Nothing Says Springtime on Mars Like Explosions of Sand

Springtime on Earth can be a riotous affair, as plants come back to life and creatures large and small get ready to mate. Nothing like that happens on Mars, of course. But even on a cold world like Mars, springtime brings changes, though you have to look a little more closely to see them.

Lucky for us, there are spacecraft orbiting Mars with high-resolution cameras, and we can track the onset of Martian springtime through images.

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Where Does Mars’ Methane Go? New Study Provides Possible Answer, with Implications in the Search for Life.

For centuries, scientists have speculated about the existence of life on Mars. But it was only within the past 15 years that the search for life (past and present) really began to heat up. It was at this time that methane, an organic molecule that is associated with many forms of life here on Earth (i.e. a “biosignature”) was detected in Mars’ atmosphere.

Since that time, attempts to study Mars’ atmospheric methane have produced varying results. In some cases, methane has been found that was several times its normal concentrations; in others, it was absent. Seeking to answer this mystery, an interdisciplinary team from Aarhus University recently conducted a study where they investigated a possible mechanism for the removal of methane from Mars’ atmosphere.

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Martian Clouds Might Start with Meteor Trails Through the Atmosphere

On Earth, clouds form when enough droplets of water condense out of the air. And those droplets require a tiny speck of dust or sea salt, called a condensation nuclei, to form. In Earth’s atmosphere, those tiny specks of dust are lofted high into the atmosphere where they trigger cloud formation. But on Mars?

Mars has something else going on.

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Earth has a Water Cycle. Mars has a Dust Cycle

To say there are some myths circulating about Martian dust storms would be an understatement. Mars is known for its globe-encircling dust storms, the likes of which are seen nowhere else. Science fiction writers and Hollywood movies often make the dust storms out to be more dangerous than they really are. In “The Martian,” a powerful dust storm destroys equipment, strands Matt Damon on Mars, and forces him into a brutal struggle for survival.

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The Global Dust Storm that Ended Opportunity Helped Teach us how Mars Lost its Water

Mars in 2001. On the left, no global dust storm. On the right, global dust storm. Image Credit: By Jim Secosky picked out this NASA image NASA/JPL/MSSS - https://photojournal.jpl.nasa.gov/figures/PIA03170_fig1.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=65809875

The enduring, and maybe endearing, mystery around Mars is what happened to its water? We can say with near-certainty now, thanks to the squad of Mars rovers and orbiters, that Mars was once much wetter. In fact that planet may have had an ocean that covered a third of the surface. But what happened to it all?

As it turns out, the global dust storms that envelop Mars, and in particular the most recent one that felled the Opportunity rover, may offer an explanation.

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Rivers on Mars Flowed for More Than a Billion Years

A photo of a preserved river channel on Mars. The color is overlaid to show elevation, with blue being low and yellow being high elevation. Image Credit: NASA/JPL/Univ. Arizona/UChicago

The ancient climate of Mars is a mystery to scientists. Even with all we’ve learned about Mars, it’s still difficult to explain how lakes and rivers existed. A new study shows that Martian rivers were swollen with runoff and that they flowed far later into the planet’s history than previously thought.

The question is, how did the Martian climate create these conditions?

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ExoMars Has Sent Back its First Images From Mars

On October 19th, 2016, the European Space Agency’s Exobiology on Mars (ExoMars) mission established orbit around Mars. Consisting of the ExoMars Trace Gas Orbiter (TGO) and the Schiaparelli lander, the purpose of this mission is to investigate Mars for past signs of life. And whereas the Schiaparelli unfortunately crashed during deployment, the TGO has managed to begin its mission ahead of schedule.

A few weeks ago, the satellite achieved a near circular orbit around Mars after performing a series of braking maneuvers. Since that time, the orbiter’s Color and Stereo Surface Imaging System (CaSSIS) took a stunning image of the surface. This picture was not only the TGO’s first image of Mars, it was also a test to see if the orbiter is ready to being its main mission on April 28th.

The image captured a 40 km- (25 mi) long segment of the Korolev Crater, which is located high in Mars’ northern hemisphere. The image was a composite of three images in different colors that were taken simultaneously on April 15th, 2018, which were then assembled to produce this color image. The bright material that appears at the edge of the crater is water ice.

