Human Space Travel, Health and Risk

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Astronauts in a mock-up of the Orion space capsule, which NASA plans to use in some form as a deep-space vehicle. (NASA)

 

We all know that human space travel is risky. Always has been and always will be.

Imagine, for a second, that you’re an astronaut about to be sent on a journey to Mars and back, and you’re in a capsule on top of NASA’s second-generation Space Launch System designed for that task.

You will be 384 feet in the air waiting to launch (as tall as a 38-floor building,) the rocket system will weigh 6.5 million pounds (equivalent to almost nine fully-loaded 747 jets) and you will take off with 9.2 million pounds of thrust (34 times the total thrust of one of those 747s.)

Given the thrill and power of such a launch and later descent, everything else seemed to pale in terms of both drama and riskiness.  But as NASA has been learning more and more, the risks continue in space and perhaps even increase.

We’re not talking here about a leak or a malfunction computer system; we’re talking about absolutely inevitable risks from cosmic rays and radiation generally — as well as from micro-gravity — during a long journey in space.

Since no human has been in deep space for more than a short time, the task of understanding those health risks is very tricky and utterly dependent on testing creatures other than humans.

The most recent results are sobering.  A NASA-sponsored team at Georgetown University Medical Center in Washington looked specifically at what could happen to a human digestive system on a long Martian venture, and the results were not reassuring.

Their results, published in the Proceedings of the National Academy of Sciences  (PNAS), suggests that deep space bombardment by galactic cosmic radiation and solar particles could significantly damage gastrointestinal tissue leading to long-term functional changes and problems. The study also raises concern about high risk of tumor development in the stomach and colon.

 

Galactic cosmic rays are a variable shower of charged particles coming from supernova explosions and other events extremely far from our solar system. The sun is the other main source of energetic particles this investigation detects and characterizes. The sun spews electrons, protons and heavier ions in “solar particle events” fed by solar flares and ejections of matter from the sun’s corona. Magnetic fields around Earth protect the planet from most of these heavy particles, but astronauts do not have that protect beyond low-Earth orbit. (NASA)

 

Kamal Datta, an associate professor in the Department of Biochemistry is project leader of the NASA Specialized Center of Research (NSCOR) at Georgetown and has been studying the effects of space radiation on humans for more than a decade.

He said that heavy ions (electrically charged atoms and molecules) of elements such as iron and silicon are damaging to humans because of their greater mass compared to mass-less photons such as x-rays and gamma rays prevalent on Earth.  These heavy ions, as well as low mass protons, are ubiquitous in deep space.

Kamal Datta of Georgetown University Medical Center works with NASA to understand the potential risks from galactic cosmic radiation to astronauts who may one day travel in deep space.

“With the current shielding technology, it is difficult to protect astronauts from the adverse effects of heavy ion radiation. Although there may be a way to use medicines to counter these effects, no such agent has been developed yet,” says Datta, also a member of Georgetown Lombardi Comprehensive Cancer Center.

“While short trips, like the times astronauts traveled to the moon, may not expose them to this level of damage, the real concern is lasting injury from a long trip, such as a Mars or other deep space missions which would be much longer” he said in a release.

Datta’s team has also published on the potentially harmful effects of galactic cosmic radiation on the brain and other teams are looking at potential deep-space travel dangers the human cardio-vascular system.  Researchers are also concerned about known weakening of bone and muscle tissue, harming vision, as well as speeded-up aging during long stays in space.

With current technology, it would take about three years to travel from Earth to Mars, orbit the planet until it is in the right place for a sling-shot boost home, and then to travel back.

A radiation detection instrument on the Mars Science Laboratory (MSL),  which carried the rover Curiosity to Mars in 2011-2012, measured an estimated overall human radiation exposure for a Mars trip that would would be two-thirds of the agency’s allowed lifetime limits.  That was based on the high-energy radiation hitting the capsule, but NASA later detected radiation bursts from solar flares on Mars far higher than anything detected during the MSL transit.

All of this seems, and is, quite daunting when thinking about human travel to Mars and other deep space destinations.  And Datta is clearly sensitive about how the new results are conveyed to the public.

“I am in no way saying that people cannot travel to Mars,” he told me. “What we are doing is trying to understand the health risks so proper mitigation can be devised, not to say this kind of travel is impossible.”

“We don’t have medicines now to protect astronauts from heavy particle radiation, and we don’t have the technology now to shield them while they’re in space.  But many people are working on these problems.”

