October 4, 2015 at 07:42Why finding inhabited planets is so complicated
More than a thousand exoplanets have already been discovered, of which only 31 have been found livable:
But you should not flatter yourself with this amount - it may well turn out that although these planets are in the “habitable zone”, real conditions on them, like on our Venus, can greatly to differ from the estimated ones, and exclude life like ours on them. The reason for this is the impossibility of direct observation of planets located in the "habitable zone", which means the lack of reliable data on the most important parameters - the albedo of the planet, and the composition of its atmosphere. And without these parameters, estimates of the temperature on the surface of the exoplanet are very rough.
But let's start with the question, why is surface temperature so important? For the origin and existence of life similar to earthly, the presence of liquid water is required. Therefore, the planets on which life can exist should be included in the so-called "habitable zone", or in another way, the "Goldilocks zone" is a range of orbits in which the temperature on the planet's surface should fluctuate in the range of 0-100 degrees Celsius. It is clear that for small stars this zone is closer to the star, and for larger stars it is further:
Comparison of the inhabited zones of the Sun (yellow dwarf) and Gliese 581 (red dwarf)
Naturally, life can also arise from stars of other classes, but they will not have an enviable fate - for star class A, the life expectancy of a star will be less than 500 million years, and there is no need to talk about any evolution and development of life to complex forms.
The smallest class of M stars (brown dwarfs), although it has a lifespan of tens of billions of years, is considered bad candidates because the planet must be too close to the star to receive enough energy. This can lead to tidal forces causing the planet to rotate all the time with one side turned to the star (like our Moon turned one side to the Earth), this means eternal day on one side, and eternal night on the other. Also, such a planet will need a very dense atmosphere in order to protect life on its surface from star radiation. The probability of the simultaneous existence of both of these conditions is considered very low.
Classes of stars - suitable for life planets are sought mainly from the stars of classes K (red dwarfs) and G (like our Sun)
And so, with where and what to look for, we decided, now it remains to determine - how difficult it is to find what we need. Without accurate data on the albedo, and on the composition of the planet’s atmosphere (whether it exists at all, is there a greenhouse effect - and what is its effect on the planet), we will not be able to accurately determine the temperature on its surface. So we need to see the planet with our instruments.
The first exoplanet was captured by the ground-based 8-meter telescope of the Gemini Observatory on September 14, 2008 - this is 1RXS J160929.1-210524 b. This was not a planet in our view - its mass exceeds Jupiter by 8 times (the Earth - even by 2,500 times), and the surface temperature is 1400 degrees Celsius. In this case, planets include all objects that are not capable of supporting thermonuclear reactions inside their nucleus (this is at least 12.5 masses of Jupiter).
Star 1RXS J160929.1-210524 and a planet in its orbit. Unlike all previous spectacular photographs of planets near neutron stars and binary or triple star systems signed as “the appearance of an exoplanet in the artist’s view”, this unpretentious photo is a huge step in the field of exoplanet research.
This star is located 470 light-years from us and has a mass slightly less than the mass of the Sun. The distance between a star and a planet is approximately 330 AU. This, of course, was not the limit of measurement for this telescope, it was easiest to find such a planet that had not yet cooled down after its formation and which emitted a lot of light.
The next step was already taken on January 13, 2010 - using the Very Large Telescope, the radiation spectrum of the exoplanet HR 8799 c was obtained. The planet is at 38 AU from his star, and 130 light years from us. The surface temperature is about 800 degrees Celsius. According to the results of spectrometry, methane was detected in the atmosphere, and two more substances: ammonia / acetylene and carbon dioxide / hydrocyanic acid, depending on the interpretation of the results.
The dark blue line is the emission spectrum of the planet HR 8799 c, the light blue region is the range of possible errors (it is due to the fact that the spectrum of the planet has to be “separated” from the spectrum of a brighter star)
As you can see, these planets are almost “warmed up” ", And this is no accident. Adaptive optics and the development of electronics made it possible to achieve great success with ground-based telescopes - the influence of atmospheric disturbances was almost eliminated, only a small “blurring” of the image remained.