The ExoMars Colour and Stereo Surface Imaging System, CaSSIS, captured this view of the rim of Korolev crater (73.3ºN/165.9ºE). Copyright ESA/Roscosmos/CaSSIS

As Antoine Pommerol, a member of the CaSSIS science team working on the calibration of the data, explained in a recent ESA press release:

“We were really pleased to see how good this picture was given the lighting conditions. It shows that CaSSIS can make a major contribution to studies of the carbon dioxide and water cycles on Mars.”

Prior to the test phase, the camera team transmitted new software to the TGO, and after a few minor issues, they determined that the instrument was ready to work. The camera is one of four instruments on the TGO, which also carries two spectrometer suites and a neutron detector. The spectrometers began their science mission on April 21st by taking the first sample of the atmosphere to see how its molecules absorb sunlight.

By doing this, the TGO hopes to determine the chemical composition of Mars atmosphere and find evidence of methane and other trace atmospheric gases that could be signatures of active biological or geological processes. Eventually, the camera will help characterize features on the surface that could be related to trace gas sources. Hence the importance of this recent test.

ExoMars’ Trace Gas Orbiter (TGO) and Schiaparelli lander seperating in orbit of Mars. Credit: ESA/ATG medialab

“We aim to fully automate the image production process,” said Nicolas Thomas, the camera’s principal investigator from the University of Bern. “Once we achieve this, we can distribute the data quickly to the science community for analysis.”

A lot of challenges lie ahead, which includes a long period of data collection to bring out the details of rare (or yet to be discovered) trace gases in Mars’ atmosphere. This is necessary since trace gases (as the name would suggest) are present in only very small amounts – i.e. less than 1% of the volume of the planet’s atmosphere. But as Håkan Svedhem – the ESA’s TGO project scientist – indicated, the test image was a good start.

“We are excited to finally be starting collecting data at Mars with this phenomenal spacecraft,” he said. “The test images we have seen so far certainly set the bar high.”

By 2020, the second part of the ExoMars mission is scheduled to launch. This will consist of a Russian surface platform and a European rover landing on the surface in support of a science mission that is expected to last into 2022 or longer. Alongside NASA’s proposed Mars 2020 rover, the Red Planet is due to have several more visitors in the coming years!

Further Reading: ESA

Mars Express Captures Mars’ Moving Bow Shock

Every planet in our Solar System interacts with the stream of energetic particles coming from our Sun. Often referred to as “solar wind”, these particles consist mainly of electrons, protons and alpha particles that are constantly making their way towards interstellar space. Where this stream comes into contact with a planet’s magnetosphere or atmosphere, it forms a region around them known as a “bow shock”.

These regions form in front of the planet, slowing and diverting solar wind as it moves past – much like how water is diverted around a boat. In the case of Mars, it is the planet’s ionosphere that provides the conductive environment necessary for a bow shock to form. And according to a new study by a team of European scientists, Mars’ bow shock shifts as a result of changes in the planet’s atmosphere.

The study, titled “Annual Variations in the Martian Bow Shock Location as Observed by the Mars Express Mission“, appeared in the Journal of Geophysical Letters: Space Physics. Using data from the Mars Express orbiter, the science team sought to investigate how and why the bow shock’s location varies during the course of several Martian years, and what factors are chiefly be responsible.

Diagram of Mars’ orbit and changes to its bow shock between perihelion and aphelion. Credit: ESA/ATG medialab

For many decades, astronomers have been aware that bow shocks form upstream of a planet, where interaction between solar wind and the planet causes energetic particles to slow down and gradually be diverted. Where the solar wind meets the planet’s magnetosphere or atmosphere, a sharp boundary line is formed, which them extends around the planet in a widening arc.

This is where the term bow shock comes from, owing to its distinctive shape. In the case of Mars, which does not have a global magnetic field and a rather thin atmosphere to boot (less than 1% of Earth’s atmospheric pressure at sea level), it is the electrically-charged region of the upper atmosphere (the ionosphere) that is responsible for creating the bow shock around the planet.

