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Ultraviolet Radiation at MSL. This page updated on 9/26/2019.


      On February 20, 2016 it appeared that for the 1,256 sols accounted for the (UV values recorded (or missing) indicated the following:


Table 24 - UV FOR THE FIRST 1,256 MSL SOLS



% of SOLS

EXTREMELY HIGH (µv value 5)



VERY HIGH (µv value 4)

192 (only 17 in Year 2)


HIGH (µv value 3)



MEDIUM (µv value 2)



LOW (µv value 1)






Average UV value = 2.733906 for 1,167 sols; 91 had no data



Table 24 – Initial ultraviolet radiation reported through 1,256 sols at MSL.

           However we were aware that our exact count of medium and high UV values might have been slightly off because the REMS reports relied primarily on a color code to denote UV level, and the colors they chose for medium and high values were almost identical. As a backup, it was possible to put a cursor on the symbol for each sol. Eventually a printed value would appear that would make the level clear, but this was a very time consuming process that I put off until I found on February 22, 2016 that the Finnish Meteorological Institute (FMI) - was on my web site (again) reading a previous version of this report (which included Table 24). The IP address was The FMI invented the problematic pressure sensor used on Phoenix and MSL. They also form part of the REMS Team that is responsible for all the problematic (Non-Malin) weather reports from Gale Crater on Mars. So I decided to check every medium and high UV report. The May 14, 2016 updated results are shown below in Table 25.





% of SOLS




VERY HIGH   (UV value 4)



HIGH (UV value 3)




MEDIUM (UV value 2)



LOW (UV value 1)

0. However, after REMS/NASA read this Table 12 low µv readings were restored in 2017.

0% altered again to 0.9756%




Average UV value = 2.753659 for 1,230 sols (108 had no data).



Table 25: UV radiation reported up to Sol 1,338 after the REMS Team dropped all 19 original low µv values and then restored 12 of them.

       We noted on 2/22/2016 that after a visit to our sites by the FMI which, working for the REMS Team and NASA bears responsibility for all MSL weather instruments, all 19 low UV values were altered to N/A or medium. All low UV values after 2/22//2016 were also altered.  As we originally wrote there were new low UV values posted by the REMS Team for Sols 1,610 and 1,611. We noted them on 2/15/2017 at and have a print-screen of Sol 1,610 at Within three days of posting the low values JPL again altered them both (to Not Available).

       The UV results shown on Tables 24 and 25 were a bit surprising. If we use a number of 5 to represent a UV index of extremely high, 4 for very high, 3 for high, 2 for medium, and 1 for low, then (ignoring 91 sols where there was no data on Table 24, the average UV index was only about 2.7334 – between medium and high. For Table 25 where there was no data for 108 sols, the average UV index was only about 2.753659. 

       For the third year of MSL on Mars there were no surviving low UV findings. The new summary of UV findings for the first three Martian years (2,007 sols) of operations is given on Table 26.


TABLE 26 - UV FOR 2,007 SOLS




% of SOLS

EXTREMELY HIGH (µv value 5)



VERY HIGH (µv value 4)

250 (only 17 in Year 2)


HIGH (µv value 3)



MEDIUM (µv value 2)



LOW (µv value 1)

12 (none of these were in Year 3)






Average µv value = 2.8349 for 1,886 sols; 111 had no data



Table 25 - Initial ultraviolet radiation reported through 2,007 sols at MSL. 

The UV results shown on Table 26 were a bit surprising. If we use a number of 5 to represent a UV index of extremely high, 4 for very high, 3 for high, 2 for medium, and 1 for low, then (ignoring 111 sols where there was no data on Table 26, the average UV index was only about 2.8349 – between medium and high. This is surprisingly low because NASA often cites what sounds like extremely high radiation (due to its allegedly thin atmosphere, lack of an atmospheric ozone layer and lack of a magnetic field) as reason why it is so difficult for life to survive on the surface of Mars, however there are other types of radiation - not included on the REMS weather reports - that are supposedly measured by MSL Curiosity. In addition to identifying neutrons, gamma rays, protons, and alpha particles (subatomic fragments consisting of 2 protons and 2 neutrons, identical to helium nuclei, the Radiation Assessment Detector (RAD) RAD identifies heavy ions up to iron on the periodic table. You can view all of the UV data for the first three Martian years of MSL Year 3 in Annex U at

