ADITYA L1: THE NEW KID ON THE BLOCK

August 23 marked a historic day for India as its homemade moon lander program worked flawlessly and soft landed on the southern region of the Moon. But just one week after such a historic milestone, ISRO is set to make one more with the launch of the Aditya L1 satellite. For the first time, India is launching an observatory-class satellite to deep space.

But, Why study the sun?

To the visible eye, the Sun is just a glowing ball of fire at the centre of our solar system, providing us with light and heat but when we take a closer look, we see all sorts of wonderful things happening.

Figure 1: Structure of the Sun. (Credit: NASA/Goddard)

The sun is composed of distinct layers, both in its interior and atmosphere. Starting from the inside, the solar interior consists of:

1. The Core: This central region experiences nuclear reactions that convert hydrogen into helium. These reactions generate energy, which is eventually emitted as visible light.

2. The Radiative Zone: Extending outward from the core's outer edge to the base of the convection zone, this region transports energy primarily through radiation.

3. The Convection Zone: This outermost layer of the solar interior spans from a depth of approximately 200,000 km to the visible surface. Its surface displays motion in the form of granules and supergranules.

The solar atmosphere comprises:

1. The Photosphere: The sun's visible surface emits light.

2. The Chromosphere: Found just above the photosphere, this irregular layer exhibits a temperature increase from 6000°C to around 20,000°C.

3. The Transition Region: A thin and uneven layer that separates the much cooler chromosphere from the hot corona.

4. The Corona: The outermost atmosphere of the sun.

Beyond the corona lies the solar wind, which is the outward flow of gas from the corona. The sun's magnetic fields rise through the convection zone and manifest as phenomena like sunspots, flares, prominences, and coronal mass ejections, collectively known as solar activity.

Video: Sun sunspots close-up time-lapse

Video: Large solar flare

While these are beautiful, the destructive power of some of these flares can be in the range of millions of nuclear explosions. These massive flares of energy create blackouts disturb our communication satellites and destabilize their orbits. We have been able to predict such events more and more accurately over the past couple of years.

The sun exerts a continuous influence on Earth through radiation, heat, and an unceasing stream of particles and magnetic fields. This unending stream of particles originating from the sun is called solar wind, primarily comprised of high-energy protons. Solar wind permeates nearly all the regions within our known solar system. Concurrently, the expansive solar magnetic field also extends throughout the solar system.

The solar wind, accompanied by occurrences like Coronal Mass Ejections (CMEs), has a substantial impact on the space environment. These explosive solar events can bring about alterations in the magnetic field and the presence of charged particles in the vicinity of celestial bodies. For Earth, the interaction between our planet's magnetic field and the magnetic field carried by a CME can trigger magnetic disruptions in Earth's vicinity. Such events possess the potential to disrupt the normal operation of space assets.

Aditya-L1 is not only a scientific endeavour but also a vital component of space weather forecasting, as solar activity can significantly impact Earth's communication systems, satellites, and power grids. By scrutinizing the Sun from a vantage point about 1.5 million kilometres away from Earth, Aditya-L1 promises to expand our solar knowledge and enhance our ability to predict and manage the effects of space weather on our planet.

What is L1?

Lagrange points are positions in space where objects sent there tend to stay put. At Lagrange points, the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them. These points in space can be used by spacecraft to reduce fuel consumption needed to remain in position. There are five special points where a small mass can orbit in a constant pattern with two larger masses. The Lagrange Points are positions where the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them.

Of the five Lagrange points, three are unstable and two are stable. The unstable Lagrange points - labelled L1, L2 and L3 - lie along the line connecting the two large masses. The stable Lagrange points - labelled L4 and L5 - form the apex of two equilateral triangles that have large masses at their vertices. L4 leads the orbit of the earth and L5 follows.

Figure 2: Illustration of Lagrange points of the Sun-Earth system. ( Credit: ISRO).

The L1 Lagrange point is roughly 1.5 million km from Earth. This is the furthest ever a satellite made and launched from India will fly.

