A rendering of the Cluster satellite, designed to measure electric fields, which Andre and Cully used to detect low-energy ions high above the Earth. (Credit: European Space Agency)

Cold Plasma Flourishes In Earth’s Upper Atmosphere

Article Updated: 24 Dec , 2015



Thousands of miles above Earth, space weather rules. Here storms of high-energy particles mix the atmosphere, create auroras, challenge satellites and even cause disturbances with electric grids and electronic devices below. It’s a seemingly empty and lonely place – one where a mystery called “cold plasma” has been found in abundance and may well have implications with our connection to the Sun. While it has remained virtually hidden, Swedish researchers have created a new method to measure these cold, charged ions. With evidence of more there than once thought, these new findings may very well give us clues as to what’s happening around other planets and their natural satellites.

“The more you look for low-energy ions, the more you find,” said Mats Andre, a professor of space physics at the Swedish Institute of Space Physics in Uppsala, Sweden, and leader of the research team whose findings have been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. “We didn’t know how much was out there. It’s more than even I thought.”

Where does this enigma originate? The low-energy ions begin in the upper portion of our atmosphere called the ionosphere. Here solar energy can strip electrons from molecules, leaving atoms such as oxygen and hydrogen with a positive charge. However, physically finding these ions has been problematic. While researchers knew they existed at altitudes of about 100 kilometers (60 miles), Andre and colleague Chris Cully set their sites higher – at between 20,000 and 100,000 km (12,400 to 60,000 mi). At the edge, the amount of cold ions varies between 50 to 70%… making up most of the mass of space.

However, that’s not the only place cold plasma has been found. According to the research satellite data and calculations, certain high-altitude zones harbor low-energy ions continuously. As far fetched as it may sound, the team has also detected them at altitudes of 100,000 km! According to Andre, discovering so many relatively cool ions in these regions is surprising because there’s so much energy hitting the Earth’s high altitudes from the solar wind – a hot plasma about 1,000 times hotter than what Andre considers cold. Just how cold? “The low-energy ions have an energy that would correspond to about 500,000 degrees Celsius (about one million degrees Fahrenheit) at typical gas densities found on Earth. But because the density of the ions in space is so low, satellites and spacecraft can orbit without bursting into flames.”

A scientist examines one of the European Space Agency's four Cluster satellites, used in a recent Geophysical Research Letters study to measure low-energy ions. (Credit: European Space Agency)

Pinpointing these low-energy ions and measuring how much material is leaving our atmosphere has been an elusive task. Andre’s workshop is a satellite and one of the four European Space Agency CLUSTER spacecraft. It houses a detector created from a fine wire that measures the electronic field between them during satellite rotation. However, when the data was collected, the researchers found a pair of mysteries – strong electric fields in unexpected areas of space and electric fields that didn’t fluctuate evenly.

“To a scientist, it looked pretty ugly,” Andre said. “We tried to figure out what was wrong with the instrument. Then we realized there’s nothing wrong with the instrument.” What they found opened their eyes. Cold plasma was changing the arrangement of the electrical fields surrounding the satellite. This made them realize they could utilize their field measurements to validate the presence of cold plasma. “It’s a clever way of turning the limitations of a spacecraft-based detector into assets,” said Thomas Moore, senior project scientist for NASA’s Magnetospheric Multiscale mission at the Goddard Space Flight Center in Greenbelt, Maryland. He was not involved in the new research.

Through these new techniques, science can measure and map Earth’s cold plasma envelope – and learn more about how both hot and cold plasma change during extreme space weather conditions. This research points towards a better understanding of atmospheres other than our own, too. Currently the new measurements show about a kilogram (two pounds) of cold plasma escapes from Earth’s atmosphere every second, By having a solid figure as a basis for rate of loss, scientists may be able model what became of Mars’ atmosphere – or explain the atmosphere around other planets and moons. It can also aid in more accurate space weather forecasting – even if it doesn’t directly influence the environment itself. It is a key player, even if it doesn’t cause the damage itself. “You may want to know where the low-pressure area is, to predict a storm,” Andre noted.

Modernizing space weather forecasting to where it is similar to ordinary weather forecasting, was “not even remotely possible if you’re missing most of your plasma,” Moore, with NASA, said. Now, with a way to measure cold plasma, the goal of high-quality forecasts is one step closer. “It is stuff we couldn’t see and couldn’t detect, and then suddenly we could measure it,” Moore said of the low-energy ions. “Now you can actually study it and see if it agrees with the theories.”

Original Story Source: American Geophysical Union News Release. For Further Reading: Low-energy ions: A previously hidden solar system particle population.

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5 Responses

  1. Anonymous says:

    You know, in the old days – the very old days, long forgotten – this thread would have already turned…..

    Oh, you don’t know? Well, better not… Never mind.

    Wow, I just checked the energy of a 500.000K particle. According to E~kT (where ~ means “approximately”, and k is Boltzmann’s constant) this corresponds to an energy of about 1eV. That is indeed low-energetic, compared to a typical proton in the solar wind moving with roughly 300km/s (corresponding to a kinetic energy of E=mv^2/2 ~ 500eV).

    This also shows that the solar wind is quite collisionless (justifying the usual ideal MHD approach to model space plasmas). Otherwise the particles would gain energy quite rapidly by collisions with other more energetic particles, which would then lead to a Maxwell distribution – or in other words: the particles would then behave more like an ideal gas, instead of a plasma.

  2. Anonymous says:

    Are there any revolutionary implications for magnetohidrodynamics, which for decades has studied motion within a magnetic field, as in the upper reaches of the atmosphere and the magnetosphere? Apparently not. It seems to be merely a quantitative rather than a qualitative modification in the knowledge base. I’m just asking.

    • Torbjörn Larsson says:

      Depends. I would assume the measurement technology is as much revolutionary as the answer on near Earth conditions and weather forecasting. That would at a guess mean no one has studied MHD wakes of supersonic flows before.

      So likely more qualitative achievements than simply “more data”.

  3. Torbjörn Larsson says:

    Wow, what advances nature forces on us: “a recently developed technique based on the detection of the wake behind a charged spacecraft in a supersonic flow “.

    Btw, Mats and Chris are the Right Stuff. I slipped into some astrophysics seminars while working there, and Chris had a fun lecture on how much charge the Earth dynamo gets from rotating in the Sun magnetic field. IIRC spurred by his son asking him.

    [The answer is, IIRC, ~ 40 C. You could store more in a large capacitor bank…]

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