Asteroid Strikes on Mars Spun Out Supersonic Tornadoes that Scoured the Surface

The study of another planet’s surface features can provide a window into its deep past. Take Mars for example, a planet whose surface is a mishmash of features that speak volumes. In addition to ancient volcanoes and alluvial fans that are indications of past geological activity and liquid water once flowing on the surface, there are also the many impact craters that dot its surface.

In some cases, these impact craters have strange bright streaks emanating from them, ones which reach much farther than basic ejecta patterns would allow. According to a new research study by a team from Brown University, these features are the result of large impacts that generated massive plumes. These would have interacted with Mars’ atmosphere, they argue, causing supersonic winds that scoured the surface.

These features were noticed years ago by Professor Peter H. Schultz, a professor of geological science with the Department of Earth, Environmental, and Planetary Sciences (DEEPS) at Brown University. When studying images taken at night by the Mars Odyssey orbiter using its THEMIS instrument, he noticed steaks that only appeared when imaged in the infrared wavelength.

Artist’s conception of the Mars Odyssey spacecraft. Credit: NASA/JPL

These streaks were only visible in IR because it was only at this wavelength that contrasts in heat retention on the surface were visible. Essentially, brighter regions at night indicate surfaces that retain more heat during the day and take longer to cool. As Schultz explained in a Brown University press release, this allowed for features to be discerned that would otherwise not be noticed:

“You couldn’t see these things at all in visible wavelength images, but in the nighttime infrared they’re very bright. Brightness in the infrared indicates blocky surfaces, which retain more heat than surfaces covered by powder and debris. That tells us that something came along and scoured those surfaces bare.”

Along with Stephanie N. Quintana, a graduate student from DEEPS, the two began to consider other explanations that went beyond basic ejecta patterns. As they indicate in their study – which recently appeared in the journal Icarus under the title “Impact-generated winds on Mars” – this consisted of combining geological observations, laboratory impact experiments and computer modeling of impact processes. 

Ultimately, Schultz and Quintana concluded that crater-forming impacts led to vortex-like storms that reached speeds of up to 800 km/h (500 mph) – in other words, the equivalent of an F8 tornado here on Earth. These storms would have scoured the surface and ultimately led to the observed streak patterns. This conclusion was based in part on work Schultz has done in the past at NASA’s Vertical Gun Range.

An infrared image revealing strange bright streaks extending from Santa Fe crater on Mars. Credit: NASA/JPL-Caltech/Arizona State University.

This high-powered cannon, which can fire projectiles at speeds up to 24,000 km/h (15,000 mph), is used to conduct impact experiments. These experiments have shown that during an impact event, vapor plumes travel outwards from the impact point (just above the surface) at incredible speeds. For the sake of their study, Schultz and Quintana scaled the size of the impacts up, to the point where they corresponded to the impact craters on Mars.

The results indicated that the vapor plume speed would be supersonic, and that its interaction with the Martian atmosphere would generate powerful winds. However, the plume and associated winds would not be responsible for the strange streaks themselves. Since they would be travelling just above the surface, they would not be capable of causing the kind of deep scouring that exists in the streaked areas.

Instead, Schultz and Quintana showed that when the plume struck a raised surface feature – like the ridges of a smaller impact crater – it would create more powerful vortices that would then fall to the surface. It is these, according to their study, that are responsible for the scouring patterns they observed. This conclusion was based on the fact that bright streaks were almost always associated with the downward side of a crater rim.

IR images showing the correlation between the streaks and smaller craters that were in place when the larger crater was formed. Credit: NASA/JPL-Caltech/Arizona State University

As Schultz explained, the study of these streaks could prove useful in helping to establish that rate at which erosion and dust deposition occurs on the Martian surface in certain areas:

“Where these vortices encounter the surface, they sweep away the small particles that sit loose on the surface, exposing the bigger blocky material underneath, and that’s what gives us these streaks. We know these formed at the same time as these large craters, and we can date the age of the craters. So now we have a template for looking at erosion.”

In addition, these streaks could reveal additional information about the state of Mars during the time of impacts. For example, Schultz and Quintana noted that the streaks appear to form around craters that are about 20 km (12.4 mi) in diameter, but not always. Their experiments also revealed that the presence of volatile compounds (such as surface or subsurface water ice) would affect the amount of vapor generated by an impact.

In other words, the presence of streaks around some craters and not others could indicate where and when there was water ice on the Martian surface in the past. It has been known for some time that the disappearance of Mars’ atmosphere over the course of several hundred million years also resulted in the loss of its surface water. By being able to put dates to impact events, we might be able to learn more about Mars’ fateful transformation.

