The term “habitable zone” is a broad definition that serves the purposes of exoplanet exploration today. But the more we learn about exoplanets, the more we need a more detailed definition of habitable planets. New research suggests that vegetation can increase the habitable zone of any exoplanet that supports plant life.
Every object in the solar system has an albedo. It is a measure of how much starlight an object reflects back into space. In our solar system, Saturn’s moon Enceladus has the highest albedo due to its smooth, frosted surface. Its albedo is about 0.99, meaning that about 99% of the solar energy that reaches it is reflected back into space.
There are many dark objects in space with low albedo values. Some say that Iapetus, another moon of Saturn, has the lowest albedo. Earth, the only living planet, has an albedo of about 0.30, meaning that it reflects 30% of the sunlight that reaches it back into space. Many factors affect albedo. Earth’s albedo is affected by things like the amount of ice cover, cloud cover in the atmosphere, land cover compared to ocean cover, and even vegetation.
We live in an age of exoplanet discovery. We now know of over 5,000 confirmed exoplanets, with many more on the way. While all planets are of scientific interest, we are particularly interested in potentially habitable exoplanets.
A team of Italian researchers is investigating the habitability of an exoplanet using vegetation and albedo prism. Their work is featured in a paper accepted for publication. Monthly Notices of the Royal Astronomical Society It is titled “Effects of Vegetation Albedo on the Habitability of Earth-like Exoplanets.” The lead author is Erica Bisesi, a researcher at the Astronomical Observatory of Trieste of the Italian National Institute of Astrophysics.
“Since vegetation is generally darker than the bare surface of the continents, it can change the albedo of a planet’s surface via the Charny mechanism,” the researchers wrote in their paper. “Compared to a dead planet with bare continents, a vegetation-covered exoplanet should be hotter if both are at the same distance from similar stars.
The Charney mechanism is named after Jules Charney, an American meteorologist who is considered by many to be the father of modern meteorology. It is the relationship between vegetation and how it affects precipitation. In their study, the researchers updated the Earth’s surface temperature model to include two dynamically competing types of vegetation: grasslands and forests, with forests included in the seedling and mature stages.
“For a world with bare granitic continents, the feedback effect of vegetation and albedo is to increase the average surface temperature,” the authors explain. “Grass and trees have different albedos, thus affecting temperature to different degrees.”
The effect of vegetation on planetary albedo is the result of their dynamic competition, as grasses and trees affect albedo differently. “The change in albedo due to vegetation expands the habitable zone and increases the overall habitability of the planet beyond its traditional outer edge,” the authors write.
The researchers considered four situations:
- Complete domination of the trees (forest worlds).
- Complete domination of grass (prairie worlds).
- Tree/grass combination.
- Two-way worlds
In a two-way world, vegetation approaches grassland or forest, depending on the initial vegetation fractions. In these worlds, latitudinal seed dispersal expands the area where forests and grasslands coexist.
The researchers found that vegetation reduces the planet’s albedo and warms the climate, shifting the outer edge of the habitable zone, but they also reached more specific conclusions.
They found that dynamic competition between trees and grasses influences the latitudinal distribution of vegetation. “The resulting temperature-vegetation state is not imposed, but results from the dynamics of the vegetation-climate system,” they explain.
The researchers worked with the idea of a “pseudo-Earth”. Pseudo-Earth has a constant proportion of ocean at all latitudes, and this affects the distribution of continents and vegetation surfaces relative to the equator, where most of the sun’s energy falls on the planet.
The researchers also worked with a hypothetical dry pseudo-Earth, which has a 30% ocean coverage limit, while Earth and pseudo-Earth have 70% ocean coverage.
The team reached some conclusions about vegetation, albedo and biota.
The more continents there are on the planet, the stronger the effect of climate warming from vegetation. The effect was weaker when the simulation led to a world dominated by grass, because grass increased the albedo. The effect was greater when the simulation led to a world dominated by forest.
The key point, the researchers say, is that none of this is static. The results are determined by the competition between grasslands and forests for resources, which is determined by the average temperature in each latitude band. “In general, the resulting temperature-vegetation state is not imposed in this way, but results from the dynamics of the vegetation-climate system,” they explain.
This is particularly evident in dry pseudo-soil. Since the land cover is so extensive, vegetation has an even stronger effect on albedo and climate. “However, the share of the ocean cannot be too small, because in this case the entire hydrological cycle would be altered,” the researchers add. In general, vegetation has little effect on albedo and climate. However, we cannot ignore its effect on biodiversity.
This question is very difficult. For example, on a planet where grasslands and forests coexist, external factors such as stellar brightness and orbital fluctuations may be buffered by where the continents are and how much vegetation affects albedo simply because of location.
The authors believe their study is an important first step in this regard. It only includes certain types of grassland and forest, does not include relative water availability, and does not include CO concentrations. In the atmosphere 2.
“The dynamics investigated here are extremely simple and are only a first step in analyzing the interaction between vegetation and biome,” they write. “Future work will also include a simplified carbon balance model in the study of planetary populations.”
“This initiative should be seen as the first step in a research program that aims to incorporate fundamental relationships between climate and vegetation known on Earth into the prediction of exoplanet habitability,” they write.
Source: Port Altele
