What is the telescope designed to search for earth- size planets in the nearby region of our galaxy, termed as?

1. Basics of Space-based Astronomy (basic)

To understand why we send telescopes into space, we must first understand how we see the universe from Earth. At its simplest, a telescope acts as a 'light bucket,' collecting photons to reveal distant objects. Most modern professional telescopes are reflecting telescopes, which use large concave mirrors to gather and focus light Science, Class VIII NCERT, Light: Mirrors and Lenses, p.156. While these instruments have allowed us to discover distant planets like Uranus and Neptune through mathematical precision and powerful optics Certificate Physical and Human Geography, GC Leong, The Earth's Crust, p.3, ground-based observation faces a massive hurdle: our own atmosphere.

The Earth's atmosphere acts like a thick, turbulent blanket. It causes Atmospheric Refraction, where light from a star bends as it passes through different layers of air, making the star appear in a slightly different position and causing it to 'twinkle' Science, Class X NCERT, The Human Eye and the Colourful World, p.168. For astronomers, this twinkling is actually a blur that limits the clarity of images. Furthermore, the atmosphere is 'opaque' to many types of radiation; it blocks most Ultraviolet (UV) light, X-rays, and Gamma rays. By placing observatories in space-based orbits, we bypass this interference entirely, gaining a crystal-clear view of the cosmos across the entire electromagnetic spectrum.

Space-based astronomy isn't just about visible light. While traditional optical telescopes see stars and galaxies, specialized instruments like radio telescopes can detect a faint background glow known as the Cosmic Microwave Background (CMB). This is 'relic radiation'—the oldest light in the universe left over from the Big Bang Physical Geography by PMF IAS, The Universe, p.4. Studying these different wavelengths from space allows us to map the history of the universe and search for exoplanets (planets outside our solar system) with a precision that ground-based tools simply cannot match.

Feature	Ground-based Astronomy	Space-based Astronomy
Clarity	Limited by atmospheric blurring (twinkling).	Perfect clarity; no atmospheric distortion.
Light Range	Mostly visible light and some radio waves.	Full spectrum (X-ray, UV, Infrared, etc.).
Cost/Maintenance	Easier to build, upgrade, and repair.	Extremely expensive and difficult to service.

Sources: Science, Class VIII NCERT (Revised ed 2025), Light: Mirrors and Lenses, p.156; Certificate Physical and Human Geography, GC Leong, The Earth's Crust, p.3; Science, Class X NCERT (2025 ed.), The Human Eye and the Colourful World, p.168; Physical Geography by PMF IAS, The Universe, The Big Bang Theory, Galaxies & Stellar Evolution, p.4

2. Orbits for Astronomical Observatories (intermediate)

When we launch a space observatory, choosing its "parking spot" is just as important as the mirrors it carries. Unlike Earth-based telescopes that deal with atmospheric blurring, space telescopes must navigate the thermal and gravitational environment of the solar system. Most orbits follow an elliptical path, a concept fundamental to understanding how satellites move. Just as the Moon has a perigee (closest point to Earth) and an apogee (farthest point), any satellite in Earth orbit experiences these variations in distance Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.259.

There are three primary types of orbits used for astronomical missions, each serving a distinct purpose:

• Low Earth Orbit (LEO): At an altitude of about 500–600 km, this is where the Hubble Space Telescope resides. It is close enough for astronaut servicing but suffers from "occultation," where the Earth blocks the telescope's view for nearly half of every 90-minute orbit.
• Lagrange Points (specifically L2): For modern infrared observatories like the James Webb Space Telescope, LEO is too "noisy" and warm. Instead, they sit at the L2 point, a gravitational sweet spot 1.5 million km away. Here, the telescope can keep the Sun, Earth, and Moon all on one side, allowing its sunshield to protect the sensitive optics from heat.
• Heliocentric (Earth-trailing) Orbit: Some missions, like Kepler, don't orbit Earth at all. They orbit the Sun, slowly drifting behind Earth. This provides an incredibly stable environment, free from the magnetic interference and thermal shifts caused by orbiting a large planet like Earth.

A critical factor in mission planning is orbital velocity. According to Kepler’s second law of planetary motion, an object moves slowest when it is at its farthest point from the body it orbits (aphelion or apogee) and fastest when closest Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.256. This principle is why Earth’s summer in the Northern Hemisphere is slightly longer than winter—the Earth is further from the Sun and thus moving slower in its orbit during that period. For observatories, maintaining a stable, predictable velocity is key to capturing the long-exposure images needed to see distant galaxies.

Orbit Type	Primary Advantage	Primary Disadvantage
LEO	Low launch cost; accessible for repairs.	Earth blocks the view frequently.
Lagrange (L2)	Highly stable; allows for deep-space cooling.	Extremely far; currently impossible to repair.
Heliocentric	No interference from Earth's heat/light.	Communication gets harder as it drifts further away.