 

The Orion spacecraft in flight, as drawn by an artist. The capsule has an attached habitat module. (NASA)

 

On the medical research side, scientists have to rely on data gained from exposing mice to radiation and extrapolating those results to humans.  It would, of course, be unethical to do the testing on people.

While this kind of animal testing is accepted as generally accurate, it certainly could hide either increased protections or increased risks in humans.

Datta said that another testing issue that has been present so far is that the mice have had to be irradiated in one large dose rather than in much smaller doses over time.  It is unclear how that effects the potential damage to human organs and the breaking of DNA bonds (which can result in the growth of cancers.)  But Datta said that new instruments at NASA’s Space Radiation Laboratory (NSRL) at the Brookhaven National Laboratory on Long Island, New York, will allow for a more gradual, lower-dose experiment.

While Datta’s work has been focused on the health risks of deep space travel, galactic cosmic radiation and solar heavy particles also bombard the moon — which has no magnetic field and only a very thin atmosphere to protect it.  Apollo astronauts could safely stay on the moon for several days in their suits and their lander, but months or years of living in a colony there would pose far greater risks.

NASA has actually funded projects to shield small areas on the moon from radiation, but the issue remains very much unresolved.

Shielding also plays a major role in thinking about how to protect astronauts traveling into deep space.  The current aluminum skin of space capsules allows much of the harmful radiation to pass through, and so something is needed to block it.

 

The goal of building an inhabited colony on the moon has many avid supporters in government and the private sector. The health risks for astronauts are similar to those in deep space. (NASA/Pat Rawlings)

 

Experts have concluded that perhaps the best barrier to radiation would be a layer of water, but it is too heavy to carry in the needed amounts.  Other possibilities include organic polymers (large macromolecules with repeating subunits) such as polyethelyne.

It seems clear that issues such as these — the effects of more hazardous space radiation on astronauts in deep space and on the moon, and how to minimize those dangers — will be coming to the front burner in the years ahead.  And assuming that progress can be made, it’s a thrilling time.

What this means for space science, however, is less clear.

On one hand I recall hearing former astronaut extraordinaire and then head of the NASA Science Mission Directorate John Grunsfeld talk about how an astronaut on Mars could gather data and understandings in one week that the Curiosity rover would need a full year to match.

On the other, human space exploration is much more expensive than anything without people — yes, even including the long-delayed and ever-more-costly James Webb Space Telescope — and NASA budgets are limited.

So the question arises whether human exploration will, when it gets into high gear, swallow up the resources needed for the successors to the Hubble, Curiosity, Cassini and the other missions that have helped create what I consider to be a golden age of space science.  Risks come in many forms.

 

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Curiosity Rover Looks Around Full Circle And Sees A Once Habitable World Through The Dust

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An annotated 360-degree view from the Curiosity mast camera.  Dust remaining from an enormous recent storm can be seen on the platform and in the sky.  And holes in the tires speak of the rough terrain Curiosity has traveled, but now avoids whenever possible. Make the screen bigger for best results and enjoy the show. (NASA/JPL-Caltech/MSSS)

 

When it comes to the search for life beyond Earth, I think it would be hard to point to a body more captivating, and certainly more studied, than Mars.

The Curiosity rover team concluded fairly early in its six-year mission on the planet that “habitable” conditions existed on early Mars.  That finding came from the indisputable presence of substantial amounts of liquid water three-billion-plus years ago, of oxidizing and reducing molecules that could provide energy for simple life, of organic compounds and of an atmosphere that was thick enough to block some of the most harmful incoming cosmic rays.

Last year, Curiosity scientists estimated that the window for a habitable Mars was some 700 million years, from 3.8 to 3.1 billion years ago.  Is it a coincidence that the earliest confirmed life on Earth appeared about 3.8 billion years ago?

Today’s frigid Mars, which has an atmosphere much thinner than in the planet’s early days, hardly looks inviting, although some scientists do see a possibility that primitive life survives below the surface.

But because it doesn’t look inviting now doesn’t mean the signs of a very different planet aren’t visible and detectable through instruments.  The Curiosity mission has proven this once and for all.

The just released and compelling 360-degree look (above) at the area including Vera Rubin Ridge brings the message home.

Those fractured, flat rocks are mudstone, formed when Gale Crater was home to Gale Lake.  Mudstone and other sedimentary formations have been visible (and sometimes drilled) along a fair amount of the 12.26-mile path that Curiosity has traveled since touchdown.

