EARTH LIKE PLANETS (PART -I)

Tau Ceti:

Artist illustration of the view from one of the planets in Tau Ceti

Tau Ceti is not a planet but a star. This is very similar to our sun which is at a distance of 12 light years (3.7 parsecs).  What makes me talk about this star system is that, there are five possible planets orbiting this star, two of which are potentially in the habitable zone. Because of the debris dust around this start, any planet in this system would face far more impact events than earth did. Tau Ceti is consistently listed as a target for the search for extraterrestrial intelligence (SETI) and appears in some science fiction literatures. The principal factors which targets Tau Ceti for search of intelligence life are its proximity, its sun like characteristics and their implications for possible planets for life. After few observations, the results on what kind of planet might exist in that systems were declared. This results excludes the presence of Hot Jupiters and probably excludes any planet with minimal mass greater than or equal to Jupiter‘s mass and with orbital periods less than 15 years. However, as of 2019, analysis of the star has detected the signature of a possible planet of a few Jovian masses, with a tangential velocity of around 11.3 m/s.
     Tau Ceti is in the habitable zone only if we make any very generous assumptions.(leas author Michael Pagano) Tau Ceti f has likely resided in the habitable zone for much less than 1 billion years( researchers said). So even if the planet currently supports life as we know  it , astronomers may have a hard time finding any signs of life in the worlds atmosphere. The other three Tau Ceti planet candidates (b, c and d) all orbit considerably closer to the star than do e and f, making them likely too hot to harbours life. All five Tau Ceti worlds are likely larger than Earth. Planets e and f are estimated to be 4.3 and 6.6 times more massive than Earth, respectively; the other three worlds appear to harbour between 2 and 4 Earth masses.

COROT-7b:

CoRot-7b was previously known as CoRot-Exo-7b.  This is a exo-planet which orbits around its host star CoRot-7 in the constellation Monoceros . CoRot-7b is at a distance of 489 light years from earth. It was detected photometrically by a French led CoRot mission. CoRot-7b was the smallest exoplanet which has a diameter 1.58 times that of earth until the announcement of Kepler-10bin January 2011.This was the first potential extrasolar terrestrial planet to be found. This exoplanet has a very short orbital period-revolves around its host start in 20 hours. After studying the planet’s diameter and the planet’ mass, it was concluded that CoRot-7b was a rock like earth planet but not a gas giant such as Jupiter. The planet has a mass 5 times that of the earth and is the known planet which is the closest to its host start and also the fastest (orbits at a speed of 750,000 km/hr.). The probable temperature on its day-face is above 2000 degrees while the night face is -200 degrees. It might have lava or boiling oceans on its surface. Due to the high temperatures on the illuminated side of the planet, and the likelihood that all the surface volatiles have been depleted, silicate rock vaporization may have produced a tenuous atmosphere. But, after few observations, it was found that CoRot-7b has a cloudless atmosphere made of rocky vapours with a very low pressure. From the data available, scientists can only infer that CoRot-7b does not resemble any of the rocky planets of the solar system.

The exoplanet Corot-7b is so close to its Sun-like host star that it must experience extreme conditions. This planet has a mass five times that of Earth’s and is in fact the closest known exoplanet to its host star, which also makes it the fastest — it orbits its star at a speed of more than 750 000 kilometres per hour. The probable temperature on its “day-face” is above 2,000 degrees, but minus 200 degrees on its night face. Theoretical models suggest that the planet may have lava or boiling oceans on its surface. Our artist has provided an impression of how it may look like if it were covered by lava. The sister planet, Corot-7c, is seen in the distance.

