Anil Bhardwaj

A pulsating auroral X-ray hot spot on Jupiter

Jupiters X-ray aurora has been thought to be excited by energetic sulphur and oxygen ions precipitating from the inner magnetosphere into the planets polar regions. Here we report high-spatial-resolution observations that demonstrate that most of Jupiters northern auroral X-rays come from a ‘hot spot’ located significantly poleward of the latitudes connected to the inner magnetosphere. The hot spot seems to be fixed in magnetic latitude and longitude and occurs in a region where anomalous infrared and ultraviolet emissions have also been observed. We infer from the data that the particles that excite the aurora originate in the outer magnetosphere. The hot spot X-rays pulsate with an approximately 45-min period, a period similar to that reported for high-latitude radio and energetic electron bursts observed by near-Jupiter spacecraft. These results invalidate the idea that jovian auroral X-ray emissions are mainly excited by steady precipitation of energetic heavy ions from the inner magnetosphere. Instead, the X-rays seem to result from currently unexplained processes in the outer magnetosphere that produce highly localized and highly variable emissions over an extremely wide range of wavelengths.

Auroral emissions of the giant planets

Auroras are (generally) high-latitude atmospheric emissions that result from the precipitation of energetic charged particles from a planets magnetosphere. Auroral emissions from the giant planets have been observed from ground-based observatories, Earth-orbiting satellites (e.g., International Ultraviolet Explorer (IUE), Hubble Space Telescope (HST), and Roentgensatellit (ROSAT)), flyby spacecraft (e.g., Voyager 1 and 2), and orbiting spacecraft platforms (e.g., Galileo) at X-ray, ultraviolet (UV), visible, infrared (IR), and radio wavelengths. UV, visible, and IR auroras are atmospheric emissions, produced or initiated when ambient atmospheric species are excited through collisions with the precipitating particles, while radio and X-ray auroras are beam emissions, produced by the precipitating species themselves. The emissions at different wavelengths provide unique and complementary information, accessible to remote sensing, about the key physical processes operating in the atmospheric and magnetospheric regions where they originate. This paper reviews the development of our current understanding of auroral emissions from Jupiter, Saturn, Uranus, and Neptune, as revealed through multispectral observations and supplemented by plasma measurements.

Strong influence of lunar crustal fields on the solar wind flow

We discuss the influence of lunar magnetic anomalies on the solar wind and on the lunar surface, based on maps of solar wind proton fluxes deflected by the magnetic anomalies. The maps are produced ...

Extremely high reflection of solar wind protons as neutral hydrogen atoms from regolith in space

We report on measurements of extremely high reflection rates of solar wind particles from regolith-covered lunar surfaces. Measurements by the Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft in orbit around the Moon show that up to 20% of the impinging solar wind protons are reflected from the lunar surface back to space as neutral hydrogen atoms. This finding, generally applicable to regolith-covered atmosphereless bodies, invalidates the widely accepted assumption that regolith almost completely absorbs the impinging solar wind.

A study of Jupiter's aurorae with XMM-Newton

We present a detailed analysis of Jupiters X-ray (0.2−10 keV) auroral emissions as observed over two XMM- Newton revolutions in Nov. 2003 and compare it with that of an earlier observation in Apr. 2003. We discover the existence of an electron bremsstrahlung component in the aurorae, which accounts for essentially all the X-ray flux above 2 keV: its pr esence had been predicted but never detected for lack of sensitivit y of previous X-ray missions. This bremsstrahlung component varied significantly in strength and spectral shape over the 3.5 day s covered by the Nov. 2003 observation, displaying substantial hardening of the spectrum with increasing flux. This variabi lity may be linked to the strong solar activity taking place a t the time, and may be induced by changes in the acceleration mechanisms inside Jupiters magnetosphere. As in Apr. 2003, t he auroral spectra below 2 keV are best fitted by a superposition of line emission most likely originating from ion charge exchange, with OVII playing the dominant role. We still cannot resolve conclusively the ion species responsible for the lowest energy lines (around 0.3 keV), so the question of the origin of the ions (magnetospheric or solar wind) is still open. It is conceivable that both scenarios play a role in what is certainly a very complex planetary structure. High resolution spectra of the whole planet obtained with the XMM-NewtonReflection Grating Spectrometer in the range 0.5−1 keV clearly separate emission lines (mostly of iron) originating at low latitudes on Jupiter from the auroral lines due t o oxygen. These are shown to possess very broad wings which imply velocities of∼5000 km s −1 . Such speeds are consistent with the energies at which precipitating and charge exchanging oxygen ions are expected to be accelerated in Jupiters magnetos phere. Overall we find good agreement between our measurements and t he predictions of recently developed models of Jupiters auroral processes.

Remote energetic neutral atom imaging of electric potential over a lunar magnetic anomaly

The formation of electric potential over lunar magnetized regions is essential for understanding fundamental lunar science, for understanding the lunar environment, and for planning human explorati ...

Low energy neutral atom imaging on the Moon with the SARA instrument aboard Chandrayaan-1 mission

This paper reports on the Sub-keV Atom Reflecting Analyzer (SARA) experiment that will be flown on the first Indian lunar mission Chandrayaan-1. The SARA is a low energy neutral atom (LENA) imaging mass spectrometer, which will perform remote sensing of the lunar surface via detection of neutral atoms in the energy range from 10 eV to 3 keV from a 100km polar orbit. In this report we present the basic design of the SARA experiment and discuss various scientific issues that will be addressed. The SARA instrument consists of three major subsystems: a LENA sensor (CENA), a solar wind monitor (SWIM), and a digital processing unit (DPU). SARA will be used to image the solar wind-surface interaction to study primarily the surface composition and surface magnetic anomalies and associated mini-magnetospheres. Studies of lunar exosphere sources and space weathering on the Moon will also be attempted. SARA is the first LENA imaging mass spectrometer of its kind to be flown on a space mission. A replica of SARA is planned to fly to Mercury onboard the BepiColombo mission.

Protons in the near-lunar wake observed by the Sub-keV Atom Reflection Analyzer on board Chandrayaan-1

Significant proton fluxes were detected in the near wake region of the Moon by an ion mass spectrometer on board Chandrayaan-1. The energy of these nightside protons is slightly higher than the energy of the solar wind protons. The protons are detected close to the lunar equatorial plane at a

Radial distribution of production rates, loss rates and densities corresponding to ion masses ⩽40 amu in the inner coma of Comet Halley: Composition and chemistry

140^{\circ}

On the excitation of Io's atmosphere by the photoelectrons: Application of the analytical yield spectral model of SO2

solar zenith angle, i.e., ~50