Solar System Observing Opportunities
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Solar System Observing Opportunities D. Christian (CSUN), C. Lisse, A. Ptak, S. Murray (JHU), S. Wolk (CXC). WFXT Mission Synopsis.

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Solar System Observing Opportunities

D. Christian (CSUN), C. Lisse, A. Ptak, S. Murray (JHU), S. Wolk (CXC)

WFXT Mission Synopsis

One high resolution, high collecting area and wide FOV soft X-ray telescope with low background to image at least ½ the 0.4 – 7.0 keV sky down to very low fluxes while characterizing the spectra of millions of x-ray sources.

Key Scientific Parameters 

Constant PSF (5” goal HEW) across 1o x 1o FOV

Effective Area ~ 15 x Chandra @ 1 keV (goal 10,000 cm2)

Bandpass ~ 0.4 – 7 keV; Analog to SSDS in X-ray band

Dedicated 2 year survey mission (no GO program)

Calibrated data products released with no proprietary period

Detailed PtSrc and Extended Object Catalogues

Science Goals

Discovery and Characterization of Groups & Clusters

Evolution of AGN Population

Star Forming Galaxies

Halo Stars

Super Nova Remnants

Compact Galactic Objects

Solar System Objects & Nearby Stellar Neighborhood


The proposed WXFT mission will be performing 3 deep wide field surveys of 20000 sq. deg., 3000 sq. deg. and 100 sq. deg. that will include repeated observations and detections of foreground solar system objects throughout the course of the mission. WFXT will thus be a bonanza for solar system x-ray astrophysics. Understanding local soft x-ray emission processes, driven by scattering of solar x-rays and charge exchange with the solar wind, means understanding the nearest, best example of a stellar wind throughout interplanetary space; understanding the coupled neutral outflows from Io and their coupling to the rapidly rotating Jovian dynamo; understanding the influx and outflow of ISM H and He through the heliosphere; and understanding emission from the local hot bubble in the nearby ISM, surrounding the heliosphere.

RASS Solar System, Chandra ACIS Pointed Obs

WFXT’s sensitivity and angular scale allows for vastly improved solar system studies.

WFXT Survey Serendipitous Solar System Science

  • Detections of Known Emitters – Comets, Rocky Planets, Gas Giants, & the Heliosphere

  • Large Scale Imaging – Allows for direct, complete study of extended systems overflowing Chandra & XMM FOVs (e.g. comets, Jupiter)

  • Long term monitoring - Variation with solar wind, CMEs, flares. No solar system object has been monitored for more than a few days.

  • Large scale diffuse flux capability allows direct comparison to ENA and LENA observations of the heliopause.

  • Pointed Observations?

Bhardwaj, Lisse, et al. 2007 & Encyclopedia of the Solar System II, 2008

Known Solar System X-rays Emitters

New Possibilities with WFXT : Mercury, Uranus/Neptune? High Latitude & Main Belt Comets? Trojan Asteroids? Active Centaurs? The Heliopause?













Some of the currently known sources of X-rays in the Solar System. The complete list incl‘s the Sun, Planets, Comets, Moons, the Io Flux Torus, and the Heliosphere itself. [See excellent review by Bhardwaj, Lisse, et al. 2007 and ESS 2008]

Potential of a WFXT Solar System Survey:

Serendipitous Comet Detections in the RASS

Dennerl et al. 1997

C/Levy, Sept 1990

C/Levy, Jan 1991

C/Levy, Jan 1991


RASS detected 7 comets in 8 months down to a limit of 10-13 erg cm-2 sec-1. Based on the WFXT projected sensitivity and sky coverage, our cometary XLF, and the supply of short (~40) and long (~70) period comets reaching perihelion every year, we estimate at least 40 comet detections in the WFXT wide survey alone, tripling the number of comets seen in the x-ray. More comet detections will be found from observations of Main Belt Comets, Sungrazing comets, & Active Centaurs.

