On the 15th December 2021, history was made when the Mars Perseverance Rover photographed the very first halo from the surface of Mars. The three images shown below are from a set taken from image series Sol 292 available on the NASA Perseverance Rover website,
https://mars.nasa.gov/mars2020/multimedia/raw-images/
Whilst technically it is not the first Martian halo, that accolade having been given to a subsun photographed from orbit by the Mars Global Surveyor satellite in January 2006, it is the very first to be taken from the surface of a planet other than Earth.
So what kind of halo are we looking at? In the Martian atmosphere, both water and CO2 ice crystals are present. Taking the wide angle distortion of the Navcam lens into consideration, space artist Donald E. Davis who first noticed the halo in the Perseverance image archive wrote on Twitter that it "appears roughly consistent with a 22.5 degree radius". In all likelihood, the halo formed in water ice clouds rather than CO2; if the halo had been formed by CO2 crystals, then the radius would have been larger than what we observe. Likewise, we also have brightenings on opposite sides of the halo which are probably consistent with diffuse tangent arcs.
 |
| Image processed by Nicolas Lefaudeux. |
Donald Davies has done some truly excellent work recreating the full halo from the separate images and has even produced a superb all sky reconstruction which has all the hallmarks of becoming iconic. You can find his ground-breaking work on Twitter here:
 |
| Image processed and manipulated by Donald E Davis. |
 |
| Image processed and manipulated by Donald E Davis. |
We sincerely hope that this will be the first of many Martian halos that will be captured by the Perseverance Rover and that this will open up a whole new field in halo science.
Major Update - 28th December 2021
Since posting the news about the discovery of the first Martian halo, Nicolas Lefaudeux returned to the Mars Rover archive to see whether he could identify further previously unrecorded halos. The results of his search are staggering. Besides the initial ground breaking Sol 292, he has discovered a further seven Martian halos of varying quality and intensity. These are Sol 145, 193, 249, 285, 289, 290 and 303. These confirm that both Sol 292 was not an isolated event and also that halos on Mars are a relatively common occurrence. All images presented below processed by Nicolas.
 |
| Sol 145 |
 |
Sol 193
|
 |
| Sol 249 |
 |
| Sol 285 |
 |
| Sol 289 |
 |
| Sol 290 |
 |
| Sol 303 |
 |
| Sol 303 |
