How is the earth located at an optimum distance from the sun?
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We orbit the Sun at a distance of about 150 million kilometers. This number is actually an average, since we follow an elliptical path. At its closest point, the Earth gets to 147 million km, and at its most distant point, it's 152 million km.
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Answer:
assumption that “optimum” here pertains to habitability, we have only one example of an inhabited world, at the present time. Without any other inhabited worlds to compare earth to, one cannot in any way shape or form credibly claim that Earth is located at an “optimum” distance from the sun.
All we can say is that Earth’s location is “good enough” for us to exist, but that’s not the same as claiming it is “optimal”.
Indeed, there are many reasons to suspect that Earth’s distance from the sun isn’t an optimum at all.
The sun’s habitable zone has a width of about 1 AU, and the earth is in the innermost 1% of it.
Since stars like the sun steadily increase in brightness as they age, over billions of years, the inner edge of the habitable zone steadily migrates outward over time. With earth already within the innermost 1%, this means, that somewhere within the next 0.5 to 1.0 billion years, the innermost edge of the habitable zone will move out past Earth’s location, extinguishing all life on earth.
If Earth were anywhere in the 99% of the habitable zone that is further out, it is more than possible that Earth would have a longer period of habitability, and a longer period in which it can sustain complex life like humans.
A habitable planet’s location within the habitable zone also determines its atmospheric greenhouse gas equilibrium. You can look up the details about this elsewhere, but the end result of this equilibrium is that a habitable planet can maintain a roughly constant temperature, suitable for life, over a relatively wide range of stellar insolation. Thus the earth was only a slightly different temperature 2 billion years ago, when the younger sun was quite a bit dimmer, than it is today, once the various climate cycles and fluctuations are averaged out. This same effect theoretically should keep habitable planets throughout the habitable zone, whether in the inner 1% or the outermost 1%, roughly in the same temperature range.
What changes instead with a planet’s location in the habitable zone (and over time as the star ages and brightens) is the equilibrium concentration of greenhouse gases in the atmosphere. The closer to the inner edge of the habitable zone, the lower the concentration of greenhouse gases like carbon dioxide, while further out, the equilibrium concentrations are higher. Being on the innermost edge of the sun’s habitable zone, earth’s equilibrium greenhouse gas concentrations are as a result extremely low. CO2 for example is barely a trace gas in our atmosphere in modern times.
A low equilibrium greenhouse gas concentration makes a planet’s climate much more sensitive to non-natural additions of greenhouse gases to the atmosphere. Adding 100ppm CO2 to an atmosphere that normally has only 100 ppm CO2 doubles the greenhouse effect in that atmosphere. Adding the same 100ppm to an atmosphere that normally has 4000ppm is barely a measurement error. A planet further out in the habitable zone, with a higher baseline greenhouse gas, could theoretically be much more tolerant, climactically, of the industrial activities of any technological civilization, such as that of humans, than Earth actually is.
So it is entirely possible that, of all the possible orbital locations that Earth could be in that could support human life, out of 150 MILLION km of real estate, Earth ended up what might well be the worst 1% available.