Analysis of Searching for Another Earth in Universe-Habitability for

Exoplanet

Weiyuan Zhang

Pinghe High School, Shanghai, China

Keywords: Astronomy, Earth-like Planets, Habitability, Exoplanets.

Abstract: The search for habitable exoplanets has been quite a hot discussion over the past decades, driven by the natural

curiosity of human to know the universe and to look for a second habitat. This study evaluates the possibility

of discovering Earth-like exoplanets by generalizing the current findings of exoplanets, synthesizing

knowledge on habitability parameters, detecting methods both commonly-used, “classical” ones like transit

and new emerging ones like artificial intelligence, and searching results of habitable exoplanets. The study

also focuses on the habitable zones of exoplanets, and analyses on popular candidates for habitability like

TRAPPIST-1e, Proxima Centauri b and Kepler-452b by comparing their features to the parameters of

exoplanets. It is also stated clear that there are persisting challenges in the search for another Earth in

technological aspect and knowledge aspect. To put in a nutshell, this essay tries to analyse the possibility to

find an Earth-like planets which can carry humanity as well as lays the groundwork for future space detections

and further understanding of universe.

1 INTRODUCTION

There has been an on-going puzzle about the place in

the universe. The firm and television industry made

thousands of movies on imaginary livings outside the

solar system to fascinate generations after generations

on searching for exoplanets which are habitable for

holding lives, even for mankind. Due to the natural

urge for knowing the unknown in humanity,

explorations of exoplanets became a phenomenal

activity and a topic of conversation and research in

various fields of study on different levels (Howell,

2020). The searching of exoplanets started since the

last century, and over the years, the number of

exoplanets discovered augmented significantly.

Beginning in 1992 with the discovery of a planet with

a relatively small mass, there are all together

thousands of exoplanets found now in 2025. Thus, the

discovery of exoplanets can be considered as “a

triumph of ingenuity in observational astronomy”

(Wilkinson, 2016).

Discovering exoplanets made great contributions

to the understanding of planetary formation. Theories

evolved through studying systems of exoplanets, such

as core accretion, revealing dynamic processes

including planetary migration which is driven by

gravitational forces that reshape systems over a

period. Simultaneously, the discoveries point out a

possibility for life since increasing numbers of

exoplanets have been “found at larger distances”,

“temperate for having liquid water”, and are

“habitable for life” (Lee, 2018). Therefore, the

searching for exoplanets plays a crucial role in the

exploration of another earth-like planet which will be

discussed in later content.

Over the past decade, the search for exoplanets

has refreshed the understanding of planetary systems

beyond Solar System. The Kepler mission which is

launched in 2009, succeeded to identify more than

4,000 confirmed exoplanets, with a significant

fraction among them that reside in the habitable zone

of their host star (Fressin, et al., 2013). This statistical

result verified prevalence of small exoplanets, which

have a radius between one to four times of Earth’s,

challenging previous doubts on the diversity of

planetary system.

In 2018, NASA’s Transiting Exoplanet Survey

Satellite, also known as TESS, extended research for

exoplanets by conducting a survey on about 85% of

the sky and detected thousands of new exoplanets in

the habitable zone, including planets close to bright,

nearby stars. Notable discoveries of TESS include a

super-Earth, a planet more massive than Earth yet

180

Zhang, W.

Analysis of Searching for Another Earth in Universe-Habitability for Exoplanet.

DOI: 10.5220/0013821700004708

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 2nd International Conference on Innovations in Applied Mathematics, Physics, and Astronomy (IAMPA 2025), pages 180-185

ISBN: 978-989-758-774-0

lighter than ice giants, in the Pi Mensae system as

well as a rocky planet in the habitable zone of the M-

dwarf TOI-700 (Huang, et al., 2018; Gilbert, et al.,

2020). These findings highlighted the potential of

Earth-like worlds to exist in different stellar

environments.

Ground-based follow-up observations and

archival data analysis further enriched human’s

knowledge of “candidates” of another Earth. For

instance, radial velocity measurements, which will be

introduced in detail in the later essay, confirmed the

masses of TESS candidates, and distinguished

gaseous giants from rocky bodies. In addition,

atmospheric studies using the Hubble and Spitzer

space telescopes implied that there is water vapor and

clouds in the atmosphere of sub-Neptune, although

the definite biological signature of them remains

elusive. Human also witnessed a paradigm shift

toward characterizing planetary populations and

distribution in researches done in this decade.

