We don’t know enough about the sun
The Solar Orbiter can hover over certain locations on the Sun's surface as it rotates. (ESA/Picture)
April 24, 2020 is the 30th anniversary of the launch of the Hubble Space Telescope. Astronomers and astronomy enthusiasts around the world are celebrating this milestone. A meaningful day. Over the past 30 years, the Hubble Space Telescope has achieved fruitful results and completely changed our understanding of the universe.
But while a group of detectors represented by the Hubble Space Telescope are looking into the depths of the universe, we have actually lacked sufficient understanding of the sun for a long time. As the parent star of the solar system, the sun has irreplaceable significance to humans, other life on earth and the entire solar system. Therefore, studying the formation, evolution and impact of the sun on the earth has become one of the important tasks of astrophysicists. However, with the launch of two solar probes in 2018 and 2020, we are expected to understand this most important celestial body for mankind at an unprecedented level.
On February 10, 2020, Beijing time, the Solar Orbiter (Solar Orbiter) led by the European Space Agency (ESA) and in cooperation with the National Aeronautics and Space Administration (NASA) was launched in Cana, Florida, USA. The launch took place from Cape Villar Air Force Base. If the mission goes well, Solar Orbiter will be the first spacecraft to image the sun's north and south poles, helping researchers gain a more complete understanding of the sun.
The Solar Orbiter is part of ESA's ongoing science program called "Cosmic Vision 2015-2025". The idea of launching such a detector first originated in 1982. In 2000, ESA agreed to launch the project and reconfirmed it in 2003. ESA signed a contract with the manufacturer in 2012. It took 6 years to manufacture the detector and more than a year of testing. ESA initially planned to launch the probe in 2017, but after several delays it was finally determined to be in 2020.
The Solar Orbiter weighs 1,800 kilograms and has a wingspan of 18 meters. It carries 10 types of scientific equipment, including a magnetometer, a high-energy particle detector, and a heliosphere imager. Relying on these devices, the detector can achieve two research modes: one is to measure the space environment near the detector, including electric fields, magnetic fields, particles, etc.; the other is to take images of the sun from a distance, including the solar atmosphere and materials. jet. When the probe is closest to the sun, it will be only about 42 million kilometers away from the sun, and will be within the orbit of Mercury. The special heat insulation board can withstand the test of high temperature of 500℃, and the advanced heat insulation technology will protect the scientific equipment carried by the detector.
After the probe is successfully launched, the project team will first conduct debugging for about three months to verify that the scientific equipment carried by the probe can work properly. After that, it will take nearly two years for the probe to enter a working orbit around the sun. This special orbit is the key to the probe being able to take images of the north and south poles of the sun.
The average distance between the sun and the earth is about 150 million kilometers (1AU), which is much smaller than the distance from the earth to Pluto. But launching a probe toward the sun is no simpler than launching a probe toward Pluto. The earth is rotating around the sun at high speed all the time. The detectors launched from the earth need to slow down and continuously lower their orbit in order to get close to the sun. This deceleration process cannot be completed by the probe's own engine. Therefore, when approaching the sun, the probe does not fly straight towards the sun. Instead, it first needs to use the gravitational slingshot effect of the planet three times to achieve deceleration. These three times are deceleration relying on the gravitational slingshot effect of Venus in December 2020 and August 2021, and deceleration relying on the gravitational slingshot effect of the Earth in November 2021.
After using the Earth’s gravitational slingshot effect to slow down, the probe will fly by the sun for the first time in 2022. At this time, the distance from the sun will be about 1/3 of the distance between the sun and the earth. During the subsequent mission period, the probe will use the gravitational slingshot effect of Venus to continuously approach the sun six times, and throw itself out of the ecliptic plane of the solar system into a highly elliptical orbit around the sun.
