Guest “Let’s light this candle! Part Deux” by David Middleton
NEWS 28 SEPTEMBER 2020
Water on Mars: discovery of three buried lakes intrigues scientists
Researchers have detected a group of lakes hidden under the red planet’s icy surface.
Two years ago, planetary scientists reported the discovery of a large saltwater lake under the ice at Mars’s south pole, a finding that was met with excitement and some scepticism. Now, researchers have confirmed the presence of that lake — and found three more.
The discovery, reported on 28 September in Nature Astronomy1, was made using radar data from the European Space Agency’s Mars-orbiting spacecraft, called Mars Express. It follows the detection of a single subsurface lake in the same region in 2018 — which, if confirmed, would be the first body of liquid water ever detected on the red planet and a possible habitat for life. But that finding was based on just 29 observations made from 2012 to 2015, and many researchers said they needed more evidence to support the claim. The latest study used a broader data set comprising 134 observations from 2012 to 2019.
“We identified the same body of water, but we also found three other bodies of water around the main one,” says planetary scientist Elena Pettinelli at the University of Rome, who is one of the paper’s co-authors. “It’s a complex system.”
The team used a radar instrument on Mars Express called the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to probe the planet’s southern polar region. MARSIS sends out radio waves that bounce off layers of material in the planet’s surface and subsurface. The way the signal is reflected back indicates the kind of material that is present at a particular location — rock, ice or water, for example. A similar method is used to identify subsurface glacial lakes on Earth. The team detected some areas of high reflectivity that they say indicate bodies of liquid water trapped under more than one kilometre of Martian ice.
Why do they think these are lakes?
The Mars Express spacecraft carries an instrument called MARSIS.
MARSIS is a subsurface radar sounder with a 40-meter (130-foot) antenna on the Mars Express orbiter that will search for water and study the atmosphere.
Once Mars Express is in orbit around Mars, the MARSIS antenna will unfurl and begin its radar analysis. The main objective of MARSIS is to look for water from the martian surface down to about 5 kilometers (3 miles) below. It will provide the first opportunity to detect liquid water directly. It will also be able to characterize the surface elevation, roughness, and radar reflectivity of the planet and to study the interaction of the atmosphere and solar wind in the red planet’s ionosphere. During the lifetime of the mission, the instrument will be able to conduct ground-penetrating studies over the entire planet. [More on MARSIS: Searching for Water and Studying the Atmosphere]
How MARSIS Works
The technique used by this radar instrument has been used before on Earth. Similar instruments have been flown on low-flying aircraft to probe deep into the ice sheets of Antarctica and Greenland. At Mars, the instrument with its long antenna will fly over the planet, bouncing radio waves over a selected area and then receiving and analyzing the “echoes.” Any near-surface liquid water should send a strong signal, while ice would be more difficult to detect since its electrical radar signal would be about the same as rock. The echoes will also help characterize the materials and roughness of the surface.NASA
MARSIS is a ground/ice penetrating radar instrument.
The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board ESA’s Mars Express will employ ground penetrating radar to map underground water (if it exists) on Mars. Low frequency waves will be directed towards the planet from a 40 m long antenna which will be unfurled after Mars Express goes into orbit. The radio waves will be reflected from any surface they encounter. In most cases this will be the surface of Mars, but because low frequencies are used, a significant fraction will travel through the crust to encounter further layers of different material – perhaps even water. Analysis of the echoes produced will reveal much about the composition of the top 5 km of the crust.ESA
MARSIS is somewhat analogous to the reflection seismic surveys we use to map subsurface geology and identify hydrocarbon accumulations. In many geologic settings, particularly Cenozoic rocks in places like the Gulf of Mexico, hydrocarbon accumulations are associated with bright reflection events (“bright spots,” Direct Hydrocarbon Indicators). Subglacial lakes on Earth are also associated with bright radar reflections. MARSIS has identified several coherent bright reflection events at the interface of the south polar ice/dust layer and the Martian crust.
