Curiosity Captures Gravity Wave Shaped Clouds On Mars

This week, from March 20th to 24th, the 48th Lunar and Planetary Science Conference will be taking place in The Woodlands, Texas. Every year, this conference brings together international specialists in the fields of geology, geochemistry, geophysics, and astronomy to present the latest findings in planetary science. One of the highlights of the conference so far has been a presentation about Mars’ weather patterns.

As a team of researchers from the Center for Research in Earth and Space Sciences (CRESS) at York University, demonstrated, Curiosity obtained of some rather interesting images of Mars’ weather patterns over the past few years. These included changes in cloud cover, as well as the first ground-based view of Martian clouds shaped by gravity waves.

When it comes to cloud formations, gravity waves are the result of gravity trying to restore them to their natural equilibrium. And while common on Earth, such formation were not thought to be possible around Mars’ equatorial band, where the gravity waves were seen. All of this was made possible thanks to Curiosity’s advantageous position inside the Gale Crater.

Cirrus clouds in the Martian atmosphere may have helped keep Mars warm enough for liquid water to sculpt the Martian surface. Image: Mars Exploration Rover Mission, Cornell, JPL, NASA
Panoramic image showing cirrus clouds in the Martian atmosphere, taken by the Opportunity rover in 2006. Credit: NASA/JPL/Cornell/M. Howard, T. Öner, D, Bouic & M. Di Lorenzo

Located near Mars’ equator, Curiosity has managed to consistently record what is known as the Aphelion Cloud Belt (ACB).  As the name would suggest, this annually-recurring phenomena appears during the aphelion season on Mars (when it is farthest from the Sun) between the latitudes of 10°S and 30°N. During aphelion, the point farthest from the Sun, the planet is dominated by two cloud systems.

These include the aforementioned ACB, and the polar phenomena known as Polar Hood Clouds (PHCs). Whereas PHCs are characterized by clouds of carbon dioxide, clouds that form around Mars’ equatorial band are made up water-ice. These cloud systems them dissipate as Mars gets closer to the Sun (perihelion), where increases in temperature lead to the creation of dust storms that limit cloud formation.

During the nearly five years that Curiosity has been operational, the rover has recorded over 500 movies of the equatorial Martian sky. These movies have taken the form of both Zenith Movies (ZMs) – which involve the camera being pointed vertically – and Supra-Horizon Movies (SHM), which were aimed at a lower angle of elevation to keep the horizon in frame.

Using Curiosity’s navigation camera, Jacob Kloos and Dr. John Moores – two researchers from CRESS – made eight recordings of the ACB over the course of two Martian years – specifically between Mars Years 31 and Mars Years 33 (ca. 2012 to 2016). By comparing ZM and SHM movies, they were able to discern changes in the clouds that were both diurnal (daily) and annual in nature.

What they found was that between 2015 and 2016, Mars’ ACB underwent changes in opacity (aka. changes in density) during its diurnal cycle. After periods of enhanced early morning activity, the clouds would reach a minimum by late morning. This is followed by a second, lower peak in the late afternoon, which indicated that Mars’ early morning hours are the most favorable time for the formation of thicker clouds.

Hubble images show cloud formations (left) and the effects of a global dust storm on Mars. Credit: NASA/James Bell (Cornell Univ.), Michael Wolff (Space Science Inst.), and Hubble Heritage Team (STScI/AURA)

As for inter-annual variability, they found that between 2012 and 2016, when Mars moved away from aphelion, there was a corresponding 38% increase in the number of higher-opacity clouds. However, believing these results to be the result of a statistical bias caused by an uneven distribution of videos, they concluded that the difference in opacity was more along the lines of about 5%.

These variations were all of this is consistent with tidal temperature variations, where cooler daytime or seasonal temperatures result in greater levels of condensation in the air. The trend of increasing clouds throughout the day was unexpected, however, as higher temperatures should lead to a decrease in saturation. However, as they explained during their presentation, this too could be attributed to daily changes:

“One explanation for the afternoon enhancement put forth by Tamppari et. al. is that as atmospheric temperatures increase the throughout the day, enhanced convection lifts water vapor to the saturation altitude, therefore increasing the likelihood of cloud formation. In addition to water vapor, dust could also be lifted, which act as condensation nuclei, allowing for more efficient cloud formation.”

