017)v 13proposalssubmittedv 3Venusconcepts proposed(including VICI)
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VICI:VenusInsituCompositionInvestigationsLandermissionfocusedonunderstandingVenusthroughtimebymeasuring:
Ø NoblegasesØ Atmospherecompositionbelow12kmwhere2/3ofatmosphericmass
resides(unexplored)Ø AtmosphereinteractionwiththesurfaceØ Tesserachemistry,mineralogy,&morphology
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International Opportunities?Other agencies are also thinking about Venus
(but no firms plans)
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Currentcallfor“Medium”classmissionsisunderway
EnVision isaVenusorbiterwithradarandinfraredspectrometer
Developingaconceptcalled“Venera-D”(long-lived)
NASAisfundingUSparticipationinajointUS-RussianScienceDefinitionTeam
Missionincludesorbiters,aerialplatforms,andlanders
EUROPE
RUSSIA
Earliestlaunchprobably late2020soreven2030
Ifselected,probablywouldn’tlaunchuntillate2020s
In Summary
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After6orbitalmissionssince1978,aninsitumissionisneededtoprovidenewobservationsofVenus:
Ø tounderstandtheformationandevolutionofrockyplanets,Ø includingplanetsoutsideoursolarsystem
• VenusisverysimilartoEarthinmanyways,but…• Venusevolvedverydifferently• Wedon’tyetunderstandwhenorwhyVenusevolutiondivergedfromEarth,butweneedto
• TherearecurrentlyNOplannedVenusmissionsbyanyinternationalspaceagency