Analyses revealed that nearly every star hosts at least

one planet, and compact multi-planet systems are

common. These insights have revolutionized

previous theories on planetary formation and

abundance of potentially habitable worlds in the

universe. For further development in the future, there

are upcoming missions such as the James Webb

Space Telescope which promise to depict exoplanet

atmospheres in unprecedently reached detail, while

other large-scale surveys aim to catalog Earth

simulations. The discoveries in the past ten years

established a foundation for settling the big problem

of humanity mentioned above. Given the Earth’s

finite resources, space colonization is an alternative

that human must attach attention to. This paper will

evaluate the feasibility of discovering an Earth-like

planets—planets with conditions akin to Earth and

can support human life. Human must be aware of

such research, which is vital not just for a specific

field of study, but for securing humanity’s future and

preparing for the ultimate time when Earth can no

longer sustain human.

To be specific, the following study will

successively elaborate on the definition and features

of habitable planets, the approach and results on

searching for habitable exo-planets, and the

limitations of the current methodology and

technology.

2 HABITABILITY PARAMETERS

In order to find an exoplanet that can carry human life,

it must be first identified clearly that what such a

planet is like. The ability of a planet that is able to

support activities of “at least one know organism” is

called habitability (Cockell, et al., 2016). Here, this

study must state clearly the difference between an

earth-like planet and a habitable planet, since they are

not necessarily the same, and that there’s no

affiliation between the two concepts. Earth-like

planets, for example Kepler-452b, are rocky celestial

bodies with an earth-like size in habitable zones,

while habitable planets can broadly support life, with

even non-earth environments such as Europa’s

subsurface ocean. An Earth-like planet doesn’t mean

it’s habitable (like Venus).

Searches for habitable planets often focus on

identifying whether the physical and environmental

condition on the planet fits into the parameter of

sustaining life. These conditions, involving the

planet’s gravitational strength and atmospheric

composition, as well as topographical activity and

climate stability—together determine whether a

planet can provide a habitable environment, like

maintaining liquid water, protective environments,

and biochemical processes. While Earth is the main

reference for habitability, new findings, like

underground oceans on icy moons or other places

filled with methane, are making us to now and then

question what a habitable environment could be like.

These discoveries show that life might exist in

environments one never imagined before.

One standard included in the key parameters for

habitability is the gravity. Surface gravity number of

a planet normally ranges between 0.3 to 1.5 times

Earth’s gravity. If it’s too weak, as on Mars,

atmospheric loss will accelerate, resulting in extreme

difference in temperature of day and nights. By the

contrary, an excessively strong gravity on much

larger planets might decrease biological complexity.

Simultaneously, rotation rate is also an important

factor of habitability since it influences climate. To be

specific, extremely fast rotation, such as Jupiter’s 9.9-

hour day, brings violent storms, whereas slow

rotation, taking Venus’s 243-day cycle as an example,

creates significant temperature contrasts. Last but not

least, a feasible atmosphere ranges from 0.1 to 10

times Earth’s pressure, with gases like CO₂, O₂, and

N₂, along with other protective characteristics like

ozone layers or magnetic fields to shield the surface

against harmful radiation.

Temperature, on the other hand, depends on a

planet’s position within the habitable zone, which is

defined as that range of area around a star where water

can exist in liquid form. The Earth orbits within the

Sun’s habitable zone, for instance. Yet, even within

this zone, factors like atmosphere composition and

Analysis of Searching for Another Earth in Universe-Habitability for Exoplanet

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greenhouse effects can modify thermal conditions at

a large extent. Venus, though lying close to the inner

edge of the Sun’s habitable zone, experiences a

runaway greenhouse effect and has surface

temperatures exceeding 450°C, attributed by its thick

CO₂ atmosphere.

