319 research outputs found
Candidates for detecting exoplanetary radio emissions generated by magnetosphere-ionosphere coupling
In this paper we consider the magnetosphere-ionosphere (M-I) coupling at
Jupiter-like exoplanets with internal plasma sources such as volcanic moons,
and we have determined the best candidates for detection of these radio
emissions by estimating the maximum spectral flux density expected from planets
orbiting stars within 25 pc using data listed in the NASA/IPAC/NExScI Star and
Exoplanet Database (NStED). In total we identify 91 potential targets, of which
40 already host planets and 51 have stellar X-ray luminosity 100 times the
solar value. In general, we find that stronger planetary field strength,
combined with faster rotation rate, higher stellar XUV luminosity, and lower
stellar wind dynamic pressure results in higher radio power. The top two
targets for each category are Eri and HIP 85523, and CPD-28 332 and
FF And.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society Letter
Ultraviolet observations of the Saturnian north aurora and polar haze distribution with the HST-FOC
Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co-added, reveal the presence of an auroral emission near 80 deg N with a peak brightness of about 150 kR of total H2 emission. The maximum optical depth of the polar haze layer is found to be located approximately 5 deg equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H2+ auroral production. In this case, the observed haze optical depth requires an efficiency of aerosol formation of about 6 percent, indicating that auroral production of hydrocarbon aerosols is a viable source of high-latitude haze
Auroral signatures of multiple magnetopause reconnection at Saturn
Auroral observations capture the ionospheric response to dynamics of the whole magnetosphere and may provide evidence of the significance of reconnection at Saturn. Bifurcations of the main dayside auroral emission have been related to reconnection at the magnetopause and their surface is suggested to represent the amount of newly opened flux. This work is the first presentation of multiple brightenings of these auroral features based on Cassini ultraviolet auroral observations. In analogy to the terrestrial case, we propose a process, in which a magnetic flux tube reconnects with other flux tubes at multiple sites. This scenario predicts the observed multiple brightenings, it is consistent with subcorotating auroral features which separate from the main emission, and it suggests north-south auroral asymmetries. We demonstrate that the conditions for multiple magnetopause reconnection can be satisfied at Saturn, like at Earth
Magnetosphere-ionosphere coupling at Jupiter-like exoplanets with internal plasma sources: implications for detectability of auroral radio emissions
In this paper we provide the first consideration of magnetosphere-ionosphere
coupling at Jupiter-like exoplanets with internal plasma sources such as
volcanic moons. We estimate the radio power emitted by such systems under the
condition of near-rigid corotation throughout the closed magnetosphere, in
order to examine the behaviour of the best candidates for detection with next
generation radio telescopes. We thus estimate for different stellar X-ray-UV
(XUV) luminosity cases the orbital distances within which the ionospheric
Pedersen conductance would be high enough to maintain near-rigid corotation,
and we then consider the magnitudes of the large-scale magnetosphere-ionosphere
currents flowing within the systems, and the resulting radio powers, at such
distances. We also examine the effects of two key system parameters, i.e. the
planetary angular velocity and the plasma mass outflow rate from sources
internal to the magnetosphere. In all XUV luminosity cases studied, a
significant number of parameter combinations within an order of magnitude of
the jovian values are capable of producing emissions observable beyond 1 pc, in
most cases requiring exoplanets orbiting at distances between ~1 and 50 AU, and
for the higher XUV luminosity cases these observable distances can reach beyond
~50 pc for massive, rapidly rotating planets. The implication of these results
is that the best candidates for detection of such internally-generated radio
emissions are rapidly rotating Jupiter-like exoplanets orbiting stars with high
XUV luminosity at orbital distances beyond ~1 AU, and searching for such
emissions may offer a new method of detection of more distant-orbiting
exoplanets.Comment: 15 pages, 9 figures. In press at Mon. Not. R. Astron. So
A Statistical Survey of Low‐Frequency Magnetic Fluctuations at Saturn
