Say a Mars size object hits the Earth in such a way that it knocks the Earth in a straight 0 degree angle, and let's assume that we somehow do not go extinct.

What would happen to the poles in this scenario, in terms of temperature and volume of ice?

My guess is since now there is no longer a tilt, the poles would receive the same amount of solar input, which would increase the ice caps of both poles.
As there is no incentive to melt the caps, maybe this would even cool the planet.


closed as off-topic by EnergyNumbers, Fred, Jan Doggen, Aabaakawad, David Hammen Oct 30 '15 at 17:22

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about earth science, within the scope defined in the help center." – EnergyNumbers, Fred, Jan Doggen, David Hammen
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  • $\begingroup$ 90 degree tilt is one side pointed at the sun for 6 months, pointed away 6 months. I think you mean, 0 degree tilt. - see here: hyperphysics.phy-astr.gsu.edu/hbase/astro/imgast/tilt.gif 90 degree tilt, effectively, a day becomes a year. It would be a mess. $\endgroup$ – userLTK Oct 29 '15 at 5:28
  • 1
    $\begingroup$ I think this is better placed on Worldbuilding. There is a big problem with outlandish hypothetical questions such as this, which is that the OP really is never well placed to offer meaningful clarification of ambiguities. Of which this question has a lot. $\endgroup$ – EnergyNumbers Oct 30 '15 at 12:28
  • $\begingroup$ Btw. I just calculated that a Mars Size object would have made the Uranus to tilt this 90 degrees it now rotates; physics.stackexchange.com/questions/215049/… $\endgroup$ – Jokela Nov 1 '15 at 9:30

If we ignore the giant impact (which would have enormous effects), and just look at the effect of the Earth having a 0 degree axial tilt, the most immediately apparent effect is that the seasons would be reduced almost to nothing and the very small seasons that remain would be planet wide, not alternating between the 2 hemispheres.

The Earth is currently closest to the sun in the first week of January and furthest in the first week of July. Source, so it's pretty obvious that being closer to the sun doesn't create summer. The axial tilt is what causes the seasons, but the change in distance to the sun still has some effect.

There's a little over 3% variation in distance, see source, yielding a bit over 9% variation in energy received between the Earth's perihelion and aphelion, but that doesn't mean a 9% change in temperature. It's much smaller than that due to the Earth's oceans, atmosphere and to a lesser extent, surface are all heat sinks that take a long time to warm up or cool down. The seasonal difference in temperature would be much less than that. Maybe a few degrees, perhaps 5-10 degree difference between summer and winter, probably less than the change between night and day.

No tilt also means, you lose the 6 months of sunlight, 6 months of darkness that we currently get near the poles and the sun wouldn't be higher in the sky in summer than in winter. At the poles, you'd effectively get sunset, 24 hours a day, 365 days a year but over most of the Earth you'd have 12 hours (and a few minutes) of sunlight and nearly 12 hours of, not darkness, cause you'd still have twilight and dawn, but over the most of the planet, it would be 12 hour days pretty much.

The poles would receive less solar energy and could be colder and there wouldn't be a spring thaw or summer growth. Plant Growth would be pretty consistent all year around.

The equator would have more peak sun and could be hotter. With our current tilt, the pole to equator solar energy ratio is 0.4 to 1. Source. With no tilt, it would be 0 to 1. The poles could see an increase in permanent ice.

But, despite that increase in ice, you'd get a decrease in solar-ice-reflection, so that could mean a warmer earth, even with more ice on both poles. The equatorial region could be hotter.

Circulation is hugely complex, so that's a great big wild-card. Seasonal driven ocean and air currents would be greatly reduced but temperature driven currents should increase, though the reduction of temperature variation is difficult to predict. You still get night to day temperature variation, but the overall effect on wind and ocean currents is too hard for me to predict.

Hyper-physics says the tilt is essential to life (linked above). I'm not sure that's true, but no seasons and potentially reduced circulation due to more consistent temperatures could have a pretty big effect. The potentially worst outcome could be a significant still water in the oceans which could create large dead zones. That's by no means a certainty, but it's possible.

Article on the effects of the ocean conveyor belt stopping, if interested.

If I missed anything, comments are welcome.


The question is not very clear, but if a Mars sized object were to collide with Earth, at any angle, believe me, that would be an undoubted total extinction event for every organism on the planet. You can do a 'back of an envelope' calculation on the kinetic energy expended by such an impact. That is, E=1/2M.V^^2, where M and V are the mass and relative velocity of the impacting bolide. Then express that as thermal energy - very obviously there wouldn't be any ice left on Earth's surface. There probably wouldn't be much left of any oceans or continents either. Much of the planetary debris would be flung into space, with some being lost, some condensing into another moon (or multiple moons), and some raining down on the planet in a new 'Hadean' event. The entire geochemical distribution of the atmosphere, oceans, crust, mantle and core, would be back into the melting pot (literally) and would take between a few hundred thousand and a few million years to re-equilibrate into something resembling a normal planet.

But to address the tilt problem, if the spin axis was orthogonal to the incoming solar radiation, the nett annual insolation at the poles wouldn't change - only the seasonal distribution. Without the seasons the entire heat distribution of the planet would be radically changed, and it is impossible to estimate the myriad knock-on effects without extensive modelling on a supercomputer, and then drawing a consensus from 20 to 30 of the most sophisticated global climatic models. For example, the cloud distribution, ocean current strengths, polar vortices, rainfall distribution, river flows, groundwater storage, tropical storm distribution and frequency, CO2 absorbtion by vegetation, and many other co-variables would all be affected.


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