High resolution
X-ray views of
solar system objects
G. Branduardi-Raymont
Mullard Space Science Laboratory
University College London, UK
MSSL
UCL
12 Years of Science with Chandra
Boston, 23rd May 2011
X-ray production in the solar system
• Charge exchange (CX)
Cravens et al. 1995, Dennerl 2010
Highly ionised ions collide with neutrals/molecules
 electron capture (‘charge exchange’)
 de-excitation with X-ray line emission
Dennerl 2009
e.g. H2 + O7+  H2+ + O6+ + hn
Solar wind (SWCX) or
magnetospheric ions
In comets, heliosphere, Earth geocorona,
Venus/Mars exospheres, Jupiter aurorae
• Electron bremsstrahlung
7+
O
O7+
6+*
O
O6+*
• Electron collisions with line emission
• Elastic and K-shell fluorescent scattering of solar X-rays in
planetary atmospheres and on surfaces
OO6+6+
X-rays from Jupiter
• Ions first thought to originate in the inner magnetosphere
(8–12RJ) but first Chandra observation points to origin at >30 RJ
• What are the ion species (C or S) and thus their origin (solar
wind / magnetosphere)?
Chandra HRC-I
2000
Recent XMM-Newton &
Chandra spectra favour
magnetospheric origin
Gladstone et al. 2002
B-R et al. 2007, Hui et al. 2010
Jupiter – XMM-Newton, 2003: EPIC
OVII (0.55–0.60 keV)
FeXVII (0.70–0.75, 0.80–0.85)
OVIII (0.63–0.68 keV)
MgXI (1.30–1.40 keV)
B-R et al. 2007
Jupiter – XMM-Newton, 2003: EPIC
0.2– 1 keV
3 – 5 keV
1 – 3 keV
5 – 10 keV
Jupiter – XMM-Newton, 2003: EPIC
Auroral and disk spectra
OVII by CX
North
Disk coronal spectrum
South
Electron
bremsstrahlung
Jupiter – XMM-Newton, 2003: RGS
OVIII
OVII
FeXVII
• RGS clearly resolves auroral CX from disk soft X-ray
emission lines
• Width of OVII and OVIII lines corresponds to energies of
few MeV for O ions
Jupiter – Chandra and Hubble STIS – 2003
Chandra ACIS reveals different
spatial morphology of soft (< 2 keV,
ion CX) and hard (> 2 keV, electron
bremsstrahlung) X-ray events
 CX X-ray events map far out from
the planet
Simultaneous Hubble STIS images
show > 2 keV events coincide with
FUV auroral oval and bright features
(FUV from excitation of atmospheric
H2 and H by 10 - 100 keV electrons)
B-R et al. 2008
 Same energetic electrons responsible for both, UV and X-rays
X-rays from the Galilean satellites and the IPT
Io and Europa X-rays (Chandra
ACIS) from energetic H, O and
S ion impacts  fluorescence
Non-thermal electron bremsstr.
+ OVII em. from Io Plasma Torus
Elsner et al. 2002
On Saturn …
• Disk and polar cap X-ray emissions have similar
coronal-type spectra (unlike Jupiter)
Bhardwaj et al. 2005a
Chandra ACIS
• Flux variability suggests X-ray
emission is controlled by the Sun
Saturn’s rings
• 0.53 keV O-Ka fluorescent line (~1/3 of disk emission)
• Scattering of solar X-rays on atomic oxygen in H2O icy ring
material
Chandra ACIS
Bhardwaj et al. 2005b
X-rays from Saturn: XMM-Newton EPIC
Oct. 2002
Apr. 2005
Oct. 2005
B-R et al. 2010
Saturn and Jupiter as solar mirrors
Jupiter
Saturn
Saturn’s disk X-ray emission decreases over the years
following the decay of solar activity
Same trend observed in Jupiter
Saturn and Jupiter: a new strategy
• Evidence for enhanced solar wind affecting Jupiter’s X-ray
aurorae  same could happen on Saturn
• X-ray emission by CX: PX ~ nSW vSW
Cravens 2000
• Accurate predictions of solar wind propagation from 1 AU
now available through mSWiM code
Zieger & Hansen 2008
 monitor increasing solar activity, select enhancement
episodes  propagate and observe when shock arrives at
the planets
• Strategy applied with Chandra TOO of Saturn this month,
and hopefully with a TOO on Jupiter in Oct. 2011
Earth’s aurorae: high X-ray energies
• Since 1960s hard X-ray observations from balloons (> 20 keV)
• PIXIE experiment on Polar : > 2 keV electron bremsstrahlung
2 – 12 keV (~1.5 hr)
Ostgaard et al. 2001
Earth’s aurorae: low X-ray energies
• Evidence for auroral electron bremsstrahlung and N and O
line emission below 2 keV from Chandra HRC imaging and
simultaneous DMSP F13 electron measurements
• Aurora very variable,
with intense arcs and
patches (Bhardwaj et al. 2006)
• Not yet shown
conclusively that
ion precipitation
has a part in
X-ray production
 needs high res. spectrum!
The Earth’s geocorona
• Time variable oxygen
emission lines on the
dark side of the Moon
Wargelin
et al. 2004
Chandra ACIS
Correlation with solar wind flux  SWCX in Earth’s geocorona
• Suzaku observations of the NEP:
Increase in soft X-ray lines
correlated with solar wind
proton flux
• Systematic study with
XMM-Newton Carter et al. 2008, 2010
Fujimoto et al. 2007
Comet C/2000 WM1, 2001 Dec. 13 – 14
Optical
XMM-Newton
Dennerl et al. 2003
Cometary X-rays
• SWCX with coma neutrals well established emission process
Chandra ACIS
McNaught-Hartley
LINEAR
LINEAR
2P/Encke 2003
Lisse et al. 2005
Bodewits et al. 2007
• Cometary spectra reflect state of SW 
first global exploration of comet environs and SW conditions
at different distances from the Sun
The way forward
• Chandra and XMM-Newton combined
have demonstrated the potential of
planetary X-ray astronomy, establishing
 planetary response (including Earth’s)
to solar stimulation
 CX as the process that provides
global and remote X-ray diagnostics
of astrophysical plasma interactions
(also in ISM, stellar winds, galaxies, clusters)
XMM-Newton
• Observations at times of enhanced solar activity likely to
return the most science
• Ultimately the goal is observations in-situ at the planets to
establish X-rays on a par with other wavebands
Thank you!
MSSL
UCL
12 Years of Science with Chandra
Boston, 23rd May 2011