Low‐frequency waves are closely related to magnetospheric energy dissipation processes. The Cassini spacecraft explored Saturn's magnetosphere for over 13 years, until September 2017, covering a period of more than a complete solar cycle. Using this rich heritage dataset, we systematically investigated key physical parameters of low‐frequency waves in Saturn's magnetosphere, including their local time distribution and the dependence on solar activity. We found that the wave activity peaked in the near noon sector. For the nightside, the wave intensity also appeared to peak pre and post‐midnight. Due to the limited local time coverage for each solar phase, we were not able to draw a firm conclusion on the wave's dependence on solar activity. In general, the wave power showed a monotonically decreasing trend towards larger distances in nightside sectors especially during the declining phase, which implied that low‐frequency waves mainly originate from the relatively inner regions of the magnetosphere. On the dayside, stronger waves were mostly located at/within ∼25 Rs, near the magnetopause. The study shows a global picture of low‐frequency waves in Saturn's magnetosphere, providing important implications for how magnetospheric energy dissipates into Saturn's polar ionosphere and atmosphere
The crucial role of HST during the NASA Juno mission: a "Juno initiative"
In 2016, the NASA Juno spacecraft will initiate its one-year mission around
Jupiter and become the first probe to explore the polar regions of Jupiter. The
HST UV instruments (STIS and ACS) can greatly contribute to the success of the
Juno mission by providing key complementary views of Jupiter's UV aurora from
Earth orbit. Juno carries an ultraviolet Spectrograph (UVS) and an infrared
spectral mapper (JIRAM) that will obtain high-resolution spectral images
providing the auroral counterpart to Juno's in situ particles and fields
measurements with the plasma JADE and JEDI particle detectors. The Juno mission
will be the first opportunity to measure simultaneously the energetic particles
at high latitude and the auroral emissions they produce. Following programmatic
and technical limitations, the amount of UVS data transmitted to Earth will be
severely restricted. Therefore, it is of extreme importance that HST captures
as much additional information as possible on Jupiter's UV aurora during the
one-year life of the Juno mission. This white paper is a plea for a "Juno
initiative" that will ensure that a sufficient number of orbits is allocated to
this unique solar system mission.Comment: Paper submitted to the Space Telescope Science Institute in response
to the call for HST White Papers for Hubble's 2020 Visio
The far-ultraviolet main auroral emission at Jupiter - Part 1:dawn-dusk brightness asymmetries
The main auroral emission at Jupiter generally appears as a quasi-closed curtain centered around the magnetic pole. This auroral feature, which accounts for approximately half of the total power emitted by the aurorae in the ultraviolet range, is related to corotation enforcement currents in the middle magnetosphere. Early models for these currents assumed axisymmetry, but significant local time variability is obvious on any image of the Jovian aurorae. Here we use far-UV images from the Hubble Space Telescope to further characterize these variations on a statistical basis. We show that the dusk side sector is ~ 3 times brighter than the dawn side in the southern hemisphere and ~ 1.1 brighter in the northern hemisphere, where the magnetic anomaly complicates the interpretation of the measurements. We suggest that such an asymmetry between the dawn and the dusk sectors could be the result of a partial ring current in the nightside magnetosphere
Two fundamentally different drivers of dipolarizations at Saturn
Solar wind energy is transferred to planetary magnetospheres via magnetopause reconnection, driving magnetospheric dynamics. At giant planets like Saturn, rapid rotation and internal plasma sources from geologically active moons also drive magnetospheric dynamics. In both cases, magnetic energy is regularly released via magnetospheric current redistributions that usually result in a change of the global magnetic field topology (named substorm dipolarization at Earth). Besides this substorm dipolarization, the front boundary of the reconnection outflow can also lead to a strong but localized magnetic dipolarization, named a reconnection front. The enhancement of the north-south magnetic component is usually adopted as the indicator of magnetic dipolarization. However, this field increase alone cannot distinguish between the two fundamentally different mechanisms. Using measurements from Cassini, we present multiple cases whereby we identify the two distinct types of dipolarization at Saturn. A comparison between Earth and Saturn provides new insight to revealing the energy dissipation in planetary magnetospheres
X-rays Studies of the Solar System
X-ray observatories contribute fundamental advances in Solar System studies
by probing Sun-object interactions, developing planet and satellite surface
composition maps, probing global magnetospheric dynamics, and tracking
astrochemical reactions. Despite these crucial results, the technological
limitations of current X-ray instruments hinder the overall scope and impact
for broader scientific application of X-ray observations both now and in the
coming decade. Implementation of modern advances in X-ray optics will provide
improvements in effective area, spatial resolution, and spectral resolution for
future instruments. These improvements will usher in a truly transformative era
of Solar System science through the study of X-ray emission.Comment: White paper submitted to Astro2020, the Astronomy and Astrophysics
Decadal Surve
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