Earth's cousins

Earth 2.0: Cousin’s of Planet Earth:

According to NASA's Exoplanet Exploration page, scientists have discovered more than 4,000 exoplanets since the first such planet was verified to be circling a sun-like star in 1995. The NASA Kepler space observatory, which was deployed in 2009 with the goal of determining the prevalence of Earth-like planets throughout the Milky Way galaxy, is responsible for more than half of these findings.

Astronomers have long dreamed of finding the first real "Alien Earth," and recent exoplanet discoveries have revealed that small, rocky worlds like our own are common throughout the cosmos. A planet needs to spin in the "Habitable Zone" of its star, which is informally defined as a region where water can exist on a world's surface in liquid form and be relatively tiny (and so rocky), in order to be considered potentially life-friendly. When telescope technology advances, other factors will be taken into account, such as the planet's atmosphere and its parent star's level of activity.

What is an exoplanet?

In our solar system, every planet revolves around the sun. Exoplanets are planets that revolve around other stars. Exoplanets are extremely difficult to directly observe using telescopes. The intense light from the stars they orbit hides them.

Therefore, astronomers employ other techniques to find and research these far-off planets. By observing the impacts that these planets have on the stars they circle, astronomers look for exoplanets.

How do exoplanets form?

Planets are formed from circumstellar disks of gas and dust surrounding young stars, according to direct visual evidence. These objects, also known as protoplanetary disks, are challenging to see since they are usually surrounded by a star that is 100,000 times brighter than the disk itself. Hubble has made multiple observations of these disks thanks to its superb sensitivity and resolution, as well as its high-contrast photography, which blocks the overwhelming light from the star. Even though the disks only reflect the star's visible light, Hubble can still see their infrared glow.

This tiny sample clearly demonstrates diversity. Because planets develop within these disks, the structure of the planetary systems as they evolve should be reflected in the disks' forms. The Hubble findings are in line with observations of exoplanets, when planets are discovered grouped in orbits that are significantly different from those seen in our solar system. 

These disk studies also reflect on the formation and evolution of our solar system. In particular, it is possible that a planet collision will resemble the formation of the Pluto-Charon or Earth-Moon systems, which took place over 4 billion years ago. In certain situations, planet-sized entities collided, casting debris that eventually solidified into companion moons. With the launch of the James Webb Space Telescope, these disk systems may be observed in more detail in the infrared, potentially revealing evidence of newly formed planets.

List of some exoplanets that resemble Earth the most:

• KEPLER-452B

• KEPLER-442B

• KEPLER-186F

• KEPLER-69C

• KEPLER-62F

• KEPLER-22B

• KEPLER-1649 C

• GLIESE 667CC

• PROXIMA CENTAURI B

• TRAPPIST-1E

1. Kepler-452B

According to NASA, this planet, whose discovery was announced in 2015, is the first near-Earth-size planet to spin around a star the size of the sun. The parent star of Kepler-452b, which is 60 percent bigger than Earth, is 10 percent bigger than the sun. The exoplanet Kepler-452 orbits in the habitable zone and shares many similarities with our sun.

Kepler-452b has a "better than even chance" of being rocky because it is 1.6 times the size of Earth. Located 1,400 light-years away from Earth, Kepler-452b. Kepler-452b orbits its star in just 20 days more time than Earth does.

2. Kepler-442B

According to NASA, this exoplanet is 33 percent bigger than Earth and revolves around its star every 112 days. In 2015, Kepler-442, a star 1,194 light-years from Earth, was found.

One study discovered that this exoplanet might get enough light to support a substantial biosphere, which was published in the Monthly Notices of the Royal Astronomical Society in 2021. The possibility that several planets would be able to perform photosynthesis was examined by the researchers. They discovered that Kepler-442b receives enough radiation from its star.

3. Kepler-186F

The first confirmed Earth-size planet to circle a far-off star in the habitable zone, or the range of distance from a star where liquid water might exist on the planet's surface, is Kepler-186f. Although its mass, structure, and density are unknown, its size is known to be less than ten percent greater than Earth's. 

A planet the size of Kepler-186f is expected to be rocky, according to previous studies. Before this finding, Kepler-62f, a planet that is 40% larger than Earth and orbits in its star's habitable zone, held the "record" for being the most "Earth-like" planet. Kepler-186f is close to the outer border of the habitable zone since it orbits its star once every 130 days and receives one-third the energy from the sun that Earth does. The brightness of its star at high noon would be equal to the sun's brightness on Earth an hour before sunset if you could stand on the planet's surface. It is about 500 light-years away from Earth in the constellation Cygnus. In the system, four inner planets and a host star half the size and mass of the sun are also found.

4. Kepler-69C

Kepler-69c is a planet that, depending on how livable its surface is, may either be a "super-Venus" or a "super-Earth." However, at the time of its discovery, scientists noted that the planet shared many characteristics with Earth and that it orbited a star like our sun.

