Which planets are like Earth? The answer to this question can be approached in different ways. If, for example, the diameter and mass are taken as the main criterion, then in the solar system it is closest to our space house Venus. However, it is much more interesting to consider the question “Which planet is more similar to the Earth?” From the point of view of the suitability of objects for life. In this case, we will not find a suitable candidate within the solar system - we will have to take a closer look at the vast expanses of remote space.
Habitability zone
People engaged in the search for extraterrestrial life for a long time. At first it was only guesses, assumptions and conjectures, but as technical capabilities improved, things began to move from the category of theoretical problems to the field of practice and scientific knowledge.
Criteria were identified by which a space object can be attributed to potentially life-saving. Any planet similar to the Earth should be located in the so-called habitable zone. This term refers to a specific area around the star. Its main characteristic is the possibility of the existence of liquid water on the planet within its limits. Depending on the characteristics of the star, the habitable zone can be located closer to it or a little further, have a greater or lesser extent.
Properties of the star
Studies show that a planet similar to the Earth and potentially suitable for life should revolve around a spectral class star from G to K and a surface temperature of 7000 to 4000 K. Such luminaries emit a sufficient amount of energy, are stable for a long time, their life cycle ends in several billion years.
It is important that the star does not have significant variability. Stability both on Earth and in space is the key to a more or less calm life. Sudden outbreaks or long-term attenuation of the luminary can lead to the disappearance of organisms on the surface of the candidate for doubles of our planet.
Metallicity, that is, the presence in the material of a star of elements besides hydrogen and helium, is another important property. At low values of this feature, the probability of planet formation is extremely small. Relatively young stars have higher metallicity.
Planet Properties
And why, in fact, only a planet similar to the Earth can be potentially inhabited? Why are objects of similar size to Jupiter not included in this list? The answer lies in the optimal conditions for the development of living organisms. They are created precisely on planets similar to ours. The properties of earth-like planets on which life can exist include:
a mass close to the Earth: such planets are able to hold the atmosphere, while the plate tectonics on their surface are not as high as those of the "giants";
dominance in the composition of silicate rocks;
the absence of a dense atmosphere of helium and hydrogen, characteristic, for example, for Jupiter and Neptune;
the eccentricity of the orbit is not too large, otherwise the planet from time to time will be too far away from the star or come too close to it;
a certain ratio of the tilt of the axis and the speed of rotation necessary to change the seasons, the average length of the day and night.
These and other parameters affect the climate on the surface of the planet, geological processes in its depths. It should be noted that for different living organisms the necessary conditions may vary. The probability of meeting bacteria in space is much higher than that of mammals.
New Earth-like planets
Evaluation of all these parameters requires the presence of high-precision equipment capable of not only calculating the location of the planet, but also clarifying its characteristics. Fortunately, modern equipment "can" already have a lot, and non-stop research and development allows us to hope that in the near future people will be able to look even further into space.
Since the beginning of the century, a fairly large number of objects have been discovered, to one degree or another suitable for life. True, it is not possible to answer the question which planet is the most similar to Earth, since this requires even more accurate data.
The controversial exoplanet
On September 29, 2010, scientists announced the discovery of the planet Gliese 581 g, orbiting the star Gliese 581. It is located 20 light-years from the Sun, in the constellation Libra. To date, the existence of the planet is not confirmed. Over the five years since the discovery, it was several times supported by data from additional studies, and then refuted.
If this planet exists, then, according to calculations, it has an atmosphere, liquid water and a rocky surface. In radius, it is quite close to our space house. It is 1.2-1.5 from the earth. The mass of the object is estimated at 3.1-4.3 earthly. The likelihood of life on it is as controversial as its discovery.
First confirmed
Kepler-22 b is a planet similar to the Earth and discovered by the Kepler telescope in 2011 (December 5). She is an object whose existence is confirmed. Characteristics of the planet:
revolves around a star of spectral class G5 with a period of 290 Earth days;
mass - 34.92 earthly;
surface composition unknown;
radius - 2.4 earth;
it receives about 25% less energy from a star than the Earth from the Sun;
the distance to the star is about 15% less than from the sun to the earth.
The ratio of shorter distance and energy intake makes Kepler-22 b a candidate for the title of inhabited planet. If it is surrounded by a fairly dense atmosphere, the surface temperature can reach +22 º. At the same time, there is an assumption that the planet is similar in composition to, rather, Neptune.
Recent discoveries
The "newest" planets, similar to the Earth, were discovered in the current, 2015. This is Kepler-442 b, located at a distance of 1120 light years from the Sun. It exceeds the Earth in size by 1.3 times and is located in the habitable zone of its star.
In the same year, the planet Kepler-438 b was discovered in the constellation Lyra (470 light-years from Earth). It is also close in size to the Earth and is located in the habitable zone.
Finally, on July 23, 2015, the Kepler-452 b was announced. The planet is located in the habitable zone of the star, very similar to our star. It is approximately 63% larger than the Earth. The mass of Kepler-452 b is, according to scientists, 5 masses of our planet. Her age is also greater - by 1.5 billion years. The surface temperature is estimated at -8 º.
The existence of these three planets is confirmed. They are considered potentially livable. However, it is not yet possible to confirm or refute their habitability.
Further improvement of technology will allow astronomers to study these worlds in more detail, and, therefore, to answer the question of which planet is more similar to Earth.