Fresh from Moon mission’s success, India aims for the Sun

Fresh from the success of India’s Moon mission, the Indian Space Research Organisation (Isro) successfully launched the nation’s first Sun mission, Aditya L1, on Saturday.

The spacecraft on board the PSLV-C57 rocket blasted off from the Satish Dhawan Space Centre in Sriharikota, Andhra Pradesh, at 11:50 am.

The launch comes just 10 days after the success of Chandrayaan-3, in which Isro scientists had soft-landed a spacecraft on the lunar surface. 

As part of the $50 million, or ₹400 crore, solar mission, India will set up a space observatory on the Lagrange 1, or L1, point located about 1.5 million km from Earth, primarily to study the photosphere, the chromosphere and the corona. 

The photosphere is the Sun’s visible surface, while the chromosphere is a layer of gas above it, and the corona is the Sun’s outer atmosphere, which extends millions of kilometers into space.

The 1,500 kg satellite, which is strapped with seven payloads, is expected to take about 109 days to reach its designated orbit, or the L1 point.

The L1 point offers the spacecraft a stable position between the Earth and the Sun to orbit, and allows for the continuous observation of the Sun without any interruptions.

Explaining the significance of the L1 point, Durgesh Tripathi, who co-headed the team from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune that developed a solar ultraviolet imaging telescope (SUIT), one of the seven payloads, said: “In the Sun-Earth gravitational system, there are five Lagrange points where the gravitational forces between the two bodies balance each other. L1 is positioned between the Sun and Earth, while L2 is on Earth’s far side. These are sites where telescopes like the James Webb Space Telescope are placed. The other Lagrange points, L3 behind the Sun and L4 and L5 at angular positions, have yet to be explored.” 

The Lagrange points are named in honor of Italian-French mathematician Joseph-Louis Lagrange.

Highlighting the advantages of parking the spacecraft at L1, Tripathi said, “As the Earth orbits the Sun, the L1 point, aligned with the Sun-Earth line, also moves. A satellite at this location essentially acts like a planet circling the Sun, allowing researchers to continuously observe and study the Sun without any break.”

Elaborating further, Tripathi said, “A satellite orbiting Earth would experience periods of darkness, losing sight of the Sun. In contrast, a satellite at L1 enjoys continuous solar observation and maintains steady communication with Earth.” 

He emphasized that constant monitoring is crucial. “Orbiting Earth means missing out on solar events during night-time. At L1, the satellite has a constant view of the Sun, allowing us to capture and relay any solar activity back to Earth for ongoing research,” he said.

Elaborating on the SUIT project, Tripathi said the telescope aims to explore a puzzling aspect of the Sun’s atmosphere. 

“Think of the Sun as a fireball. As you move away from any fire, you’d expect the temperature to drop. But in the Sun’s atmosphere, it actually rises to a million degrees from a surface temperature of around 6,000 degrees. This defies conventional physics, and we want to understand how this happens,” he said.

Tripathi said that while many studies have been conducted, a specific wavelength range of 2,000 to 4,000 angstroms, which covers the Sun’s lower and middle atmosphere, remains underexplored.

“When planning a new observing facility, it’s crucial to address gaps in existing knowledge. We chose to focus on this wavelength range because it’s critical for understanding not only temperature variations in the Sun’s atmosphere but also the impact of those variations on Earth’s climate,” he said. 

“Radiation in this range affects Earth’s ozone layer and even our weather. Understanding the radiation emitted in this wavelength is essential for comprehending its various components and impacts, which is why we’ve decided to study this particular range,” he added.

The other payloads onboard the spacecraft include the Visible Emission Line Coronagraph (VELC), the Solar Low Energy X-ray Spectrometer (SoLEXS), the High Energy L1 Orbiting X-ray Spectrometer (HEL1OS), the Aditya Solar wind Particle Experiment (ASPEX), the Plasma Analyser Package For Aditya (PAPA), and the Advanced Tri-axial High Resolution Digital Magnetometers.

The VELC will take pictures and measurements of the Sun’s outer halo, also known as the corona, to help understand its properties and high temperatures. Arvind Paranjpye, director of the planetarium at Nehru Centre in Mumbai, said the device will allow scientists to study why the temperature of the Sun’s corona is much higher than its surface temperature.

“One of the most intriguing questions that we have in solar physics is why the temperature of the corona is so much higher than that of the surface of the sun. Many theories have been proposed to explain this phenomenon. To test those theories, we need observational data,” Paranjpye said. 

“We can observe the corona of the sun during a solar eclipse. However, one can’t be sure that this would give us the complete picture. One needs to observe it continuously,” he added. 

The whole mission is slated to run for five years, with the VELC expected to send about 1,440 images of the Sun each day to the Indian Space Data Centre for in-depth scientific analysis.

Among the remaining payloads, while SoLEXS will study the Sun’s low-energy X-rays, HEL1OS will focus on its high-energy X-rays; ASPEX will measure particles in the solar wind, while PAPA will study electrically charged particles from the Sun, and the magnetometers will measure the Sun’s magnetic fields.

Yashwant Gupta, director at the National Centre for Radio Astrophysics in Pune, said, “The mission is very important for astrophysics as well as for space science and technology, especially the newer trends in interplanetary physics and astronomy. The mission will go a long way in deepening our understanding of astrophysics and showcasing the capability of Indian science.”