Atmospheric composition is another determinant

of habitability. Oxygen or chemical imbalance might

suggest livings, while CO₂ is able to ensure heat and

liquid water on the planet. However, more research

on “the interior dynamics and evolution of the solid

planet” and its relationship with the atmosphere, and

this includes pursuing “experimental and modelling

constraints on the interactions between the

atmosphere and interior over long time scales” (Kane

& Gelino, 2012).

3 PLANET SEARCHING

APPROACHES

Searching for exoplanets revolutionized human’s

knowledge of the universe above them, using both

established and common techniques and innovative

ones which are developed in recent years. Below, the

essay would list some of these approaches that had

helped human detect exoplanets, and these

methodologies play a crucial role in the possibility to

find another Earth in the planetary system.

According to NASA’s data, the transit method has

successfully detected more than 4000 exoplanets

including Earth-sized candidates in habitable zones,

significantly exceeding all other methods, and it is

often employed by missions like Kepler Space

Telescope and TESS. To be specific, this method

detects planets by observing periodic dips in a star’s

brightness when another planet passes in front of it,

and the depth of the light curve dip is correspondent

to the planet’s size relative to the star. Multiple

transits would be able to confirm the planet’s orbital

period. Transit is highly efficient to studies of

searching for exoplanets, indicated by the number of

planets it found. However, it restraining stays clear: it

is limited to short- to moderate-period orbits for

signal frequency able for detection.

It's the second-most used technique and has

detected more than 1000 exoplanets. This technique

measures the Doppler shifts in a star’s spectral lines

caused by tis gravitational interactions with orbiting

planets. By detecting these shifts, scientists can infer

planetary mass and orbital periods. In fact, the

method led to the first confirmed exoplanet, 51 Pegasi

b, a hot Jupiter orbiting its host star in just 4.2 days.

It limitations sate clear that while its highly effective

for identifying massive planets close to their stars, it

struggles with planets with lower mass and longer

period.

Direct imaging focuses on emitting photons or

photons reflected by planets by using coronagraphs to

block stellar glare. The advantage of the method is

that its most effective for searching for massive

planets separate from their host stars in wide orbits.

Noted examples include the JWST, also known as

James Webb Space Telescope, which recently imaged

the HR 8799 system and resolved four gas giants as

well as analysed their atmospheric carbon dioxide

signatures. A historic milestone was achieved in 2004

when Very Large Telescope (VLT) was employed at

Paranal Observatory, Chile, to directly image

2M1207b as shown in Fig. 1, the first exoplanet

confirmed via this method (Dai et al., 2021).

Gravitational microlensing can detect exoplanets

by making use of the gravitational field of a

foreground star or star-planet system as lens which

could bend and amplify light from a background star,

and it creates a temporary brightening. When a planet

is present, it introduces detectable anomalies in the

light curve like brief spikes or asymmetries. This

method is most useful at finding low-mass planets

(including Earth-sized), wide-orbit planets, and free-

floating worlds, independent of the light emitted by

the planet. Notable discoveries include OGLE-2003-

BLG-235Lb: it is the first microlensing exoplanet in

history.

Figure 1: The CCD frame of 2M1207b (Dai et al., 2021).

The study introduces a novel approach to find

exoplanets by using AI, specifically CNNs

(convolutional neural networks), to solve the

drawbacks of earlier methods like least-squares

optimization and matched filtering. Traditional

techniques are highly dependent on hand-coded

metrics, struggling with noise and stellar variability,

which set a barrier especially for Earth-sized planets

with shallow transits. Researchers train a CNN on

identifying simulated light curves and incorporating

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diverse planetary parameters like orbital periods and

transit depths and use systematic noise to mimic

stellar variability and instrumental effects. The CNN

learns transit features directly from data, and avoids

establishing dependence on predefined models.

Compared to methods like support vector machines

and box least-square, the CNN achieves much higher

accuracy (which is about 99.7% in training and 91.5%

in testing) and robustness in noisy conditions,

particularly for signals near or below the noise floor.

The CNN’s performance stays stable even when it’s

applied to interpolated or incomplete data,

demonstrating its ability to generalize. Validated on

Kepler mission data, this approach successfully

identifies known exoplanets and predicts their orbital

periods by analysing phase-folded light curves. It’s

highlighted that the CNN is highly potential for future

surveys like TESS and PLATO, in which automated,

efficient processing of large datasets is essential

(Pearson, et al., 2017).

