Astronomers said recently that the so-called "habitable zone" around some stars may be about 30% larger than previously estimated. If this statement is confirmed, it will greatly increase the possibility of habitable planets in the galaxy.
Artist's performance of the red dwarf star GJ1214 and its surrounding planets
The basis of the study is a comparative analysis of the relationship between the radiation emitted by red dwarfs and the albedo of the ice and snow surfaces of the planets orbiting it. Red dwarfs are a class of small-mass stars. Correspondingly, their temperature is also lower than that of the "medium" stars of the spectral type G represented by the sun, so their radiant energy is mainly concentrated in a longer wavelength range. Ice and snow have greater absorption of radiation energy than reflection in these bands. This will heat the surface of the planet covered with ice and snow, melt part of the ice and produce liquid water, which is considered to be a necessary condition for the existence of life.
The scientists who conducted this study were Dr. Manoj Joshi from the National Center for Atmospheric Sciences and Dr. Robert Haberle from the NASA Ames Research Center. Josie said: "We know that red dwarfs have different radiation bands, so we want to understand what this means for the albedo of the planets orbiting these stars."
In our Milky Way, red dwarfs (spectral type M) account for 80% of the total number of stars, and because of their small mass, they have extremely long lives. For these reasons, it will be very important to investigate and understand the habitable zone surrounding these stars.
In this work, it is crucial to study the albedo of the ice and snow surfaces of these planets, because this constitutes an important part of the so-called "positive feedback mechanism". The increase in the amount of snow and ice on the planet's surface means more reflection, which will increase the planet's heat dissipation efficiency, which will cause the planet to cool down, and this process will in turn lead to more ice and snow, such a vicious circle. On the contrary, the melting of part of the ice and snow will mean a decrease in the radiation heat dissipation rate of the planet, which will cause the planet to heat up and cause more ice and snow to melt.
For these reasons, any effect that can reduce the albedo of planets covered by snow and ice will have positive meteorological significance. This is the same as the situation on the earth. Although the snow and ice area on the earth is very small, its role in regulating the climate is still not to be underestimated.
Despite the rapid advancement of our observation capabilities in deep space, so far we can only basically guess what the conditions of the planets outside the solar system are: what is the distribution of the land and land on their surface? How much snow and ice coverage? But At least we have indeed found evidence of planets around some red dwarfs.
The researchers used two red dwarfs: Gliese 436 and GJ 1214 to study the effect of their long-wave radiation on the surface albedo of a nearby planet with a surface temperature of about 200k (about -73.15 degrees Celsius). This temperature value is the condensation temperature of carbon dioxide at an atmospheric pressure. It is often used by researchers as a metric to delineate the outer boundary of the habitable zone of the galaxy-if a planet falls outside this range , Then its surface temperature is too low, and life may not be able to survive on its surface.
Scientists have found that when the effect of long-wave radiation on ice and snow albedo is taken into account, the surface temperature of planets covered by a large amount of snow and ice will be higher than previously estimated. In fact, this effect is very obvious, so that once this effect is included, the outer boundary of the entire livable zone will move outward from the current position by 10% to 30% overall. Qiao Xi said: "In previous studies, we did not take into account the subtle effects of this change in snow and albedo, but we are still surprised that the effects are so significant."
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