Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere

Abstract

The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth’s twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.

Can interplanetary magnetic field reach the Venus surface?

“…Magnetic field data from the Venus Express are used as a reference from 300 km to 180 km (Villarreal et al, 2015) and further down to 130 km (Zhang et al, 2016). The former data set is from a single event, but is illustrative in the model construction in that the transition is smooth with a magnetic pileup and an asymptotic behavior at higher altitudes (solid curve in black above an altitude of 170 km in the third panel of Fig.…”

“…(1) B 0 = 40.0 nT (offset value), B 1 = 50.0 nT (height of the secant bell shape), and d = 7.0 km (width of the bell shape) for z 0 ≥ 200 km, and (2) B 0 = 6.5 nT, B 1 = 83.5 nT, and d = 12.0km for z 0 ≤ 200 km. The uncertainty of the magnetic field model is referred from the statistical fluctuations shown inZhang et al (2016),…”

Structure and Thermal Evolution of Exoplanetary Cores

“…Most of the large rocky bodies in the solar system present evidence of past and/or present magnetic activity (Breuer et al., 2010; Schubert & Soderlund, 2011; Stevenson et al., 1983), with the potential exception of Venus, for which no current magnetic field has been detected and no record of past activity is available (Dumoulin et al., 2017; Konopliv & Yoder, 1996; Nimmo, 2002; Zhang et al., 2016). Magnetic fields are generated through the dynamo mechanism in a large volume of an electrically conducting liquid in the planet's interior.…”

Parameterisations of interior properties of rocky planets

“…Amongst the large rocky bodies in our Solar System, most of them present evidence of a past and/or present magnetic field (Stevenson et al 1983), with the exception of Venus, for which no significant intrinsic magnetic field has been detected and no record of a past global magnetic field is available (Zhang et al 2016). Planetary magnetic fields are generated by the dynamo effect in large volumes of electrically conducting liquid.…”