TOI 700 d:

TOI 700d orbits it‘s M-type dwarf star 16% the distance of the earth orbits the sun. TESS has discovered its first Earth Sized planets in its stars habitable zone. TOI 700d is one of the only few Earth-size planets discovered in a star’s habitable zone as of now. Others include several planets in the TRAPPIST-1 system and other world.  TOI 700 is a small, cool M dwarf star located just over 100 light years away in the southern constellation Dorado.  It is roughly 40% of the Sun’s mass and size and about half its surface temperature.  The innermost planets, called TOI 700b, is almost exactly Earth-size, is probably rocky and completes an orbit every 10 days. The middle planet, TOI 700c, is 2.6 times larger than Earth- between the sizes of Earth and Neptune-orbits every 16 days and is likely a a-dominated world. TOI  700d, the outermost known planet in the system and the only one in the habitable zone, measures 20% larger than earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth . The #D climate models examined a variety of surface types and atmospheric compositions typically associated with what scientists regard to be potentially habitable worlds. Because TOI 700d is tidally locked to its star, the planer’s cloud formations and wind patterns may be strikingly different from Earth’s.
One simulation included an ocean-covered TOI 700d with a dense, carbon-dioxide-dominated atmosphere similar to what scientists suspect surrounded Mars when it was young. The model atmosphere contains a deep layer of clouds on the star-facing side. Another model depicts TOI 700 d as a cloudless, all-land version of modern Earth, where winds flow away from the night side of the planet and converge on the point directly facing the star.

“Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model,” Engelmann-Suissa said. “It’s exciting because no matter what we find out about the planet, it’s going to look completely different from what we have here on Earth.”

Gliese 667Cc:

GJ667Cc is accompanying a red dwarf star of spectral type M .Most stars that host exoplanets are expected to be cool M-dwarfs, which makes the case of GJ667Cc particularly interesting. GJ667Cc is much closer to its star at a distance between 0.11AU and 0.23AU. GJ667Cc receives a radiation flux which is about 90% of what we receive from our Sun on Earth. Although most of this radiation is emitted in the Infrared (IR), it is most likely enough to allow for liquid water on the planetary surface.   The temperature could be a pleasant 30 degree C if we assume a planetary atmosphere that is similar to the Earth’s.  Further observations are needed to answer if GJ 667Cc truly supports liquid water and if the conditions on this planet are appropriate for the hosting life.

Kepler-69c 

Kepler-69c can be also considered as Super-Earth /Super-Venus. This is a debatable planet among scientists as they still are researching weather it’s an earth like planet or much as Venus like planet.   It revolves around its host star namely Kepler-69 at a distance which is 0.64 times that of earth every 242 days (close to Venus orbital period). Kepler-69 is a G-type star which is orbited by two planets. The surface temperature of this star is around 5368 K with an estimated age of around 400 million years. Kepler-69c is a confirmed super-earth extrasolar planet, which is a rocky planet. It is located 2,430  light years (746 parsecs)  from earth. This planet is present in a habitable zone  , and by considering its distance from its host star, there is a chance that Kepler-69c  might have water in it or even a global ocean on its surface.

Kepler-20f

NASA’s Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system. The planets, called Kepler-20e and Kepler-20f, are too close to their star to be in the so-called habitable zone where liquid water could exist on a planet’s surface, but they are the smallest exoplanets ever confirmed around a star like our sun. Kepler-20f is the closest object to the Earth in terms of size ever discovered. With an orbital period of 20 days and a surface temperature of 800 degrees Fahrenheit, it is too hot to host life. It is an exoplanet which orbits its host star Kepler-20 which is about 921.4 light years (285.4 pc) from the solar system. Kepler-20 is 0.9 times more massive compared with our sun. The surface temperature of this star is 5502 degrees which has few spectral types of G8 stars.  Kepler-20f orbits its star every 19.6 days with as distance of 0.14 AU (20,883,862.7km).

There are many more planets which were discovered. But, the range of planets listed can’t be seen here(the list is huge). What do you think, will we ever find any intelligent life on other planet any time soon?

Here is a link where you can participate in planet hunting and in various other activities.
Learn how Transit method works and if possible, even how to detect black holes /neutron star collisions.

SEE HOW TESS WORKS

Sources:
1) Tau Ceti
Sol Station
2) CoRoT 7b
Image
arxiv
3)TOI 700d
planet hunters
4) Gliese 667Cc
arxiv
5) Kepler-69c
open exo-planet catalogue
6) Kepler-20f
Exoplanetkyoto
arxiv

Common Source

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