CHAPTER 1

INTRODUCTION

The Sun is the life-giving star that has been studied for centuries. In the last 500 years
or so, more detailed observations of the Sun’s structure – both internal and atmosphere–
have been studied. After discovering that the outer solar atmosphere was more than a
million degrees hot in the 1940s, it was realized that to get a comprehensive understanding
of the Sun, it is mandatory to go to space.
In the last several decades, several spacecraft have been flown by The National Aero-
nautics and Space Administration (NASA), the European Space Agency (ESA), and the
Japan Aerospace Exploration Agency (JAXA). Some of the most important missions are
Yohkoh (Acton et al. 1992), the Solar and Heliospheric Observatory (SoHO; Domingo
et al. 1995), the Transition Region and Coronal Explorer (TRACE; Handy et al. 1999),
the Solar Terrestrial Relations Observatory (STEREO; Socker et al. 2000), Hinode (Ko-
sugi et al. 2007), the Solar Dynamics Observatory (SDO; Pesnell et al. 2012), the Interface
Region Imaging Spectrometer (IRIS; De Pontieu et al. 2014) and the two most recently
launched missions namely the Parker Solar Probe (PSP; Fox et al. 2016) and the Sola
Orbiter (M¨uller et al. 2013, 2020). These, in addition to multiple ground-based observatories
vatories, have provided a wealth of information that has enhanced our understanding ofthe
working of our star Although observations and modeling have allowed a great leap toward
understanding. the Sun, numerous unsolved problems remain. These problems relate to the
coupling of the magnetized solar atmosphere, heating of the upper solar atmosphere, nature of
solar wind, and dynamics of the inner heliosphere. Moreover, how and why the high energy
radiation, particularly in the near ultraviolet, changes and affects the Earth’s atmosphere
is not fully comprehended.
One of the most challenging tasks related to coronal heating is measuring the coronal
magnetic field. Currently, there is no direct measurement available. Such measurement
vatories, have provided a wealth of information that has enhanced our understanding ofthe
working of our star.
will not only help understand the heating mechanism but also provide crucial information
related to solar eruptions and possibly forecasting the direction of interplanetary mag-
netic field (IMF) associated with interplanetary coronal mass ejections (ICMEs). The
other equally challenging task has been to determine the kinematic profiles of Coronal
Mass Ejections (CMEs) during their early phases of evolution. Currently, regular kine-
matic profiles of CMEs are available using the coronagraphic observations made using
the Large Angle and Spectrometric Coronagraph (C2 ad C3) on board SoHO. However,
these are only available beyond 2.5 R . However, observations have shown that 90% of
the acceleration in CMEs occur below 2 R (Bein et al. 2011). Therefore, with the exist-
ing facilities, it is impossible to obtain a good handle on the early phase of the kinematics
of CMEs. In turn, that becomes one of the primary sources of uncertainties in predicting
the arrival time of CMEs. It has also been shown that a significant amount of activity,
such as magnetic reconnections leading to the bifurcation of flux rope as well post CME
reconnection, may occur well below 2.5 R (Gilbert et al. 2001; Tripathi et al. 2006,
2007).
CMEs are often associated with flares, which are the intense eruption of electromag-
netic radiation. Flares are observed routinely in Soft X-rays using Geostationary Op-
erational Environmental Satellite Network. However, it has been shown that they have
counterparts across the electromagnetic spectrum (Benz 2017). While flares are specular
in X-ray and have been used for monitoring the space weather, it has been shown that
more than ∼70% of the flare energy is contained in other wavelengths such as visible
and near-ultraviolet (Neidig 1989; Kretzschmar 2011). While this may have substantial
implications on the physics of solar flares, it may have significant effects on the total and
spectral irradiance of the Sun (Kretzschmar et al. 2010).
It is also known that the total solar irradiance varies slowly on decadal and longer
time scales. The variation during the recent solar magnetic cycle has been about 0.1%
and that up to 60% of the total irradiance variations are produced at wavelength below
400 nm (Krivova et al. 2006). Of these, the wavelength band of 200–400 nm is of partic-
ular importance due to its direct effects on the chemistry of Ozone and Oxygen in the
stratosphere of Earth. It thereby plays a crucial role in Sun-climate relations.
Using the observations taken by SOlar Stellar Irradiance Comparison Experiment(
SOLSTICE) and Spectral Irradiance Monitor (SIM), both on board SOlar Radiation &
Climate Experiment (SORCE), Haigh et al. (2010) showed that there is a considerable
discrepancy between the solar spectral irradiance observed and modeled by Lean (2000).
For the wavelength regions below 400 nm, the models under predicts the irradiance, while
for the wavelengths larger than 400 nm, the irradiance is over-predicted. Such discrepancy
may have a substantial impact on modeling the Sun-climate relations. Note that the
observations are recorded using the Sun-as-a-start spectrum. These results suggest that
some missing physics is crucial for accurately modeling the sun-climate relations.
The Aditya-L1 mission is the flagship mission of the Indian Space Research Organiza-
tion (ISRO). It is ISRO’s first solar observatory in space. The satellite will be launched in
2023 by PSLV-XL and inserted in a halo orbit around the First Lagrangian Point (L1),
which is about 1.5 million kilometers from the Earth on the Sun-Earth line. The primary
science goals of Aditya-L1 mission are:
(PMOD/WRC)
To address the above-mentioned questions, the spacecraft will carry seven payloads
performing remote sensing from Hard X-ray to infrared and in situ measurements in a
broad energy range, including interplanetary magnetic field measurements. The seven
payloads are:
In the rest of the paper, we shall discuss and describe the uniqueness and salient
features of different payloads and the science questions they aim to address.
Aditya-L1 is an Indian space mission designed to study the Sun. The name "Aditya" is derived
from the Sanskrit word for the Sun. The primary objective of the Aditya-L1 mission is to observe
the outermost layer of the Sun's atmosphere, known as the corona, and understand various
processes such as solar winds and magnetic activities.
Key goals of the Aditya-L1 mission may include:

