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Posted by: tanjent Dec 10 2013, 03:37 PM

According to this BBC article, http://www.bbc.co.uk/news/science-environment-25287806

satellite measures of surface temperatures on Earth confirm an observed range of 163.9 degrees; (-93.2c to +70.7c); thus wider than the differences between summer highs and winter lows experienced by Spirit and Opportunity. The low figure falls slightly above the measurements taken by Phoenix just before contact was lost in October 2008.

It is surprising to me that between these two planets with very similar axial tilts and rotation times, the wider range of observed temperatures appears likely to be found on the Earth despite its much thicker atmosphere. (To confirm this, high and low extremes for Mars would have to be measured using the same satellite-based approach.)

Posted by: Gerald Dec 11 2013, 06:47 PM

The earth is closer to the sun; this means a larger difference between dayside and nightside incoming radiation.
The earth is larger than mars slowing down global temperature exchange.
Cold slope winds in south polar valleys will result in cold air lakes in those valleys during polar night.
Atmospheric CO2 freezes out at some point on mars and will prevent cooling down further.

Just some ideas, why "thinner atmosphere = higher temperature differences" won't be that straightforward.

Posted by: djellison Dec 12 2013, 03:00 PM

As you alude to - you're comparing highs and lows from near the Martian equator - with Highs of Earth's equatorial region and lows of high altitude Antarctic region.

You're not comparing apples with apples.

I would argue that winter polar minimums on Mars could very well take that range and make it pretty much as large as that for Earth.

Posted by: tanjent Dec 14 2013, 09:50 PM

After a little extra Googling, I see that the Viking Orbiters measured global extreme temperatures of -143 and 27, for a Martian range of 170 degrees, which does exceed the Terran range measured by Landsat, quoted in the initial post. So Doug's expectation is confirmed.

http://www-k12.atmos.washington.edu/k12/resources/mars_data-information/temperature_overview.html

Gerald's first point about distance from the sun is valid too, because in the extreme case, a free-floating planet without any star to warm it would (I assume) not experience any temperature variation at all. An alternative way to correct for the distance from the heat source would be to measure the ranges in degrees Kelvin and then convert to percentages. In this case, the range for the Earth would be given as ( 343.85 / 179.95 ) - 1 = 91.08% . The Martian range would be ( 300.15 / 130.15 ) - 1, or 130.61% . So, the Martian range is much wider by this measure, as we might expect for a smaller body with less atmospheric insulation.


(Footnotes)

To make an equivalent comparison for the other rocky planets, Venus has no reported diurnal variation at the surface, which has been measured at 464 degrees centigrade or 737.15 kelvin. http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html

Elevation differences matter on Venus, but I have still not found a satisfactory figure for the difference between the highest and lowest points on the surface.
Interpolating on the basis of this table,

http://en.wikipedia.org/wiki/Atmosphere_of_Venus

and assuming a 13 k elevation difference indicates that the temperature difference may be about 100 degrees. Thus, the percentage spread for Venus works out to about
15.7 percent, (737.15-637.15) - 1.

For Mercury the percentage spread is extremely sensitive to the polar minimum values. For example, a sunward temperature of 440 K and a polar minimum of 40 K would give a percentage range of 1000%. This would be a very conservative estimate.