Payloads onboard Aditya L1

Aditya L1 will make a noticeable difference in the quality of observation, prediction and understanding of space weather. The major focus of the mission will be to understand the initiation of CME and flares. This coupled with the Aditya Solar wind Particle Experiment (ASPEX) and Plasma Analyser Package for Aditya (PAPA) payloads which study the solar wind and energetic ions, as well as their energy distribution is going to make some major lead in understanding the solar dynamics.

Aditya L1 is also equipped with a Visible Emission Line Coronagraph (VELC), which is used to study the solar corona and the dynamics of Coronal Mass Ejections. The Solar Ultra-Violet Imaging Telescope (SUIT) payload scans the solar photosphere and chromosphere in near ultraviolet (UV) and detects fluctuations in solar irradiance in near UV. The Solar Low Energy X-ray Spectrometer (SoLEXS) and the High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) study the Sun's X-ray flares across a wide X-ray energy range. At the L1 point, the Magnetometer payload can measure interplanetary magnetic fields.

Figure 3: Aditya-L1 payload locations on the spacecraft. R, P, and Y represent the spacecraft's Raw, Pitch, and Roll axes. SWIS and STEPS comprise the ASPEX payload. (Credit: ISRO)

Other Solar Observatories in Space.

Space-based solar observatories have revolutionized our understanding of the Sun, allowing us to study its various layers and phenomena in unprecedented detail. Here's a brief overview of some notable solar observatories and missions from the USA, Europe, Japan, and China:

1. NASA's Solar Dynamics Observatory (SDO): Launched in 2010, SDO is a flagship mission dedicated to observing the Sun. It captures high-definition images of the Sun's surface, measures the Sun's magnetic field, and records extreme ultraviolet emissions. SDO has greatly contributed to our understanding of solar activity and its impact on Earth.

2. ESA/NASA's Solar and Heliospheric Observatory (SOHO): Launched in 1995, SOHO is a joint mission by the European Space Agency (ESA) and NASA. It continuously observes the Sun, monitoring solar wind, coronal mass ejections (CMEs), and sunspots. SOHO has provided crucial data for space weather prediction.

3. ESA's Solar Orbiter: Launched in 2020, the Solar Orbiter is an ESA mission designed to study the Sun's polar regions. It will investigate the solar wind, magnetic fields, and the Sun's heliosphere. Solar Orbiter aims to provide a comprehensive view of the Sun's activity.

4. JAXA's Hinode (Solar-B): Launched in 2006 by the Japan Aerospace Exploration Agency (JAXA), Hinode observes the Sun's magnetic fields and their impact on solar activity. It provides insights into the Sun's outer atmosphere and how it influences space weather.

5. China's Advanced Space-based Solar Observatory (ASO-S): It was launched using the Long March-2D carrier rocket from the Jiuquan Satellite Launch Center in northwestern China in October 2022. ASO-S is China's first full-scale instrument dedicated to studying Earth's closest star. As per Zhu Cheng, the chief engineer of the ASO-S platform system it is also the world's first solar telescope in space that can simultaneously monitor solar flares and coronal mass ejections.

6. ESA's Solar Wind Analyser (SWA) on the BepiColombo Mission: Although primarily focused on Mercury, ESA's BepiColombo mission carries the SWA instrument to study the solar wind near Mercury. It provides insights into how the Sun's influence extends to the innermost planet.

7. Parker Solar Probe (USA): Launched by NASA in 2018, the Parker Solar Probe is designed to fly closer to the Sun than any previous spacecraft. It samples particles and magnetic fields in the solar corona, aiming to understand the Sun's outermost layer better. PSP follows an elliptical orbit that gradually takes it closer to the Sun. It approaches within approximately 4 million miles (6.5 million kilometres) of the Sun's surface, making it the closest human-made object to the Sun.

In summary, Aditya-L1 distinguishes itself by focusing on the solar corona, being stationed at L1, serving as a space weather observatory, collaborating internationally, and possessing tailored instrumentation. It contributes to our global understanding of the Sun and its impact on space weather while furthering India's space exploration heritage.

The launch of PSLV-C57 from Satish Dhawan Space Centre, Sriharikota scheduled for September 02, 2023, at 11:50 AM. The launch is going to be broadcast live on ISRO's YouTube Channel.

Link to Broadcast