The photograph of the working telescope of the Keck Observatory, the laser beam of the working adaptive optics system is clearly visible, the blurry stars in the photo are the result of the long exposure of the photo, which was needed in order to capture the laser beam.
But the 2.4 meter old Hubble, who turned 25 this year, can no longer compete with the ground giants, reaching 10.5 meters. And as you know, our atmosphere practically does not transmit infrared rays, and even at such a high-altitude observatory as the Keka Observatory in Hawaii (4145 m), it allows you to use the maximum - visible light and the near infrared. So they are not able to get direct photographs of planets having a temperature of about 300 K (like ours) - most of their radiation falls on the far infrared region, and the visible part is some crumbs.
The future James Webb Space Telescope will have a 2.7 times larger mirror than the Hubble, which means the area in which it can see exoplanets will expand by the same amount. He will be able to see the same weak objects as ground-based telescopes, and most importantly - to "see" the planets that emit in the infrared. This will give a huge step in the search for exoplanets suitable for life. The possibility of obtaining the emission spectrum of such planets will give us the opportunity to move from “estimates” of temperatures to their accurate measurement. And this is the main factor by which the search for suitable planets is carried out.
The largest existing and projected telescopes with the dates of their commissioning. Telescopes for the first time photographed an exoplanet (Gemini North and South) are located in the center one above the other (blue and green). The telescopes that made the first spectral analysis (Very Large Telescope) are below. Future telescopes: the James Webb spacecraft from bottom to bottom, ground-based telescopes from bottom to top: Giant Magellan telescope, European extremely large telescope, Thirty-meter telescope. And the person for the scale is lower right.
phl.upr.edu/projects/habitable-exoplanets-catalog Catalog of exoplanets suitable for life
www.gemini.edu/sunstarplanet The first photo of an exoplanet
Spatially resolved spectroscopy of the exoplanet HR 8799 c. M. Janson, C. Bergfors, M. Goto, W. Brandner, D. Lafreniere Article on the first spectral analysis of exoplanets
But you should not flatter yourself with this amount - it may well turn out that although these planets are in the “habitable zone”, real conditions on them, like on our Venus, can greatly to differ from the estimated ones, and exclude life like ours on them. The reason for this is the impossibility of direct observation of planets located in the "habitable zone", which means the lack of reliable data on the most important parameters - the albedo of the planet, and the composition of its atmosphere. And without these parameters, estimates of the temperature on the surface of the exoplanet are very rough.
But let's start with the question, why is surface temperature so important? For the origin and existence of life similar to earthly, the presence of liquid water is required. Therefore, the planets on which life can exist should be included in the so-called "habitable zone", or in another way, the "Goldilocks zone" is a range of orbits in which the temperature on the planet's surface should fluctuate in the range of 0-100 degrees Celsius. It is clear that for small stars this zone is closer to the star, and for larger stars it is further:
Comparison of the inhabited zones of the Sun (yellow dwarf) and Gliese 581 (red dwarf)
Naturally, life can also arise from stars of other classes, but they will not have an enviable fate - for star class A, the life expectancy of a star will be less than 500 million years, and there is no need to talk about any evolution and development of life to complex forms.
The smallest class of M stars (brown dwarfs), although it has a lifespan of tens of billions of years, is considered bad candidates because the planet must be too close to the star to receive enough energy. This can lead to tidal forces causing the planet to rotate all the time with one side turned to the star (like our Moon turned one side to the Earth), this means eternal day on one side, and eternal night on the other. Also, such a planet will need a very dense atmosphere in order to protect life on its surface from star radiation. The probability of the simultaneous existence of both of these conditions is considered very low.
Classes of stars - suitable for life planets are sought mainly from the stars of classes K (red dwarfs) and G (like our Sun)
And so, with where and what to look for, we decided, now it remains to determine - how difficult it is to find what we need. Without accurate data on the albedo, and on the composition of the planet’s atmosphere (whether it exists at all, is there a greenhouse effect - and what is its effect on the planet), we will not be able to accurately determine the temperature on its surface. So we need to see the planet with our instruments.
