When Earth's axial tilt were like Uranus ?

[skysurfer]

I tried just for fun with Stellarium how the sky is when the axial tilt of Earth is like Uranus.
Very funny. On June 21, virtually the whole northern hemisphere is in sunlight and on the North Pole the Sun is almost in the zenith (82º). Australia has 24/7 sun for months (nov-jan) and 24/7 darkness for months (may-jul). *Every* winter is far worse than the very cold spells in the US last winter, at least because there is no daylight.
I guess that the Earth is uninhabitable because in summer, strong winds are blowing from the heated hemisphere over the equator area (including Darwin) to the dark hemisphere which is very cold in winter and very extreme season differences occur.

What are your opinions on this ?

You might try it with Stellarium by adding the following block to "ssystem.ini" where the planets are described. When added, select 'xearth' as 'planet' and have fun.
*

[xearth]
name = xearth
parent = Sun
radius = 6378.
halo = false
color = 0.,0.,0.
tex_map = earth-clouds.png
tex_halo = star16x16.png
coord_func = earth_special
lighting = false
albedo = 0.0
rot_periode = 23.9344694
rot_rotation_offset = 280.5
rot_epoch = 2451545.0
rot_precession_rate = 1.39639 #degrees/j.century (annual rate 50.27 arcseconds)

orbit_Epoch = 2451545.0
orbit_Period = 1.00000000000000
orbit_SemiMajorAxis = 1.000000000000
orbit_Eccentricity = 0
orbit_Inclination = 0
orbit_AscendingNode = 0
orbit_LongOfPericenter = 0
orbit_MeanLongitude = 0

orbit_visualization_period = 365.25
rot_pole_ra = 257.43  # value for Uranus
rot_pole_de = -15.10  # value for Uranus
hidden = true

[Eratosthenes (Peter)]

.....was the Earth's axial tilt ever that extreme as it is with Uranus today?

When looking at long term climate variations (ie thousands of years) the Milankovitch cycles are referred to and one of these cycles is driven by the Earth's axial tilt angle. I dont think it varies more than a few degrees over about 35,000 years though.

I can't imagine much plant life on a permanently dark hemisphere. Couple that with extremely low temperatures and life in general may struggle to establish itself. May need an indirect source of energy like the thermal vents on the ocean floor, or life forms that metabolise elements like sulphur etc.

The hemisphere that will be facing the sun 24/7 all year round has its own problems of extreme temperatures etc.

Isn't the planet Mercury in a similar type of orbit where one side is facing away from the Sun? Temperatures must be very cold on that side, even though Mercury is very close to the sun.

Life seems to like a relatively narrow and predictable range of conditions to flourish - although it can survive in amazingly extreme environments on our planet. And if the conditions do vary, most of the life on the earth prefers short cyclical regimes - daily, or seasonal over a year. There are exceptions of course.

One example on the earth of long term sunlight followed by darkness would be at the poles. In Antarctica for example, the summer period can last for about 4 months where the sun never sets, whilst the winter period in dark for 8 months. Life still manages to survive

[skysurfer]

Originally Posted by Eratosthenes

The hemisphere that will be facing the sun 24/7 all year round has its own problems of extreme temperatures etc.

Not all year round, but only in summer, just like Antarctica from the arctic circle 67 deg S in December now, shrinking gradually to the south pole on 21 Mar, but then from 8 deg S (e.g. Bali) on 21 Dec, which means with a Uranian axial tilt the arctic circle passes over Bali.

Originally Posted by Eratosthenes

Isn't the planet Mercury in a similar type of orbit where one side is facing away from the Sun? Temperatures must be very cold on that side, even though Mercury is very close to the sun.

That is a different issue, that is tidal locking which does not occur at Uranus. Here I am talking about extreme axial tilt, so Earth's rotation remains 24 hours.

Originally Posted by Eratosthenes

In Antarctica for example, the summer period can last for about 4 months where the sun never sets, whilst the winter period in dark for 8 months. Life still manages to survive

This must be 6 months / 6 months and the dark period centered on 21 Jun is strictly 3-4 months as in a month before Sep 23 and after Mar 21 there is twilight.

[Eratosthenes (Peter)]

So is there any evidence that the earths axial tilt was ever at 90 odd degrees? The Milankovitch axial tilt cycle is only a few degrees in variance and occurs over 35,000 years (roughly)

I wonder what the variation in atmospheric conditions would be on both hemispheres if the Earth's axial tilt was similar to that of Uranus?