Coronal Dynamics: Studying the dynamics of the solar corona to gain insights into its behavior
and understand the mechanisms driving phenomena like solar flares and coronal mass
ejections.

Solar Wind: Investigating the properties and acceleration mechanisms of the solar wind, which
is a stream of charged particles emanating from the Sun and influencing the space environment
around it.

Magnetic Fields: Examining the magnetic fields on the solar surface and their impact on solar
activities.

Space Weather: Understanding the Sun's influence on space weather and its potential impact
on Earth, including effects on communication systems, satellites, and power grids.

The Aditya-L1 mission is part of India's space exploration initiatives, and it is expected to
contribute valuable data to the global scientific community's understanding of the Sun and its
influence on our solar system.

For the latest and most accurate information about the Aditya L1 mission, I recommend
checking with official sources such as the Indian Space Research Organisation (ISRO) or other
reputable space-related websites for updates beyond my last knowledge update in January
2022.
Aditya L1 is the first space based observatory class Indian solar mission to study the Sun. The
spacecraft is planned to be placed in a halo orbit around the Lagrangian point 1 (L1) of the Sun-
Earth system, which is about 1.5 million km from the Earth. A satellite placed in the halo orbit
around the L1 point has the major advantage of continuously viewing the Sun without any
occultation/ eclipse. This will provide a greater advantage of observing the solar activities
continuously. The spacecraft carries seven payloads to observe the photosphere,
chromosphere, and the outermost layers of the Sun (the corona) using electromagnetic and
particle detectors. Using the special vantage point of L1, four payloads ABOUT ADITYA-L1
directly view the Sun and the remaining three payloads carry out in-situ studies of particles and
fields at the Lagrange point L1. The suit of Aditya L1 payloads are expected to provide most
crucial information to understand the problems of coronal heating, Coronal Mass Ejection, pre-
flare and flare activities, and their characteristics, dynamics of space weather, study of the
propagation of particles, and fields in the interplanetary medium etc.
 CHAPTER 2
WHY STUDY SUN

