Jeff Morgenthaler, Ph.D.Planetary Science Institute

How to verify a lot of quantum h i l l l ti ith t d i mechanical calculations without doing

any quantum mechanics

High-quality astrophysics with h l l h isophomore-level physics

What I did for my summer vacation l t last year

Mike Combi (U. Michigan)( g )Walt Harris (U.C. Davis)Paul Feldman (Johns Hopkins)(J p )Hal Weaver (Johns Hopkins Applied Physics Lab)Galaxy Evolution Explorer (GALEX) team

Karl Forster (Cal Tech)Tim Conrow (IPAC)Tim Conrow (IPAC)Susan Neff (NASA/GSFC)

JPL HORIZONS: Jon GiorginiJ O ONS: Jo G o g

BackgroundBackgroundWhat is a comet – why do we care?How do we “measure” comets?Why do we need accurate molecular/atomic physics to measure comets?

h b l fMeasuring the carbon ionization lifetimeNext step: COAlong the way: OFinal phase: OH

NC

Nucleus (10—100 km)Head/Coma (neutral

NA

SA/JPL

Caltech/U

M

emission lines, 100—106

km) – ballistic motionDust tail (white 107 km)

L-MD

/McR

Dust tail (white, 107 km)Ion tail (blue , 107 km)

Co

RhEL

opyright ©hem

ann(A ©

1997 by A

ustria) G

erald

Comets are some of the most primordial material left over from the formation of the material left over from the formation of the solar system

Solar system formation modelsSolar system formation models

Comets may have Comets may have delivered water and the seeds of life to Earth, maybe Mars, Venus, etc.

d h bAmino acids have been observed

IDEAL: Cryogenic IDEAL: Cryogenic Nucleus Sample Return (CNSR)Bring back a core sampleBillions of d lldollarsNot any time

soon

Prialnik 2004

Next best thing:Next best thing:Take the lab to the cometRosetta: European Space Agency (ESA) p g y ( )Orbiter/LanderComet 67P/Churyumov-Gerasimenko

Astrium - E. Viktor

First approximation: First approximation: Stardust mission flew through the tail of comet Wild 2 collected comet dust

d t it b k t and sent it back to Earth

NASA

Second approximation: Deep Impact impactorSecond approximation: Deep Impact impactorExcavated comet material

NA

MA

SA/JPL-C

Maryland/Co Caltech/U

nornell

niversity of

Deep Impact pre-impact view Stardust revisit

Tried and true: Remote sensingg

Look at what is coming off of the comet and figure out what it is made ofVolatiles:Molecule 1P/HalleyH2O 100CO 3.5—11CO2 3—4CH4 <0.8C H 0 3

The Mayall 4-meter telescope at the KittPeak National Observatory near Tucson, Arizona.

C2H2 0.3C2H6 0.4CH3OH 1.8

A i h h d iA spectrum is worth a thousand pictures103PP/H

artly22 (EPO

XI ttarget; Weeaver et al.. 1992)

S i i Spectro-imaging is priceless

Carbon 1561 Å and 1657 Å and 1657 Å multiplets

Carbon comaCarbon coma

NASA Small Explorer missionWorks for comets too!Works for comets too!

Morrissey et al. 2005FUV

NUV UV

Weaver et al. 1992Weaver et al. 1992

FUV NUVVisible

Different emission Different emission lines have differentscale lengthsg

NUV

S h d d t bSmushed data cube

Mcphaate

et al. 19999

FUV NUV

P d i Production rate, Q(C), derived from total from total emission

Q(C) related to C ( )in the nucleus

Reality: most i instruments don’t “swallow” all swallow all the light

Aperture pcorrections

Require accurate knowledge of spatial distributionNow measured for carbon (Morgenthaler et al. 2011)

K Key parameters:τ = lifetimev = outflow

velocityvτ = scale length

Haser (1957) model: Consider comet nucleus isotropicallyemitting particles at rate Q, velocity v, lifetime τ.D i ti i l ft i t th d ☺

τvr

e−

=Qn(r)

Derivation is left as an exercise to the reader ☺

2-component Haser model:π

evr 24

n(r)

n = number densityQ d i

2 component Haser model:“Parent/mother” = 1“Daughter” = 2k bi ti f l l thQ = production rate

τ = lifetimev = velocity

⎟⎟⎞

⎜⎜⎛

−=−−

22112

Qn(r) ττ vr

vr

eek

k = combination of scale lengths

yr = dist. from comet ⎟

⎠⎜⎝2

24n(r)

πeek

vr

Integrate along line of sight to convert number density to column density

Carbon is a daughter speciesCarbon is a daughter speciesv1~ 1 km/s (bulk outflow velocity)v ~ 4 km/s (ejection velocity)v2~ 4 km/s (ejection velocity)> 3 x 105 km, just carbon ionization

Best-fit Haserd l d t i model determines

carbon ionization lifetime

Best-fit Haser model determines carbon ionization Best-fit Haser model determines carbon ionization lifetime

Qk r−

22

224

Qk n(r) τ

πve

vr

−

=

Problem: BACKGROUND!

Comet moves: Stars can be erasedComet moves: Stars can be erasedBackground exposure ~1 month prior – good enough?

What changes over a FOV of 1 degree?What changes over a FOV of 1 degree?Not the GalaxyS l t ? FUV di l li ht t b i ht Solar system? FUV zodiacal light not bright enoughEarth’s atmosphere: AirglowEarth s atmosphere: Airglow

Photochemical effect

C i i Correction is analogous to extinction

shadowextinctionSpent summer vacation

sun orbit

vacation picturing GALEX orbit and Earth’s shadow in 3DAeronomyy

Sujatha et al. (2009) airglow used solar activity

Airglow ~uniform over 1 degreeConstant offset of background imageg g

Solar photoionization only

Comet Machholz’s heliographic latitude was 30° during solar min Edge of slow solar wind zone

Morgenthaler et al. 2011

F b l i d b i t t For carbon, solar wind can be more important than solar photoionization!IMPORTANT: standard reference (Huebner IMPORTANT: standard reference (Huebner, Keady, and Lyon 1992) only includes photoratesSolar wind ionization important for all long-lived species

Ph t lif ti > 500 000 Photo lifetimes > 500,000 se.g. H, C, O, CO

Previous production rates need to be revisited! Previous production rates need to be revisited! Comet “carbon puzzle” (Festou 1984) may be solved

Verified ionization cross section calculations Verified ionization cross section calculations for carbon over a wide range of photon energies

Verified carbon-proton charge exchange cross p g gsection

Verified carbon-electron collisional cross section

Verified ionization cross section calculations Verified ionization cross section calculations for carbon over a wide range of photon energies

Assume solar spectrum is well knownVerified carbon-proton charge exchange cross section

Assume solar wind speed and density well knownVerified carbon-electron collisional cross section

A d t i l l i dAssumed comet was in slow solar wind

Mcphaate

et al. 19999

FUV NUV

Next step:CO withCO withFUV grism

Morgenthaler et al. 2011

Why does [OI] Why does [OI] oxygen distribution in Hale-Bopp look like a comet?Metastable [OI] prompt emission really traces H O really traces H2O and OH

Morgenthaler et al. 2001

Residuals aren’t as cleanResiduals aren t as cleanNeed 3D coma models – jets, emission asymmetries ion lines?asymmetries, ion lines?

It is possible to reliably measure atomic and It is possible to reliably measure atomic and molecular lifetimes using wide-field observations of comets

C was easy – isotropicCO will be harder with grism dataOH requires sophisticated coma models

GALEX could be used as an upper-atmosphere h t ti (700 k ltit d )research station (700 km altitude)