Parker Solar Probe: Diving into the solar atmosphere

The Parker Solar Probe is designed to unveil a great secret of the sun. To do so, it must travel closer to our star than any other spacecraft before it to collect data in a hellish environment.

For decades, solar researchers have been searching for an explanation for a mysterious phenomenon: how is it possible that the atmosphere of the sun is up to five hundred times hotter than its surface? In the atmosphere around the sun, known as the Sun's 'corona,' temperatures of several million degrees Celsius prevail. But the visible surface below it, from which the corona gets its heat, is only about 5800 degrees.

The incredible, unparalleled heat of the corona is a central question in solar physics. Scientists suspect the underlying mechanism probably also holds relevance for the formation of the so-called solar winds.

Hellish conditions

Our Sun is a glowing hot ball of gas from which matter constantly escapes into space - this is known as 'solar wind.' It flows out of the hot corona, and consists mainly of ionized hydrogen, electrons and protons.

This electrically charged particle stream also blows toward the Earth, where it meets the Earth's magnetic field. It acts as a protective shield and, for the most part, keeps the particle shower away from our planet.

Explosive processes in the Sun, such as coronary mass ejections and sudden radiation bursts - called 'flares' - can cause turbulence and transform the uniformly flowing solar wind into a storm.

With a flare, the intensity of 'x-rays' often increases by more than a thousand times. Those are high-energy protons and electrons. That radiation reaches us unhindered after just eight minutes. While the particle streams reach Earth 10 to 30 minutes later.

In a coronary mass ejection, the Sun hurls huge clouds of electrically charged gas into space. These clouds can have a mass of several tens of billions of tons and reach a speed of over 2000 kilometers per second!

The explosive mass ejections cause shock waves within the constantly flowing solar wind, comparable to the supersonic bang of an aircraft.

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Earth in the line of fire

If these shock waves hit Earth, the particles from the Sun can overcome Earth's protective shield with their powerful speed, penetrating its magnetic field.

This means strong solar storms can cause enormous damage. They influence the structure of electromagnetic waves and interfere with mobile radio and satellite navigation.

On March 13th, 1989, a nine-hour power outage occurred in Quebec, Canada. Millions of people were without electricity. A violent solar storm had induced strong currents in the overhead lines and caused transformers to burn through.

The electrically charged particles from the sun can decelerate satellites and even shorten their lifetime by destroying electronic components.

Electronics and satellite technologies are playing an increasingly important role in our lives. Now more than ever, it's important to predict such solar storms. But before this can be done, the researchers must understand how solar storms form.

Space probe to unveil secrets

It is hoped the Parker Solar Probe can fill the gaps in our understanding; showing us how the solar atmosphere is heated and how the particles of the solar wind are accelerated.

Solar physicists have already developed different theories in answer to these questions. Only in March this year an international team led by Samuel D.T. Grant published anarticle in the renowned journal "Nature Physics".

In this paper, the researchers propose that the heating takes place via plasma waves in the transition layer between the surface and the corona of the sun. Other theories attribute the heating of the corona to processes in the Sun's magnetic field, such as the sudden fusion of magnetic field loops.

The Parker Solar Probe is designed to collect data for the first time in the region where the solar wind is generated. To do this, the satellite must approach our central star like no other probe before it. The spaceship has to dive into the corona of the sun and get as close as six million kilometers to the fiery red-hot ball of gas. 

Long journey to the sun

For decades, solar physicists have dreamt about sending satellites into the corona of the sun. In 1958, the year NASA was founded, such a mission was put on the agenda. But it would be decades before the necessary technologies were developed to protect the space probes from the extreme radiation and the enormous heat in the solar corona.

It will be a few more years before the Parker Solar Probe can explore this hellish region at close range. The probe's success is contingent on the help of Venus. After all, braking is not easy when flying a spaceship into the inner solar system. Therefore, the research probe must fly past Venus seven times. During each of these so-called 'swing-by' maneuvers, it transfers some energy to the planet. It slows down, changes its course and continues to advance towards the sun.

After the last fly-by in November 2024, the Parker Solar Probe will finally reach the speed at which it can approach the Sun by only six million kilometres. It will then fly through the solar atmosphere at a speed of 200 kilometres per second. That's approximately 30 times faster than the speed at which the International Space Station currently travels through space. With its four scientific instruments, it is to measure the particles buzzing around and the magnetic fields of our star.

Three times, the spacecraft is scheduled to fly into the vicinity of the Sun and give us completely new insights into its turbulent processes. Once off the ground, the Parker Solar Probe will be the fastest spaceship ever launched by humans.

