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2026-06-12

Mastcam-Z Spots Space Weather with “Artemis Taus”!

By Mark Lemmon, 12 June 2026

What do monitoring Martian atmospheric dust and protecting astronauts have in common? How about spectacular auroras and the energy that drives whirling Martian dust devils? They all involve the Sun. Mastcam-Z on the Perseverance rover images the Sun on a near-daily basis in order to track Martian weather. The Sun’s brightness as seen by the rover rises and falls with the sky’s dust content. The parameter that defines how much the Sun’s light is dimmed by atmospheric dust is often called “t” (the Greek letter tau), because the attenuation is exponential and can be mathematically described as “ e–t ”.  We measure tau because Martian atmospheric dust is a major driver of the weather: it heats the atmosphere and drives it into motion, and it moves with (and traces) the winds. In fact, solar heating drives Martian weather, from the smallest dust devils to planet-encircling dust storms.

Where do astronauts and auroras come in? The Sun has its own weather, which drives what we call ‘space weather’: giant events that spread their influence across the solar system. Sunspots, when they are big enough, can be the source of coronal mass ejections (CMEs) also known as “proton events”. These events, when they reach the Earth, can cause low-latitude auroras and interfere with satellites or even power stations. Mars and several other planets also have auroras. The key links to astronauts are that Perseverance’s Mastcam-Z cameras can observe the largest sunspots (those capable of major CMEs; Figure 1), that the biggest CMEs pose potential threats to astronaut safety when they are traveling beyond low Earth orbit, and that Mars and Earth generally see different parts of the Sun.

Figure 1. Sunspots imaged by Mastcam-Z across the “far side” of the Sun (from Earth’s perspective) on 16 May 2026.

During the April 2026 Artemis II mission around the Moon, Mars could see most of the Sun’s far side (from Earth’s perspective). Mastcam-Z took higher-fidelity images of the Sun to produce better sunspot maps, and the Perseverance team shared the results with the Artemis II team. Because of the connection to the mission, we started calling these observations “Artemis taus.”  An example image is shown in Figure 2.

Figure 2. A Mastcam-Z solar image from the lead up to the Artemis II mission on 20 March 2026 (left). On the right, the Sun’s ‘limb darkening’ has been removed to more clearly show sunspots (but a circle was drawn at the edge of the Sun).

We took this a step further and projected the images as a map of the Sun. In the Figure 3 below, the blue area was visible from Earth (and could be a source of flares or CMEs headed for the astronauts). The gray was visible from Mars, but we masked out the hard-to-see limb area, so our image covers less than half of the map. The map also has Solar latitude lines; the longitude lines indicate how far each part of the Sun is from the sub-Earth point (zero longitude), since that measure was more useful to mission planners than any other definition of longitude.

Figure 3. Map of the Sun as seen by Mastcam-Z on 20 March 2026.

Mastcam-Z’s images provided a look, before Artemis II launched as well as during the mission, at what would be coming around the corner to become Earth-facing in the next few days. Since there was a gap between the Martian view and the Earth- (and Moon-) facing side, we also mapped images of the Sun from the most recent several days. Figure 4 below shows such a map; instead of longitude lines, it shows where the limb, as seen from Earth, will be at 2, 4, 6, and 8 days in the future. This allowed mission planners to track sunspots as they rotated around the Sun.

Figure 4. Map of 8 sols of Mastcam-Z sunspot images made on 22 March 2026 for Artemis II support.

The sunspots seen in Mastcam-Z Artemis tau images from Mars evolved over the course of days; new ones popped up, and some disappeared. Some of the sunspots tracked by Mastcam-Z persisted long enough to come around and be seen from Earth, as shown in Figure 5 below. For example, the largest sunspot in the upper right of the SDO/HMI image originated 4 sols after the area left Mars’ view, before it reached Earth’s view, and the spots to the lower left are new as well. 

A solar image taken from Earth by the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager (SDO/HMI) on 30 March 2026 is compared to Mastcam-Z images from the previous two weeks.

The higher-fidelity Sun images that we acquired around the Artemis II mission required a bit more rover time and downlink data volume than we needed for “normal” atmospheric monitoring. However, support for the Artemis II mission was so successful that the Perseverance team has upgraded our routine Sun imaging, so that these Artemis tau observations are becoming the new normal.  The feature image for this blog post is one of the first of this new set (converted into a stereo view if you cross your eyes), and [this link] takes you to an example of what it looked like to a mission designed for solar science: by this time, the Solar Orbiter satellite was sharing Mars’ view of the Sun.

Mastcam-Z’s solar images cannot compete with the dedicated solar telescopes and cameras around Earth and on the solar-orbiting satellites. However, sometimes our camera has a unique view. In January of 2026, Mars was directly opposite Earth. By early 2027, they will be aligned. From late 2027 to mid-2028, Mars will again see the side of the Sun that is about to rotate into Earth’s line of sight. Sometimes, Solar Orbiter will also see the far side of the Sun, but it orbits faster, with its point of view constantly changing.

Mastcam-Z will remain capable of supplementing the solar science fleet when Mars is not aligned with Earth, and we will be able to calibrate its measurements against Earth’s measurements when they do align. Looking ahead, Artemis IV is planned to land on the Moon sometime around early 2028 (as of May 2026), when Mars has an ideal view of the Sun. If that schedule holds, we will plan to resume our focused monitoring of the area just about to rotate toward Earth. In the future, perhaps astronauts may even voyage to Mars while Perseverance operates, with Mastcam-Z monitoring the Sun throughout their journey!

For even more details about Artemis taus:

  1. See the NASA “Perseverance views sunspots” story, at https://science.nasa.gov/photojournal/perseverance-views-sunspots]
  2. Read the American Astronomical Society meeting abstract by Lemmon et al. (2026), “Monitoring sunspots with Mars rovers,” which also describes some more information about how the Mars Science Laboratory Curiosity rover’s Mastcam instrument — Mastcam-Z’s older cousin on Mars — also observed sunspots during the Artemis II mission.
  3. View the poster that Mark Lemmon presented at that AAS meeting, at this link.