The study of these streaks could also be used to differentiate between the impacts of asteroids and comets on Mars – the latter of which would have had higher concentrations of water ice in them. Once again, detailed studies of Mars’ surface features are allowing scientists to construct a more detailed timeline of its evolution, thus determining how and when it became the cold, dry place we know today!

Further Reading: Brown University, Science Direct

 

What is the Weather like on Mars?

Welcome back to our planetary weather series! Today, we take a look at Earth’s neighbor and possible “backup location” for humanity someday – Mars!

Mars is often referred to as “Earth’s Twin”, due to the similarities it has with our planet. They are both terrestrial planets, both have polar ice caps, and (at one time) both had viable atmospheres and liquid water on their surfaces. But beyond that, the two are quite different. And when it comes to their atmospheres and climates, Mars stands apart from Earth in some rather profound ways.

For instance, when it comes to the weather on Mars, the forecast is usually quite dramatic. Not only does Martian weather vary from day to day, it sometimes varies from hour to hour. That seems a bit unusual for a planet that has an atmosphere that is only 1% as dense as the Earth’s. And yet, Mars manages to really up the ante when it comes to extreme weather and meteorological phenomena.

Mars’ Atmosphere:

Mars has a very thin atmosphere which is composed of 96% carbon dioxide, 1.93% argon and 1.89% nitrogen, along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates that measure 1.5 micrometers in diameter, which is what gives the Martian sky its tawny color when seen from the surface. Mars’ atmospheric pressure ranges from 0.4 to 0.87 kPa, which is the equivalent of about 1% of Earth’s at sea level.

This image illustrates possible ways methane might get into Mars’ atmosphere and also be removed from it. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

Because of this thin atmosphere, and its greater distance from the Sun, the surface temperature of Mars is much colder than what we experience here on Earth. The planet’s average temperature is -63 °C (-82 °F), with a low of -143 °C (-226 °F) during the winter at the poles, and a high of 35 °C (95 °F) during summer and midday at the equator.

Due to the extreme lows in temperature at the poles, 25-30% of the carbon dioxide in the atmosphere freezes and becomes dry ice that is deposited on the surface. While the polar ice caps are predominantly water, the Martian North Pole has a layer of dry ice measuring one meter thick in winter, while the South Pole is covered by a permanent layer that is eight meters deep.

Trace amounts of methane and ammonia have also been detected in the Martian atmosphere. In the case of the former, it has an estimated concentration of about 30 parts per billion (ppb), though the Curiosity rover detected a “tenfold spike” on December 16th, 2014. This detection was likely localized, and the source remains a mystery. Similarly, the source of ammonia is unclear, though volcanic activity has been suggested as a possibility.

Meteorological Phenomena:

Mars is also famous for its intense dust storms, which can range from small tornadoes to planet-wide phenomena. Instances of the latter coincide with dust being blown into the atmosphere, causing it to be heated up from the Sun. The warmer dust-filled air rises and the winds get stronger, creating storms that can measure up to thousands of kilometers in width and last for months at a time. When they get this large, they can actually block most of the surface from view.

Image capturing an active dust storm on Mars. Image credits: NASA/JPL-Caltech/MSSS

Due to its thin atmosphere, low temperatures and lack of a magnetosphere, liquid precipitation (i.e. rain) does not take place on Mars. Basically, solar radiation would cause any liquid water in the atmosphere to disassociate into hydrogen and oxygen. And because of the cold and thin atmosphere, there is simply not enough liquid water on the surface to maintain a water cycle.

Occasionally, however, thin clouds do form in the atmosphere and precipitation falls in the form of snow. This consists primarily of carbon dioxide snow, which has been observed in the polar regions. However, small traces of frozen clouds carrying water have also been observed in Mars’ upper atmosphere in the past, producing snow that is restricted to high altitudes.

One such instance was observed on September 29th, 2008, when the Phoenix lander took pictures of snow falling from clouds that were 4 km (2.5 mi) above its landing site near the Heimdal Crater. However, data collected from the lander indicated that the precipitation vaporized before it could reach the ground.

Aurorae on Mars:

Auroras have also been detected on Mars, which are also the result of interaction between magnetic fields and solar radiation. While Mars has little magnetosphere to speak of, scientists determined that aurorae observed in the past corresponded to an area where the strongest magnetic field is localized on the planet. This was concluded by analyzing a map of crustal magnetic anomalies compiled with data from Mars Global Surveyor.