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Two sister probes

On August 20th 1977 NASA lauched Voyager 2 for a record flight that is still going. Shortly after, on September 5th, the identically built Voyager 1 followed. The initial aim of the mission was to obtain more information about Jupiter and Saturn, planets which were still largely unexplored at the time. Thanks to the long-lasting plutonium batteries, both spacecraft are still active.

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Staying power

Weighing 825 kg or 1,818 pounds (on Earth), the Voyager probes are among NASA's biggest success stories. Both still regularly send reliable data from space. They're moving farther and farhter away from Earth, but the radio connection is expected to work until 2030.

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Leaving the solar system

On August 25th 2012 Voyager 1 crossed the heliopause, one of the borders of our solar system. There, the interstellar space of our galaxy - the Milky Way - beginns. Voyager 1 is the man-made object most distant from Earth - currently at about 139 times the distance between Earth and Sun.

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Flight routes

The solar system has different borders: The first is the "termination shock." That's where the solar winds slow down dramatically. After the heliosphere comes the heliopause. That's the edge of the space bubble where solar flares shield us from interstellar rays. NASA measured a 40 times higher plasma density after Voyager 1 crossed the heliopause.

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Big planet, lots of pictures

There was a lot the spacecraft has discovered so far: Voyager 1 sent back this image of Jupiter on January 1, 1979. In all, Voyager 1 took a total of 17,477 images of the planet and four of its moons. The existence of the thin ring system surrounding Jupiter was detected for the first time through these images.

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Detailed photos

Voyager 1 also documented atmospheric flows on Jupiter, as seen in this picture. After the Jupiter flyby, Voyager 1 reached a speed of 16 kilometers per second.

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True colors

Voyager 2 sent this full-color photo of Saturn back to Earth. The probe reached the sixth planet in our solar system in 1981. In outer space terms, this photo is a real close-up: it was taken from a distance of just 21 million kilometers (about 13 million miles).

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Everything under control

The distant probes are monitored and controlled, as far as that's possible, by the control center of the Voyager mission at the California Institute of Technology in Pasadena, seen here in 1980. Today, the equipment is much more modern. But NASA regularly has to consult with the engineers who designed and built the Voyager spacecraft - even though they have long been in retirement.

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Sounds of Earth for alien ears

In the event the probes encounter life on their endless journey, they have these gold discs along for the ride. The record contains pictures and sounds of people, animals and nature on Earth. In case the aliens don't own a record player, a needle and picture instructions are provided.

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Space art

For decades, the Voyager missions have not only fascinated space fans - even artists have been inspired. In 1977, just before the launch, an anonymous American artist imagined the Voyager 1 Saturn flyby.

Everybody's looking for the little black dot

A tiny black spot - this is how Mercury looks in front of the solar disk, which it passed on Monday. It took the planet more than seven hours to travel the entire length.

View from Bavaria

An astronomer took those pictures with an 800mm telescope from Kempten in the Allgäu region of Bavaria. The sun is shining with such intensity that the planet is reduced to a small shadow. Even this picture could only be taken because the telescope has been darkened with a special sunray-filter.

Zooming in

This picture is from 2006. Italy's National Institute of Astrophysics took it during a previous Mercury flyby. At least here it is easy to distinguish between the planet and frequently ocurring sunspots, or coronal mass ejections, which also appear as dark spots on the surface of the sun. The planet, however, is clearly round with sharp edges before the background of solar flares.

How to get even closer

Only a spacecraft will do. NASA's spacecraft Messenger took the best pictures of Mercury so far. The probe circled the planet from 2011 to 2015 until it finally crashed there.

Just like the Moon?

Messenger found a planet with a surface which does not look too differently from our Earth-Moon - at first glance: rock, sand, gravel and lots of craters left behind by meteorite impacts. But there are big differences, too: temperatures on Mercury are much more extreme. Because there is practically no atmosphere, it can get icy cold. On the other hand, the sun can make it extremely hot.

Mercury in all its beauty

This picture is a composite from thousands of pictures taken by different spectrometers in the course of countless orbits around the planet. For the first time, there is a really high-resolution image of Mercury.

Messenger's final resting place

This area shows the eventual crash site where Messenger came down in 2015. Clearly visible: meteorite impact craters of all sizes.

Highland plains in sunshine

The astronomers who have watched Monday's Mercury flyby did not see pictures like this. The photo taken by Messenger shows an area of plains formed by volcanic activity. The different colors indicate different rock materials.