Solar Winds and the Planets

FROM THE LECTURE SERIES: A Field Guide to the Planets

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

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

A solar storm heading toward the planet Earth.
The corona, a layer of the Sun’s atmosphere, is where solar winds originate. (Image: Naeblys/Shutterstock)

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

Creation of 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 chromosphere layer, which is a few thousand kilometers thick. The temperature increases with height here reaching about 10,000° at the top of the chromosphere. Fibrous jets known as spicules appear and travel through the photosphere in about 10 minutes, carrying plasma to higher altitudes.

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

The temperature spikes to around two million Kelvin. But since the density of the plasma is much lower than at the photosphere, we don’t usually see the light from this region. The Sun emits about 1.5 million tons of superheated plasma per second out into the solar wind. Speeds can vary a lot based on the Sun’s magnetic field and from what region it gets emitted, 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 Planets

A solar flare originating from the sun.
Electrons and other charged particles
from geomagnetic storms can disrupt
electronics and satellites on Earth.
(Image: NASA/Public domain)

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

This rain of plasma particles can collide with particles high up in a planet’s atmosphere, giving the atmospheric particles enough energy to escape 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 from the video series A Field Guide to the Planets. Watch it now, Wondrium.

Space Weathering Caused by Solar Winds

Solar winds also cause ‘space weathering’ on airless bodies like Mercury and most of the moons in the solar system. Space weathering can cause some substances to vaporize from the surface or cause other particles to become fused. For example, the topcoat of regolith on the Moon is much darker because of extensive space weathering.

Learn more about Pluto and Charon: the binary worlds.

Dangers of Geomagnetic Storms Caused by the Solar Wind

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

Here, the magnetic fields create large arcing loops over the plasma, like a net holding a fish. A coronal mass ejection is a plasma storm that occurs when those magnetic fields experience reconnection events that realign the magnetic fields.

A large geomagnetic storm originating from the sun.
Electrons and other charged particles from geomagnetic storms can also disrupt electronics, including radio transmissions and satellites.
(Image: NASA/Public domain)

After a reconnection event, there is a big hole in the net, and solar plasma can explode out of it. This explosion causes a much bigger mass of plasma than usual to be hurled through the hole and into space. Sometimes, that plasma is directed towards the Earth. If so, the huge flood of ionized particles can disrupt our magnetosphere and cause new currents to flow. We call this a geomagnetic storm.

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

Instances of Geomagnetic Storms on the Earth

These geomagnetic storms have also been known to knock out power grids. For example, in March of 1989, the Sun released a coronal mass ejection whose energy was equivalent to thousands of nuclear bombs. The interaction with Earth’s geomagnetic field caused the province of Quebec in Canada to lose power for nine hours. Then in August, the computers used in the Toronto Stock Exchange lost power, halting 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 sea mines that the U.S. Navy had placed in coastal waters near Vietnam. These mines had magnetic triggers intended to explode when a metal ship floated by. 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 voltage increases in telegraph wires resulted in shocks to telegraph operators and even the ignition of fires.

Back then, people weren’t as heavily reliant 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 trillions of dollars of damage to power grids and satellites. There would be widespread power blackouts. Some scientists estimate that it would take years to get power restored if enough damage is done.

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

Learn more about water on Mars and prospects of life.

Other Dangers of Solar Storms

One concern for long-time 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 the astronauts—maybe, enough to be fatal. So this will be a rare but important obstacle when trying to plan human voyages to Mars or further.

Forecasting Space Weather

There have been several missions designed to observe the Sun and help us begin to forecast the so-called ‘space weather’. In geosynchronous orbit around 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 features that occur here.

For example, SDO can see energetic gases that trace out the Sun’s magnetic field in coronal loops. It can even image solar flares that involve gasses at millions of degrees in temperature.

Orbiting the Sun from an Earth-like distance, the Solar Terrestrial Relations Observatory, or STEREO, used two telescopes at two different and changing locations to get stereo images of the Sun. This has allowed for the determination of the three-dimensional structure of solar features, like the extent 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 at almost half a million miles per hour through the outer corona of the Sun, where it will travel less than four million miles from the Sun’s surface.

This is close enough to study how coronal mass ejections form. The primary goal is to begin to develop an ability to predict their direction, timing, and intensity. Anticipating when a solar plasma storm is headed toward Earth would let us disconnect before it hits us.

The Positive Aspect of Solar Wind

The solar wind also defines the boundary 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 Earth’s magnetic field shields 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 boundary of the heliosphere, just like 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 the Planets

Q: Can solar winds affect the Earth?

Yes, the solar storms or the coronal mass injections can greatly disrupt the magnetosphere of the Earth. Solar storms can also damage satellites and electrical grids.

Q: Why is solar wind important?

Solar wind is important because it forms the heliosphere of the Sun or the boundary of our solar system.

Q: Why is solar wind dangerous?

It is dangerous because solar storms can disrupt the magnetosphere of the earth. Solar storms can also damage satellites and electrical grids.

Q: Do solar winds cause the northern lights?

The radiation from a geomagnetic storm can cause northern lights or aurora to appear even at lower latitudes.

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