Mars has magnetized rocks in its crust that create localized, patchy magnetic fields (left). In the illustration at right, we see how those fields extend into space above the rocks. At their tops, auroras can form. Credit: NASA

A notable example is the one that took place on August 14th, 2004, and which was spotted by the SPICAM instrument aboard the Mars Express. This aurora was located in the skies above Terra Cimmeria – at geographic coordinates 177° East, 52° South – and was estimated to be quite sizable, measuring 30 km across and 8 km high (18.5 miles across and 5 miles high).

More recently, an aurora was observed on Mars by the MAVEN mission, which captured images of the event on March 17th, 2015, just a day after an aurora was observed here on Earth. Nicknamed Mars’ “Christmas lights”, they were observed across the planet’s mid-northern latitudes and (owing to the lack of oxygen and nitrogen in Mars’ atmosphere) were likely a faint glow compared to Earth’s more vibrant display.

To date, Mars’ atmosphere, climate and weather patterns have been studied by dozens of orbiters, landers, and rovers, consisting of missions by NASA, Roscomos, as well as the European Space Agency and Indian federal space program. These include the Mariner 4 probe, which conducted the first flyby of Mars – a two-day operation that took place between July 14th and 15th, 1965.

The crude data it obtained was expanded on by the later later Mariner 6 and 7 missions (which conducted flybys in 1969). This was followed by the Viking 1 and 2 missions, which reached Mars in 1976 and became the first spacecraft to land on the planet and send back images of the surfaces.

Since the turn of the century, six orbiters have been placed in orbit around Mars to gather information on its atmosphere – 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN, Mars Orbiter Mission and ExoMars Trace Gas Orbiter. These have been complimented by rover and lander missions like Pheonix, Spirit and Opportunity, and Curiosity.

In the future, several additional missions are scheduled to reach the Red Planet, which are expected to teach us even more about its atmosphere, climate and weather patterns. What we find will reveal much about the planet’s deep past, its present condition, and perhaps even help us to build a future there.

We have written many interesting articles about Martian weather here at Universe Today. Here’s Mars Compared to Earth, It Only Happens on Mars: Carbon Dioxide Snow is Falling on the Red Planet, Snow is Falling from Martian Clouds, Surprise! Mars has Auroras Too! and NASA’s MAVEN Orbiter Discovers Solar Wind Stripped Away Mars Atmosphere Causing Radical Transformation.

For more information, check out this NASA article about how space weather affects Mars.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.

Sources:

Winged Telescope Detects Martian Atomic Oxygen

SOFIA in flight, with its telescope exposed. Image: NASA/Jim Ross

Finding atomic oxygen in the Martian atmosphere is very difficult to do, which explains why it’s been 40 years since it was last detected. In the 1970’s, NASA’s Viking and Mariner missions detected Martian atmospheric oxygen, and now, the Stratospheric Observatory for Infrared Astronomy (SOFIA) has detected atomic oxygen in the upper portion of the Martian atmosphere called the mesosphere.

SOFIA is a specially modified Boeing 747 aircraft which carries a 100 inch telescope. It flies at altitudes between 37,000 to 45,000 feet, which puts it above most of the moisture in Earth’s atmosphere. This moisture would otherwise block the infrared radiation that SOFIA “sees.”

“Atomic oxygen in the Martian atmosphere is notoriously difficult to measure,” said Pamela Marcum, SOFIA project scientist. “To observe the far-infrared wavelengths needed to detect atomic oxygen, researchers must be above the majority of Earth’s atmosphere and use highly sensitive instruments, in this case a spectrometer. SOFIA provides both capabilities.”

A close-up of SOFIA's telescope and primary mirror. Image: NASA/Tom Tschida
A close-up of SOFIA’s telescope and primary mirror. Image: NASA/Tom Tschida

A special detector on board SOFIA, the German Receiver for Astronomy at Terahertz Frequencies (GREAT) allowed researchers to distinguish Martian atmospheric oxygen from Earthly oxygen. SOFIA-GREAT only detected half the amount of oxygen that scientists expected to find, which is probably due to changes and variations in the atmosphere. These results were published in a 2015 paper in Astronomy and Astrophysics.

Atomic oxygen has a strong effect on Mars’ atmosphere because it affects how other gases escape the atmosphere. It’s extreme volatility means it bonds with nearby molecules very easily; oxygen will combine with almost all chemical elements, except for the noble gases.

SOFIA is the largest airborne observatory in the world, and is a joint project between NASA and the German Aerospace Center. SOFIA has a 20 year mission timeline. Researchers will continue using SOFIA to study the Martian atmosphere, in order to better understand the variations in oxygen content.