If these are subglacial lakes of liquid water, it would be a very significant discovery. However, until we drill through the Martian icecaps to see what’s underneath, we’ll never know whether these are bodies of liquid water, slush or something else.
There appear to be extensive fluvial and fluvio-lacustrine features on Mars (sedimentary formations formed by and in streams, rivers and lakes). If these features were the result of subglacial fluvio-lacustrine processes, it would be consistent with the presence of these subglacial lakes today. The conditions that enable the presence of liquid water also appear to allow for the existence of life. These potential subglacial lakes are probably hyper-saline, and not conducive to the presence of life today. However, it does appear that in the distant past, liquid water was common on the Martian surface or beneath glacial ice. If life ever evolved on Mars, fossil evidence for it should be present in the sedimentary rocks, particularly the mudstones deposited in Mars’ ancient lakes.
Gale Crater – Curiosity Rover
We Just Got More Solid Evidence Mars’ Gale Crater Once Held a Vast Salty Lake
CARLY CASSELLA 7 OCTOBER 2019
From its red and rugged surface, Mars looks like a lifeless planet, both dry and desolate. But that hasn’t always been the case.
NASA’s Curiosity Rover has now collected even more evidence of an ancient salty lake that once lapped the edges of the Gale crater some 3.7 billion years ago.
Analysing soil samples collected from the crater’s bedrock, researchers from Caltech have turned up a diverse range of salts not observed in other rocks on Mars.
Dating back roughly 3.3 to 3.7 billion years ago, the team proposes that these sulfates are left over from evaporated water, indicating the existence of ancient brines, or salty pools, that could have once held tiny forms of life.
Satellite observations of the Red Planet certainly suggest that during this time frame, known as the Hesperian period, some sort of climatic transition took place. And now, the discovery of evaporated salts also indicates a shift to more arid weather on a similar timeline.
The calcium and magnesium sulfates discovered are predicted to have come from Martian basalts, producing soils rich in sulfate and chloride and poor in iron.
Curiosity has been the closest thing yet to having human field geologists on Mars. It even has a hand lens (MAHLI, Mars Hand Lens Imager).
Curiosity is providing sufficiently detailed observations to construct stratigraphic columns.
Curiosity has enabled the identification of geological formations that are morphologically consistent with fossil microbial life on Earth. Although, won’t know if these formations are related to fossilized microbial life until human geologists and paleontologists examine them. Even then, we might not know for sure.
Jezero Crater – Perseverance Rover
The Perseverance rover is currently en route to Mars and expected to land on 18 February 2021.
It will explore Jezero crater, where evidence of both clay mineralogy (phyllosilicates) and lacustrine carbonates have been detected. Perseverance will cache rock and regolith samples for potential future recovery.
NASA’s Mars 2020 will land in Jezero Crater, pictured here. The image was taken by instruments on NASA’s Mars Reconnaissance Orbiter, which regularly takes images of potential landing sites for future missions.
On ancient Mars, water carved channels and transported sediments to form fans and deltas within lake basins. Examination of spectral data acquired from orbit show that some of these sediments have minerals that indicate chemical alteration by water. Here in Jezero Crater delta, sediments contain clays and carbonates.
Image Credit: NASA/JPL-Caltech/ASULast Updated: June 18, 2019Editor: Yvette SmithNASA
While robotic geologists can tell us a lot about Martian geology, they probably will never be able to tell us if there is fossil evidence of past life.
Why We Can’t Depend on Robots to Find Life on Mars
By Meghan Bartels August 22, 2018
A Senate subcommittee asked for reasons to support sending humans to Mars, and, boy, did they get one from Ellen Stofan, NASA’s former chief scientist.
Stofan, who now leads the Smithsonian’s National Air and Space Museum, argued that if we truly want to find and understand any potential traces of ancient life on the Red Planet, robots can’t do it alone — we’ll need humans on the ground.
