Will Mars soon be hidden under a veil of dust? Let’s hope not. We explore the current storm and the planet’s upcoming close opposition.
Atmospheric scientists may pray for a global dust storm to blow up on Mars, but the rest of us … please, no! Just as the Red Planet began to inch into the evening sky, a swath of bright, yellow dust clouds lit up over the dark albedo feature Mare Acidalium at the end of May.
Within days, the gale had moved south and expanded, covering much of Sinus Meridiani, Oxia Palus, and Margaritifer Sinus and coursing the length and breadth of the sprawling Martian canyon system Valles Marineris. This is a big storm. Under the eye of NASA’s Mars Reconnaissance Orbiter, it measures more than 18 million square km (7 million square miles), an area greater than the continent of North America.
While there’s no way to foretell if the gale will balloon into a planet-girdling storm, NASA’s Opportunity rover team has taken precautions to protect the rolling robot, which sits squarely in the storm’s path in Sinus Meridiani. Science operations have been suspended to conserve power.
“A dark, perpetual night has settled over the rover’s location in Mars’ Perseverance Valley,” reads the most recent agency press release, referring to thick clouds blowing dust in the area.
Opportunity made it through the last bad storm in 2007, but this one’s worse. Dust blocks the sunlight used by the rover’s solar panels to create the power needed to run its instruments and stay warm. Mars is no picnic. Although dust storms can limit temperature extremes — analogous to a cloudy day on Earth — the longer they last, the less power available to the rover. Batteries only last so long.
The good news is that NASA engineers received a transmission from Opportunity on Sunday morning, a welcome sign that despite the worsening storm, the rover still has enough battery power to communicate with ground controllers. Meanwhile, the Mars Curiosity rover is still in the clear in the opposite hemisphere, though an increase in dust is expected in the coming days.
The current storm is significantly larger than the 2005 storm but so far pales in comparison to the global storm that wracked the Red Planet in 2001. That one began in the bright, circular feature Hellas, an ancient impact basin with a floor 9 km deep in the planet’s southern hemisphere. The ~10° temperature difference between basin bottom and surface drove winds that spawned a modest storm. But on June 27th that year, the storm exploded in size, spilling out of the basin to eventually cover the entire planet.
No one’s certain on exactly how a big storm gets rolling, but it appears that a positive feedback loop can turn a zephyr into a monster under the right conditions:
“One theory holds that airborne dust particles absorb sunlight and warm the Martian atmosphere in their vicinity,” said Phil Christensen, planetary geologist at the University of Arizona, referring to the 2001 storm. “Warm pockets of air rush toward colder regions and generate winds. Strong winds lift more dust off the ground, which further heats the atmosphere.” More heat means more energy and stronger winds, which lift even more dust into the air, amplifying a small disturbance into a large one.
This storm is a little different. Instead of occurring at the height of southern summer as in 2001 and 2005, it erupted in the northern hemisphere only days after the northern fall equinox. Similar to how arctic fronts descend one after another on North America during late fall and winter, multiple storm fronts parade along the north polar cap during Martian fall. Some of these can break off and head south, where they feast on warmer air and burgeon into much bigger storms.
From an observer’s point of view, let’s hope the dust settles … literally. Mars is finally coming into its own. At magnitude –1.6, it’s now brighter than any star in the night sky. On Monday morning (June 11th) I easily found it in my 8×50 finderscope at sunrise and did all my observing in a blue sky. Mars’s apparent diameter has swelled to nearly 18″ (arcseconds) on its way to a chunky 24.3″ when it reaches opposition on July 27th. Closest approach to the Earth occurs on July 31st at 57.6 million kilometers, its most neighborly position since the 2003 opposition.
Provided the storm takes a chill pill, telescopic observers have lots to see now through fall. First off, the south polar cap is obvious, and we’ll be able to watch it shrink as its dry-ice shell sublimes in the intensifying spring heat. Large, dark albedo features like Syrtis Major, Hellas, Mare Tyhrrhenum, Mare Cimmerium, Solis Lacus (the Eye of Mars), Aurorae Sinus, Sinus Meridiani, and Sinus Sabaeus can be discerned in good seeing and with practice. A red filter and magnifications of 150× and higher will help to bring out them out.
Observers in mid-northern latitudes will have to work harder than more southerly skywatchers to get their Mars fix. The planet spends much of the summer and fall in southern Capricornus, south of declination –20°. The seeing at that elevation is rarely good, the reason I recommend observing Mars near the meridian and as often as possible, the better to catch it on those rare nights of serene seeing and fine definition.
Be aware that even if we make it past the current storm, we’re not out of the woods. Summer’s a comin’ for the south. As carbon dioxide ice vaporizes from the southern pole cap, expect new winds to develop and a good possibility for major storms to return in August and September. If you routinely observe Mars, a dust storm will betray itself by color (yellow-orange), brightness and the plain fact that a feature you saw a few nights has seemingly disappeared. I’ve watched them evolve night to night — most exciting!
Resources to enhance your Mars experience: