Mars Rings in Year 39 as Northern Vernal Equinox Marks New Seasonal Cycle

Mars has just ticked over into a new year—Mars Year 39—marked not by a calendar date but by a celestial milestone: the northern hemisphere vernal equinox. Planetary scientists track the Red Planet’s seasons using solar longitude, or Ls, which measures Mars’ position along its orbit. Each season spans 90 degrees of Ls across the full 360-degree circuit. The new year began at Ls = 0° in late September by Earth’s calendar.

For NASA’s Curiosity rover, the changeover comes with a seasonal shift at its home in Gale Crater, which lies just south of the Martian equator. There, the new year corresponds to autumn conditions—an atmospheric turning point that researchers watch closely because it influences clouds, dust, and the daily rhythm of lighting and temperatures.

On the ground, Curiosity’s science team spent sols 5036 through 5042 finishing up a focused drilling campaign at a site called “Basque Lakes.” The week’s work largely centered on closing out drill-related tasks before the rover departs the area on the weekend. After reviewing results from laboratory analyses carried out the previous week, scientists operating Curiosity’s Sample Analysis at Mars (SAM) suite opted to run an additional gas chromatograph/mass spectrometry (GCMS) experiment. GCMS measurements can demand substantial power, but the planning schedule included four sols at the start of the week—enough breathing room to accommodate the extra lab run without sidelining other investigations.

That flexibility allowed the team to keep up a broad mix of science. Alongside SAM’s work, Curiosity carried out remote observations using its Mastcam and ChemCam instruments. The rover also performed “contact science” on drill tailings—the small piles of powdered rock and minerals left behind after sampling—an approach that helps link what the drill extracted with what the rover sees at the surface.

The weekend plan extends the closeout window with a couple more sols dedicated to wrapping remaining drill activities at Basque Lakes and gathering any final targets of opportunity, both up close and at a distance. After that, Curiosity is expected to begin driving away, heading back toward unusual crystalline features previously spotted in the “Chiu Chiu” region.

While rover operations proceed, Mars’ atmosphere is offering its own signs of seasonal change. Autumn at Gale Crater brings back high-altitude twilight clouds—thin layers that become strikingly visible when the low Sun near sunset lights them from the side. Cloud activity typically increases as the season advances, but Curiosity’s late-afternoon cloud movies taken on Wednesday already captured the first high-altitude clouds of the new autumn.

Most clouds over Gale are “suboptical,” meaning they are so tenuous they are difficult to detect by eye—or even with Curiosity’s cameras. Twilight clouds are the exception: they can be bright enough to stand out in the rover’s raw Navigation Camera images. For atmospheric researchers, the return of these clouds signals the start of another season of tracking how Mars’ skies evolve day by day.

Why it matters

Seasonal shifts on Mars affect everything from atmospheric circulation to visibility and power planning for surface missions. Curiosity’s combined drilling, lab work, and cloud monitoring helps connect the planet’s geology with present-day environmental conditions. As autumn deepens in Gale Crater, scientists will be watching for increased twilight cloud activity and what it reveals about high-altitude water-ice processes on Mars.