You might have noticed in images of Mars that its surface is covered with dust. In events called dust storms, this dust is lifted off the surface and into the air by winds.
Dust storms on Mars range in their size and duration. The smaller storms cover only a local region and dissipate within a week, if not a few days.
The larger ones can span continent-sized areas, cover the red planet, and cause a sharp dip in sunlight on the surface. These are known as global dust storms and can last anywhere between a few weeks to a few months.
While local dust storms make it difficult to carry out observations of that particular area, the global storms are the ones that threaten viewing both from Earth and on Mars itself.
Storms also affect spacecraft on the Martian surface and orbiting above its atmosphere from functioning optimally. They are also prevented from communicating with scientists on Earth. Additionally, since the storms mask surface features on Mars, there isn’t much observation that can be done during a global dust storm.
The good news is that these dust storms are quite rare: only 10 such global storms were documented in the past century. However, the storms themselves can be seen with a 6-inch telescope.
What Causes Martian Dust Storms?
When sunlight heats the Martian surface, hot air rises. Although Mars has just one percent of Earth’s atmospheric density, it does produce fast winds but with much lower strength.
These winds carry dust particles from the Martian surface, causing dust storms. Dust storms are local, regional, and global; their nature decides how long they last.
When sunlight reaches the Martian surface, it heats it up. Although Mars is frigid in darkness, it can reach 95° F in direct sunlight. This hot air rises, taking the dust particles along with it—the first ingredient for the recipe of a storm.
Dust storms predictably occur during Martian summers, when the southern hemisphere is tilted towards the Sun. This increases the intensity of sunlight by 20%, causing drastic temperature differences in the area—the second ingredient to start a storm.
The first two ingredients take care of the ideal temperatures to fuel a storm, but the main ingredient is still missing: the dust.
For smaller storms, dust from the surface constitutes the storm. But, many storms originate in the desert regions on Mars. One such popular hotspot is the Hellas Basin.
At 6 km deep and 2,000 km wide, the Hellas Basin is the biggest impact crater in the solar system, so much so that the temperature difference between the top layer of the basin and its bottom is 10 degrees.
The Basin is also filled with dust, and the temperature difference drives winds (and takes the dust along with it). Approximately every 3 Martian years, which is about 5 ½ Earth years, a small storm grows into a global one with maximum speeds reaching 60 miles per hour.
There is a cycle to these dust storms: they begin, live their duration, and then they dissipate. But how does a global dust storm that covers the entire planet clear up?
As we learned, global dust storms prevent sunlight from reaching the surface, thereby reducing the temperature on the inside. Since this high surface temperature was the very reason that the dust storm was thriving in the first place, the darkness it causes works against it. The winds reduce, causing the storm to die.
When Are Storms Most Likely to Occur?
Storms on Mars are most likely to occur during Martian summers when the planet is 50 million km closer to the Sun than throughout the rest of the year and the intensity of sunlight is 20% higher.
While this naturally increases temperatures, the fact that Mars is axially titled means that the southern hemisphere (which faces the Sun) experiences summers and storms more severely than the northern hemisphere.
What Is It Like Inside a Dust Storm?
As much fascinating Mars might seem for human exploration, you would not want to be present over there during dust storms.
On the positive side, because the Martian atmosphere is only 1% as thick as the Earth’s, if you were to stand on Mars during the 60 mph storm, you would only experience the wind as a strong as a breeze.
(The winds are definitely not as strong as shown in the movie The Martian. Mars is simply not capable of generating such strong winds.)
On the negative side, the dust particles are, on average, 3 micrometers in diameter—a size so small that it will lead to health issues if inhaled over long periods.
Moreover, these dust particles are electrically charged via a process called triboelectric effect (when particles are in contact or are constantly rubbed against one another, electrons from one object enter the other, leaving both objects ‘charged’).
You might, however, be fortunate enough to enjoy the rare sight of Martian lightening. Dust storms on Mars, especially the global ones, are up to 30 km high and, at this height, they can generate lightning.
You won’t be surprised to learn that it can get pretty dark inside a storm that’s been raging for weeks. As a benefit, this blanket of dust will also prevent the temperatures from fluctuating rapidly.
Can I See Dust Storms From Earth?
Local and regional storms are usually too small to be caught in a telescope, but you can certainly see global Martian dust storms with telescopes of 6 inches and up. The best chance of seeing them is when Mars is closer to Earth at opposition.
For example, the 2007 global dust storm enveloped the planet so thickly for about a month that it blocked 99% of the sunlight. Previously, large dust storms have occurred in 1977, 1982, 1994, and 2001.
While viewing a storm, there is no single location that you need to zoom in on; global dust storms cover the entire planet so your view will be the same no matter where you look. As long as you know where and when to spot Mars, you’ll be fine.
Consider adding a red telescope filter to your kit, they provide the highest contrast for the Martian surface, allowing you to view the bright dust. When storms are in their initial stages, they also have a tiny amount of vapor in them, which can be seen as ice crystals via blue and violet filters.
How Long Do Martian Dust Storms Last?
Local dust storms that cover a small area might last only for a few hours. These occur all the time and aren’t always documented. Regional storms originate in places where the Sun zooms past directly overhead, are larger and can last for up to a week.
The global dust storms that occur roughly every three Martian years can last anywhere from two weeks to one or two months.
The storms originating from the Hellas Basin, a prime source of dust, last a lot longer than storms that originate elsewhere. The Thaumasia and the Libra-Isidis regions also guarantee strong, long-lasting storms.
Dust storms are a common occurrence on Mars.
They occur due to the rise in surface temperature when sunlight hits Mars, causing hot air to rise and carry the small particles of dust along with it. These storms vary in their nature by their size and how long they last.
All storms usually begin in the lighter desert regions on Mars and cover the darker regions as they grow.
The smaller local and regional storms are neither visible from Earth through a backyard telescope, nor are they well documented.
Global storms cover the entire planet for up to two months. These can harm spacecraft on the planet, prevent their communication to Earth, and cause a dip in global temperature. Ultimately, it’s this temperature decrease that ends the storm.
Global storms are visible from Earth, provided Mars is nearby and you are looking at it with at least a 6-inch telescope.
I hope you’ll remember these points the next time you try to catch one with your telescope!