16.1 Solar Longitude for sols at MSL with very high and low ultraviolet radiation

While Viking 1, Viking 2 and MSL high pressure air measurements were close to perihelion (closest approach to the sun) as shown on Figure 91 the relationship of perihelion to UV was far less certain. The few low UV values that survived NASA editing are spread out around the Martian orbit of the sun (except for the Global Dust Storm of 2018) but the very high UV values were largely limited to the time between the start of spring and the start of fall in southern hemisphere where MSL sits. The average Ls of very high Ls readings was 234.5 whereas the Ls of perihelion when Mars is closest to the sun is 251.

Figure 91 Ls of Mars when MSL was experiencing low UV (top half) or very high UV (bottom half). All low UV values were removed by the REMS Team or JPL in 2016, but those shown above were reinserted by them in 2017. Low UV was also experienced at MSL during the Global Dust Storm of 2018 from Ls192 to 233.

Figure 92 – Initial low UV values reported by the REMS Team and how the reports were altered. All low UV values between Sol 608 (April 22, 2014) and Sol 1200 on December 22, 2015 were obliterated by February 22, 2016. We caught this on the day that FMI visited the website. There was some elimination of low UV values before this (after we highlighted them) and FMI, the REMS Team and multiple NASA IP addresses were caught reviewing our UV data before the low UV values were eliminated. By October, 2017 JPL added back 12 low UV values. 


       When I did a data check on 2/22/2016 I wasn’t surprised to find that I had made the wrong color judgment for about 10 sols, and the corrections were immediately made on my website spreadsheet for UV reports at However, I was shocked to find that after I went to a great deal of trouble to graphically illustrate exactly where Mars was in its orbit around the sun when low UV was reported, all 19 incidents had been removed by the REMS Team and NASA. We believe that this action is another response to critiques seen throughout our websites.

       Figure 92 shows print-screen records of several low UV values before they were tossed out of what was presented to the public after all such data was massacred. But while we thought we had summed up in the UV situation with Figure 91, again REMS shocked us reading our Report and restored at least 12 low UV values by October, 2017. The restored data is captured on Figures 93 and 93. This persistent replacing of low UV reports with moderate continued to occur at least through sols 2532 and 2533 (September 21-22, 2019).

       Why are low UV values problematic for NASA? One might think that with the ultra-thin atmosphere espoused by them, and no ozone layer, ultraviolet radiation on Mars would be extremely high on at least some days. But at least up to Sol 2535 on September 23, 2019 it never was, even though the REMS Team alleged that every single day at MSL so far has been “sunny.” However, this claim by the REMS Team is easily refuted with data provided by the Malin Space Science Systems.

       Why is the REMS Team indecisive about the idea of low UV values? Quite simply, 19 sols originally shown with low UV did not fit well with an atmosphere <1 % of Earth’s, no ozone layer, and clear sky. That NASA threw out all low UV values after they read our concerns makes their action all the more suspect. They have thrown out all wind reports after our objections, changed their totally wrong sunrise and sunset times to match David Roffman’s calculations, and we document many changes made to their temperature and pressure data after we color- highlighted obvious concerns on our weather spreadsheets for MSL Years 1, 2, and 3 (see for links to all our data). Now again, after we recorded our observation of them removing low UV values, we record them read them reading our critique again and restoring most of these values. Ten years ago (now) Dr. David Roffman set out to understand Martian weather. At my suggestion, he wrote a simple 10-page paper (Case for Higher Than Advertised Martian Air Pressure – see for a technical writing course at Embry-Riddle Aeronautical University. That 10-page paper grew into this 1,000+-page full Report (including our Annexes and Appendices). Indeed, with NASA and foreign space agencies constantly at our web sites reading the latest edition of this Report we can state that this Report is becoming a controlling factor in what NASA tells the world about Mars and in what the world believes about NASA’s credibility on this topic. As such, we never took down our graphics about the original low UV values posted by the REMS Team. We are right. NASA is wrong. They know it, and thus as Figures 91 and 92 and 93 show, even on this they caved in to us and restored most of the low UV values.  The low UV values during the 2018 Global Dust Storm which blocked out the sun also speak volumes about much higher than advertised Martian air density and pressure.

