X-rays from Saturn: a study with<i>XMM-Newton</i>and<i>Chandra</i>over the years 2002–05

Branduardi‐Raymont, G.; Bhardwaj, Anil; Elsner, Ronald F.; Rodríguez, P.

doi:10.1051/0004-6361/200913110

Cited by 44 publications

(51 citation statements)

References 36 publications

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“…A combination of elastic and fluorescent scattering of solar X-rays in the H 2 and CH 4 atmosphere can account for Saturn's disk, polar cap and ring emissions. As for Jupiter, the flux from the disk tracks that of solar X-rays (Bhardwaj et al 2005a,b;Branduardi-Raymont et al 2010). Fluorescence also explains most of the disk emissions observed from Venus and Mars.…”

Section: Planetary Emissionsmentioning

confidence: 94%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

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Both heliophysics and planetary physics seek to understand the complex nature of the solar wind's interaction with solar system obstacles like Earth's magnetosphere, the ionospheres of Venus and Mars, and comets. Studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in con- text by observations from far and extreme ultraviolet (FUV, EUV), hard X-ray, and energetic neutral atom imagers (ENA). Each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the KelvinHelmholtz instability) generates diagnostic plasma density structures. The significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, Venus, and Mars or global magnetospheric/ionospheric convection at Earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. This paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1-2.0 keV) X-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles. The introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. In situ measurements confirm the existence of time-and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at Venus, Mars, comets, and the Earth. However, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. Remote sensing observations provide global information about auroral ovals (FUV and hard X-ray), the terrestrial plasmasphere (EUV), and the terrestrial ring current (ENA). ENA instruments with low energy thresholds (∼ 1 keV) have recently been used to obtain important information concerning the magnetosheaths of Venus, Mars, and the Earth. Recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft X-ray imagers.Section 2 describes proposed dayside interaction mechanisms, including reconnection, the Kelvin-Helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. It focuses upon the questions that remain as yet unanswered, such as the significanc...

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Section: Planetary Emissionsmentioning

confidence: 94%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

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“…None, however, has been detected to date. Almost all of the observed X-ray flux from Saturn is caused by scattered solar X-rays , with the possible exception of X-rays from its rings (Bhardwaj et al 2005c), where other processes may also contribute, like lightning induced electron beams, which might energise the icy particles in the rings and cause them to emit fluorescent O-K α radiation (Branduardi-Raymont et al 2010). The lack of any observable auroral X-ray emission from Saturn is consistent with its low FUV emission compared to Jupiter, and by its at least ∼ 20 times lower surface magnetic field, magnetic moment, and magnetic particle density, which makes it likely that any auroral X-ray emission is below the sensitivity limit of current instrumentation, as pointed out by Branduardi-Raymont et al (2010).…”

Section: Magnetic Planets With Atmospheresmentioning

confidence: 99%

Charge Transfer Reactions

Dennerl

2010

Space Sci Rev

101

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Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

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“…We thus have high confidence that we have an actual detection (Bhardwaj et al 2007, Branduardi-Raymont et al 2010, Collier et al 2014, Cravens et al 2003, Dennerl 2002, 2010, or (3) charge exchange of energetic solar wind or magnetospheric energetic ions with cometary or planetary neutrals.…”

Section: Jul -03 Aug 2015 Measurementsmentioning

confidence: 71%

The puzzling detection of x-rays from Pluto by Chandra

Lisse

McNutt

Wolk

et al. 2017

Icarus

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Using Chandra ACIS-S, we have obtained low-resolution imaging X-ray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. Observations were obtained in a trial "seed" campaign conducted in one visit on 24 Feb 2014, and a follow-up campaign conducted soon after the New Horizons flyby that consisted of 3 visits spanning 26 Jul -03 Aug 2015. In a total of 174 ksec of on-target time, in the 0.31 -0.60 keV passband, we measured 8 total photons in a co-moving 11 x 11 pixel 2 box (the 90% flux aperture determined by observations of fixed background sources in the field) measuring ~121,000 x 121,000 km -100 MW, in the middle range of X-ray power levels seen for other known solar system emission sources: auroral precipitation, solar X-ray scattering, and charge exchange (CXE) between solar wind (SW) ions and atmospheric neutrals. We eliminate auroral effects as a source, as Pluto has no known magnetic field and the New Horizons Alice UV spectrometer detected no airglow from Pluto during the flyby. Nano-scale atmospheric haze particles could lead to enhanced resonant scattering of solar X-rays from Pluto, but the energy signature of the detected photons does not match the solar spectrum and estimates of Pluto's scattered X-ray emission are 2 to 3 orders of magnitude below the 3.9 ± 0.7 x 10 -5 cps found in our observations.Charge-exchange-driven emission from hydrogenic and heliogenic SW carbon, nitrogen, and oxygen (CNO) ions can produce the energy signature seen, and the 6 x 10 25 neutral gas escape rate from Pluto deduced from New Horizons' data (Gladstone et al. 2016) can support the ~3.0 +3.0/ -1.5 x 10 24 X-ray photons/s emission rate required by our observations. Using the solar wind proton density and speed measured by the Solar Wind Around Pluto (SWAP) instrument in the vicinity of Pluto at the time of the photon emissions, we find a factor of 40 +40/ -20 lower SW minor ions flowing planarly into an 11 x 11 pixel 2 , 90% flux box centered on Pluto than are needed to support the observed emission rate. Hence, the SW must be somehow significantly focused and enhanced within 60,000 km (projected) of Pluto for this mechanism to work.

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X-rays from Saturn: a study withXMM-NewtonandChandraover the years 2002–05

Cited by 44 publications

References 36 publications

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Charge Transfer Reactions

The puzzling detection of x-rays from Pluto by Chandra

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