The stability of the solar wind

June 20, 2016, Harvard-Smithsonian Center for Astrophysics
An artist's conception of the Wind spacecraft. Astronomers have used data from Wind to make the first complete analysis of two key instabilities in the plasma flow of the solar wind. Credit: NASA/Wind

NASA's Wind spacecraft observes the solar wind before it impacts the magnetosphere of Earth. Launched in 1994 into an orbit more than two hundred Earth-radii away, one of Wind's prime objectives is to investigate the basic physical processes occurring in the ionized gas in the near-Earth solar wind. One of the open issues is the stability of the solar wind plasma.

The three main particle in the solar wind are protons, electrons, and helium nuclei (two protons and two neutrons). Unlike particles in a conventional dense gas, the charged particles in the wind can have motions and collective behaviors that are not characterized simply by their temperature. For example, the wind can host regions of different temperatures and densities that propagate along as waves, or that dissipate, and the energy in the wind can be converted between different modes. Moreover the wind can host two unmixed gases with different temperatures and flows in the same vicinity, and these regions can react differently to the magnetic fields that are present.

CfA astronomer Mike Stevens and his colleagues used the Wind spacecraft to analyze two key instabilities in the wind, the first such analysis that includes all three species of particles. One of the instabilities results when the forward pressure is large enough to generate ripples in the plasma, and the other results when pressure builds up within in the wind, causing them to break up. The scientists concluded from the Wind data that protons were the species that dominated for both of these instabilities, but that the presence of the other two species was significant, contributing about one third of the observed effects for each instability. They also concluded that for the majority of the time, the is stable. The new results will be useful for other situations involving astrophysical plasmas.

Explore further: Swept up in the solar wind

More information: Multi-Species Measurements of the Firehose and Mirror Instability Thresholds in the Solar Wind. arxiv.org/abs/1606.02624

Related Stories

Swept up in the solar wind

May 10, 2016

From our vantage point on the ground, the sun seems like a still ball of light, but in reality, it teems with activity. Eruptions called solar flares and coronal mass ejections explode in the sun's hot atmosphere, the corona, ...

The solar wind breaks through the Earth's magnetic field

June 10, 2014

Space is not empty. A wind of charged particles blows outwards from the Sun, carrying a magnetic field with it. Sometimes this solar wind can break through the Earth's magnetic field. Researchers at the Swedish Institute ...

Heating the solar wind

April 3, 2013

(Phys.org) —The Sun glows with a surface temperature of about 5500 degrees Celsius. Meanwhile its hot outer layer (the corona) has a temperature of over a million degrees, and ejects a wind of charged particles at a rate ...

Recommended for you

Superflares from young red dwarf stars imperil planets

October 18, 2018

The word "HAZMAT" describes substances that pose a risk to the environment, or even to life itself. Imagine the term being applied to entire planets, where violent flares from the host star may make worlds uninhabitable by ...

Blazar's brightness cycle confirmed by NASA's Fermi mission

October 18, 2018

A two-year cycle in the gamma-ray brightness of a blazar, a galaxy powered by a supermassive black hole, has been confirmed by 10 years of observations from NASA's Fermi Gamma-ray Space Telescope. The findings were announced ...

Astronomers catch red dwarf star in a superflare outburst

October 18, 2018

New observations by two Arizona State University astronomers using the Hubble Space Telescope have caught a red dwarf star in a violent outburst, or superflare. The blast of radiation was more powerful than any such outburst ...

Magnetic fields may be the key to black hole activity

October 17, 2018

Collimated jets provide astronomers with some of the most powerful evidence that a supermassive black hole lurks in the heart of most galaxies. Some of these black holes appear to be active, gobbling up material from their ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.