“While I’m optimistic that life did evolve on Mars, I’m not optimistic that it got very complex, so we’re talking about finding fossil microbes,” Stofan told a Senate subcommittee devoted to science issues on Aug. 1, adding that those fossils would be incredibly hard to find. [The Search for Life on Mars (A Photo Timeline)]
Robots versus humans
Mars has attracted eight successful landers and rovers over the years, with its highest-profile current resident being NASA’s Curiosity rover. That mission was carefully designed to look for places where life might once have thrived — but not to look for traces of that life.
And it has done just that, identifying mudstones in Gale Crater as particularly promising and spotting ancient organic molecules not necessarily created by life. But robots aren’t perfect, and there are still plenty of lingering questions about Martian geology, he added. “There are rocks that rovers have visited and imaged and analyzed and we’re still arguing about what they are,” McMahon said. [Ancient Mars Lakes & Laser Blasts: Curiosity Rover’s 10 Biggest Moments in 1st 5 Years]
Because Martian life likely never got larger than microbial, the features scientists are looking for are going to fit within a robot’s view. But there are some ways humans still outpace robots, particularly when it comes to looking at the bigger picture of life on Mars. “Biologists, geologists and chemists on the ground could do more than identify evidence of past life on Mars,” Stofan told the senators. “They could study its variation, complexity and relationship to life on Earth much more effectively than our robotic emissaries.”
And Westall said that she doesn’t think robots will ever match human geologists for their knowledge and instincts in the field, or their productivity. “I’m a geologist and I go into the field and I need to see things with my eyes, and if I had the chance I’d go to Mars,” she said. “A human geologist can do in a week what the Mars rovers can do in a year.”
“A human geologist can do in a week what the Mars rovers can do in a year.”
Apollo 17 astronauts Jack Schmitt (a human geologist) and Gene Cernan covered nearly 36 km in 22 EVA hours during their 3 day stay on the Moon. Curiosity took 7 years to cover 20 km on Mars. The rovers are great… They even carry the lab with them into the field… But only humans can recognize and convey the context of their observations, particularly if they are trained field observers.
PROFESSOR LEE SILVER: THE ORIGINAL ROCK STAR TEACHER
How do you get a group of test pilot/engineers interested in a bunch of rocks? How can you teach these hard-nosed astronauts to be geologist detectives around rocks and soil, especially on the surface of the Moon? For some time the Apollo astronauts (and would-be geology students) had been bombarded with jargon filled classroom geology lectures that did not excite them. This had been a nagging problem for NASA as they prepared for the Moon landings. After all, one cannot spend billions of dollars going to our nearest planetary neighbour just for pretty pictures.
Neil Armstrong himself broke the mission parameters, exploring beyond the Apollo 11 landing camera’s field of view to collect 80 kilograms of interesting lunar rock samples. He began the “meat part” of the Apollo missions, but not seeing where he had collected the rocks from, there was no detailed context to their story.
Enter Caltech Professor of Geology Lee Silver. As an Apollo lunar sample investigator, Silver had been invited by his old student Harrison “Jack” Schmitt to meet with James Lovell and Fred Haise (assigned to Apollo 13) to discuss teaching the astronauts some basic field geology.
Given the chance to spend a week proving his teaching methods and the absolute need for good planetary science on Apollo, Silver took a party of astronauts on a camping field trip into the Californian Orocopia Mountains.
With the beautiful Orocopias at their feet, Silver’s students including James Lovell, Fred Haise, John Young, Charlie Duke and Jack Schmitt, entered a new and beautiful world of geological discovery. Silver began organising further cross country field trips with a hungry enthusiasm, investigative acumen and sharpness akin to a test pilot’s that spoke the same language and spread among his Apollo apprentices.
Soon after, further astronauts joined the field trips including David Scott and James Irwin whose geological findings from Apollo 15 are attributable to Professor Silver’s teachings.
Using the Earth’s natural environment as a stand in for the Moon’s was a masterstroke. The new geology students practiced dress rehearsals of their missions, standing by Lunar Module substitutes (trees) and describing the 360 degree landscape views as a geologist would.