The first exoplanet was captured by the ground-based 8-meter telescope of the Gemini Observatory on September 14, 2008 - this is 1RXS J160929.1-210524 b. This was not a planet in our view - its mass exceeds Jupiter by 8 times (the Earth - even by 2,500 times), and the surface temperature is 1400 degrees Celsius. In this case, planets include all objects that are not capable of supporting thermonuclear reactions inside their nucleus (this is at least 12.5 masses of Jupiter).
Star 1RXS J160929.1-210524 and a planet in its orbit. Unlike all previous spectacular photographs of planets near neutron stars and binary or triple star systems signed as “the appearance of an exoplanet in the artist’s view”, this unpretentious photo is a huge step in the field of exoplanet research.
This star is located 470 light-years from us and has a mass slightly less than the mass of the Sun. The distance between a star and a planet is approximately 330 AU. This, of course, was not the limit of measurement for this telescope, it was easiest to find such a planet that had not yet cooled down after its formation and which emitted a lot of light.
The next step was already taken on January 13, 2010 - using the Very Large Telescope, the radiation spectrum of the exoplanet HR 8799 c was obtained. The planet is at 38 AU from his star, and 130 light years from us. The surface temperature is about 800 degrees Celsius. According to the results of spectrometry, methane was detected in the atmosphere, and two more substances: ammonia / acetylene and carbon dioxide / hydrocyanic acid, depending on the interpretation of the results.
The dark blue line is the emission spectrum of the planet HR 8799 c, the light blue region is the range of possible errors (it is due to the fact that the spectrum of the planet has to be “separated” from the spectrum of a brighter star)
As you can see, these planets are almost “warmed up” ", And this is no accident. Adaptive optics and the development of electronics made it possible to achieve great success with ground-based telescopes - the influence of atmospheric disturbances was almost eliminated, only a small “blurring” of the image remained.
The photograph of the working telescope of the Keck Observatory, the laser beam of the working adaptive optics system is clearly visible, the blurry stars in the photo are the result of the long exposure of the photo, which was needed in order to capture the laser beam.
But the 2.4 meter old Hubble, who turned 25 this year, can no longer compete with the ground giants, reaching 10.5 meters. And as you know, our atmosphere practically does not transmit infrared rays, and even at such a high-altitude observatory as the Keka Observatory in Hawaii (4145 m), it allows you to use the maximum - visible light and the near infrared. So they are not able to get direct photographs of planets having a temperature of about 300 K (like ours) - most of their radiation falls on the far infrared region, and the visible part is some crumbs.
The future James Webb Space Telescope will have a 2.7 times larger mirror than the Hubble, which means the area in which it can see exoplanets will expand by the same amount. He will be able to see the same weak objects as ground-based telescopes, and most importantly - to "see" the planets that emit in the infrared. This will give a huge step in the search for exoplanets suitable for life. The possibility of obtaining the emission spectrum of such planets will give us the opportunity to move from “estimates” of temperatures to their accurate measurement. And this is the main factor by which the search for suitable planets is carried out.
The largest existing and projected telescopes with the dates of their commissioning. Telescopes for the first time photographed an exoplanet (Gemini North and South) are located in the center one above the other (blue and green). The telescopes that made the first spectral analysis (Very Large Telescope) are below. Future telescopes: the James Webb spacecraft from bottom to bottom, ground-based telescopes from bottom to top: Giant Magellan telescope, European extremely large telescope, Thirty-meter telescope. And the person for the scale is lower right.
phl.upr.edu/projects/habitable-exoplanets-catalog Catalog of exoplanets suitable for life
www.gemini.edu/sunstarplanet The first photo of an exoplanet
Spatially resolved spectroscopy of the exoplanet HR 8799 c. M. Janson, C. Bergfors, M. Goto, W. Brandner, D. Lafreniere Article on the first spectral analysis of exoplanets