Solar winds and planets

By Sabine Stanley, Ph.D., Johns Hopkins University

Light and heat aren’t the only things that come from the sun. There is also ionized mass from the Sun hitting the planets, what we call the solar wind. Solar winds can cause severe disruption to our solar system, especially a planet like Earth. What are these possible disruptions and how can they be mitigated?

The mass in solar winds is composed of plasma, the fourth state of matter. Plasma occurs when atoms have so much energy that they separate into protons, electrons, and helium nuclei. This plasma originates in the solar atmosphere.

Creating solar winds on the sun

The Sun’s atmosphere is divided into two layers: chromosphere and corona. Above the opaque photosphere or the surface of the sun is the chromospheric layer, which is a few thousand kilometers thick. The temperature rises with altitude here reaching around 10,000 ° at the top of the chromosphere. Fibrous jets known as spicules appear and travel through the photosphere in about 10 minutes, carrying the plasma to higher altitudes.

Above the chromosphere is the corona, which is several million kilometers thick. The corona can be best seen during a solar eclipse because it appears as a halo surrounding the blocked Sun’s disk. The corona is where the solar wind originates. The gravitational force of the Sun is too weak in the corona to hold this energetic hot plasma, and therefore the plasma is accelerated to high speeds.

The temperature rises to about two million Kelvin. But because the density of the plasma is much lower than that of the photosphere, we usually don’t see light from this region. The Sun emits about 1.5 million tons of superheated plasma per second in the solar wind. Speeds can vary greatly based on the Sun’s magnetic field and which region it is emitted from, but it can reach speeds of 750 kilometers per second!

Learn more about a solar system time machine and meteorites.

The impact of solar winds on the planets

The ionized particles in the solar wind are coupled with the solar magnetic field to form a spiral structure in space known as a “Parker spiral”. These high-energy solar wind particles cause aurora on planets with a magnetic field, but they can also be disruptive to the planet’s atmosphere and surfaces.

This shower of plasma particles can collide with particles high up in a planet’s atmosphere, providing atmospheric particles with enough energy to escape a planet. This is called solar wind stripping an atmosphere and may have been partly responsible for the dramatic change in the atmosphere and climate on Mars.

This is a transcript of the video series A field guide to the planets. Watch it now, on The Great Courses Plus.

Space Weathering caused by solar winds

Solar winds also cause “space weather” on airless bodies such as Mercury and most of the solar system’s moons. Space weather can evaporate some substances from the surface or melt other particles. For example, the regolith coating on the Moon is much darker due to extensive weathering.

Learn more about Pluto and Charon: the binary worlds.

Dangers of geomagnetic storms caused by the solar wind

The solar wind becomes more dangerous for the Earth during a solar storm. Much of the plasma in the Sun’s corona is typically confined to regions where the Sun has strong magnetic fields, such as in sunspots.

Here, magnetic fields create large arc rings on the plasma, like a net holding a fish. A coronal mass ejection is a plasma storm that occurs when those magnetic fields undergo reconnection events that realign the magnetic fields.

After a reconnection event, there is a large hole in the grid and solar plasma can explode from it. This explosion causes a much larger than normal mass of plasma to be thrown through the hole and into space. Sometimes, that plasma is headed for the Earth. If so, the enormous flow of ionized particles can disrupt our magnetosphere and cause new currents to flow. We call it a geomagnetic storm.

Radiation from these events can cause aurora to appear at lower latitudes than they normally would. And not only is the aurora pretty, but the light signals can also give us hours of early warning for the next mass of plasma. Electrons and other charged particles from geomagnetic storms can also disrupt electronics, including radio transmissions and satellites. For example, GPS coordinates can move several meters away during a thunderstorm. It might not seem like much until you realize planes are landing via GPS.

Instances of geomagnetic storms on Earth

These geomagnetic storms are also known to destroy power grids. For example, in March 1989, the Sun released a coronal mass ejection whose energy was equivalent to thousands of nuclear bombs. Interaction with the Earth’s geomagnetic field caused the Quebec province of Canada to lose power for nine hours. Then, in August, the computers used on the Toronto Stock Exchange lost power, stopping all trading.

Another geomagnetic storm in 1972 led to typical radio blackouts and damage to solar panels on satellites. But it also resulted in the unintended detonation of marine mines that the US Navy had placed in coastal waters near Vietnam. These mines had magnetic triggers intended to explode when a metal ship floated nearby. But the geomagnetic storm triggered the magnetic sensors, inadvertently causing about two dozen explosions in 30 seconds.

The largest geomagnetic storm occurred in 1859. It is known as the Carrington Event in which a coronal mass ejection traveled from the Sun to Earth in just 18 hours. Sudden increases in voltage in telegraph cables shocked the telegraph operators and even ignited fires.

Back then, people weren’t so heavily dependent on electronics, but scientists can estimate what would have happened today if a plasma storm the size of the Carrington event had occurred. It would likely cause trillions of dollars in damage to power grids and satellites. There would have been widespread power blackouts. Some scientists estimate that it would take years to restore electricity if enough damage was done.

So when will the next geomagnetic storm occur? When the Sun has many sunspots, coronal mass ejections occur about three times a day. When there are few sunspots, it only occurs once every five days.

Learn more about water on Mars and the prospects for life.

Other dangers of solar storms

A concern with long-term space travel is the effect of solar storms on astronauts. A solar storm hitting a spacecraft would result in severe exposure to high-energy radiation by astronauts, perhaps enough to be fatal. So this will be a rare but important obstacle when trying to plan human travel to Mars or beyond.

Spatial weather forecast

There have been several missions designed to observe the Sun and help us begin predicting so-called “space time”. In the geosynchronous orbit around the Earth is the Solar Dynamics Observatory or SDO. Imagine the Sun’s photosphere and atmosphere in many different wavelengths of light to study the magnetic and high-energy characteristics that occur here.

For example, SDO can see energetic gases tracing the Sun’s magnetic field in coronal rings. It can even display solar flares involving gases at millions of degrees of temperature.

Orbiting the Sun from a distance similar to Earth, the Solar Terrestrial Relations Observatory, or STEREO, used two telescopes in two different and changing positions to obtain stereo images of the Sun. This enabled the determination of the three-dimensional structure of the solar characteristics. such as the extension of giant coronal mass ejections.

Parker Solar Probe

The closest mission to the Sun is the Parker Solar Probe, which orbits the Sun in a highly elliptical orbit of 88 days. This mission will eventually zoom in at nearly half a million miles per hour through the Sun’s outer corona, where it will travel less than four million miles from the Sun’s surface.

This is close enough to study how coronal mass ejections are formed. The main goal is to start developing the ability to predict their direction, timing and intensity. Anticipating when a solar plasma storm is headed towards Earth would allow us to disconnect before it hits us.

The positive aspect of the solar wind

The solar wind also defines the boundary of the solar system. The wind carries the solar magnetic field lines and these magnetic field lines can act as a bubble that protects the solar system from the interstellar wind. This is similar to how the Earth’s magnetic field protects our planet from the solar wind.

The bubble in space sculpted by the Sun’s magnetic field and the solar wind is known as the heliosphere. The heliopause is the outer boundary of the heliosphere, just as the magnetopause is the outer boundary of the earth’s magnetosphere. Beyond the heliopause, the interstellar wind is more powerful than the solar wind.

Common questions about solar winds and planets

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