In the solar system, the orbits of the planets around the sun are basically in a plane, which has only a small angle with the equatorial plane of the sun itself. Therefore, when telescopes on the earth or telescopes on satellites observe the sun, they have a relatively good understanding of the sun's equatorial region, but their observations of the sun's north and south poles are very limited. ESA and NASA jointly launched the Ulysses solar probe in October 1990, which continued to operate until June 2009. The Ulysses probe once measured the space area near the sun's poles in an inclined orbit, but the Ulysses probe was too far away from the sun and did not carry a camera, so it was unable to photograph the sun's poles.
After entering a highly elliptical orbit with the help of the gravitational slingshot effect, the Solar Orbiter can reach a position with an inclination angle of more than 17° to the sun's equatorial plane within the planned five-year mission; according to the mission During the mission period when it is necessary and possible to extend the mission, the inclination angle can reach a maximum of 33°. In this way, the detector can observe and photograph the north and south poles of the sun. At the same time, the maximum speed of the Solar Orbiter can almost reach the rotation speed of the sun, so the detector can hover over certain locations on the surface of the sun as it rotates, and then study how a certain feature of the sun evolves over time.
Researchers have long known that the cycle of solar activity is about 11 years, but the models describing this cycle have never been able to match the observations. The important reason is the lack of data from the solar polar regions. The information obtained by Solar Orbiter will be a key piece of the puzzle in improving models of the Sun's magnetic field, allowing researchers to understand the forces driving solar activity.
Researchers can use the data obtained by the detector to study the inner workings of the sun, observe the high-energy particles emitted by the sun and track the movement of these particles through the solar system in the form of solar wind, in order to better understand and Predict space weather. Solar storms can impact power grids, air transport and communications, and threaten the safety of astronauts conducting spacewalks. The Carrington Event in 1859 is considered the strongest solar storm on record. Since then, solar storms that have had a serious impact on human life have become common. If we can conduct timely and accurate space weather forecasts, we can shut down communication equipment in advance, plan flights reasonably, and stop astronauts’ out-of-vehicle operations to minimize the impact of solar storms on us.
In this regard, ESA Science Director Günther Hasinger said on the ESA official website: "Human beings have always been familiar with the importance of the sun to life on earth, observe the sun and carefully Study how the sun works, but we also know that powerful solar storms have the potential to disrupt our daily lives, and by the end of Solar Orbiter's mission, we will be aware of changes in the sun's behavior and its impact on our planet. We need to know more about the power behind it.”
Thomas Zurbuchen, NASA’s deputy director of science, also stated on NASA’s official website: “The Solar Orbiter will be used with other recent NASA missions. By studying the sun together, we will also gain unprecedented new knowledge about this star. Together with our European partners, we will enter a new era of solar physics research."
Launch of the Solar Orbiter. Liftoff diagram. (ESA/Photo)
The launch of the Solar Orbiter Probe is a microcosm of the booming solar research in recent years and is also the latest attempt by humans to explore the sun. In addition to cooperating to launch the Ulysses probe, ESA and NASA collaborated to launch the Solar and Heliospheric Observatory (SOHO) in December 1995. The probe was planned to work for 2 years when it was launched, but it has been working for more than 24 years so far, and the mission may be extended to 2022.
Thomas Zobuchen mentioned that a key part of NASA’s recent solar mission is the Parker Solar Probe. On August 12, 2018, Beijing time, the Parker Solar Probe was launched and flew towards the sun. The mission of this probe is to study the corona and solar wind to deepen our understanding of solar physics. The detector is named after 92-year-old American astrophysicist Eugene Parker, who first proposed the solar wind theory 1958 years ago.
If all goes according to plan, the Parker Solar Probe will create many firsts. For example, it will be the closest probe ever to the sun. During the mission cycle, the probe's closest distance to the sun is only about 6 million kilometers, which is almost 1/7 of the previous closest probe to the sun, Helios B. Because the corona extends more than 10 million kilometers from the surface of the sun, Parker will also be the first detector to enter the corona for observations.
