ESA: Phobos Occults

Credit: ESA/DLR/FU Berlin (G. Neukum)

Mars' moon Phobos has already been extensively observed – this image is just one example, taken in 2009 – so its occultation of ESA Mars Express on 28 April 2014 is not expected to yield dramatic discoveries.

But science lies in the smallest things – like obtaining a 'snapshot in time' of continuous change.

The occultation meant that, for a brief time, Phobos passed between ESA Mars Express and Earth, blocking the spacecraft's radio signal.

The break in the signal was small – about nine seconds – but the precise start and end times are valuable information.

These will allow scientists to calculate the orbit of Phobos with great precision – specifically the mean distance from Mars, which is notoriously difficult to pin down because Phobos' natural motion around the planet changes over time.

Phobos and sister moon Deimos are formidable scientific enigmas.

There is no confirmed theory of their origin that offers a satisfactory explanation for their current orbits and appearances.

They could be excellent targets for future robotic landings.

ESA experts analysed yesterday's data from the tracking station and found the occultation to have started just before 01:08:24 GMT, lasting until shortly before 01:08:33 GMT.

Now, we'll know the orbit of Phobos with just a little more precision, at least for a while.

ESA Mars Express: Seasonal Ozone Layer Over The Martian South Pole

Ozone production over Mars southern winter pole.
Credit: ESA/ATG medialab.

For the past decade, ESA's Mars Express orbiter has been observing atmospheric structure on the Red Planet.

Among its discoveries is the presence of three separate ozone layers, each with its own characteristics.

A new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone above the planet's southern winter pole.

Ozone (O3) is a form of oxygen gas which contains three atoms, rather than two.

On Earth, ozone is a pollutant at ground level, but at higher altitudes it provides an essential protective layer against harmful solar ultraviolet (UV) light.

However, ozone molecules are easily destroyed by solar ultraviolet light and by chemical reactions with hydrogen radicals, which are released by photolysis (splitting) of water molecules.

The role of pollution in its destruction has been a major focus of attention since the mid-1980s, when a hole in the ozone layer was discovered above Antarctica.

Until the early 1970s, no one could be sure whether ozone existed on any of the other planets. Ozone was then detected on Mars and it has since been discovered on Venus by ESA's Venus Express mission.

ESA's Mars Express orbiter

On Mars, the ozone concentration is typically 300 times thinner than on Earth, although it varies greatly with location and time.

In recent years, the SPICAM UV spectrometer on board Mars Express has shown the presence of two distinct ozone layers at low-to-mid latitudes.

These comprise a persistent, near-surface layer below an altitude of 30 km, and a separate layer, which is only present in northern spring and summer, and whose altitude varies from 30 to 60 km.

In recent years, SPICAM has also provided evidence for the existence of a third ozone layer which exists 40-60 km above the southern winter pole, with no counterpart above the North Pole.

In a paper published in the journal Nature Geoscience, Franck Montmessin and Franck Lefevre, two scientists from LATMOS in Guyancourt, France, have analysed approximately 3000 occultation sequences and vertical ozone profiles collected by SPICAM on the night side of Mars.

Mars crater may actually be ancient supervolcano

Seen above, for the basin and surrounding area, higher elevations (reds and yellows) and lower elevations (blues and grays) are indicated. Credit: NASA/JPL/GSFC

A research project led by Joseph R. Michalski, Senior Scientist at the Planetary Science Institute, has identified what could be a supervolcano on Mars – the first discovery of its kind.

In a paper published Oct. 3 in the journal Nature, Michalski and co-author Jacob E. Bleacher of NASA Goddard Space Flight Center describe a new type of volcanic construction on Mars that until now has gone unrecognized.

The volcano in question, a vast circular basin on the face of the Red Planet, previously had been classified as an impact crater.

Researchers now suggest the basin is actually the remains of an ancient supervolcano eruption.

Their assessment is based on images and topographic data from NASA's Mars Odyssey, Mars Global Surveyor and Mars Reconnaissance Orbiter (MRO) spacecraft, as well as the European Space Agency's Mars Express orbiter.

In the Nature paper Michalski and Bleacher lay out their case that the basin, recently named Eden Patera, is a volcanic caldera. Because a caldera is a depression, it can look like a crater formed by an impact, rather than a volcano.

"On Mars, young volcanoes have a very distinctive appearance that allows us to identify them," Michalski said. "The long-standing question has been what ancient volcanoes on Mars look like. Perhaps they look like this one."

Above, the dark color indicates younger material draped across the Eden Patera depression. 

Credit: ESA

The researchers also suggest a large body of magma loaded with dissolved gas (similar to the carbonation in soda) rose through thin crust to the surface quickly.

Like a bottle of soda that has been shaken, this supervolcano would have blown its contents far and wide if the top came off suddenly.

"This highly explosive type of eruption is a game-changer, spewing many times more ash and other material than typical, younger Martian volcanoes," Bleacher said.

"During these types of eruptions on Earth, the debris may spread so far through the atmosphere and remain so long that it alters the global temperature for years."

After the material is expelled from the eruption, the depression that is left can collapse even further, causing the ground around it to sink.

Eruptions like these happened in ages past at what is now Yellowstone National Park in the western United States, Lake Toba in Indonesia and Lake Taupo in New Zealand.

More information: www.nature.com/nature/journal/v502/n7469/full/nature12482.html

ESA Mars Express Orbiter (MRO) image: Thaumasia Planum region

Colour-coding shows the relative depth of two craters on Mars, in particular the depth of the central pits. 

The left-hand crater penetrates deeper than the right one, Arima crater. 

The ESA Mars Express Orbiter spacecraft (MEO) captured the image of Thaumasia Planum region on January 4, 2013.

Credit: ESA 

Further studies of Thaumasia Planum in Geophysical Research Letters

Nasa Mars Reconnaissance Orbiter Images