 

An image of Vera Rubin Ridge in traditional Curiosity color, and the same view below with filters designed to detect hematite, or iron oxide. That compound can only be formed in the presence of water. (NASA/JPL-Caltech)

 

The area the rover is now exploring contains enough hematite — iron oxide — that its signal was detectable from far above the planet, making this area a prized destination since well before the Mars Science Laboratory and Curiosity were launched.

Like Martian clays and sulfates that have been identified and explored, the hematite is of great interest because of its origins in water.  Without H2O present many eons ago, there would be no hematite, no clay, no sulfates.  But as Mars researchers have found, there is a lot of all three.

I like to return to Mars and especially Curiosity because it provides something unique in the cosmos:  an environment where scientists today have ground-truthed the hypothesis that early Mars was once habitable, and found unambiguous results that it was.

That doesn’t mean that the planet necessarily ever gave rise to, or supported, living organisms.  But it’s a lot more than can be said for other targets for life beyond Earth.

NASA’s Europa Clipper may determine some day that beneath the ice crust of that moon of Jupiter is an ocean that is, or was, habitable.  But that determination is still years away.  Same with Saturn’s moon Enceladus, which some see as habitable beneath its ice, but no mission is currently approved to determine that.

And when it comes to exoplanets and possible life on them, it is both a logical and alluring conclusion that some support living organisms — there are, after all, billions and billions of exoplanets, and the cosmos is filled with the elements and compounds we find on Earth.

But we remain quite far away from consensus on what an exoplanet biosignature might be, and much further away from being able to confidently detect the probable biosignature elements and compounds on distant exoplanets.

And so for now we have Mars as our most plausible target for life beyond Earth.

 

Vera Rubin Ridge, with its high concentration of both red and green hematite. (NASA/JPL-Caltech)

 

It wasn’t that long ago that the NASA exploration mantra for Mars was “follow the water,”  under the assumption that life needed water to survive.

But Curiosity and satellites orbiting Mars have found abundant proof that water did play a major role in the planet’s early times.  Not only has Curiosity found that a lake existed on and off for hundreds of millions of years at Gale Crater, but researchers recently announced the presence of a large reservoir of liquid water beneath the southern polar region.

What’s more, evidence of briny surface streams on steep Martian cliffs in their warm season has grown stronger, though it remains a much-debated finding.

But with the water story well established, researchers are focused more on organics, minerals and what can be found beneath the radiation-baked surface.

Curiosity has been working for months around Vera Rubin Ridge, though for much of that time with a big handicap — the rover’s long-armed drill wasn’t working.  Important internal mechanisms stopped performing in late 2016, and it wasn’t until late spring of 2018 that a workaround was ready.

After one successful drilling, the next two failed.  But there was no drill problem with those two; the rock on the ridge was just too hard to penetrate.  It makes sense that the rock would be very hard because it has withstood millions of years of powerful winds blowing across Gale Crater, while other nearby rock and sediments were carried away.

The best way to discover why these rocks are so hard is to drill them into a powder for the rover’s two internal laboratories. Analyzing them might reveal what’s acting as “cement” in the ridge, enabling it to stand despite wind erosion.

Most likely, said Curiosity project scientist Ashin Vasavada, groundwater flowing through the ridge in the ancient past had a role in strengthening it, perhaps acting as plumbing to distribute this wind-proofing “cement.” In this case, it would be some variation of hematite, which in crystal form can be pretty hard on its own.

On its third attempt — and after a prolonged search for a “soft” spot in the ridge — the Curiosity drill did succeed in digging a hole and bringing back some precious powdered contents for study in the two onboard labs.

After the exploration of Vera Rubin Ridge and its hematite will come explorations of large deposits of sulfates and phyllosilicates (clays) — both formed in water as well — further up Mt. Sharp.

 

Curiosity’s pathway over the past six years, from near the Bradbury Landing site to the successful drilling at Vera Rubin Ridge. The route has gone through fossil lake beds, dune fields, the underlying rock formation of Mt. Sharp and now up to the hematite concentrations. (NASA/JPL=Calgtech)

 

I find the landscape of Mars that Curiosity shows us to be captivating, but also sobering when it comes to the search for life beyond Earth.

