Some THEMIS IR images show surprisingly high temperatures at high northern latitudes on Mars. The data for the examples below are taken from the data labels for the images. You'll need to download and open in a program such as NASAView or programs specifically written for THEMIS the Brightness Temperature Image files of file type .IMG on each of the linked pages to read this data.

THEMIS Image Data Page for I11896042.
CENTER_LATITUDE = 49.5458
CENTER_LONGITUDE = 349.094
MINIMUM_BRIGHTNESS_TEMPERATURE = 145.350
MAXIMUM_BRIGHTNESS_TEMPERATURE = 296.671
http://themis-data.asu.edu/img/I11896042


THEMIS Image Data Page for I05548016.
CENTER_LATITUDE = 34.5145
CENTER_LONGITUDE = 202.03
MINIMUM_BRIGHTNESS_TEMPERATURE = 304.961
MAXIMUM_BRIGHTNESS_TEMPERATURE = 314.052
http://themis-data.asu.edu/img/I05548016


THEMIS Image Data Page for I03396032.
CENTER_LATITUDE = 45.524
CENTER_LONGITUDE = 164.151
MINIMUM_BRIGHTNESS_TEMPERATURE = 302.723
MAXIMUM_BRIGHTNESS_TEMPERATURE = 311.785
http://themis-data.asu.edu/img/I03396032


THEMIS Image Data Page for I02967002.
CENTER_LATITUDE = 76.7838
CENTER_LONGITUDE = 128.354
MINIMUM_BRIGHTNESS_TEMPERATURE = 267.048
MAXIMUM_BRIGHTNESS_TEMPERATURE = 314.033
http://themis-data.asu.edu/img/I02967002


THEMIS Image Data Page for I029674002.
CENTER_LATITUDE = 78.274
CENTER_LONGITUDE = 288.536
MINIMUM_BRIGHTNESS_TEMPERATURE = 258.639
MAXIMUM_BRIGHTNESS_TEMPERATURE = 296.812
http://themis-data.asu.edu/img/I02974002


THEMIS Image Data Page for I02834003.
CENTER_LATITUDE = 40.1813
CENTER_LONGITUDE = 349.993
MINIMUM_BRIGHTNESS_TEMPERATURE = 306.029
MAXIMUM_BRIGHTNESS_TEMPERATURE = 322.379
http://themis-data.asu.edu/img/I02834003


THEMIS Image Data Page for I01913037.
CENTER_LATITUDE = 49.7447
CENTER_LONGITUDE = 272.881
MINIMUM_BRIGHTNESS_TEMPERATURE = 265.707
MAXIMUM_BRIGHTNESS_TEMPERATURE = 312.959
http://themis-data.asu.edu/img/I01913037

The maximal temperatures in these cases are significantly higher than the maximal temperatures expected at the given latitudes, especially for the temperatures above 300K, which would be expected only near the equator, at least in the Northern hemisphere.
How accurate are these THEMIS brightness temperatures?

You can do your own search for high temperatures by going to the page:

THEMIS Public Data Releases.
http://themis-data.asu.edu/

and clicking on the Advanced tab. Then you can enter the latitudes, longitudes and temperature ranges you want to search for.



Bob Clark

That's 120.6°F max (49.2 °C)
Hot, hot hot!

Some of these images contain noise so it needs to be determined how valid these measurements are. What might help is to locate where these maximal temperatures are occurring within the image and try to relate them to geomorphology in visible light images.
It would also help to find out if these high temperatures are maintained in subsequent IR imaging.

It is interesting that one of the images lies within Cydonia:

THEMIS Image Data Page for I02834003.
CENTER_LATITUDE = 40.1813
CENTER_LONGITUDE = 349.993
MINIMUM_BRIGHTNESS_TEMPERATURE = 306.029
MAXIMUM_BRIGHTNESS_TEMPERATURE = 322.379
http://themis-data.asu.edu/img/I02834003

and contains a feature that has been claimed to appear as a "smoking pyramid". It's an area in visible light imaging that has light colored areas giving the appearance of gas or water vapor release. It would be interesting to find out if the maximal temperature in the IR image corresponds to this "smoking pyramid".
Some visible light images of the region:

MOC narrow-angle image E01-01908.
http://barsoom.msss.com/moc_gallery/.../E0101908.html

THEMIS Image Data Page for V02834004.
http://themis-data.asu.edu/img/V02834004.html


Bob Clark

I don't find that any more interesting than any other warm image or any other location. Especially since it's been shown, repeatedly, that Bob's "observations" are completely meaningless.

