Enormous Martian Clouds Still Perplex Astronomers
On March 21, 2012, amateur astronomers noticed that strange things were afoot in Mars’s southern hemisphere. Enormous cloud-like plumes were forming at very high altitudes over the Terra Cimmeria region, and continued to develop over the subsequent weeks.
Both the massive size of these plumes, which stretched up to 1,000 kilometers across, and their curious position in the upper atmosphere defy our current expectations of what is possible on Mars.
“No existing atmospheric model predicts the required conditions to form clouds or auroras of such magnitude,” astrophysicist Agustin Sánchez-Lavega told me over email.
The 2012 protrusion. Image: W. Jaeschke, D. Parker, NOAA, and Grupo Ciencias Planetarias (GCP)—UPV/EHU
Sánchez-Lavega is the lead author of a new paper about the 2012 event, published today in Nature. In it, he and his colleagues outline two potential explanations for the mysterious phenomena—that it was either an extremely elevated cloud of dust or ice, or that it was an aurora. The authors note, however, that both of these preliminary theories still challenge and conflict with our understanding of Mars.
For instance, take the cloud hypothesis. Large plumes of Martian dust do frequently get kicked up into the atmosphere, and water and carbon dioxide often condense into cloud-forming crystals. Data collected both by spacecraft and Earth-based telescopes has consistently suggested that these clouds have an upward limit of about 100 kilometers, or 62 miles.
But the plumes observed in 2012 reached heights of 250 kilometers, well into the Martian ionosphere and exosphere. According to Sánchez-Lavega’s team, it would have to be irregularly cold for water and carbon dioxide crystals to form at that height, and the presence of dust would require some kind of special, undiscovered vertical push off the surface. It’s also not the right time of the sol for an event like this to take place—dust is most likely to ascend around noon, and the massive cloud plumes were observed on Mars’s morning terminator.
“The cloud explanation we propose is an exploratory and open hypothesis,” said Sánchez-Lavega of this scenario. “It has pros and cons.”
The other explanation is that the protrusion was actually an unusually brilliant Martian aurora. While Mars’s lack of a magnetic field normally precludes these charged light shows, the region over which the plumes were observed does have a history of producing auroras. This is due to a localized magnetic force called a crustal magnetic anomaly—a throwback to when Mars had a planetary magnetic field.
„The Martian magnetic field is different from that of Earth, whose origin is in a dynamo action in the interior of our planet,” explained Sánchez-Lavega. „On Mars, the magnetic field is crustal with anomalies related to the presence of some magnetized substance buried beneath the surface.”
ISS view of Earth’s auroras. Image: NASA
So where Earth’s auroras are generated by its powerful, core-driven magnetic field, Martian auroras are created by chunks of material that retain some of the planet’s magnetic past, which then direct solar wind particles into the atmosphere, producing local auroras.
But even taking the presence of a crustal anomaly into consideration, the 2012 event was atypically bright and large. On top of that, an aurora of that magnitude would require a surge of charged particles from the Sun to fuel it, and there is no evidence of any particular influx of solar radiation during the event’s appearance.
With this paper, Sánchez-Lavega and his colleagues have provided the first in-depth investigation of these bizarre Martian plumes. But astronomers need more observations and hypothetical models if this mystery is going to be unraveled any further. It goes to show that though Mars is the most studied planet in our solar system besides Earth, it still has a lot of secrets to spill.
http://motherboard.vice.com/read/enormous-martian-clouds-still-perplex-astronomers
Massive clouds erupted 260km into Martian atmosphere – and no one knows why
Enormous cloud-like plumes reaching 260km above the surface of Mars have left scientists baffled. This is way beyond Mars’s normal weather, reaching into the exosphere where the atmosphere merges with interplanetary space. None of the conventional explanations for such clouds make sense – neither water or carbon dioxide ice nor dust storms nor auroral light emissions usually hit such heights.
These “mystery clouds” came as a surprise, in particular when considering they were first spotted by a string of amateur astronomers in 2012. After all, an international fleet of five orbiters and two rovers is currently operating on and around Mars, and one may be excused thinking the red planet has little left to hide and its exploration has become routine.
A survey of images from the Hubble Space Telescope and amateur astronomers revealed massive clouds had been seen on Mars before, but none as prominent as the 2012 observations.
So what caused these clouds? An international team of scientists led by Agustin Sánchez-Lavega has now published an investigation in the journal Nature.
Martian lights?
Perhaps these clouds could be aurorae – similar to the northern lights (aurora borealis) here on Earth, or their southern counterpart aurora australis. These displays happen when the Earth’s magnetic field channels charged particles emitted by the Sun towards the poles, where they interact with the atmosphere and emit light.
Mars does not have a global magnetic field, only pockets of magnetisation. The mystery clouds were spotted over one of these so-called magnetic anomalies, and auroral lights have been observed there previously.
However, to explain the 2012 observations, an aurora would have had to be 1,000 times brighter than the northern lights. This would require an increased flow of charged particles from the Sun, but its activity was not unusually high during the time.
Storms and smashes
Could dust be the culprit? A volcanic eruption or an asteroid impact were among the earliest theories about these clouds’ origin.
New eruptions on Mars are plausible, though we’re yet to observe any active volcanoes on the planet. The youngest lava flows reported are a few million to tens of million years old, which is recent in geological terms.
Mars’s thin atmosphere offers little protection against asteroids, and its surface is pockmarked with impact craters. Cameras on board NASA’s Mars Reconnaissance Orbiter have documented the appearance of hundreds of new craters in the nine years since the spacecraft arrived at Mars.
However, both theories were quickly discarded because they were inconsistent with the behaviour of the clouds. Continued observations showed that they disappeared during the Martian daytime, were not visible in the evening, and reappeared each morning for at least ten consecutive days.
This also rules out dust storms, which frequently engulf large areas of the planet’s surface. Furthermore, the wavelength profile of the light reflected by the mystery clouds is a poor match for Martian dust particles.
Not cold enough for ice
That leaves water or carbon dioxide ice particles, which fit the wavelength profile of the reflected light. Both water and carbon dioxide molecules also occur naturally in the atmosphere at these heights.
However, to form these clouds both substances would need to condense into ice particles. This would require the atmospheric temperature at these heights to drop suddenly by up to 100˚C. We’ve no idea what would cause such a drop, and we’re yet to spot such a massive, localised cold snap.
Sánchez-Lavega and co-workers thus declare that their “explanations defy our current understanding of Mars’ upper atmosphere” and their investigation only partially lifts the shroud surrounding these mysterious clouds.
Martian mysteries
High altitude clouds are not the only Martian mysteries keeping researchers on their toes. One question driving the exploration of the red planet is whether there has ever been life on Mars. Latest results by NASA’s Curiosity rover reaffirm that the planet provided habitable conditions in its past.
Water is the most important prerequisite for life. One explanation for the ongoing formation of gullies and related features, for example, is liquid water at or near the Martian surface even during the currently prevailing extreme dry and cold conditions. And while there are many possible explanations for the enigmatic whiffs of methane observed on Mars, one of the most exciting is the production by microorganisms living just below the surface.
Part of the fascination of Mars exploration is that it is very much about understanding our own origins and future. As the example of the mystery cloud observations shows, everybody has a chance to participate in unravelling the red planet’s mysteries.
https://georgevalah.wordpress.com/