The sun is the nearest star and therefore can be studied in much more detail as compared to
other stars. By studying the sun we can learn much more about stars in our Milky Way as well
as about stars in various other galaxies. The sun is a very dynamic star that extends much
beyond what we see. It shows several eruptive phenomena and releases immense amount of
energy in the solar system. If such explosive solar phenomena is directed towards the earth, it
could cause various types of disturbances in the near earth space environment. WHY STUDY
SUN? Various spacecraft and communication systems are prone to such disturbances and
therefore an early warning of such events is important for taking corrective measures
beforehand. In addition to these, if an astronaut is directly exposed to such explosive
phenomena, he/she would be in danger. The various thermal and magnetic phenomena on the
sun are of extreme nature. Thus, the sun also provides a good natural laboratory to understand
those phenomena which cannot be directly studied in the lab.
The sun constantly influences the Earth with radiation, heat and constant flow of particles and
magnetic fields. The constant flow of particles from the sun is known as solar wind and are
mostly composed of high energy protons. The solar wind fills nearly all the space of the known
solar system. Along with the solar wind, the solar magnetic field also fill the solar system. The
solar wind along with other explosive/ eruptive solar events like Coronal Mass Ejection (CME)
affects the nature of space. During such events, the nature of magnetic field and charge particle
environment near to the planet change. In case of the Earth, the interaction of Earth magnetic
field with the field carried by CME can trigger a magnetic events can affect the functioning of
space assets. THE SPACE WEATHER Space weather refers to disturbance near the Earth. Such
changing environmental conditions in space in the vicinity of Earth and other planets. We use
more and more technology in space, as understanding space weather is very important. Also,
understanding near Earth space weather sheds light on the behaviour of space weather of
other planets. The Sun's gravity holds the solar system together, keeping everything – from the
biggest planets to the smallest particles of debris – in its orbit. The connection and interactions
between the Sun and Earth drive the seasons, ocean currents, weather, climate, radiation belts
and auroras. Though it is special to us, there are billions of stars like our Sun scattered across
the Milky Way galaxy.
 CHAPTER 3
MAJOR SCIENCE OBJECTIVES

The Aditya-L1 mission is a pioneering endeavor by the Indian Space Research Organisation
(ISRO) with a primary focus on advancing our understanding of the Sun. The mission's scientific
objectives are diverse and comprehensive, encompassing the observation and analysis of
various solar phenomena. Here are the major science objectives of the Aditya-L1 mission
1. Introduction:
The Aditya-L1 mission represents a milestone in solar and heliophysics, aiming to unravel the
mysteries of the Sun. This extended exploration delves into the major science objectives across
various domains, highlighting the mission's significance in advancing our understanding of the
dynamic solar system.

2. Coronal Dynamics and Solar Atmosphere:

The Aditya-L1 mission aims to study the outermost layer of the Sun's atmosphere, known as the
corona. The dynamics of the solar corona play a crucial role in shaping space weather
phenomena, including solar flares and coronal mass ejections. By closely examining the corona,
scientists hope to uncover the underlying processes that govern its behavior, shedding light on
the mechanisms responsible for solar activities and their potential impacts on the solar system.

2.1 Background:
The solar corona, with its exceedingly high temperatures and dynamic behavior, remains a
subject of intense scientific interest. Aditya-L1 endeavors to scrutinize the coronal dynamics,
seeking to unlock the mechanisms governing solar flares, prominences, and other eruptive
events.

2.2 Objectives:
Temperature and Density Profiling: Aditya-L1 aims to map the temperature and density
variations within the solar atmosphere, providing critical insights into the physical processes
shaping the corona.

Eruptive Phenomena Studies: Through high-resolution imaging and spectral analysis, the
mission intends to capture detailed observations of solar flares and coronal mass ejections,
unraveling their initiation and propagation mechanisms.
Long-Term Behavior Analysis: By monitoring the long-term behavior of the solar corona, Aditya-
L1 will contribute to understanding the cyclic nature of solar activity and its implications for
space weather.

3. Solar Wind Characteristics:

The solar wind, a continuous stream of charged particles flowing from the Sun, shapes the
space environment throughout the solar system. Aditya-L1 seeks to investigate the
characteristics of the solar wind, including its speed, composition, and variability. By analyzing
the solar wind's properties, the mission aims to unravel the intricacies of its acceleration
mechanisms and the influence of solar magnetic fields. This research is crucial for
comprehending the Sun's impact on interplanetary space and understanding how solar wind
disturbances can affect Earth's magnetosphere and contribute to space weather events.

3.1 Background:
The solar wind, a continuous stream of charged particles emanating from the Sun, plays a
pivotal role in shaping the interplanetary medium. Aditya-L1's focus on solar wind
characteristics aims to deepen our understanding of its properties and dynamics.

3.2 Objectives:
Speed and Composition Analysis: Aditya-L1 instruments will measure the speed and
composition of the solar wind, shedding light on its variability and contributing factors.

Solar Magnetic Fields and Wind Acceleration: By examining the role of solar magnetic fields in
wind acceleration, the mission aims to uncover the mechanisms driving the solar wind.

Interplanetary Influence: The mission's observations will extend to the outer reaches of the
heliosphere, providing insights into how solar wind interacts with the interstellar medium.