Another interesting case is:

THEMIS Image Data Page for I02026005.
CENTER_LATITUDE = 39.1376
CENTER_LONGITUDE = 251.959
MINIMUM_BRIGHTNESS_TEMPERATURE = 302.213
MAXIMUM_BRIGHTNESS_TEMPERATURE = 322.192
http://themis-data.asu.edu/img/I02026005

This happens to lie in Alba Patera, the volcanic region. This image is much more free of noise making it more likely the measurement is an accurate one.
Here's a visible light image:

THEMIS Image Data Page for V02026006.
http://themis-data.asu.edu/img/V02026006

Again it would be interesting to find out if the highest temperature in the IR image is reached where there is geomorphological evidence of venting in the visible light images, such as pseudocraters for example.


Bob Clark

To determine the validity of these measurements I need to know what are the calibrations for the raw data and how do you determine the specific coordinates where the maximum temperature occurs within an image.



Bob Clark

Bob,

As far as I know THEMIS has a resolution of 100 meters per pixel. Does this mean that by MINIMUM_BRIGHTNESS_TEMPERATURE is meant the lowest reading in the picture? And if so, does this mean that such a reading is actually an average over a 100 by 100 meter surface? If it really contains a smoker or something like that we can expect this thing to be much smaller than 100 meters, which means that the highest temperature in the picture will actually be a lot higher than the MAXIMUM_BRIGHTNESS_TEMPERATURE mentioned.

I also understand that the official point of view with regards to this instrument is that it did NOT discover any hotspots on Mars. What do you think of that?

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A good article on this is:

Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results.
Science, Vol 300, Issue 5628, 2056-2061, 27 June 2003
http://www.sciencemag.org/cgi/conten.../300/5628/2056 [full text available with free registration]

The authors observed that temperature differences from that of the surrounding terrain are common on slopes of all types, canyons, craters, etc., from 5 to 15K hotter. They conclude these differences are due to a greater concentration of rocks on these slopes. However, this doesn't mean internal heating sources can not exist, only that such sources are not required to explain the observed temperature differences.
One way to eliminate this as an explanation of higher heat in a region might come with better resolution imaging showing there is not a larger concentration of rocks in a localized site showing higher temperatures.
One thing I would have liked to have seen answered is the method for determining the actual surface temperatures from the brightness temperatures observed from orbit. The article mentions both and rather vaguely implies they are taking them to be approximately equal but does not specifically say so.



Bob Clark

Then perhaps you should be looking for answers somewhere other than on internet web forums.

Correction. The article suggests the night-time brightness temperatures reflect more closely the thermal properties, from which I deduce they mean the brightness temperture is close to the actual surface temperature.
But they also suggest the daytime temperatures are affected by several different factors, not just the thermal properties of the surface. The relationship of the brightness temperature to the actual surface temperature is more unclear in this case.
This is discussed more fully in the Supporting Online Material, linked to after the text of the article.


Bob Clark

Thanks Bob.
BTW, at what local time where those IR measurements taken? I would think that to find internal heating you must look late at night, to exclude solar heating. But looking at the temperatures given they must be daytime values. I'm probably missing something obvious here....

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When you click on the link for each image the local time when the image was taken is given.
I was only looking for high temperatures so I didn't restrict it to night-time observations.
In my list as I recall only one was at night and that one had alot of noise making the measurement uncertain. It would be nice if these images had a corresponding night time image but areas are imaged as the spacecraft flies over at whatever time so not every spot will have a corresponding night time image. I believe specific areas can be targeted for night time imaging though.


Bob Clark

Nick Hoffman described how to read the THEMIS brightness images here:

How to do it with NASAVIEW.
Posted by Nick Hoffman on 8/7/2005 6:02:09 AM
In Reply to: re: Martian high north latitude hot spots? posted by Robert Clark on 8/6/2005 5:06:41 AM
http://habitablezone.com/space/messages/390308.html


He discussed this image:

THEMIS Image Data Page for I02026005.
CENTER_LATITUDE = 39.1376
CENTER_LONGITUDE = 251.959
MINIMUM_BRIGHTNESS_TEMPERATURE = 302.213
MAXIMUM_BRIGHTNESS_TEMPERATURE = 322.192
http://themis-data.asu.edu/img/I02026005

He observed the hottest areas were in the Sun-facing walls in the image, which argues against the maximum temperature being due to a hot spot.
But a key fact about this image is that even the minimum temperature is quite hot for this latitude. Do a search for instance on http://themis-data.asu.edu . Click the Advanced button, then search on the IR images in the latitude range 37 to 41. You'll get a couple of thousand images. The highest maximal temperatures you'll see will be overwhelmingly in the 250's. There are only perhaps 2 or 3 in the 300's. So this particular image even has it's minimal temperature 40 to 50 degrees hotter than most other maximum temperatures at that latitude.
In reading some articles about the brightness temperatures it turns out they are affected by albedo as well as surface temperature. So you might guess this is an unusually bright area. But the corresponding visual image does not give that impression:

THEMIS Image Data Page for V02026006.
http://themis-data.asu.edu/img/V02026006

It would be interesting to find out if current or past Mars Global Surveyor TES imaging also shows this to be an unusually warm area.


