We don't know enough about the sun.

Solar orbit detectors can hover over some positions on the surface when the sun rotates. (ESA/Map)

April 24th, 2020 is the 30th anniversary of the launch of Hubble Space Telescope. Astronomers and astronomy enthusiasts all over the world are celebrating this landmark day. Over the past 30 years, the Hubble Space Telescope has achieved fruitful results and completely changed our understanding of the universe.

However, although some probes, such as the Hubble Space Telescope, can go deep into the universe, we have actually lacked sufficient knowledge about the sun for a long time. As the parent star of the solar system, the sun is of irreplaceable significance to human beings, other life on earth and the whole solar system, so it is one of the important tasks for astrophysicists to study the formation, evolution and influence of the sun on the earth. However, with the launch of two solar probes in 20 18 and 2020, we are expected to understand this most important celestial body for human beings at an unprecedented level.

On February 10, Beijing time, the solar orbiter led by the European Space Agency (ESA) and cooperated by the National Aeronautics and Space Administration (NASA) was launched at Cape Canaveral Air Force Base in Florida, USA. If the mission goes well, the solar orbiter will be the first detector to take pictures of the South Pole and the North Pole of the sun, thus helping researchers to understand the sun more comprehensively.

The solar orbit detector is a part of the scientific plan called "Cosmic Vision 20 15-2025" being implemented by ESA. The idea of launching this detector first came from 1982. In 2000, ESA agreed to start this project, which was reconfirmed in 2003. ESA signed a contract with the manufacturer in 20 12. It took six years before and after the detector was manufactured, and it passed the test of 1 for many years. ESA originally planned to launch the probe in 20 17, but after several delays, it finally decided to launch it in 2020.

The solar orbit detector weighs 1800 kg and has a wingspan 18 m. It carries 65,438+00 kinds of scientific equipment, including magnetometer, high-energy particle detector and solar heliosphere imager. With these devices, the detector can realize two research modes: one is to measure the space environment near the detector, including electric field, magnetic field and particles; The other is to take photos of the sun from a distance, including the sun's atmosphere and material ejection. When the probe is closest to the sun, it is only about 42 million kilometers away from the sun and will be in the orbit of Mercury. The special heat insulation board can withstand the test of high temperature of 500℃, and advanced heat insulation technology will protect the scientific equipment carried by the detector.

After the detector is successfully launched, the project team will first debug it for about 3 months to verify whether the scientific equipment carried by the detector can work normally. After that, it will take nearly two years for the probe to enter the orbit around the sun. This special orbit is the key for the detector to take photos of the north and south poles of the sun.

The average distance between the sun and the earth is about1.500 million kilometers (1AU), which is much smaller than the distance between the earth and Pluto. However, it is no easier to send a probe to the sun than to Pluto. The earth has been revolving around the sun at high speed, and the detectors launched from the earth need to slow down and lower their orbits to get close to the sun. This deceleration process cannot be completed by the detector's own engine. Therefore, in the process of approaching the sun, the detector does not fly directly to the sun, but first needs to slow down three times with the help of the gravitational slingshot effect of the planet. These three times were slingshot effect deceleration of Venus gravity in February 2020 and August 20021year, and slingshot effect deceleration of Earth gravity in October 20021year, 165438.

After slingshot effect is slowed down by the gravity of the earth, the probe will fly over the sun for the first time in 2022, and the distance from the sun is about 1/3 of the distance between the sun and the earth. During the subsequent mission, the probe will use Venus' gravitational slingshot effect to approach the sun six times, throw itself out of the ecliptic plane of the solar system and enter a highly elliptical orbit around the sun.

In the solar system, the orbits of 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 or satellites on the earth observe the sun, they know more about the equatorial region of the sun, but the observation of the north and south poles of the sun is very limited. ESA and NASA jointly launched the Ulysses solar probe in June 1990+00, and the probe worked until June 2009. Ulysses detector used to measure the space area near the sun's poles in an inclined orbit, but Ulysses detector was too far away from the sun and didn't carry a camera, so it couldn't photograph the sun's poles.

After the solar orbit detector enters the highly elliptical orbit with the help of gravitational slingshot effect, it can reach a position with an inclination greater than17 with the equatorial plane of the sun within the planned five-year mission period. In the task period that may be extended according to the needs of the task, the maximum inclination angle can reach 33. In this way, the detector can observe and photograph the north and south poles of the sun. At the same time, the highest speed of the solar orbit detector can almost reach the rotation speed of the sun, so the detector can hover over some positions on the surface when the sun rotates, and then study how a certain feature of the sun evolves with time.

For a long time, researchers have learned that the period of solar activity is about 1 1 year, but the model describing this period can never match the observation results. The important reason is the lack of data on the solar poles. The information obtained by the solar orbit detector will become a key puzzle to improve the solar magnetic field model, so that researchers can understand the forces driving the solar activity.

Researchers can study the internal working mechanism of the sun, observe the high-energy particles emitted by the sun and track the movement of these particles in the solar system in the form of solar wind, so as to better understand and predict space weather. Solar storm will affect power grid, air transportation and communication, and threaten the safety of astronauts walking in space. The carrington event that occurred in 1859 is considered as the strongest solar storm in history, and solar storms that seriously affected human life are also common. If we can make timely and accurate space weather forecast, we can turn off communication equipment in advance, plan flights reasonably, stop astronauts' extravehicular operations, and minimize the impact of solar storms on us.

