Mysterious Plumes On Mars Baffle Astronomers

A high-altitude plume at the Martian terminator (marked with a red circle) on March 21 03:21 UTC by D. Parker / A. Sánchez-Lavega et al., 2015 Nature
Janet Fang 18 Feb 2015, 00:51

Astronomers are puzzled by enormous cloud-like plumes that ascended high up into the Martian atmosphere. They’re larger than anything previously observed on Mars, and according to work published in Nature this week, the plumes seem to defy our current understanding of atmospheric physics on the red planet. 

The two mysterious clouds were detected in March and April of 2012 by amateur astronomers, who reported protrusions above the southern hemisphere of Mars. The first arose within just 10 hours, changing shapes as it ascended up 200-250 kilometers (124-155 miles) to where the atmosphere is very thin. It lasted for 11 days and eventually grew to around 1,000 kilometers across (621 miles). "I was really quite amazed that it was sticking out the side of the planet quite prominently," Damian Peach of Selsey, U.K., tells New Scientist. Peach was one of the first to spot the cloud-like blob. Within a couple of weeks, another plume popped up, also lasting longer than a week. 

The simplest explanation, Nature reports, is that dust storms whirling across Mars kicked up dust. However, not only has dust not been seen at altitudes higher than 50 kilometers (31 miles), unusual weather conditions would be required to convey the dust up so high. “At about 250 kilometers (155 miles), the division between the atmosphere and outer space is very thin, so the reported plumes are extremely unexpected,” Agustin Sánchez-Lavega from Universidad del País Vasco explains in an ESA news release

To see what might have created the unusually large, high-altitude plumes, Sánchez-Lavega and a large international team collected pictures taken by over a dozen amateur observers from 2001 to 2014, and they searched through the archive of images captured from the Hubble Space Telescope between 1995 and 1999. They explored two explanations: that the plumes formed from frozen particles of water or carbon dioxide, or that they’re the result of auroral activity. (Like the northern lights on Earth, a Martian aurora results from charged particles from the sun interacting with our magnetic field.)

Their conclusion: Neither idea is fully consistent with the giant size of the plumes. The existence of frozen particles would require the atmosphere to be much colder than what circulation models have previously predicted for that altitude, Nature reports. And the magnetic field of Mars is too weak and patchy compared to Earth.

Close-up observations from telescopes or spacecrafts in orbit might help, BBC explains, otherwise astronomers may need to just wait for the plumes to reappear before they can solve the mystery of their source. Pictured below, Mars with the plume circled in yellow. To its left are augmented views of the plume as it changed shapes on March 21, 2012. The background image is of a region on Mars called Terra Cimmeria, where the plume formed.

Images: D. Parker/A. Sánchez-Lavega et al., 2015 Nature (top), W. Jaeschke and D. Parker and NOAA/Grupo Ciencias Planetarias (GCP)¬–UPV/EHU (middle)

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