However, what was most interesting was the fact that during one of day of observation – Sol 1302, or April 5th, 2016 – the team managed to observe something surprising. When looking at the horizon during an SHM, the NavCam caught sight of parallel rows of clouds which all pointed in the same direction. While such ripples are known to happen in the polar regions (where PHCs are concerned), spotting them over the equator was unexpected.

Sunset photographed from Gale Crater by the Mars Curiosity rover on April 15, 2015 taken using the left eye of the rover’s Mastcam. Credit: NASA/JPL-Caltec

But as Moore explained in an interview with Science Magazine, seeing an Earth-like phenomenon on Mars is consistent with what we’ve seen so far from Mars. “The Martian environment is the exotic wrapped in the familiar,” he said. “The sunsets are blue, the dust devils enormous, the snowfall more like diamond dust, and the clouds are thinner than what we see on the Earth.”

At present, it is not clear which mechanism could be responsible for creating these ripples in the first place. On Earth, they are caused by disturbances below in the troposphere, solar radiation, or jet stream sheer. Knowing what could account for them on Mars will likely reveal some interesting things about its atmosphere’s dynamics. At the same time, further research is necessary before scientists can say definitely that gravity waves were observed here.

But in the meantime, these findings are fascinating, and are sure to help advance our knowledge of the Red Planet’s atmosphere and the water cycle on Mars. As ongoing research has shown, Mars still experiences flows of liquid salt water on its surface, and even experiences limited precipitation. And in telling us more about Mars’ present-day meteorology, it could also reveal things about the planet’s watery past.

To see the recordings of Martian clouds, click here, here and here.

Further Reading: USRA, Science Magazine

What is the Weather like on Mars?

Welcome back to our planetary weather series! Today, we take a look at Earth’s neighbor and possible “backup location” for humanity someday – Mars!

Mars is often referred to as “Earth’s Twin”, due to the similarities it has with our planet. They are both terrestrial planets, both have polar ice caps, and (at one time) both had viable atmospheres and liquid water on their surfaces. But beyond that, the two are quite different. And when it comes to their atmospheres and climates, Mars stands apart from Earth in some rather profound ways.

For instance, when it comes to the weather on Mars, the forecast is usually quite dramatic. Not only does Martian weather vary from day to day, it sometimes varies from hour to hour. That seems a bit unusual for a planet that has an atmosphere that is only 1% as dense as the Earth’s. And yet, Mars manages to really up the ante when it comes to extreme weather and meteorological phenomena.

Mars’ Atmosphere:

Mars has a very thin atmosphere which is composed of 96% carbon dioxide, 1.93% argon and 1.89% nitrogen, along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates that measure 1.5 micrometers in diameter, which is what gives the Martian sky its tawny color when seen from the surface. Mars’ atmospheric pressure ranges from 0.4 to 0.87 kPa, which is the equivalent of about 1% of Earth’s at sea level.

This image illustrates possible ways methane might get into Mars’ atmosphere and also be removed from it. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

Because of this thin atmosphere, and its greater distance from the Sun, the surface temperature of Mars is much colder than what we experience here on Earth. The planet’s average temperature is -63 °C (-82 °F), with a low of -143 °C (-226 °F) during the winter at the poles, and a high of 35 °C (95 °F) during summer and midday at the equator.

Due to the extreme lows in temperature at the poles, 25-30% of the carbon dioxide in the atmosphere freezes and becomes dry ice that is deposited on the surface. While the polar ice caps are predominantly water, the Martian North Pole has a layer of dry ice measuring one meter thick in winter, while the South Pole is covered by a permanent layer that is eight meters deep.

Trace amounts of methane and ammonia have also been detected in the Martian atmosphere. In the case of the former, it has an estimated concentration of about 30 parts per billion (ppb), though the Curiosity rover detected a “tenfold spike” on December 16th, 2014. This detection was likely localized, and the source remains a mystery. Similarly, the source of ammonia is unclear, though volcanic activity has been suggested as a possibility.

Meteorological Phenomena:

Mars is also famous for its intense dust storms, which can range from small tornadoes to planet-wide phenomena. Instances of the latter coincide with dust being blown into the atmosphere, causing it to be heated up from the Sun. The warmer dust-filled air rises and the winds get stronger, creating storms that can measure up to thousands of kilometers in width and last for months at a time. When they get this large, they can actually block most of the surface from view.

