With opposition only weeks away, will the current global dust storm finally break? We look at the prospects.
Mars rises brilliant and inviting these July nights, but the view through a telescope reveals little more than a blurry, orange ball devoid of surface features. Many of us knew in advance we'd have to put up with poor seeing because of the planet's southerly declination. We also knew of the possibility of dust storms. But few expected such a massive, planet-girdling storm to occur this early in the most favorable apparition of the Red Planet since 2003.
Though sometimes compared to the 2001 global storm, that event occurred closer to the start of Martian summer and in a more traditional location, the familiar tempest-breeding grounds of Hellas Basin in Mars's southern hemisphere. The current global storm took shape in the northern hemisphere and much earlier than usual, only nine days into southern hemisphere spring.
"All of the historical dust storms of this size began in the southern hemisphere, in the areas of Hellas, Noachis, or Argyre," said Venable in an e-mail. "The present global dust storm began in Mare Acidalium. There has been considerable dust activity in Mare Acidalium in the last several apparitions, but nothing on this scale was expected."
Instead of settling down, the storm metastasized and struck south and west for Chryse, Sinus Meridiani, and kept going. One feature after another succumbed to billows of rusty dust until, by June 19, the storm achieved global domination. Amateurs gritted their teeth.
We're now fewer than three weeks away from opposition, and so much airborne grit still chokes the Martian atmosphere that once-prominent dark albedo features such as Sinus Meridiani, Syrtis Major, and Mare Cimmerium are practically unrecognizable. Even the south polar cap hasn't escaped the squall. It looks like a dollop of peach ice cream!
Dust also continues to keep NASA's Opportunity Rover hunkered down, sucking away the sunlight the rover's solar panels need to recharge its batteries. Mission control checks the rover every day but has received no response since Opportunity put itself into sleep mode after last contact on June 10.
Like you, I've attempted visual observations in 10-inch and 15-inch telescopes but have been stymied to identify much of anything. At best I've seen a few ambiguous gray markings, a vague, low-contrast south polar cap, and the white northern rim of the planet betraying the presence of the north polar hood. Otherwise, Mars is mostly a tease right now: brilliant and big in the telescope but cloaked in a gritty fog.
Have you noticed the change in the planet's color? Normally reddish-orange or even pink, Mars now glows pumpkin-orange. Even my eyes can see the difference. ALPO assistant coordinator Richard Schmude has also noted an increase in brightness of ~0.2 magnitude concurrent with the color change.
Naked-eye skywatchers can use the boost to their advantage by attempting to see Mars in daylight shortly after sunrise. Italian amateur Giorgio Rizzarelli has spotted it on five different mornings from the balcony of his home several minutes after sunrise. Locate the planet low in the southwestern sky in twilight and line it up with a building or tree. Keep an eye on it as sunrise approaches. Mars is currently magnitude —2.5 and about 10° high (from mid-30° to mid-40° latitudes) minutes after sunrise. Because it's sinking lower each morning, now is the time to make this rare sighting.
The 2001 storm blew up in July and finally dissipated about three months later in October, some four months after opposition. The current storm, which has evolved in a similar manner, may follow the same trajectory and linger for another couple months, putting a serious crimp in amateurs' observing goals. One thing is certain. While Martian dust, heated by the Sun, has warmed the atmosphere, the same dust has reduced the amount of solar radiation reaching the ground, gradually cutting off the storm's energy supply. As the surface cools, the gale will lose its power, dust will settle, and skies will clear eventually.
Venable notes that the number of denser "dust cores" has declined since the start of July, a sign that the storm may be losing strength.
"Generally, once the dense dust cores cease to occur, a relatively uniform haze of dust continues over the entire planet for a couple of months, gradually settling," said Venable. "The normal albedo features of the planet gradually reappear, regaining their normal contrast."
Scott Guzewich, atmospheric scientist at NASA’s Goddard Space Flight Center, struck a note of optimism, writing in a July 5th blog that "the amount of dust over Gale Crater has been slowly declining over the last two weeks, and it’s possible the dust storm has reached its ‘peak"'.
When a broader clearing will happen remains unknown. And while I've heard of other minor clearings at this and that Martian longitude, the whole planet remains under a pall of dust, thicker here, thinner there. Meanwhile, opposition looms. If we have to wait several months for the storm to clear as in 2001, good views of surface features will elude observers until the start of September, when Mars will have faded to magnitude –2 but still sport a respectable 20″ disk.
But we're not out of the woods yet. With Mars at perihelion on September 16 and summer approaching in the planet's southern hemisphere, conditions are ideal for — you guessed it — dust storm formation! Just as skies begin to clear from the present tempest, Mars could get wracked by another. Is there no justice?
"I wish we could predict when and how long these storms come and go, but every time I try, Mars changes, and nothing works out like we think," said Jeff Beish, former ALPO Mars Recorder, in an e-mail. "In any case I suspect plenty of dust will remain in Mars's atmosphere for the next 6 months, and it will create lots of H2O and CO2 clouds."
Beish's observation about clouds helps us to take stock of what we can enjoy should nature dally in cleaning up this mess. With the planet rising earlier every night, opportunities for observation increase throughout the summer. I use Sky & Telescope's Mars Profiler to find out which hemisphere of the planet faces my location at the time I'm observing. If the seeing's decent, I'll up the magnification to 200x or higher and try to make out the most prominent dark markings or the polar cap. Having trouble seeing anything? Try a red filter to improve surface feature contrast; a Wratten 25 or 29 (for bigger scopes) works well. For vapor clouds, use a Wratten 80A or 82A.
While the planet may look virtually featureless at the moment, keep in mind we're seeing one of the grandest and possibly the most unique dust storm in decades. When you share views of the Red Planet with friends, family and the public, give them a sense of its size (as large as all the land mass of Earth) and duration. The Dust Bowl of 1930s America barely compares.
Photos taken of the Martian north and south polar regions from orbit reveal a laminated terrain with alternating layers of ice and dust deposited by storms like the present one. Think about it — we're witnessing the creation of a new layer in the climatological record of the Red Planet. One day perhaps, astronauts will excavate a core sample from the south pole and trace the signature of the 2018 global storm.
Dust means lots of nuclei available for cloud formation. Keep an eye out for clouds; they look like bright patches and show up best near the planet's limbs. Planetary observers know that the more you look the more you see including the the planet's return to normal. Always expect surprises, too ... but of course you knew that already 🙂