Earth at Mar's Orbit: What Would Climate Be Like?

Suppose the earth were tobe at the same distance from the Sun, that Mars is now at: what would the Earth be like? Would the oceans all be frozen? Or would the earth be slightly colder than now? I suspect that Mars receives only about 1/3 the solar radiation that the earth does, so days would be colder-but even Mars gets warm (at the equatorial regions). Anyway, assuming everything being equal-would the earth be in an Ice Age if at Mar’s orbital distance?

The semi-major axis of Mars orbit is about half again as far from the Sun as the Earth, which gives it roughly 39% of the luminous output at Earth’s mean radius. It’s hard to say exactly what the climate would be like–climatology is a difficult enough science when we can observe the effects rather than infer their possiblity–but it certainly wouldn’t be able to support life as we know it, and it seems likely that the atmosphere (assuming you’re starting with Earth’s normal composition) would be far more arid, less capable of holding heat.

In addition, if we assume that Earth is placed in Mars’ current orbit, you have to account for the increase in variability; the orbit of Mars has an eccentricity over five times greater than that of Earth. Since you’re already farther from the Sun to begin with the variability is of less effect than it would be at Earth orbit, but there would certainly be more variation in what energy impinges upon the Earth.


The black body temperature for objects in earth’s and mars’ orbits are -2°F and -81°F respectively.
The average surface temperture of the earth is about 59°F, so the earth is about 61° warmer than its equilibrium black body temperature. If that difference holds when the earth is moved out to the position of mars, the average surface temperature would be -20°F.
I expect the increased snow cover, hence albedo, would eventually cause the average temperature to drop well below that.

If the early atmosphere of MOE (Mars Orbit Earth) was heavy in greenhouse gases then. It could be warm enough for liquid water and by extension life. After all Venus is kept hellishly hot by its dense atmosphere.

For that matter, I seem to recall that at the equator, the surface temperature of Mars can even still occasionally edge a bit above freezing. And certainly in the past, when Mars had a thicker atmosphere, liquid water was not a stranger to most of its surface.

We have all heard the “Goldie- lox” zone to be where Earth orbits now around our sun extending some percentage towards Venus and Mars. It may be only half way towards Venus, but likely overlaps the orbit of Mars when Mars is at Perihelion. Which means the old saying that if we were a fraction closer or further life would not be possible IS WRONG. First of all the statement “a fraction closer or further” is NOT quantified. Mars at perihelion is 1.38 AU which corresponds to 52.5 % of the luminous output Earth receives. Mars, with its thin atmosphere has less of a greenhouse effect than Earth, yet the highest temperature recorded on Mars at perihelion during it’s Summer peaked at 80 deg F at equatorial regions in valleys (45 degrees is more common when at aphelion in the hottest regions, while the South Pole can be -220 F, at distance of 1.67 AU=aphelion). As pointed out in an earlier posting, the black body temperature of an object at Earth’s orbit is 83 degrees warmer than an average Mars orbit, but that does not take Earth’s thicker more greenhouse like atmosphere and surface albedo into account. Earth would definitely enter an ice age, but at the warmest equatorial – desert regions, Earth with it’s stronger greenhouse effect, could still hit in excess of 90 degrees (versus 135 to 140 where it is now). However, as the ice built from the poles southward, the surface albiedo would increase, reflecting more heat and leading eventually to colder temperatures. With less oceans to supply ice, the surface of Earth would be warmer. It’s doubtful permanent ice shelf’s would reach equatorial regions, but possibly down to 25 - 30 degrees North and South of the equator. … Though the climate dynamics would be hard to calculate with any exactness. … weather patterns could help push ice shelfs down to 15-20 degrees North and South of the equator but no-one knows with certainty. Point is, life would still persist, even if Earth was pushed to 1.38- 1.40 AU, though there would be massive extinctions. Better move Mars out a bit too … If you could move Earth, then also reduce its 23 and a half degree tilt to about 5 degrees. This would ensure pleasant equitorial regions for Earth at 1.38 ot 1.4 AU.

Earth in its present orbit may have frozen over entirely at one point in its history. That would, of course, be more likely if it were farther from the Sun.

Anne Neville… Yes, some 650 to 680 million yrs ago, there is evidence of a huge glacial period… still not known if it reached near the equator, additionally, the Sun’s output was estimated to be 70 % of what it is today… the Sun’s output luminosity is very slowly increasing over time.