Image capturing an active dust storm on Mars. Image credits: NASA/JPL-Caltech/MSSS

Due to its thin atmosphere, low temperatures and lack of a magnetosphere, liquid precipitation (i.e. rain) does not take place on Mars. Basically, solar radiation would cause any liquid water in the atmosphere to disassociate into hydrogen and oxygen. And because of the cold and thin atmosphere, there is simply not enough liquid water on the surface to maintain a water cycle.

Occasionally, however, thin clouds do form in the atmosphere and precipitation falls in the form of snow. This consists primarily of carbon dioxide snow, which has been observed in the polar regions. However, small traces of frozen clouds carrying water have also been observed in Mars’ upper atmosphere in the past, producing snow that is restricted to high altitudes.

One such instance was observed on September 29th, 2008, when the Phoenix lander took pictures of snow falling from clouds that were 4 km (2.5 mi) above its landing site near the Heimdal Crater. However, data collected from the lander indicated that the precipitation vaporized before it could reach the ground.

Aurorae on Mars:

Auroras have also been detected on Mars, which are also the result of interaction between magnetic fields and solar radiation. While Mars has little magnetosphere to speak of, scientists determined that aurorae observed in the past corresponded to an area where the strongest magnetic field is localized on the planet. This was concluded by analyzing a map of crustal magnetic anomalies compiled with data from Mars Global Surveyor.

Mars has magnetized rocks in its crust that create localized, patchy magnetic fields (left). In the illustration at right, we see how those fields extend into space above the rocks. At their tops, auroras can form. Credit: NASA

A notable example is the one that took place on August 14th, 2004, and which was spotted by the SPICAM instrument aboard the Mars Express. This aurora was located in the skies above Terra Cimmeria – at geographic coordinates 177° East, 52° South – and was estimated to be quite sizable, measuring 30 km across and 8 km high (18.5 miles across and 5 miles high).

More recently, an aurora was observed on Mars by the MAVEN mission, which captured images of the event on March 17th, 2015, just a day after an aurora was observed here on Earth. Nicknamed Mars’ “Christmas lights”, they were observed across the planet’s mid-northern latitudes and (owing to the lack of oxygen and nitrogen in Mars’ atmosphere) were likely a faint glow compared to Earth’s more vibrant display.

To date, Mars’ atmosphere, climate and weather patterns have been studied by dozens of orbiters, landers, and rovers, consisting of missions by NASA, Roscomos, as well as the European Space Agency and Indian federal space program. These include the Mariner 4 probe, which conducted the first flyby of Mars – a two-day operation that took place between July 14th and 15th, 1965.

The crude data it obtained was expanded on by the later later Mariner 6 and 7 missions (which conducted flybys in 1969). This was followed by the Viking 1 and 2 missions, which reached Mars in 1976 and became the first spacecraft to land on the planet and send back images of the surfaces.

Since the turn of the century, six orbiters have been placed in orbit around Mars to gather information on its atmosphere – 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN, Mars Orbiter Mission and ExoMars Trace Gas Orbiter. These have been complimented by rover and lander missions like Pheonix, Spirit and Opportunity, and Curiosity.

In the future, several additional missions are scheduled to reach the Red Planet, which are expected to teach us even more about its atmosphere, climate and weather patterns. What we find will reveal much about the planet’s deep past, its present condition, and perhaps even help us to build a future there.

We have written many interesting articles about Martian weather here at Universe Today. Here’s Mars Compared to Earth, It Only Happens on Mars: Carbon Dioxide Snow is Falling on the Red Planet, Snow is Falling from Martian Clouds, Surprise! Mars has Auroras Too! and NASA’s MAVEN Orbiter Discovers Solar Wind Stripped Away Mars Atmosphere Causing Radical Transformation.

For more information, check out this NASA article about how space weather affects Mars.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.

Sources:

How Can Mars Sometimes Be Warmer Than Earth?

Remember a few weeks ago when the weather on Mars was making the news? At the time, parts of the Red Planet was experiencing temperatures that were actually warmer than parts of the US. Naturally, there were quite a few skeptics. How could a planet with barely any atmosphere which is farther from the Sun actually be warmer than Earth?