Traditional methods like transit and radial

velocity are still mainstream of exoplanet research,

while innovative technique, including spanning radio

astronomy, relativistic optics, and AI, are expanding

frontiers in this field of study. Together, they enhance

human’s ability to look for Earth-like worlds and

unravel planetary diversity. Future missions like the

Habitable Worlds Observatory aim to synthesize

these approaches and target atmospheric

biosignatures and refining the cosmic context as well.

4 SEARCHING RESULTS

The first confirmed detection of an exoplanet in 1995,

and since then the field of astronomy has experienced

remarkable growth, with over 5,500 exoplanets

having been identified until April 2025 according to

NASA Exoplanet Archive. Early discoveries are

mainly attentive on depicting of worlds beyond solar

system, but recently there has been a shift toward

identifying planets with potential habitability because

of the natural curiosity towards finding another Earth

mentioned before. This kind of exoplanets found

must support Earth-like life, so that it had the

possibility to provide humanity with a new habitat.

Defining Habitability: Key Parameters

Among all the exoplanets that scientists found,

approximately 50-60 are located within their stars'

habitable zones. These are potentially temperate

worlds and they vary widely: some may have Earth-

like surface temperatures which is 0–30°C if they

hold atmospheres with greenhouse gases, and others

orbit stars alike to the sun and might have stable

climates, but with uncertain properties like gaseous or

rocky. A large number of planets in habitable-zone

orbit red dwarfs, who set challenges like tidal locking

and stellar flares, and may affect climate stability.

Future studies would focus on refining models of the

unstable environments. The following passage would

introduce some examples of the candidate exoplanets

of “the second” Earth.

TRAPPIST-1 is 40 light-years away for Earth in

the constellation Aquarius. It has gained wide notice

as in 2017 seven exoplanets were announced to be

found Earth-sized (Gillon, et al., 2017). Among the

seven, TRAPPIST-1e, detected in 2016) orbits within

the star's habitable zone, making it a competitive

candidate for habitability. The red dwarf is an ultra-

cool red dwarf, and is dramatically dimmer and cooler

than the Sun so the habitability zone is shifted much

closer to the star. TRAPPIST-1e’s mass is of 0.69

Earth masses and its radius is of 0.91 Earth radii,

demonstrating a rock composition similar to Earth.

Modelling shows that the star TRAPPIST-1e,

under the assumption of a 1-bar nitrogen-oxygen

atmosphere, has a stellar flux comparable to Earth

(Wolf, et al., 2017). Not beyond that, the star's low

luminosity determines the planet, however, to be most

probably tidally locked, that is to say one hemisphere

turns face to the star all the time, whereas the other is

left in permanent darkness. Although such conditions

could result in very sharp temperature differences,

that would probably be prevented with the strong

climate circulation which the latest models predict.

As for characterization of the atmosphere, the planet's

discovery is more challenging since the star is very

faint. Planets with the same mass as Earth or heavier

positively correspond with the conditions required for

life. Several JWST missions are likely to address such

topics.

Proxima Centauri b, another well-known

exoplanet, is situated at a distance of 4.2 light-years

from the Sun in 2016 and orbits a star named Proxima

Centauri, which is the closest stellar companion to the

solar system. Going in the same orbit with this M5.5V

red dwarf, this planet is heavier than Earth (at least

1.07 times). Besides that, Proxima b is situated at the

distance from the star that is at least an order of

magnitude shorter (only 0.05 astronomical units),

which means that the planet can complete an orbit

around the star in 11.2 days. Being right under the star,

Proxima b is subjected to acting tremendous stellar

flares, which could at some point strip away its

atmosphere. Nevertheless, probably Proxima b is

superior to Earth: it has the same mass as Earth, is in

the habitable zone, and is the primary ground for

studies to find new habitable world.

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By means of a spectroscopic analysis, the

atmosphere of the world has not been explored yet.