Parker can fly by the sun 24 times during its mission cycle, so that the probe has enough time to collect data. During its last three approaches to the sun, Parker's maximum speed will reach 200 kilometers per second, making it the fastest detector in history.
In more than a year since its launch, the Parker Solar Probe has brought us many surprises. In the early morning of December 5, 2019, Beijing time, NASA released to the media the first batch of research results obtained by researchers based on the first three flybys of the Parker Solar Probe. Four research papers were also published in Nature on the same day. superior.
On February 3, 2020, The Astrophysical Journal published a supplement with the theme of Parker, publishing 47 papers based on the observation data of the Parker Solar Probe. These papers are also based on the first three flybys of Parker. Some are supplements to papers published in Nature, and some are newly completed research. The papers follow an introduction written by American space physicist Marcia Neugebauer, who first detected Parker's solar wind.
In these four papers published in "Nature" at the end of 2019, researchers reported preliminary research results. They found that although space is full of dust, there may be dust-free regions in regions of space close to the sun because the dust is heated into gas. The data shows that the dust gradually decreases from about 11 million kilometers away from the sun to about 6 million kilometers away. The truly dust-free area may be 3 million to 4 million kilometers away from the sun, and the Parker Solar Probe is expected to reach this area in 2020.
The solar wind observed by researchers near Earth is a relatively uniform flow of plasma. But the solar wind has already traveled 150 million kilometers by the time it reaches Earth, so much of the information that could help researchers understand the mechanisms by which the sun heats and accelerates the solar wind has been erased. The Parker Solar Probe observed very different conditions in the solar wind near the sun. Rapid changes in the magnetic field in the plasma and sudden, fast-moving jets of material make the solar wind more unstable than near Earth. These details are key to helping researchers understand how the solar wind spreads energy throughout the solar system.
One special phenomenon that attracted the attention of the research team is the unexpected change in the sun's magnetic field lines, which will turn 180° within a few seconds to a few minutes. In a paper in "Nature", the researchers conducted a preliminary discussion, and in a paper in a supplement to the "Astrophysics Journal" they conducted a further analysis, but they are not yet able to explain this Phenomenon. In addition to the 4 and 47 papers published successively, more research based on data obtained from the first three flybys will be published one after another.
The Solar Orbiter Probe enters preparations before launch.
ESA and NASA have established close cooperation in the field of solar research. A detector led by each can cooperate with other on-orbit detectors and ground-based observation equipment to outline a more complete picture of solar physics. image. Solar Orbiter and Parker Solar Probe have different characteristics. Parker Solar Probe is much closer to the sun than Solar Orbiter to better study the origin of the solar wind, but Parker does not carry a camera to take pictures of the sun directly. The equipment carried by the Solar Orbiter can not only conduct long-distance measurements of the sun, but also observe the space environment around the probe. These can provide more information for interpreting the observation data of the Parker Solar Probe. Cameras onboard Solar Orbiter can image Parker Solar Probe's position so that Solar Orbiter can take pictures of Parker behind it as it measures the plasma. From the complementary data of the two detectors, researchers can discover more scientific content, achieving the effect of one plus one being greater than two.
Holly Gilbert, NASA Solar Orbiter project scientist, said: "Solar Orbiter and Parker Solar Probe will share the same secrets on this extraordinary journey. The biggest mysteries of the sun and its atmosphere. The powerful combination of the two missions and their amazing technological advances will push our understanding of the sun to new heights."
Researchers are studying the sun. Detailed research can not only answer many questions about the sun itself and better assess the impact of solar activity on human life and future space exploration missions, but is also expected to deepen our understanding of the mechanism of stellar evolution. At the same time, as humans have discovered thousands of extraterrestrial planets, these studies also help scientists speculate whether there is life on extraterrestrial planets orbiting sun-like stars. There is no doubt that heliophysics research is entering a golden age.
Southern Weekend staff writer Ju Qiang