Well, according to recent data obtained by the Curiosity rover, temperatures in the Gale Crater reached a daytime high of -8 °C (17.6 °F) while cities like Chicago and Buffalo were experiencing lows of -16 to -20 °C (2 to -4 °F). As it turns out, this is due to a number of interesting quirks that allow for significant temperature variability on Mars, which at times allow some regions to get warmer than places here on Earth.

It’s no secret that this past winter, we here in North America have been experiencing a bit of a record-breaking cold front. This was due to surges of cold air pushing in from Siberia and the North Pole into Canada, the Northern Plains and the Midwest. This resulted in many cities experiencing January-like weather conditions in November, and several cities hitting record-lows not seen in decades or longer.

Credit: NASA/JPL/University of Arizona
Carbon dioxide ice on Mars, which experiences sublimation from solar warming to create  polygonal structures. Credit: NASA/JPL/University of Arizona

For instance, the morning of November 18th, 2014, was the coldest since 1976, with a national average temperature of -7 °C (19.4 °F). That same day, Detroit tied a record it had set in 1880, with a record low of -12 °C (11 °F).

Five days earlier, the city of Denver, Colorado experienced temperatures as cold as -26 °C (-14 °F) while the city of Casper, Wyoming, hit a record low of -33 °C (-27 °F). And then on November 20th, the town of Jacksonville, Florida broke a previous record (which it set in 1873) with an uncharacteristic low of -4° C (25 °F).

Hard to believe isn’t it? Were it not for the constant need for bottled oxygen, more people might consider volunteering for Mars One‘s colonizing mission – which, btw, is still scheduled to depart in 2023, so there’s still plenty of time register! However, these comparative figures manage to conceal a few interesting facts about Mars.

For starters, Mars experiences an average surface temperature of about -55 °C (-67 °F), with temperatures at the pole reaching as low as a frigid -153 °C (-243.4 °F). Meanwhile, here on Earth the average surface temperature is 7.2 °C (45 °F), which is also due to a great deal of seasonal and geographic variability.

The eccentricity in Mars' orbit means that it is . Credit: NASA
The eccentricity in Mars’ orbit around the Sun means that it is 42.5 million km closer during certain times of the year. Credit: NASA

In the desert regions near the equator, temperature can get as high as 57.7 °C, with the hottest temperature ever recorded being 70.7 °C (158.36 °F) in the summertime in the desert region of Iran. At the south pole in Antarctica temperatures can reach as low as -89.2 °C (-128.6 °F). Pretty darn cold, but still balmy compared to Mars’ polar ice caps!

Also, since its arrival in 2012, the Curiosity Rover has been rolling around inside Gale Crater – which is located near the planet’s equator. Here, the planet’s temperature experiences the most variability, and can reach as high as 20 °C (68 °F) during midday.

And last, but not least, Mars has a greater eccentricity than all other planet’s in the Solar System – save for Mercury. This means that when the planet is at perihelion (closest to the Sun) it is roughly 0.28 AUs (42.5 million km) closer than when it is at aphelion (farthest from the Sun). Having just passed perihelion recently, the average surface temperatures on Mars can vary by up to an additional 20 ºC.

In short, Mars is still, and by far, the colder of the two planets. Not that it’s a competition or anything…

Further Reading: NASA

Today’s Martian Weather: Partly Cloudy

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Changing seasons in Mars’ northern hemisphere brings a change in the weather, and the clouds have rolled in to cover part of the polar surface in this intriguing image from the Mars Odyssey spacecraft.

Mars Odyssey’s THEMIS visual imager (VIS) captured this image on Jan. 24, 2012, as it passed over the Red Planet’s northern pole during one of its 2-hour-long orbits.

Clouds on Mars have been seen before, both from orbit and from the surface. They are made up of fine water ice particles and are usually at altitudes of 10 to 15 km high. Read more about Martian weather here.

The full THEMIS scan of the area is below.

Martian polar clouds as seen by THEMIS

The area imaged is about 21 km wide by 73 km high  (13 x 45 miles).

Image credit: NASA / JPL / Arizona State University. Hat-tip to Mr. Bill Dunford at Riding With Robots (@ridingrobots).