However, there is theoretical implication if Proxima

b has a lead shield and a thick atmosphere, it could

keep enough gases so that there was liquid water on

its surface. The article, which is dated back to 2020,

and which also belongs to the residing in the original

findings, simulated various climates of Proxima b and

concluded that the atmosphere of that world must be

composed predominantly of CO₂, otherwise the

average surface temperature would range between the

values of 0 and 40 degrees Celsius, which is optimal

for supporting the existence of surface water.

Consequently, fluctuations in stellar flares activity

still pose a threat factor for Proxima b. On the other

hand, it is much easier to monitor Proxima b

compared to other exoplanets, since the distance and

position let further investigations (Anglada-Escudé,

et al., 2016).

Kepler-452b was initially discovered in 2015 (by

the Kepler Space Telescope) and orbits a star of the

G-type category at the distance of 1,800 light-years.

This planet is 1.6 times bigger in its radius and

estimated five times heavier than Earth, so it can be

classified as a super-Earth. With 385 days of the

orbital period, this planet is just touching slightly the

sphere of the habitable zone of its star, so, it is getting

10% more energy from it. This possibility stands for

the theory that it has liquid water on the surface, but

its bigger size and mass give the hint that there is the

dense atmosphere or the surface cover by ocean or sea.

Super-Earths are no selecting criteria for habitability,

however, the discovery of Kepler-452b and planets

similar to it as a class of exoplanets indicates the

tendency to search potentially habitable planets

around the Sun-like stars. The planet is to Earth as

humans are to the "good enough" planet, with which

one has so much in common, from the respective

orbital periods to the neighbouring states (of a

government type), Planet Earth.

5 LIMITATIONS & PROSPECTS

It must be admitted that there are limitations rooted in

rather narrow observations and inadequate

assumptions. Most exoplanets, including those in

habitable zones, are detected indirectly through

methods like transit or radial velocity, so the data isn’t

complete on aspects like surface conditions,

atmospheric composition, and geological activity.

Take TRAPPIST-1e and Proxima Centauri b for an

example, although they are both candidates for

habitability, they have close proximity to faint red

dwarfs and intense stellar flares, and it hinders

detailed characterization in atmosphere. On top of

that, the definition of "habitability" is only generated

dependent on Earth-like parameters such as liquid

water, and an atmospheric construction of mainly

nitrogen and oxygen, overlooking other exotic

environments where human life might thrive.

In the future, progress must keep an eye on

technology leaps and try to expand the knowledge of

scientific frameworks. Missions like the James Webb

Space Telescope make direct inspection of exoplanet

atmospheres possible, and are capable of detecting

biosignatures on planets like TRAPPIST-1e.

Innovative, next-generation telescopes would be

more precise in measuring planetary mass and radius

as well as clarifying compositions of super-Earths

like Kepler-452b. Meanwhile, astrobiology must

evolve to move to consideration of broader

habitability like subglacial oceans, radiation-tolerant

ecosystems, or non-habitable-zone liquid water.

Climate models and geological processes will better

assess whether long-term habitability exist, which is

better than static classifications on the habitable zone

because it’s more dynamic and straight-forward.

These advancements would help enhance the chance

of finding a real second habitat for human.

6 CONCLUSIONS

In conclusion, this study analysed the viability of

finding Earth-like exoplanets through continuously

improving detection methods and habitability

frameworks. Key findings include the discovery of

50–60 exoplanet candidates, in habitable zone, use

examples including TRAPPIST-1e, which is tidally

locked with potential atmospheric heat redistribution,

Proxima Centauri b with atmospherically resilience in

spite of stellar flares, and Kepler-452b, a super-Earth

in a Sun-like system. What’s more, the essay

demonstrates breakthroughs in detecting methods

from transit to artificial intelligence which achieved

more 90% accuracy. Yet, limitations such as

incomplete atmospheric data and constrained concept

of habitability parameter assumptions have

acknowledged gaps in human’s current knowledge.

Future missions like the JWST will prioritize solving

problems of atmospheric biosignatures and improve

habitability standard to more precisely identify

habitable planets. This work not only refines

humanity’s search for extraterrestrial life but also

generalized and laid critical groundwork for

sustainable interstellar colonization ahead, providing

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a trustable answer for both curiosity of human and the

need to secure humanity’s future beyond Earth.

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