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 an ionized mass of the Sun hitting the planets – what we call the solar wind. Solar winds can cause major disturbances to our solar system, especially on a planet like Earth. What are these possible disturbances and how can they be mitigated?

The mass of solar winds is made up 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 comes from the Sun’s atmosphere.

Creation of solar winds on the sun

The Sun’s atmosphere is divided into two layers: the chromosphere and the corona. Above the opaque photosphere or the surface of the sun is the layer of chromosphere, which is a few thousand kilometers thick. The temperature increases with height reaching here about 10,000 ° at the top of the chromosphere. Fibrous jets called spicules appear and pass 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 solar disk. The corona is the source of the solar wind. 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 reaches around two million Kelvin. But because the density of plasma is much lower than that of the photosphere, we usually don’t see light from that region. The Sun emits about 1.5 million tonnes of superheated plasma per second in the solar wind. Speeds can vary a lot depending on the Sun’s magnetic field and the region it is emitted in, but it can reach speeds of 750 kilometers per second!

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The impact of solar winds on the planets

Ionized particles from the solar wind are coupled to the solar magnetic field to form a spiral structure in space known as the “Parker Spiral”. These high-energy solar wind particles cause auroras on the planets with a magnetic field, but they can also disrupt the atmospheres and surfaces of the planets.

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

Alteration of space caused by solar winds

Solar winds also cause “ space weathering ” on airless bodies like Mercury and most moons in the solar system. Bad weather can cause some surface substances to vaporize or other particles to melt. For example, the topcoat of regolith on the Moon is much darker due to extensive spatial weathering.

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Dangers of geomagnetic storms caused by solar wind

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

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

After a reconnection event, there is a large hole in the net and solar plasma may explode. This explosion causes a much larger mass of plasma than usual to be thrown through the hole and into space. Sometimes this plasma is directed towards Earth. If so, the huge stream 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 auroras to appear at lower latitudes than they normally would. And not only do the aurorae look pretty, but the light signals can also give us hours of early warning for the plasma mass to come. Electrons and other charged particles from geomagnetic storms can also disrupt electronics, including radio transmissions and satellites. For example, GPS coordinates can deviate by several meters during a storm. It may not seem like much until you realize the planes are landing via GPS.

Instances of geomagnetic storms on Earth

These geomagnetic storms are also known to knock out power grids. For example, in March 1989, the Sun released a coronal mass ejection the energy of which was equivalent to thousands of nuclear bombs. Interaction with the earth’s geomagnetic field caused the province of Quebec in Canada to lose electricity for nine hours. Then, in August, the computers used at the Toronto Stock Exchange lost power, halting all operations.

Another geomagnetic storm in 1972 led to typical radio failures and damage to solar panels on satellites. But it also led to the unintentional explosion of sea mines that the US Navy had placed in coastal waters near Vietnam. These mines had magnetic triggers intended to explode when a metal vessel floated. But the geomagnetic storm triggered the magnetic sensors, inadvertently setting off about two dozen explosions in 30 seconds.

The largest geomagnetic storm occurred in 1859. It is known as the Carrington event where a coronal mass ejection traveled from the Sun to the Earth in just 18 hours. Sudden increases in voltage in the telegraph wires caused shocks to telegraph operators and even the ignition of fires.

Back then, people weren’t so dependent on electronics, but scientists can estimate what would happen today if a plasma storm as large as the Carrington event occurred. It would likely cause billions of dollars in damage to power grids and satellites. There would be widespread blackouts. Some scientists believe it would take years to restore power if enough damage is done.

So when will the next geomagnetic storm hit? When the Sun has a lot of sunspots, coronal mass ejections occur about three times a day. When there are few sunspots, this only happens once every five days.

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Other dangers of solar storms

The effect of solar storms on astronauts is a concern for long-term space travel. A solar storm hitting a spacecraft would result in severe exposure to high-energy radiation by astronauts – possibly enough to be fatal. So this will be a rare but significant hurdle when trying to plan human trips to Mars or beyond.

Space weather forecast

There have been several missions designed to observe the Sun and help us start forecasting so-called “space weather”. In a geosynchronous orbit around the Earth is the Solar Dynamics Observatory or SDO. It images 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 that trace the Sun’s magnetic field in coronal loops. He can even imagine solar flares that involve gases at millions of degrees of temperature.

Orbiting the Sun at a distance similar to that of Earth, the Earth Solar Relations Observatory, or STEREO, used two telescopes at two different and changing locations to obtain stereo images of the Sun. This made it possible to determine the three-dimensional structure of solar features, such as the extent of giant coronal mass ejections.

Parker solar probe

The closest mission to the Sun is the Parker solar probe, which circles the Sun in an 88-day highly elliptical orbit. This mission will eventually zoom in at nearly half a million miles per hour through the Sun’s outer corona, where it will travel within four million miles of the Sun’s surface.

This is close enough to study the formation of coronal mass ejections. The main goal is to begin to develop an ability to predict their direction, timing and intensity. Anticipating when a solar plasma storm is heading towards Earth would allow us to disconnect before it hits us.

The positive aspect of the solar wind

The solar wind also defines the limit of the solar system. The wind carries solar magnetic field lines with it, and these magnetic field lines can act as a bubble shielding 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 carved out by the Sun’s magnetic field and solar wind is known as the heliosphere. The heliopause is the outer limit of the heliosphere, just as the magnetopause is the outer limit 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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