Abstract
Abstract. We propose a new method to estimate ion escape from unmagnetized planets that combines observations and models. Assuming that upstream solar wind conditions are known, a computer model of the interaction between the solar wind and the planet is executed for different ionospheric ion production rates. This results in different amounts of mass loading of the solar wind. We then obtain the ion escape rate from the model run that best fits observations of the bow shock location. As an example of the method, we estimate the heavy-ion escape from Mars on 1 March 2015 to be 2×1024 ions s−1, using a hybrid plasma model and observations by the Mars Atmosphere and Volatile Evolution (MAVEN) and Mars Express (MEX) missions. This method enables studies on how escape depends on different parameters as well as studies on escape rates during extreme solar wind conditions; moreover, the technique is applicable to studies of escape in the early solar system and at exoplanets.
Highlights
Ion escape to space is important for the evolution of planetary atmospheres
We describe the algorithm for estimating the escape of ionospheric ions from observations of the upstream solar wind and the location of the bow shock: 1. We start with an observed state of the upstream solar wind – the magnetic field and the solar wind density, velocity, and temperature
An ongoing investigation is to apply the method to a large number of orbits and verify that the model-estimated escape rates are consistent with observed escape rates
Summary
Ion escape to space is important for the evolution of planetary atmospheres. For planets in our solar system, we can observe the present-day escape of planetary ions by directly observing the ion flux near a planet. This is done using an ion detector on a spacecraft and gives us the flux of ions along the trajectory of the spacecraft. As the flux of escaping ions is highly variable both temporally and spatially, accurately estimating the escape of ions can require observations over many years to get an average escape rate. Investigating how the escape rate of ions depends on different parameters (e.g., upstream solar wind conditions) is even more difficult due to the large amounts of observations needed to get sufficient statistics
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