4. Magnetic Fields on the Solar Surface:

Magnetic fields are fundamental to solar activities, influencing phenomena such as sunspots,
solar flares, and CMEs. Aditya-L1 is equipped with instruments designed to map and analyze the
magnetic fields on the solar surface with unprecedented precision. The mission's observations
will provide insights into the structure, strength, and evolution of these magnetic fields,
advancing our understanding of the complex interplay between magnetic forces and solar
dynamics. This information is crucial for predicting and comprehending solar eruptions and
their potential impacts on space weather.

4.1 Background:
Magnetic fields are fundamental to solar activities, influencing sunspots, flares, and other
phenomena. Aditya-L1 carries instruments designed to provide unprecedented insights into the
structure and dynamics of solar magnetic fields.

4.2 Objectives:
Magnetic Field Mapping: Aditya-L1 will generate high-resolution maps of solar magnetic fields,
enabling a detailed examination of their topology and evolution.

Sunspot and Active Region Studies: By focusing on regions of magnetic activity, the mission
aims to decipher the processes leading to the formation and dissipation of sunspots and their
impact on solar dynamics.

Connection to Solar Eruptions: The mission seeks to establish connections between magnetic
field configurations and solar eruptions, enhancing our ability to predict and understand these
events.

5. Space Weather and Earth's Magnetosphere:

Aditya-L1 contributes significantly to the field of space weather research. The mission aims to
investigate the Sun's influence on space weather phenomena, including geomagnetic storms
and their impact on Earth's magnetosphere. By understanding the mechanisms that drive space
weather events, the mission facilitates the development of predictive models, enabling more
accurate forecasts of solar-induced disturbances and their potential effects on communication
systems, navigation technology, and power grids.

5.1 Background:
Understanding the Sun's influence on space weather is crucial for safeguarding technological
infrastructure on Earth. Aditya-L1 contributes significantly to this field, exploring the
connections between solar activity and geomagnetic storms.

5.2 Objectives:
Geomagnetic Storm Prediction: Aditya-L1 aims to develop models for predicting geomagnetic
storms by analyzing solar activities and their impact on Earth's magnetosphere.
Communication and Navigation Impact Studies: The mission seeks to quantify the effects of
space weather on communication systems, navigation technology, and power grids, providing
valuable data for mitigating potential disruptions.

Solar-Earth Connection: By studying the intricate links between solar phenomena and
terrestrial effects, Aditya-L1 enhances our understanding of the broader solar-terrestrial
relationship.

6. International Collaboration and Data Sharing:

Beyond its specific scientific goals, the Aditya-L1 mission embodies India's commitment to
international collaboration in space research. By fostering partnerships with the global scientific
community, the mission seeks to share data, expertise, and insights. Collaborative efforts
enhance the mission's scientific impact, providing a broader context for interpreting results and
advancing our collective knowledge of the Sun and heliophysics.

In conclusion, the Aditya-L1 mission stands as a testament to India's dedication to advancing

solar and heliophysics. Through its exploration of the solar corona, analysis of solar wind
characteristics, investigation of magnetic fields, and contributions to space weather research,
Aditya-L1 is poised to significantly enhance our understanding of the Sun and its dynamic
influence on the solar system. As the mission unfolds, it holds the promise of delivering
groundbreaking insights that will shape the future of solar and space research.

6.1 Background:
Scientific progress often thrives on collaboration. Aditya-L1 embodies India's commitment to
fostering international partnerships in space research, recognizing the collective nature of solar
and heliophysics.

6.2 Objectives:
Data Sharing and Accessibility: The mission aims to establish robust mechanisms for sharing
data with the global scientific community, promoting transparency and collaboration.

Joint Research Initiatives: Aditya-L1 seeks opportunities for joint research initiatives,
encouraging scientists from different regions to collaborate on data analysis, modeling, and
interpretation.
Capacity Building: Through collaborative efforts, the mission aims to contribute to capacity
building in solar and heliophysics, fostering the development of expertise and infrastructure
worldwide.

7. Conclusion:
In conclusion, the Aditya-L1 mission's major science objectives span a comprehensive range of
solar and heliophysics domains. From probing the mysteries of the solar corona to unraveling
the dynamics of solar wind and magnetic fields, the mission promises to deliver groundbreaking
insights with implications for our understanding of the Sun and its influence on the solar
system. Furthermore, its commitment to international collaboration underscores the
collaborative spirit essential for advancing the frontiers of space research. As Aditya-L1 embarks
on its mission, it holds the promise of reshaping our understanding of the Sun and paving the
way for future advancements in solar and heliophysics.