University:
Boston University
Course:
CAS AS 311 | Planetary Physics
Academic year:

2023
Views:

144

Pages:

13
Author:

siekesaal7j58

AURORAL X-RAY EMISSION AT THE OUTER PLANETS Overview   Observations at the Jovian polar cap Ion precipitation vs. electron precipitation  Why  is ion precipitation necessary? X-ray emission models  Atmospheric effects  The ions must be accelerated, why? And how?  Why don’t we see auroral X-rays from Saturn? Io footprint main oval polar cap emission Polar UV emissions apparent in HST images (many references over many years -- cf. Clarke al. 2000) Polar UV (auroral) Flare (Waite et al. 2001) 20:27:30 - 20:31:30 21:04:50 - 21:08:50 22:01:54 - 22:06:54 22:38:52 - 22:45:32 possible association with “active” region (Pallier and Prange, N. 2001, 2003; Grodent et al., 2003, …) CXO Image of Jupiter: Feb. 2003 (Elsner et al., 2005) X-Ray Emission *Auroral Emission ≈ 1 GW in x-rays Polar Caps *Disk emission: ≈ 1 GW in x-rays scattering and Fluorescence of solar x-rays (Maurellis et al., 2000; Cravens et al., 2005) Recent Auroral X-ray Observations    Spectrum of auroral x-ray emission by CXO and XMM - sulfur and oxygen lines and maybe carbon -outer magnetosphere ions and acceleration (Elsner et al., 2005; Branduardi-Raymont et al. 2004, 2005, 2007, 2008). Spectrum of auroral x-ray emission by XMM-Newton -- possible solar wind ion precipitation (BranduardiRaymont et al., 2004). Grating spectrum of auroral x-ray emission by XMM-Newton -- - Doppler broadened oxygen emission (Branduardi-Raymont et al., 2007). Bremsstrahlung x-ray emission observed from the Jovian aurora (E > 1 keV photons) with a distinct spatial morphology (Branduardi-Raymont et al., 2007, 2008). •Simultaneous HST – CXO observation on Northern aurora in 2003. •FUV and x-rays overplotted •Large dots: E > 2 keV (bremsstrahlung) Small dots: E < 2 keV •Co-located with bright FUV auroral region Time Variation     ~45 min pulsation period of x-ray hot spot observed by CXO in 2000 (Gladstone et al. 2002) Similar periodicity as high latitude radio and energetic electron bursts observed by Ulysses --- QP 40 bursts (MacDowall et al. 1993) 5 RJ accel. electrons. source No periodicity match when compared to solar wind or interplanetary magnetic field At later time (2003), the 45 min variation was absent from XMM-Newton and CXO observations (Elsner et al. 2005, Branduardi-Raymont et al. 2004, 2005)  Character of the variability may change from organized to chaotic Characteristics of the X-ray Emissions Elsner et al. (2005) CXO Feb. 2003 ACIS-S Spectra S9+,S10+ lines O6+, O7+ lines C5+ lines Comet Why is ion precipitation necessary?    Observations by CXO and XMM-Newton confirmed that the x-ray emissions originating at high latitudes on Jupiter are line emissions from sulfur, oxygen and maybe carbon (K-shell emissions) and NOT bremsstrahlung Need ions not electrons! Spectrum of Jovian auroral x-rays modeled with sulfur, oxygen, and carbon lines (Kharchenko et al, 2007; Hui et al., 2009, 2010a; Ozak et al., 2010) using new complete set of cross sections (Schultz et al., 2011 in prep). Possible Explanations for X-ray Mechanism (Cravens et al. 2003)  1. Accelerated (200 keV) solar wind heavy ions in the cusp region (the SWCX mechanism)  However no evidence of carbon in the spectrum to indicate solar wind origin  2. Accelerated (≈ 10 MeV) S and O ions in the outer magnetosphere.  Low charge state ions with high energies will strip the electrons and become highly charged  Highly charged ions will charge exchange, become excited and release an x-ray photon as they decay to ground state Jovian Ion Precipitation Model Ozak et al. (2010) Monte Carlo model with altitudedependent effects like opacity and quenching. Follow low state ions with different initial energies as they penetrate the atmosphere Collision Processes  Electron stripping process: O(q-1)+ + H2   Charge transfer collisions: Oq+ + H2 O(q-1)+* + H2+ X-ray emission: O(q-1)+*  O(q-1)+ + hν (X-ray) Ionization: Oq+ + H2  Oq+ + H2 + e- Oq+ + H2+ + e- Excitation: Oq+ + H2 Oq+ + H2*