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The weird long cloud on Mars is finally revealing some of its secrets

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Old March 13th 21, 03:27 PM posted to alt.astronomy
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Default The weird long cloud on Mars is finally revealing some of its secrets


(Going to the citation lets one see the pictures and graphics.)

The weird long cloud on Mars is finally revealing some of its secrets
By Chelsea Gohd 3 days ago

A European spacecraft is unraveling the secrets of the weird long cloud
that has been appearing again and again in the Martian sky for years.

The Arsia Mons Elongated Cloud is a peculiar feature on Mars: a long,
bright water ice cloud stretching out over the Martian surface,
extending over the planet's Arsia Mons volcano all the way to the
volcano Olympus Mons, the tallest mountain in the solar system. The
strange phenomenon has been recurring every year around Mars' southern
solstice, with the cloud forming and fading daily for 80 or more days at
a time on the Red Planet.

However, while the cloud is no new presence, it is challenging to
observe in its entirety because of the changing Martian atmosphere and
the difficulties of observing from orbit. Still, the European Space
Agency's Mars Express orbiter has managed to get an in-depth look at the
peculiar cloud using a special tool: the Visual Monitoring Camera (VMC),
perhaps better known by its nickname the Mars Webcam.

In a new study, astronomers using this data are gleaning new details
about the long cloud, including how big it can really get and details of
the intricate dynamics at play in the climate system surrounding it.

Photos: Red Planet views from Europe's Mars Express

A Mars Express image of Arsia Mons on Mars and its strange long cloud,
taken on July 19, 2020.

A Mars Express image of Arsia Mons on Mars and its strange long cloud,
taken on July 19, 2020. (Image credit: ESA/GCP/UPV/EHU Bilbao)
Cloud-hunting tools
The VMC was originally installed to spot the Beagle 2 lander, a British
Mars lander that was declared lost and is speculated to have crashed.

"However, recently, the VMC was reclassified as a camera for science,"
Jorge Hernández Bernal, an astronomer at the University of the Basque
Country in Spain and lead author of this new study of the cloud who also
is part of a long-term project studying the cloud, said in a statement.

"Repurposing the VMC has successfully enabled us to understand this
transient cloud in a way that wouldn’t have been possible otherwise,"
ESA's Mars Express project scientist Dmitrij Titov said about the VMC in
the same statement.

The Arsia Mons Elongated Cloud.

The Arsia Mons Elongated Cloud. (Image credit: DSA/GCP/UPV/EHU Bilboa
The tool allows scientists to "track clouds, monitor dust storms, probe
cloud and dust structures in the Martian atmosphere, explore changes in
the planet’s polar ice caps, and more," Titov added.

For this study, astronomers used both the VMC observations and data from
other Mars Express instruments in addition to data from other missions
including NASA's Mars Atmosphere and Volatile Evolution (MAVEN) Mars
Reconnaissance Orbiter (MRO), the Viking 2 missions and the Indian Space
Research Organization's Mars Orbiter Mission (MOM).

"We were especially excited when we dug into Viking 2’s observations
from the 1970s," Bernal said. "We found that this huge, fascinating
cloud had already been partially imaged that long ago — and now we’re
exploring it in detail."

Mars Illusion Photos: The 'Face on Mars' and Other Martian Tricks

Cloudy clues
Many missions have helped scientists to study this strange cloud on Mars.

Many missions have helped scientists to study this strange cloud on
Mars. (Image credit: ESA)
The researchers found that, at its largest, the cloud measures out to be
about 1,118 miles (1,800 kilometers) long and 93 miles (150 km) across.
The cloud is "orographic," meaning it forms when wind is pushed upward
by surface features like mountains (in this case, Arsia Mons), and is
the largest cloud of this type ever seen on the planet.

The cloud is also highly dynamic, they found, forming before sunrise
then expanding rapidly for two and a half hours. It can grow at a
mind-boggling speed of over 373 mph (600 kph) before it stops
expanding. It then detaches from where it formed and is stretched even
more before evaporating in the late morning. On Earth, orographic clouds
are never as big as this Martian cloud, nor as dynamic, making it
especially strange.

Now that the researchers have better handle on the life cycle and
patterns of this phenomena, it will enable them to more easily target
and observe the cloud.

"Many Mars orbiters cannot begin observing this part of the surface
until the afternoon due to the properties of their orbits, so this
really is the first detailed exploration of this interesting feature —
and it’s made possible by not only Mars Express’ diverse suite of
instruments, but also its orbit," study co-author Agustin
Sánchez-Lavega, the science lead for the VMC and a professor of physics
at the University of the Basque Country, said in the same statement.

This work was first published Dec. 20in a study in the Journal of
Geophysical Research and was released in Volume 126 of Issue 3 in March

Email Chelsea Gohd at or follow her on Twitter
@chelsea_gohd. Follow us on Twitter @Spacedotcom and on Facebook.

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