In this regard, Günther Hasinger, scientific director of ESA, said at the ESA official website: "Humans have always been familiar with the importance of the sun to life on earth, observing the sun and carefully studying how the sun works. But at the same time, we also know that powerful solar storms may disturb our daily life. By the end of the solar orbit probe mission, we will better understand the forces behind the changes in solar behavior and its impact on our planet. "

Thomas Zurbuchen, deputy director of science at NASA, also said on NASA's official website: "The solar orbiter will study the sun together with other recent NASA missions, and we will gain unprecedented new knowledge about this star. We will enter a new era of solar physics research with our European partners. "

The emission map of the solar orbit detector. (ESA/Map)

The launch of the solar orbital probe is a microcosm of the booming solar research in recent years, and it is also the latest attempt of human beings to explore the sun. In addition to the joint launch of Ulysses probe, ESA and NASA jointly launched the Solar and Heliospheric Observatory in June 65438+June 0995+February 65438. 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 its mission period may be extended to 2022.

Thomas Zobuchen mentioned that a key part of NASA's recent solar mission was the Parker solar probe. On August 2nd, 20 18, Beijing time, Parker Solar Probe was launched and flew to the sun. The mission of this detector is to study the corona and solar wind, so as to deepen our understanding of solar physics. The probe was named after 92-year-old American astrophysicist Eugene Parker, who first proposed the solar wind theory 1958 years ago.

If the mission goes smoothly as planned, Parker Solar Probe will create many firsts. For example, it will be the closest probe to the sun ever. During the mission, the distance between the probe and the sun is only about 6 million kilometers, which is almost 1/7 of Helios B, the closest probe to the sun. Since the corona extends over 6.5438+million kilometers from the surface of the sun, Parker will also be the first probe to enter the corona layer for observation.

Parker can fly over the sun 24 times during the mission, so that the detector has enough time to collect data. In the last three approaches to the sun, Parker's top speed will reach 200 km/s, making it the fastest probe ever.

In the more than one year after its launch, Parker Solar Probe has brought us many surprises. In the early morning of February 5th, 20 19, Beijing time, NASA released to the media the first batch of research results obtained by researchers based on the first three flybys of Parker Solar Probe, and four research papers were also published in Nature on the same day. On February 3, 2020, Astrophysics Journal published a supplement with Parker as the theme, and published 47 papers based on the observation data of Parker solar detector. These papers are also based on Parker's first three flights, some of which are supplements to the papers published in Nature, and some are newly completed studies. Before these papers, Mathea Gebauer, an American space physicist, wrote an introduction, and it was she who first detected the solar wind proposed by Parker.

In these four papers published in Nature at the end of 20 19, the researchers reported the preliminary results. They found that although space is full of dust, there may be dust-free areas in space near the sun because dust is heated into gas. The data show that the dust is gradually reduced from about 1 1 10,000 kilometers away from the sun to about 6 million kilometers. The real dust-free zone may be 3-4 million kilometers away from the sun, which is expected to be reached by Parker Solar Detector in 2020.

The solar wind observed by researchers near the earth is a relatively uniform plasma flow. However, when the solar wind reached the earth, it had traveled 65.438+0.5 billion kilometers, so many information that could help researchers understand the mechanism of solar heating and accelerating the solar wind was erased. Parker's solar probe observed a completely different situation in the solar wind near the sun. The magnetic field in the plasma will change rapidly, and at the same time, there will be a sudden and fast-moving material jet, which makes the solar wind more unstable than when it is near the earth. These details are key information to help researchers understand how the solar wind propagates energy in the solar system.

A special phenomenon that attracted the research team's attention is the unexpected change of the solar magnetic field line, which will turn 180 in a few seconds to a few minutes. In a paper in Nature, the researchers made a preliminary discussion, and in a supplementary paper in Astrophysics, they made a further analysis, but at present they can't explain this phenomenon. In addition to the four and 47 papers published successively, more studies based on the data obtained from the first three overflights will be published one after another.

Preparations for launching the solar orbit probe.

ESA and NASA have established close cooperation in the field of solar research. Together with other on-orbit detectors and ground observation equipment, a detector led by them can outline a more complete solar physical image. Solar orbit detector and Parker solar detector have different characteristics. Parker's solar detector is closer to the sun than the solar orbital detector to better study the origin of the solar wind, but Parker did not take a camera to shoot the sun directly. The equipment carried by the solar orbit detector can not only measure the sun from a distance, but also observe the space environment around the detector, which can provide more information for interpreting the observation data of Parker solar detector. The camera installed on the solar orbit detector can take pictures of the position of Parker's solar detector, so that when Parker measures the plasma, the solar orbit detector will take pictures of it at the back. From the complementary data of the two detectors, researchers can find more scientific contents and realize the effect that one plus one is greater than two.

Holly Gilbert, a scientist of NASA's solar orbit probe project, said: "The solar orbit probe and Parker solar probe will uncover the biggest mystery of the sun and the solar atmosphere on this extraordinary journey. The powerful combination of these two tasks and its amazing technological progress will push our understanding of the sun to a new height. "

By studying the sun in detail, researchers can not only answer many questions about the sun itself, but also better evaluate the impact of solar activities on human life and future space exploration tasks, and hope to deepen their understanding of the evolution mechanism of stars. At the same time, in the case that thousands of extraterrestrial planets have been discovered, these studies will also help scientists speculate whether there is life on extraterrestrial planets orbiting sun-like stars. There is no doubt that solar physics research is entering a golden age.

Southern Weekend Special Contributor Ju Qiang