Sources: Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.259; Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.256

3. India's Contribution: ASTROSAT and XPoSat (exam-level)

While India’s space program initially focused on socio-economic benefits like communication and remote sensing, it has evolved to include sophisticated Space Astronomy. This field involves placing telescopes outside the Earth's atmosphere to observe celestial objects without the distortion or absorption caused by air. India's hallmark achievements in this area are AstroSat and the more recent XPoSat.

AstroSat, launched in September 2015, was India’s first dedicated multi-wavelength space observatory Science, Class VIII NCERT, Keeping Time with the Skies, p.185. Unlike most space telescopes that focus on a single band of the electromagnetic spectrum, AstroSat is unique because it can observe the universe in Ultraviolet (UV), Optical, and X-ray wavelengths simultaneously. This "multi-eye" approach allows scientists to study complex phenomena, such as the birth of stars and the behavior of black hole systems, in a comprehensive manner.

Building on that success, ISRO launched XPoSat (X-ray Polarimeter Satellite) in January 2024. This is a specialized mission designed to study the polarization of X-rays from cosmic sources. When light or X-rays are emitted from extreme environments—like the vicinity of a neutron star or a black hole—the light waves often vibrate in a specific direction. By measuring this polarization, XPoSat provides a deep look into the intense magnetic fields and geometry of these distant, violent objects. Remarkably, XPoSat makes India only the second country in the world (after the USA with NASA's IXPE) to have a dedicated mission for X-ray polarimetry.

Feature	AstroSat (2015)	XPoSat (2024)
Primary Objective	Multi-wavelength observation (broad survey)	X-ray Polarimetry (specialized physics)
Key Capability	Simultaneous UV, Optical, and X-ray data	Measuring the orientation/angle of X-ray waves
Global Status	First Indian dedicated astronomy mission	World's second dedicated polarimetry mission

Sources: Science, Class VIII NCERT (Revised ed 2025), Keeping Time with the Skies, p.185

4. Exoplanets and the Goldilocks Zone (intermediate)

When we look at the night sky, we are looking at billions of stars, many of which are parent suns to their own planetary systems. An exoplanet (extra-solar planet) is simply any planet that orbits a star outside our own solar system. Detecting these distant worlds is challenging because stars are incredibly bright compared to the tiny planets orbiting them. However, scientists use the 'wobble' method—observing tiny gravitational tugs that a planet exerts on its host star—to confirm their existence Science-Class VII . NCERT, Earth, Moon, and the Sun, p.186.

The most critical concept in the search for life is the Habitable Zone, colloquially known as the Goldilocks Zone. Just like the porridge in the fairy tale, this region is 'just right'—it is the range of orbital distances from a star where the temperature allows liquid water to exist on a planet's surface. If a planet is too close (like Venus), water evaporates; if it is too far (like Mars), water freezes. As seen with our own Earth, being in this zone is essential for the development and sustenance of life Science, Class VIII . NCERT, Our Home: Earth, a Unique Life Sustaining Planet, p.215.

To find these worlds, NASA launched the Kepler Space Telescope in 2009. Unlike the Hubble Telescope, which is a general-purpose observatory, Kepler was a dedicated 'planet hunter.' Its specific mission was to survey a portion of the Milky Way to identify Earth-sized exoplanets orbiting Sun-like stars. Over its nine-year mission, Kepler revolutionized astronomy by discovering more than 2,600 confirmed exoplanets. Perhaps its most profound finding was statistical: there are likely more planets in our galaxy than there are stars.

Feature	Goldilocks Zone Condition	Significance
Temperature	Neither too hot nor too cold	Prevents atmospheric loss or total freezing.
Water State	Liquid form (H₂O)	Essential solvent for biological chemistry.
Orbital Path	Nearly circular	Ensures stable temperatures year-round Science, Class VIII . NCERT, Our Home: Earth, a Unique Life Sustaining Planet, p.225.

Sources: Science-Class VII . NCERT, Earth, Moon, and the Sun, p.186; Science, Class VIII . NCERT, Our Home: Earth, a Unique Life Sustaining Planet, p.215; Science, Class VIII . NCERT, Our Home: Earth, a Unique Life Sustaining Planet, p.225

5. Major International Observatories (Hubble vs JWST) (intermediate)

To understand the leap from the Hubble Space Telescope (HST) to the James Webb Space Telescope (JWST), we must first look at the physics of how we see the stars. Most modern space observatories are reflecting telescopes, which use large curved mirrors to gather light. Specifically, they utilize a large concave mirror as the primary collector Science, Class VIII. NCERT (Revised ed 2025), Light: Mirrors and Lenses, p.156. While Hubble revolutionized our view of the cosmos using mostly visible and ultraviolet light, the JWST was designed to see what Hubble cannot: the very first stars and galaxies formed after the Big Bang.

