Which planets are similar to Earth? The answer to this question can be approached in different ways. If we take, for example, the diameter and mass as the main criterion, then in the solar system, Venus is closest to our cosmic home. However, it is much more interesting to consider the question “Which planet is more like the Earth?” in terms of the habitability of objects. 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.
Habitable zone
People have been looking for extraterrestrial life for a long time. At first, these were only guesses, assumptions and conjectures, but as technical capabilities improved, the matter began to move from the category of theoretical problems to the field of practice and scientific knowledge.
Criteria were identified, according towhich a space object can be classified as potentially life-friendly. Any planet similar to Earth must be located in the so-called habitable zone. This term refers to a certain 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 luminary
As studies show, a planet similar to Earth and potentially suitable for life should revolve around a star of spectral class from G to K and surface temperature from 7000 to 4000 K. Such luminaries emit a sufficient amount of energy, are stable for a long time, their life cycle is completed in a few 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 peaceful life. Sudden flashes or long-term fading of the luminary can lead to the disappearance of organisms on the surface of a candidate for twins of our planet.
Metallicity, that is, the presence of elements in the star's matter in addition to hydrogen and helium, is another important property. At low values of this attribute, the probability of planet formation is extremely small. Relatively young stars have higher metallicity.
Properties of planets
And why, in fact, only a planet similar to the Earth can be potentially habitable? Why this list does not include objects that are close inthe size of Jupiter? The answer lies in the optimal conditions for the development of living organisms. They are created on planets similar to ours. Properties of Earth-like planets that could support life include:
-
a mass close to the Earth's: such planets are able to hold the atmosphere, while the plate tectonics on their surface is not as high as that of the "giants";
- dominance in the composition of silicate rocks;
- lack of a dense atmosphere of helium and hydrogen, characteristic, for example, of Jupiter and Neptune;
- not too much eccentricity of the orbit, otherwise the planet from time to time will be too far away from the star or too close to it;
- a certain ratio of axial tilt and rotational speed needed to change the seasons, the average length of 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 differ. Bacteria are more likely to be found in space than mammals.
New Earth-like planets
Evaluation of all these parameters requires high-precision equipment that can not only calculate the location of the planet, but also refine its characteristics. Fortunately, modern equipment “can” already do a lot, and unstoppable research and development allows us to hope that in the near future peoplewill be able to look even further into space.
Since the beginning of the century, a sufficiently large number of objects have been discovered that are more or less suitable for life. True, it is not possible to answer the question which planet is more similar to the Earth than others, since this requires even more accurate data.
Disputed exoplanet
September 29, 2010, scientists announced the discovery of the planet Gliese 581 g, orbiting the star Gliese 581. It is located at a distance of 20 light years from the Sun, in the constellation of Libra. To date, the existence of the planet has not been confirmed. In the five years since its discovery, it has been supported by additional research data several times, and then refuted.
If this planet exists, it is calculated to have an atmosphere, liquid water, and a rocky surface. In radius, it is quite close to our space home. It is 1.2-1.5 from the earth. The mass of the object is estimated at 3.1-4.3 Earth. The likelihood of life on it is as controversial as its discovery itself.
First confirmed
Kepler-22 b is an Earth-like planet discovered by the Kepler telescope in 2011 (December 5). She is an object whose existence is confirmed. Planet characteristics:
- rotates around a G5 star with a period of 290 Earth days;
- mass - 34, 92 Earth;
- surface composition unknown;
- radius - 2, 4earthly;
- from a star receives about 25% less energy than the Earth from the Sun;
- the distance to a star is about 15% less than from the Sun to the Earth.
The ratio of shorter distance and energy input makes Kepler-22 b a candidate for the title of a habitable planet. If it is surrounded by a sufficiently dense atmosphere, the temperature on the surface can reach +22 ºС. At the same time, there is an assumption that the composition of the planet is rather similar to Neptune.
Recent discoveries
The "newest" Earth-like planets were discovered this year, 2015. This is Kepler-442 b, located at a distance of 1120 light years from the Sun. It exceeds the Earth 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 Earth and located in the habitable zone.
Finally, on July 23, 2015, the discovery of Kepler-452 b was announced. The planet is located in the habitable zone of the luminary, very similar to our star. It is larger than the Earth by about 63%. The mass of Kepler-452 b is, according to scientists, 5 masses of our planet. Its age is also older - by 1.5 billion years. The surface temperature is estimated at -8 ºС.
The existence of these three planets is confirmed. They are considered potentially habitable. However, to confirm or refute themhabitability is not yet possible.
Further improvement of technology will allow astronomers to study these worlds in more detail, and therefore answer the question of which planet is more similar to Earth.
