From ESA: ” Atmospheric exhaust and low gravity…”

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European Space Agency

2.8.18
Robin Ramstad
Swedish Institute of Space Physics, Kiruna, Sweden
Email: robin.ramstad@irf.se

Dmitri Titov
ESA Mars Express Project Scientist
Email: dmitri.titov@esa.int

Markus Bauer
ESA Science Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int

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Magnetospheres of terrestrial planets.

Print Artist (not to scale) that idealizes how the solar wind shapes the magnetosphere of Venus (above), Earth (center) and Mars (below). Unlike Venus and Mars, Earth has an internal magnetic field that deflects the charged particles of the solar wind as you move away from the Sun, forming a “bubble” (the magnetosphere) around the globe. Mars and Venus, which do not generate an internal magnetic field, the main obstacle to the solar wind is the upper atmosphere or ionosphere. As in the earth, the solar ultraviolet radiation separates electrons from the atoms and molecules in this region, creating a region of ionized gas electrically charged: the ionosphere. Mars and Venus, this ionized layer directly interacts with the solar wind and magnetic field to create an induced magnetosphere, which acts to decelerate and deflect the particles of the solar wind around the planet. Credit: ESA.

Low gravity and the absence of magnetic field Mars make its outer atmosphere easy to be driven by the solar wind white, but new findings Mars Express ESA show that solar radiation could play a surprising role in the atmospheric escape.

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ESA Mars Express

Understand the different ways that evolution took on rocky planets of the inner solar system along 4,600 million years is key to determining what makes a planet habitable. While Earth is a world rich in water, our youngest neighbor, Mars lost much of its atmosphere at the beginning of its history, from being a warm and humid environment to become the arid and cold planet we know it present. By contrast, our other neighbor, Venus, currently uninhabitable and with a comparable size to Earth, has a thick atmosphere.

It is often noted that one of the ways the atmosphere of a planet is protected by a magnetic field is generated internally, as in the case of the Earth. The magnetic field deflects the charged solar wind particles that escape the sun, creating a protective bubble around the planet ‘s magnetosphere.

Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

As Mars and Venus do not generate this internal magnetic field, the main barrier to the solar wind is its high atmosphere, or ionosphere. As in the case of Earth, ultraviolet radiation separates electrons from the atoms and molecules of that area, creating a region of electrically charged gas. Mars and Venus, this ionized layer, the ionosphere directly interacts with the solar wind and magnetic field to create an induced magnetosphere, which acts slowing and deflecting the solar wind around the planet.

Mars Express ESA has been watching for 14 years charged oxygen and carbon dioxide, for example space freed to better understand the rate at which the atmosphere of the planet escaping ions.

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Illustration ion exhaust Mars. As on Earth, solar ultraviolet radiation separates electrons from atoms and molecules (blue particles), creating a region of ionized gas electrically charged: the ionosphere. This ionised layer interacts directly with the solar wind and magnetic field to create an induced magnetosphere, which acts to decelerate and deflect the particles of the solar wind around the planet. In a new study of Mars Express, it was discovered that ionizing radiation nature of the sun produces more ions that can remove the solar wind. Although the increased production of ions helps protect the lower atmosphere of the energy carried by the solar wind, the heating of the electrons seem to be enough to drag ions in all conditions, creating a “polar wind”. The weak gravity of Mars, about a third of the Earth means that the planet can not hold on to these ions and easily escape into space, regardless of the extra energy provided by a strong solar wind. Credit: ESA.

The study has revealed a surprising effect, because ultraviolet radiation from the sun has a much more important role than previously thought.

“We thought that the escape of ions was due to effective energy transfer from the solar wind, through induced Mars, into the ionosphere magnetic barrier,” says Robin Ramstad, the Swedish Institute of Space Physics and lead author study of Mars Express.

“In a way that perhaps defies our intuition, what we actually see it is that the increased production of ions caused by solar ultraviolet radiation shielding the planet’s atmosphere energy carrying the solar wind, but the ions require very little energy to escape by themselves, given the low gravity connecting the atmosphere to Mars. ”

It has been found that ionizing radiation nature of solar produces ions which can drag the solar wind. Although the increased production of ions helps protect the lower atmosphere energy carrying the solar wind, the heating of the electrons seem to be enough to drag ions in all conditions, creating a sort of ‘polar wind’. The weak gravity of Mars, about a third of the Earth, causes the planet can not hold these ions and that these escaping into space, regardless of the extra energy that brings a strong solar wind.

Venus, where gravity is similar to Earth, much more energy is needed to atmosphere in this way is lost, and the ions leaving the sunny side could return to the planet by the opposing face unless you step up to some way.

“Thus, we conclude that, today, the escape of Mars ions is mainly limited by production and not for energy, while Venus is likely to be limited due to energy, given the greater gravity of the planet and the highest rate of ionization, being closer to the Sun, “adds Robin.

“In other words, it is likely that the direct effect of the solar wind in the amount of atmosphere that Mars has lost over time is minimal, and simply enhances the acceleration of particles escaping”.

“The continuous observation of Mars since 2004, covering changes in solar activity from the minimum to solar maximum, has provided us with a large data set that is vital to understand long-term planetary atmospheres and their interaction behavior with the Sun, “says Dmitri Titov, Mars Express project scientist at ESA. “Collaboration with the MAVEN mission NASA, which carries on Mars since 2014, also allows us to study the atmospheric escape processes in more detail.”

The study also has implications for finding similar to that of Earth atmospheres elsewhere in the universe.

protecting the atmosphere of a planet, its magnetic field is not as important as its gravity, which defines how the planet retains its atmospheric particles once they have been ionized by the sun’s radiation, regardless of the strength of the solar wind, “adds Dmitri.

Science paper
Global Mars-solar wind ion coupling and escape, Ramstad et al, is published in Journal of Geophysical Research: Space Physics (2017)

The study is based on data collected by the ASPERA-3 instrument (Space Plasma Analyzer and energized atoms) of Mars Express.

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ESA ASPERA-3 instrument

Venus Express ESA, which completed its mission in 2014, had an identical instrument.

See the full article here .

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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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