At the same time, Mars relatively small size, mass and gravity allows for the formation of an extended atmosphere (i.e. an exosphere). In this portion of Mars’ atmosphere, gaseous atoms and molecules escape into space and interact directly with solar wind. Over the years, this extended atmosphere and Mars’ bow shock have been observed by multiple orbiter missions, which have detected variations in the latter’s boundary.

This is believed to be caused by multiple factors, not the least of which is distance. Because Mars has an relatively eccentric orbit (0.0934 compared to Earth’s 0.0167), its distance from the Sun varies quite a bit – going from 206.7 million km (128.437 million mi; 1.3814 AU) at perihelion to 249.2 million km (154.8457 million mi; 1.666 AU) at aphelion.

Illustration showing how Mars and Earth interact with solar wind. Credit: NASA

When the planet is closer, the dynamic pressure of the solar wind against its atmosphere increases. However, this change in distance also coincides with increases in the amount of incoming extreme ultraviolet (EUV) solar radiation. As a result, the rate at which ions and electrons (aka. plasma) are produced in the upper atmosphere increases, causing increased thermal pressure that counteracts the incoming solar wind.

Newly-created ions within the extended atmosphere are also picked up and accelerated by the electromagnetic fields being carried by the solar wind. This has the effect of slowing it down and causing Mars’ bowshock to shift its position. All of this has been known to happen over the course of a single Martian year – which is equivalent to 686.971 Earth days or 668.5991 Martian days (sols).

However, how it behaves over longer periods of time is a question that was previously unanswered. As such, the team of European scientists consulted data obtained by the Mars Express mission over a five year period. This data was taken by the Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer (ELS), which the team used to examine a total of 11,861 bow shock crossings.

What they found was that, on average, the bow shock is closer to Mars when it is near aphelion (8102 km), and further away at perihelion (8984 km). This works out to a variation of about 11% during the Martian year, which is pretty consistent with its eccentricity. However, the team wanted to see which (if any) of the previously-studied mechanisms was chiefly responsible for this change.

The moving Martian bow shock. Credit: ESA/ATG medialab

Towards this end, the team considered variations in solar wind density, the strength of the interplanetary magnetic field, and solar irradiation as primary causes – are all of which decline as the planet gets farther away from the Sun. However, what they found was that the bow shock’s location appeared more sensitive to variations in the Sun’s output of extreme UV radiation rather than to variations in solar wind itself.

The variations in bow shock distance also appeared to be related to the amount of dust in the Martian atmosphere. This increases as Mars approaches perihelion, causing the atmosphere to absorb more solar radiation and heat up. Much like how increased levels of EUV leads to an increased amount of plasma in the ionosphere and exosphere, increased amounts of dust appear to act as a buffer against solar wind.

As Benjamin Hall, a researcher at Lancaster University in the UK and the lead author of the paper, said in an ESA press release:

“Dust storms have been previously shown to interact with the upper atmosphere and ionosphere of Mars, so there may be an indirect coupling between the dust storms and bow shock location… However, we do not draw any further conclusions on how the dust storms could directly impact the location of the Martian bow shock and leave such an investigation to a future study.”

In the end, Hall and his team could not single out any one factor when addressing why Mars’ bow shock shifts over longer periods of time. “It seems likely that no single mechanism can explain our observations, but rather a combined effect of all of them,” he said. “At this point none of them can be excluded.”

Looking ahead, Hall and his colleagues hope that future missions will help shed additional light on the mechanisms behind Mars shifting bowshock. As Hall indicated, this will likely involve “”joint investigations by ESA’s Mars Express and Trace Gas Orbiter, and NASA’s MAVEN mission. Early data from MAVEN seems to confirm the trends that we discovered.”

While this is not the first analysis that sought to understand how Mars’ atmosphere interacts with solar wind, this particular analysis was based on data obtained over a much longer period of time than any previously study. In the end, the multiple missions that are currently studying Mars are revealing much about the atmospheric dynamics of this planet. A planet which, unlike Earth, has a very weak magnetic field.

What we learn in the process will go a long way towards ensuring that future exploration missions to Mars and other planets that have weak magnetic fields (like Venus and Mercury) are safe and effective. It might even assist us with the creation of permanent bases on these worlds someday!

Further Reading: ESA, Journal of Geophysical Research: Space Physics