Mysterious plasma jet streams spotted in Mars' magnetosheath

What is a magnetosheath jet? 

On Earth, a magnetosphere is an area dominated by a strong magnetic field. It is made up of several components that protect the planet and its atmosphere from harmful solar radiation particles. 

The magnetosheath is one of the components of the magnetosphere. A magnetosheath forms a thin boundary between the bow shock area and magnetopause.

To simplify it further, the bow shock occurs before the magnetopause, which separates the plasma of the solar wind from the plasma of the magnetosphere.

While on Mars, the team saw magnetosheath jets (plasma flowing in the magnetosheath) three times by the MAVEN spacecraft on January 28-29, 2017, and June 10, 2020. These jets appear to be faster or denser in comparison to their surroundings. 

“We have already seen that magnetosheath jets generate waves and that they can move through the entire magnetosheath and into the region of stronger magnetic fields further down. We have just discovered that they exist on Mars, and it will be exciting to find out more about them and the role they play in the interaction between Mars and the solar wind,” explained Gunell.

How the jets form remains unclear

However, it is unclear what those jets are doing on Mars, as the planet lacks strong magnetic fields. 

“It was not obvious that we would find them on Mars, as there are important differences between the two planets [Earth]. For example, Mars is smaller than Earth and lacks a global magnetic field, so the magnetosheath on Mars is much smaller than on Earth. Despite these differences, we now know that Mars also has magnetosheath jets,” explained Gunell.

MAVEN, or Mars Atmosphere and Volatile Evolution, is a spacecraft developed specifically to study how the Martian atmosphere was stripped away some billions of years ago. It has been in orbit above Mars since 2014, and it is crucial in studying the planet's atmospheric characteristics, notably its interaction with the solar wind.

The study results have been published in the journal Science Advances.

Study abstract:

Plasma entities, known as magnetosheath jets, with higher dynamic pressure than the surrounding plasma, are often seen at Earth. They generate waves and contribute to energy transfer in the magnetosheath. Affecting the magnetopause, they cause surface waves and transfer energy into the magnetosphere, causing throat auroras and magnetic signatures detectable on the ground. We show that jets exist also beyond Earth’s environment in the magnetosheath of Mars, using data obtained by the MAVEN spacecraft. Thus, jets can be created also at Mars, which differs from Earth by its smaller bow shock, and they are associated with an increased level of magnetic field fluctuations. Jets couple large and small scales in magnetosheaths in the solar system and can play a similar part in astrophysical plasmas.