Interpreting each other’s detailed descriptions each of the astronauts became quick students in geological observation. Under Silver’s tutelage, their innate curiosity ran wild, collecting a variety (or a “suite”) of rock samples each one telling a line in the story about the evolution of the Orocopia Mountains. Silver imposed time and sample limits on collecting these rock suites, just as the astronauts would face on the Moon and their rock collections became more refined, much to the later benefit of the actual missions.
Observing and sampling within the exposed strata of geological time on the Earth, the Apollo astronauts, now armed with the tools of scientific observation, were prepared to tell the story of the Moon.
When the true scientific “J” missions began on Apollo, Silver himself was in the back-room of Mission Control steering the geology ground teams and acting as a back seat driver for the lunar roving astro-geologists on the Moon.
Dave Scott and Jim Irwin had been trained to find anorthosite during their Apollo 15 mission, a piece of the primordial lunar crust that would prove the Moon’s age. On August 1, 1971 on Hadley Delta, Scott radioed back to the ground that he and Irwin had found just that. The “Genesis” rock would later prove to be 4.5 billion years old giving rise to the widely accepted theory that a Mars sized body had collided with the Earth spinning off matter that later formed the Moon.
Silver himself described this find as “hitting a home run” which validated his supreme teaching efforts to embed science within the Apollo missions.
Were it not for Lee Silver, the Moon’s story and relationship with the Earth would still be relatively unknown. His unique and exciting teaching methods imbued a sense of urgent exploration, not just of the Moon but of science, always looking to push the boundaries of knowledge and follow the observational evidence wherever it leads.UNSUNG HEROES OF THE APOLLO PROGRAM
You see the story yet? It’s all pretty much here.
In a language you can’t yet understand, but it’s here.
A tale of upheaval and battles won and lost.
Gothic tales of sweeping change, peaceful times, and then great trauma again.
And it all connects to our little friend.
That’s what we are, we geologists.
That’s what you gentlemen are going to become.
And how does this relate to the moon? From 240,000 miles away you have to give the most complete possible description of what you’re seeing.
Not just which rocks you plan to bring back but their context.
That and knowing which ones to pick up in the first place is what might separate you guys from those little robots.
You know, the ones some jaded souls think should have your job.You see, you have to become our eyes and ears out there.
And for you to do that, you first have to learn the language of this little rock here.David Clennon as Dr. Leon (Lee) Silver, From the Earth to the Moon, Episode 10, Galileo Was Right, 1998 (Moon Rock Mineralogy: Yes, the Apollo missions were real, QEDirt)
A robot would not know how to look for the right rocks or explain their context. The astronauts were trained to collect a “suite” of rock samples.
Now, we can, if we’re very clever, we can figure out a lot about an area like this by putting together what we call “the suite”. What the hell is he talking about? The suite. I’m talking about a dozen hand-sized rocks that tell the story of this place in all of its diversity from the typical, right to the exotic. You got ten minutes.David Clennon as Dr. Leon (Lee) Silver, From the Earth to the Moon, Episode 10, Galileo Was Right, 1998 (Moon Rock Mineralogy: Yes, the Apollo missions were real, QEDirt)
No robot could have collected a suite of rocks and conveyed the context of those rocks the way the astronauts did, particularly during the J missions.
Lauro, S.E., Pettinelli, E., Caprarelli, G. et al. Multiple subglacial water bodies below the south pole of Mars unveiled by new MARSIS data. Nat Astron (2020). https://doi.org/10.1038/s41550-020-1200-6
Orosei, R. et al. Radar evidence of subglacial liquid water on Mars. Science https://doi.org/10.1126/science.aar7268 (2018).
Thompson, L. M., et al. (2016), Potassium‐rich sandstones within the Gale impact crater, Mars: The APXS perspective, J. Geophys. Res. Planets, 121, 1981– 2003, doi:10.1002/2016JE005055.