SOFIA is not the only mission with eyes on Mars’ atmosphere. NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) was launched in 2013 to explore the upper atmosphere of Mars, and how it’s affected by the solar wind. It’s thought that Mars’ atmosphere was much thicker in the past, and has been stripped away over time. Atomic oxygen played a role in Mars’ escaping atmosphere in the past, and no doubt will play a role in the future. SOFIA and other missions like MAVEN will hopefully shed some light on Mars’ past and future atmospheres.

Weekly Space Hangout – Nov. 6, 2015: Astronaut Mike Massimino

Host: Fraser Cain (@fcain)

Special Guest: Mike Massimino, Former Astronaut; Senior Advisor for Space Programs at the Intrepid Sea, Air & Space Museum; Full-time instructor at Columbia University; Human-machine systems, space robotics, and human space flight.

Guests:
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Kimberly Cartier (@AstroKimCartier )
Continue reading “Weekly Space Hangout – Nov. 6, 2015: Astronaut Mike Massimino”

How Can Mars Sometimes Be Warmer Than Earth?

Remember a few weeks ago when the weather on Mars was making the news? At the time, parts of the Red Planet was experiencing temperatures that were actually warmer than parts of the US. Naturally, there were quite a few skeptics. How could a planet with barely any atmosphere which is farther from the Sun actually be warmer than Earth?

Well, according to recent data obtained by the Curiosity rover, temperatures in the Gale Crater reached a daytime high of -8 °C (17.6 °F) while cities like Chicago and Buffalo were experiencing lows of -16 to -20 °C (2 to -4 °F). As it turns out, this is due to a number of interesting quirks that allow for significant temperature variability on Mars, which at times allow some regions to get warmer than places here on Earth.

It’s no secret that this past winter, we here in North America have been experiencing a bit of a record-breaking cold front. This was due to surges of cold air pushing in from Siberia and the North Pole into Canada, the Northern Plains and the Midwest. This resulted in many cities experiencing January-like weather conditions in November, and several cities hitting record-lows not seen in decades or longer.

Credit: NASA/JPL/University of Arizona
Carbon dioxide ice on Mars, which experiences sublimation from solar warming to create  polygonal structures. Credit: NASA/JPL/University of Arizona

For instance, the morning of November 18th, 2014, was the coldest since 1976, with a national average temperature of -7 °C (19.4 °F). That same day, Detroit tied a record it had set in 1880, with a record low of -12 °C (11 °F).

Five days earlier, the city of Denver, Colorado experienced temperatures as cold as -26 °C (-14 °F) while the city of Casper, Wyoming, hit a record low of -33 °C (-27 °F). And then on November 20th, the town of Jacksonville, Florida broke a previous record (which it set in 1873) with an uncharacteristic low of -4° C (25 °F).

Hard to believe isn’t it? Were it not for the constant need for bottled oxygen, more people might consider volunteering for Mars One‘s colonizing mission – which, btw, is still scheduled to depart in 2023, so there’s still plenty of time register! However, these comparative figures manage to conceal a few interesting facts about Mars.

For starters, Mars experiences an average surface temperature of about -55 °C (-67 °F), with temperatures at the pole reaching as low as a frigid -153 °C (-243.4 °F). Meanwhile, here on Earth the average surface temperature is 7.2 °C (45 °F), which is also due to a great deal of seasonal and geographic variability.

The eccentricity in Mars' orbit means that it is . Credit: NASA
The eccentricity in Mars’ orbit around the Sun means that it is 42.5 million km closer during certain times of the year. Credit: NASA

In the desert regions near the equator, temperature can get as high as 57.7 °C, with the hottest temperature ever recorded being 70.7 °C (158.36 °F) in the summertime in the desert region of Iran. At the south pole in Antarctica temperatures can reach as low as -89.2 °C (-128.6 °F). Pretty darn cold, but still balmy compared to Mars’ polar ice caps!

Also, since its arrival in 2012, the Curiosity Rover has been rolling around inside Gale Crater – which is located near the planet’s equator. Here, the planet’s temperature experiences the most variability, and can reach as high as 20 °C (68 °F) during midday.

And last, but not least, Mars has a greater eccentricity than all other planet’s in the Solar System – save for Mercury. This means that when the planet is at perihelion (closest to the Sun) it is roughly 0.28 AUs (42.5 million km) closer than when it is at aphelion (farthest from the Sun). Having just passed perihelion recently, the average surface temperatures on Mars can vary by up to an additional 20 ºC.

In short, Mars is still, and by far, the colder of the two planets. Not that it’s a competition or anything…

Further Reading: NASA