Bob Clark

That is on the flank of Alba Patera, one of the largest vulcanoes on mars!
If there is any place on Mars one would expect a hotspot, its right here I guess.

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The THEMIS image is actually in the caldera of Alba Patera, which you would expect for a geothermal hot spot.
This MGS image near the same area shows two dark streaks at the bottom:

MOC narrow-angle image R16-00268
North middle-latitude crater in Alba Patera caldera.
http://www.msss.com/moc_gallery/r16_.../R1600268.html

They both have the feature of widening from a central origin point. I consider this characteristic of material being vented and then being spread aerially by wind. If they arose simply from a dust deposit, you would expect the streaks to only extend straight out from the deposit with the width staying the same as the width of the deposit. Alba Patera is known to have had recent lava flows. Dark streaks whatever their cause would have to be geologically recent. Due to dust cover we would actually expect dark streaks to only have a lifetime measured in millenia or less.
There are many other dark streaks in the accompanying context image which also have the feature of widening from a central point. The famous "slope dark streaks" near the equator also have this feature, but those are due clearly to gravity-induced flow down a slope. The dark streaks in the Alba Patera region have the appearance of wind carried flow, as well as being far from the equator. However, the slopes directions do need to be checked by MOLA measurements to be sure of this.
But particular evidence these streaks are wind-developed as well as to the possibility of venting is provided by the upper of the two steaks in image R1600268. This streak appears not to originate from a nearby crater, but slightly above the crater in the image. But by enlarging the image you see this streak actually does originate from the crater. What happens is the streak is directed upwards in the image, then horizontally to the right. This could be due to a venting directing the vented material in one direction initially, then the prevailing wind directing it to the right afterwards.
I argued as well this characteristic of a wind-developed streak widening from the origin point as indicative of a venting here:

Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology
From: rgregorycl...@yahoo.com (Robert Clark)
Date: 13 Feb 2004 07:03:49 -0800
Subject: Re: Active volcanic vent on Mars?
http://groups.google.com/group/sci.g...98bf4b3a4d15ec

Another released THEMIS image in the Alba Patera area, though on the flanks not the caldera, also shows streaks:

Alba Patera Windstreaks (Released 1 June 2005)
http://themis.asu.edu/zoom-20050601A.html

The accompanying caption discusses an unusual feature of these streaks, the dark streaks seem to split apart in two in the lee of a crater. The caption ascribes this to a vortex in the lee. However, similar features near craters at the south pole have been ascribed to venting of CO2 by Mars scientists:

Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology
From: rgregorycl...@yahoo.com (Robert Clark)
Date: 13 Mar 2004 20:31:20 -0800
Subject: Re: Active volcanic vent on Mars?
http://groups.google.com/group/sci.g...da137b7c3474c4

It would be interesting to find out by experiments which if either of these explanations can reproduce this effect.


Another image of the Alba patera caldera might show indications of wide-spread venting:

MOC Image m0300999 - Browse Page.
http://ida.wr.usgs.gov/html/m03009/m0300999.html

The image shows a highly pockmarked surface that could indicate gas release: rather than simply being a highly cratered surface, the holes here have the appearance of being due to surface or subsurface processes.
However, another interpretation of this surface is that it is karst terrain. Karst terrain is due to acidic water dissolution of evaporitic deposits such as carbonate and sulfate:

A KARST PRIMER.
http://csweb.winona.edu/semnwrb/file...t/sprkarst.htm

Karst in Alba Patera has been proposed before. See the caption here:

THEMIS: Image Detail: Alba Patera.
http://www.marstoday.com/news/viewsr.html?pid=5278

This image also has the appearance of karst terrain:

Relay 16 Test traverse in western caldera of Alba Patera
http://www.msss.com/moc_gallery/e01_.../E0502944.html

This dissolution of the surface material causing a pockmarked surface is also described here:

SIMPLE NON-FLUVIAL MODELS OF PLANETARY SURFACE MODIFICATION, WITH
APPLICATION TO MARS. A. D. Howard1, 1Department of Environmental Sciences, P.O. Box 400123, University
of Virginia, Charlottesville, VA 22904-4123, *****@virginia.edu
http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1054.pdf

A related phenomenon proposed to exist in Alba Patera is thermokarst, similar to karst except it occurs in permafrost:

Possible thermokarst and alas formation in Utopia Planitia, Mars
Richard J. Soare,1 J.M. Wan Bun Tseung1 and Claude Peloquin.1 Dept. of Geography, Planning and Environment,
Concordia University, 1455 De Maisonneuve W., Montreal, Canada, H3G 1M8. E-mail: ******@colba.net
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1103.pdf

If thermokarst, we would expect the age to young as well perhaps less than millenia, in connection to the relative youth of permafrost which arises and disappears with periodic ice ages.



Bob Clark