The need for JWST arises from a phenomenon called redshift. As discovered by Edwin Hubble, the universe is constantly expanding, causing galaxies to drift apart Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), The Universe, The Big Bang Theory, Galaxies & Stellar Evolution, p.3. This expansion stretches the light waves traveling through space. Light that started as visible or ultraviolet from the earliest stars has been stretched so much over billions of years that it now reaches us as Infrared radiation. Because Hubble is optimized for visible light, it hits a "brick wall" when looking back in time; JWST, an infrared specialist, can pierce through cosmic dust to see these ancient, redshifted signals.

Feature	Hubble (HST)	James Webb (JWST)
Primary Light Type	Visible and Ultraviolet	Near and Mid-Infrared
Mirror Diameter	2.4 meters (Single mirror)	6.5 meters (18 hexagonal segments)
Orbit Location	Low Earth Orbit (~570 km)	Lagrange Point 2 (1.5 million km away)
Scientific Goal	Studying the "Adolescent" Universe	Studying the "Infant" Universe & First Stars

Another critical difference lies in their location. Hubble orbits the Earth, which allowed it to be serviced by Space Shuttles. However, because infrared telescopes detect heat, JWST must stay extremely cold to avoid being "blinded" by its own thermal signature or the heat of the Earth and Sun. This is why JWST is stationed at the Second Lagrange Point (L2), where it stays in line with the Earth as it orbits the Sun, shielded by a massive sunshield.

Sources: Science, Class VIII. NCERT (Revised ed 2025), Light: Mirrors and Lenses, p.156; Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), The Universe, The Big Bang Theory, Galaxies & Stellar Evolution, p.3-4

6. The Kepler Mission: The Planet Hunter (exam-level)

The Kepler Space Telescope, launched by NASA in 2009, stands as one of the most successful missions in the history of space astronomy. Often referred to as the 'Planet Hunter,' its primary scientific objective was to conduct a statistical survey of our galaxy to determine the frequency of Earth-sized planets orbiting Sun-like stars. While older missions like the Voyagers were designed to physically travel past planets in our own solar system Physical Geography by PMF IAS, The Solar System, p.39, Kepler was a deep-space observatory that remained in an Earth-trailing orbit, staring at a single, fixed patch of the Milky Way for years.

The mission relied on the Transit Method of detection. This involves monitoring the brightness of over 150,000 stars simultaneously; if a planet passes between the star and the telescope, it causes a tiny, periodic dip in the star’s light. This method allows scientists to calculate the planet's size and orbital period. The mission was named in honor of Johannes Kepler, the astronomer who formulated the laws of planetary motion, which describe how planets move in elliptical orbits and how their orbital speed changes based on their distance from the sun Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.257.

Key achievements of the Kepler mission include:

• Exoplanet Discovery: It confirmed more than 2,600 exoplanets, proving that planets are everywhere in our galaxy.
• Habitable Zones: It identified numerous planets in the 'Goldilocks Zone' — the region around a star where temperatures are just right for liquid water to exist, similar to the conditions that allow life on Earth Certificate Physical and Human Geography, The Earth's Crust, p.2.
• Earth 2.0: It sought 'Earth's twins' by looking for planets with a similar mass, density, and size to our own Certificate Physical and Human Geography, The Earth's Crust, p.2.

Feature	Kepler Mission	Hubble Telescope
Primary Role	Dedicated 'Planet Hunter' (Statistical Survey)	General-purpose observatory (Imaging/Deep Space)
Detection Method	Transit Photometry (Measuring light dips)	Visible, UV, and Near-Infrared imaging
Observation Style	Stared at one fixed field of stars for years	Points at various targets across the sky

Sources: Physical Geography by PMF IAS, The Solar System, p.39; Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.257; Certificate Physical and Human Geography, The Earth's Crust, p.2

7. Solving the Original PYQ (exam-level)

Now that you have mastered the concepts of exoplanets and the habitable zone, this question serves as the perfect bridge to see how those scientific theories are applied in real-world space exploration. The building blocks you learned regarding planetary transits—where a planet blocks a tiny fraction of its host star's light—are the exact scientific foundation upon which this specific mission was built. To answer this correctly, you must differentiate between general-purpose space observatories and those designed with a singular, specialized mission.

When walking through the reasoning, focus on the phrase "search for earth-size planets." While the Hubble telescope is a legendary and versatile tool, it was designed for broad deep-space imaging. In contrast, the Kepler Space Telescope was a dedicated "planet hunter" launched by NASA in 2009 specifically to conduct a statistical survey of our Milky Way galaxy. It monitored over 150,000 stars simultaneously to find those elusive Earth-sized worlds, making (B) Kepler telescope the only correct answer. NASA Kepler Mission Overview

UPSC frequently uses famous names as distractors to test your precision. A common trap is selecting Hubble due to its name recognition, even though its primary purpose is not planetary surveys. Similarly, Copernicus and Newton are iconic figures in astronomy, but their names are associated with different projects; for instance, Copernicus is the name of the European Union's current Earth observation program, while Newton (XMM-Newton) is an X-ray observatory. Always look for the specific mission objective provided in the stem of the question to avoid these nomenclature traps. Wikipedia: Kepler Space Telescope