Kepler-69c is an exoplanet around 2,700 light-years away from Earth and was acclaimed as the alien planet that resembles Earth the most when it was first found. Since then, there has been some debate regarding whether it is more like Venus or Earth. For instance, NASA pointed out that Kepler-69c's orbit, at 242 days, is comparable to Venus's in our own solar system.

However, at the time of its discovery, scientists were debating whether there would be liquid water, or even a worldwide ocean, on its surface. One quipped that there might even be cunning dolphins there. Kepler-69c appeared to be orbiting an area where this might be conceivable.

5.  Kepler-62F

Nearly 1,200 light-years away from Earth, Kepler-62f may have an Earth-like planet. The planet is in orbit around a star that is slightly fainter and smaller than the sun, and is just 1.4 times smaller than Earth. It revolves around its star in what is thought to be the habitable zone.

 The planet was discovered in 2013 as part of a larger discovery that included seven exoplanets that were discovered near the stars Kepler-62 and Kepler-69. Kepler-62e, which is likewise in the habitable zone and is around the size of Earth (at 1.6 times the radius), was another significant discovery made at the same time. Separate modeling studies of the planets Kepler-62e and Kepler-62f revealed that they would probably be covered in water, which would result in life that is significantly different from our own.

6. Kepler-22B

The first earth-like planet, or exoplanet, discovered by the Kepler Space Telescope in its star's habitable zone is Kepler-22b. It is believed to be a good location to look for life. But since this planet is 600 light-years away, more powerful telescopes might be needed to examine it in greater detail.

Kepler-22b, which was announced in 2011, is thought to be 2.4 times larger in diameter than Earth and has a pleasant average surface temperature of 72 degrees Fahrenheit (22 degrees Celsius). But since then, scientists have disagreed on how habitable the planet actually is. In February 2011, NASA first revealed Kepler-22b as one of a group of 54 potentially habitable planets. The Kepler Space Telescope discovered each and every one of these planets. By monitoring dips in the light of the parent star as the planet rapidly passes it, the telescope searches for extraterrestrial worlds.

7. Kepler-1649C

Scientists found Kepler-1649c after analysing data from NASA's Kepler space telescope. It was discovered that the exoplanet orbited in its star's habitable zone and was around the same size as Earth.

According to NASA, a computer algorithm mistakenly recognized the astronomical body during the initial data collection from the telescope, but in 2020 it was found to be a planet.

Only 1.06 times larger than Earth, Kepler-1649c is 300 light-years away. Scientists discovered that this exoplanet receives 75% of the light that Earth receives from the sun when comparing the light that the two worlds receive from their sources.

8.  Gliese 667CC

According to NASA's Jet Propulsion Laboratory, this exoplanet, which is only 22 light-years away from Earth, is at least 4.5 times as large as Earth. The exoplanet Gliese 667Cc orbits its host star in just 28 days, but because the star is a red dwarf that is much colder than the sun, the exoplanet is believed to be in the habitable zone.

Gliese 667Cc, which was found using the 3.6-meter telescope of the European Southern Observatory in Chile, may orbit near enough to be cooked by flares from the red dwarf.

9. PROXIMA CENTAURI B

One of the most fascinating exoplanet discoveries to date was made a few years ago when astronomers found a solid planet with a size comparable to Earth orbiting Proxima Centauri, the sun's nearest neighbor. The ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) spectrograph on the Very Large Telescope (VLT) in Chile has now supplied that extra and more thorough confirmation, even though the detection appeared to be reliable. On May 28, 2020, the University of Geneva (UNIGE) released the information, and the planet was named as Proxima Centauri B.

With a mass of 1.17 Earth masses, Proxima Centauri b is extremely comparable to Earth in terms of size. In comparison to our planet's annual journey around the sun, it completes its orbit around its star in just 11.2 days. This indicates that Proxima Centauri b is far closer to its star than the sun is to the Earth. However, because the star is a red dwarf, which is smaller and cooler than our sun, it is in fact in Proxima Centauri's habitable zone. Surprisingly, Proxima Centauri b receives from its star roughly the same amount of solar radiation that Earth does from our sun.

10. Trappist-1E

A nearly Earth-sized exoplanet called TRAPPIST-1e, also known as 2MASS J23062928-0502285 e, orbits the ultra-cold dwarf star TRAPPIST-1, which is situated around 39 light-years from Earth in the constellation Aquarius.

It was one of seven new exoplanets found around the star by Spitzer Space Telescope investigations. The exoplanet is situated in the habitable region of the star. Scientists are now better able to comprehend its nature thanks to the physical properties' improved definition since its initial presentation. With almost the same mass, radius, density, gravity, temperature, and stellar flux as Earth, TRAPPIST-1e is strikingly comparable to our planet. A tight atmosphere similar to that of the terrestrial planets in our solar system is also verified to exist.

Is it possible to have two Earths?

Some scientists believe that since there is already one Earth that is teeming with life, there is no reason why there shouldn't also be another planet in our galaxy that is quite similar to our Earth under comparable conditions. It might have established life and even been capable of developing intelligent life. Even though scientists haven't found another planet like Earth, they have hope that they will.