Xihe ushered in the "solar exploration era", what grand plans will there be in the future?

Solar exploration can improve solar physics research and space weather forecasting capabilities, lead to the improvement of space science, space technology, and space applications, and provide services for social and economic development. It is a hot spot for international space exploration activities.

On October 14, 2021, my country successfully launched its first solar exploration satellite, Xihe, using the Long March 2D carrier rocket at the Taiyuan Satellite Launch Center. Xihe is my country's first space solar probe, marking the country's entry into the "solar exploration era."

Xihe Probe

Exploring the Sun is of great significance

The sun is about 150 million kilometers away from the earth. It is the closest star to the earth and the one that has the closest relationship with humans. Nuclear fusion occurs in the sun every moment, radiating energy to the outside world continuously, bringing warmth and light to our homeland and nurturing the development of human civilization.

Since ancient times, people have worshipped, been curious about and longed for the sun, and have tried to explore its mysteries. The earliest record of sunspots with a clear date is preserved in the "Book of Han: Records of the Five Elements". In modern times, with the development of science and technology, especially the rapid progress of aerospace technology, human exploration and research on the sun has entered a new era of innovation.

Solar exploration has great scientific significance and application value.

The sun is the closest star to the earth and is the only star whose detailed structure and physical processes can be observed, and observations can be made with high temporal, spatial and spectral resolution. Solar exploration can help us understand major scientific issues such as the origin and evolution of stars, the energy generation mechanism inside stars, the structure and dynamics of the sun, and the impact of stars on celestial bodies and life processes.

Solar activity is the source of space weather disasters and has a significant impact on human activities. When violent activities such as solar flares and coronal mass ejections occur, the sun will emit rapidly increasing electromagnetic radiation, high-energy particle flows and high-speed plasma clouds, driving major changes in the Earth's space environment.

This kind of solar storm had little impact on the production and life of ancient humans, but in modern times, our society is highly dependent on satellites and other space and ground infrastructure. Solar storms may cause disastrous consequences to aerospace, navigation and communication systems, as well as ground oil, power and gas pipelines, causing huge losses. Therefore, we must strengthen the monitoring of solar activity and space weather to avoid disasters.

Multiple ways to explore the sun

Scientists explore the sun using spectroscopy methods, combining large ground-based telescopes with satellites and other space detection methods to conduct full-band, all-round, and multi-angle observations of the sun, from gamma rays, X-rays, ultraviolet rays to visible light, infrared, and radio waves.

Most of the energy of solar radiation is concentrated in the visible light and near-infrared bands. This part of electromagnetic radiation can penetrate the earth's atmosphere to reach the ground, so ground-based telescopes play an important role in solar observation. In 1984, my country built the Huairou Solar Observatory of the National Astronomical Observatory and built a number of advanced solar observation equipment to observe the full solar disk or active area of ​​the sun's three-dimensional vector magnetic field, various monochrome images and white light images, with very powerful performance.

Solar flares, coronal mass ejections, prominences and other solar eruptions, energy phenomena appear in other bands. Coronal radiation mainly occurs in the extreme ultraviolet and X-ray bands, and the electromagnetic radiation of solar wind, interplanetary shock waves and high-energy particle phenomena is mainly between tens of kHz and tens of MHz, belonging to the solar very low frequency band. This part of information will be absorbed and interfered by the Earth's atmosphere, and their observation can only rely on space detection.

Since the 1970s, the United States, Europe, Japan and other countries and regions have launched more than 100 satellites to explore the sun and solar wind. They have carried out detections of solar eruption activities, the solar magnetic field, the propagation and evolution of the solar wind, and the formation and evolution of the space environment. They have achieved many milestone results and accumulated a massive amount of systematic and complete data on the solar magnetic field, atmospheric structure and solar activity.

Especially in recent years, with the improvement of aerospace capabilities such as launch vehicles, orbit design, deep space tracking and control, and advanced payloads, countries can launch more advanced solar probes to achieve close-in detection of the sun and cross-polar detection, further uncovering the mysteries of the sun.

Xihe data open to the world

On October 14, 2021, Xihe was launched into space and entered a dawn-dusk sun-synchronous orbit at an altitude of 517 kilometers to carry out scientific observations and technical experiments.

Xihe Probe

The satellite orbit plane is located near the Earth's terminator, the boundary between the night and day parts of the Earth's surface. Satellites in terminator orbits will not be continuously blocked by the Earth's shadow. In this "dusk chasing dawn" orbit, satellites can obtain almost uninterrupted observation opportunities of the sun.

"Xihe" weighs 510 kilograms, and its payload is a Hα imaging spectrometer. Although spectral detection of various bands of the sun has been carried out internationally, spectral imaging detection in the Hα band is the first time, filling the gap in high-quality observation data in the source region of solar flares.

The Hα line is a visible red emission line of hydrogen. Hydrogen is the most abundant element in the chemical composition of the sun and is also the raw material for nuclear fusion. The Hα band line is the strongest chromospheric line in solar explosions and can directly reflect the characteristics of the source region of the explosion.

By analyzing Hα spectral data, we can obtain information about the lower atmosphere of the sun and deduce changes in physical quantities such as atmospheric temperature and velocity during solar eruptions, providing important support for solving scientific problems such as physical modeling of the entire process of energy transmission and release from the inside to the surface of solar eruptions.

"Xihe" uses two methods to observe the sun. One is white light continuous spectrum imaging to obtain an image of the entire solar disk; the other is spectral scanning imaging. By scanning the entire solar disk, more than 4,600 spectra can be obtained in 46 seconds, and each spectrum can restore an image of the solar disk.

The observation data of "Xihe" will be open to users around the world, which is an important contribution of my country to international solar physics and space physics research. As the first space solar exploration mission, "Xihe" also has important reference value for the implementation of similar missions in my country.

my country to launch grand solar exploration campaign

The sun has an 11-year activity cycle, and the new cycle is expected to reach its peak in 2025. Phenomena such as flares and coronal mass ejections will increase significantly, and a new round of solar exploration enthusiasm will also emerge, with various new types of detectors coming into place.

In addition to Xihe, my country will launch the Advanced Space-Based Solar Observatory satellite. The Advanced Space-Based Solar Observatory has a mass of about 1 ton and will operate in a 720-kilometer dawn-dusk sun-synchronous orbit, focusing on "one magnetic field and two storms" observations. Among them, "one magnetic field" refers to the solar magnetic field, and "two storms" refer to solar flares and coronal mass ejections. The observation data will be used to study the origin of the solar magnetic field, solar flares and coronal mass ejections and the relationship between the three.

In the future, my country will also carry out more ambitious solar space exploration activities. In 2021, my country approved the project "Design and Key Technologies of Solar All-round Stereoscopic Exploration System". This project is to study and design future solar space exploration plans, focusing on two major issues: "The generation and evolution of the solar magnetic field and its relationship with solar flares" and "Solar flares and propagation mechanisms and their impact on disastrous space weather", and to form relevant suggestions for subsequent exploration activities.

my country will gradually carry out solar exploration activities in accordance with the principle of starting from far to near and from single to three-dimensional, from Earth orbit to the Sun-Earth Lagrange point, and then to the Sun's proximity, to carry out all-round and comprehensive observations of the Sun. Solar exploration can promote the overall improvement of my country's space technology and application level, and provide strong support for science and technology, economic, social development and national security.