Figure 93 After the REMS Team (a) dropped all UV values and (b) read our concerns about their behavior they changed at least 12 sols back to low UV. See Figure 94 for the rest of such changes


Figure 94 After the REMS Team (a) dropped all UV values and (b) read our concerns about their behavior they changed at least 12 sols back to low UV. Figure 93 shows such changes that were not documented on Figure 92.


Figure 95 Not all changes away from low UV were restored. As for October 12, 2017 no such restoration has been made yet for Sol 1006.

       The data published by the REMS Team/JPL also mention opacity, but as of September 8, 2018 none of the 2,165 reports ever varied from SUNNY. There is reason to question the validity of this data, and in fact it is refuted by photos taken by the Mars Reconnaissance Orbiter and published by Malin Space Science Systems (MSSS).

       Relative humidity is higher than expected in some parts of Gale Crater (see Figures 62 and 63 earlier in Section 14). There is brine underground and JPL has indicated that possible RSL have also been seen on the slopes of Mount Sharp in Gale crater (the location of the Curiosity rover), but that has not been confirmed yet. It is also not yet known if the rover would be able to reach them. But given the possibility of so much water, it seems odd that not one day at MSL has been reported to be cloudy by the REMS Team.

       Clouds can be seen drifting by behind the Telltale wind device on Phoenix on its Sol 103, but Phoenix landed in the Martian arctic. Stratus clouds were seen 16 km above the Mars Pathfinder - see Figure 57. It landed at 19.1° North which like MSL Curiosity is in the tropics).

       Clouds were seen at MER Opportunity ( It landed at 1.9462°S 354.4734°E.The MSL curiosity landed at a latitude of 4.59° South. The approximate difference in latitude (4.59-1.95) is only 2.64 degrees. As each one degree difference of latitude in Mars is about 59 km, these clouds, though not at the longitude of MSL, were only 155.76 km (96.7847769 miles) north of Curiosity's latitude.  

       Malin Space Science Systems (MSSS) showed that, as we suspected, the claim up through Mars Science Laboratory (MSL) Curiosity Rover Sol 2,165 that all 2,165 sols reported were “sunny” is a false claim. Rather, it appears, NASA/JPL and in particular Malin have permitted the truth to be published, but not on the primary weather reporting site run by the REMS Team. We think the entire REMS Team should immediately be replaced by Malin, with a possible degree of oversight exercised by the Roffman Mars Correct Team in the U.S. and our partners in Europe – Marco de Marco and Matteo Fagone.

       The MSSS images were derived from the Mars Reconnaissance Orbiter Mars Color Imager. A selection of weekly image videos for the period of time from MSL's landing on August 6, 2017 up through September 10, 2017 was shown earlier as Table 14 in Section 9 of this report.  The selection was for weeks when MSSS reported weather that seemed to contradict the never-changing sunny reports provided by the REMS Team. All the images were from MARCI (Mars Color Imager) which produces a global weather map of Mars to help characterize daily, seasonal, and year-to-year variations in the red planet's climate. MARCI also observes processes such as dust storms and changes in the polar cap using five visible bands.  In addition, MARCI makes ultraviolet observations at two wavelengths to detect variations in ozone, dust, and carbon dioxide in the atmosphere. MARCI observes these processes on scales of tens of kilometers. The Principal Investigator is Mike Malin.

       Figure 96 shows sols that were labelled sunny by the REMS Team, but were dubious when we examined the Malin record. From October 29, 2012 to November 4, 2012 rather than describe Gale Crater as being sunny, MSSS indicates that water ice clouds persisted at equatorial latitudes including near the Curiosity Rover site in Gale Crater.

Figure 96 Sunny skies advertised for MSL Sols 82 to 88 were not backed by the MSSS MARCI images.