C/T-K, Nov 1990

C/T-K, Jan 1991

faintest comet

ever detected

in Xrays

45P/HMP, Jul 1990

C/Arai, Nov 1990

flux ratios of all observed comets:

cold, fast

warm, slow


hot, fast, disturbed


Chandra spectra of comets suggest different emission characteristics as the solar wind varies









  • Three competing emission features:

  • C and N emission below 500 eV

  • O VII emission at 565 eV

  • O VIII emission at 654 eV










low abundance of highly charged oxygen cold wind

high abundance of highly charged oxygen  hot wind

O VIII / O VII flux increases


Bodewits et al. 2007

WFXT Planetary Observation Capabilities: SWCX Processes in the Earth’s GeoCorona.

Detection of heavy neutral atoms in the Earth’s magneto- sphere implies interaction of the extended cold H envelope of the Earth with the solar wind via CXE.

N.B. - SWCX more important than Jeans

escape for terrestrial H loss budget!


- Atmosphere Explorer C 1974

- Arecibo Incoherent Scatter Radar of e- and

neutral H abundances (Maher and Tinsley 1977)

- IMAGE/LENA observations of magnetosheath

quiescent solar behavior (Collier et al. 2001)

- IMAGE/HENA - CME response (Brandt 2001)

Yohkoh SXT

0.25 – 4.0 keV



WFXT Planetary Observation Capabilities: Venus Disk + Exosphere

Venus’ emission Is

dominated by a large

x-ray scattering

component due to

Its proximity to the


Chandra ACIS-I

0.4 – 0.9 keV

GOES-7, 8, 10, 12

1.6 – 12.4 keV

Dennerl et al. 2008

WFXT Planetary Observation Capability:

X-ray images of Mars in individual emission lines

Dennerl et al. 2009

Emission centered

on disk.

Emission in crescent

offset towards the Sun.

Emission above and below

Poles (!?) or in limb-effect


Major science question : what, if any, is the effect of Martian weather

(winter/summer, dust storms, etc.) on the x-ray emission?

WFXT Planetary Observation Capability: Jovian X-rays = Disk Scattering of Solar X-rays + Auroral Precipitation + Polar SWCX

Io, Europa, Ganymede, and the Io Plasma Torus have been marginally detected in the X-ray. Does the IPT provide the S, O atoms for Jupiter’s Polar X-ray emission? Need simultaneous map of whole system!Have we detected the root of Europa’s Neutral Atom Torus (Mauk et al. 2003)?

WFXT Planetary Capability: Saturn’s Rings Shine in Oxygen K Fluorescence

WFXT Planetary Capability: Saturn’s X-ray Lightcurve Follows the Sun’s Closely; No Auroral Emission Yet Detected



Cravens et al. 2002

WFXT can map instreaming neutral HI, HeI ISM emitting SWCXE xrays in the Heliosphere



Koutroumpa et al.


WFXT all-sky, long term monitoring capability critical to finding the SWCXE spectral signature in heliospheric


XMM RGS, Snowden et al. 2004

DXS Background

McCammonet al. 2002

ACIS-S Lunar night-side emission, Wargelin et al. 2004 (see also Wargelin et al. 2009 Chandra posters @

this meeting)

WFXT Survey Serendipitous Solar System ScienceSummary & Conclusions

  • There is a rich collection of known solar system x-ray objects - Comets, Rocky Planets, Gas Giants, & the Heliosphere for WFXT to study. Most objects have been detected with only a few photons.

  • There is an important list of solar system objects that have yet to be detected in the x-ray : Mercury, the ice giants Uranus/Neptune, the Main Belt comets,KBOs, and the heliopause.

  • Large Scale WFXT Imaging will allow for direct, complete study of extended systems overflowing Chandra & XMM FOVs (e.g. bright comets, Jupiter + Moons + magnetosphere)

  • Long term WFXT monitoring will allow for direct study of x-ray emission variation with solar wind, CMEs, flares, planetary rotation & weather. No solar system object has been monitored for more than a few days.

  • Large scale diffuse flux capability allows direct comparison to ENA and LENA observations of the heliopause.

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