Here is the planet closest to Earth (during some orbits, at least), one that has been determined to be habitable 3 to 4 billion years ago,  one that can be studied with rovers on the ground and orbiting satellites — and still we can’t determine if it ever actually supported life, and probably won’t be able to for decades to come.

The big confounding factor on Mars really is time.  Life could have come and gone billions of years ago, and intense surface radiation could have erased that history and made it appear as if life was never there.  (This is one reason why Mars scientists want to dig deeper below the surface, where the effects of radiation would be much reduced.)

Time may be a powerful obstacle when it comes finding signs of life on exoplanets as well.  If life exists elsewhere in the cosmos, it surely comes and goes, too.  The odds of us catching it when it’s present may be low, despite all those billions and billions of planets. (Given the way that exoplanet biosignatures work, the life needs to be present at the time of observation.)

Or maybe the time for life in the cosmos has really just begun.

Harvard-Smithsonian astrophysicist Avi Loeb argued several years ago that life on Earth may be a premature flowering, compared with what may well happen later and elsewhere. (Column on his intriguing ideas is here.)

A majority of stars in the cosmos are red dwarfs, or M stars.  They take eons to stabilize and then generally continue in a steady state for much longer than a G star like our sun.  So, he argued,  life in the cosmos around red dwarfs may not become widespread for some time, and then could last for a very long time if and when it did arise.

But enough about time — other than to perhaps take a little more time to enjoy the 360-degree view of Mars and Curiosity that brings thoughts like these to mind.

 

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Large Reservoir of Liquid Water Found Deep Below the Surface of Mars

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Artist impression of the Mars Express spacecraft probing the southern hemisphere of Mars, superimposed on a radar cross section of the southern polar layered deposits. The leftmost white line is the radar echo from the Martian surface, while the light blue spots are highlighted radar echoes along the bottom of the ice.  Those highlighted areas measure very high reflectivity, interpreted as being caused by the presence of water. (ESA, INAF. Graphic rendering by Davide Coero Borga )

Far beneath the frigid surface of the South Pole of Mars is probably the last place where you might expect the first large body of Martian liquid water would be found.  It’s -170 F on the surface, there are no known geothermal sources that could warm the subterranean ice to make a meltwater lake, and the liquid water is calculated to be more than a mile below the surface.

Yet signs of that liquid water are what a team of Italian scientists detected — a finding that they say strongly suggests that there are other underground lakes and streams below the surface of Mars.  In a Science journal article released today, the scientists described the subterranean lake they found as being about 20 kilometers in diameter.

The detection adds significantly to the long-studied and long-debated question of how much surface water was once on Mars, a subject that has major implications for the question of whether life ever existed on the planet.

Finding the subterranean lake points to not only a wetter early Mars, said co-author Enrico Flamini of the Italian space agency, but also to a Mars that had a water cycle that collected and delivered the liquid water.  That would mean the presence of clouds, rain, evaporation, rivers, lakes and water to seep through surface cracks and pool underground.

Scientists have found many fossil waterways on Mars, minerals that can only be formed in the presence of water, and what might be the site of an ancient ocean.

But in terms of liquid water now on the planet, the record is thin.  Drops of water collected on the leg of NASA’s Phoenix Lander after it touched down in 2008, and what some have described as briny water appears to be flowing down some steep slopes in summertime.  Called recurrent slope lineae or RSLs, they appear at numerous locations when the temperatures rise and disappear when they drop.

This lake is different, however, and its detection is a major step forward in understanding the history of Mars.

Color photo mosaic of a portion of Planum Australe on Mars.  The subsurface reflective echo power is color coded and deep blue corresponds to the strongest reflections, which are interpreted as being caused by the presence of water. (USGS Astrogeology Science Center, Arizona State University, INAF)

The discovery was made analyzing echoes captured by the the radar instruments on the European Space Agency’s Mars Express, a satellite orbiting the planet since 2002.  The data for this discovery was collected from observation made between 2012 and 2015.

 

A schematic of how scientists used radar to find what they interpret to be liquid water beneath the surface of Mars. (ESA)

Antarctic researchers have long used radar on aircraft to search for lakes beneath the thick glaciers and ice layers,  and have found several hundred.  The largest is Lake Vostok, which is the sixth largest lake on Earth in terms of volume of water.  And it is two miles below the coldest spot on Earth.

So looking for a liquid lake below the southern pole of Mars wasn’t so peculiar after all.  In fact, lead author Roberto Orosei of the Institute of Radioastronomy of Bologna, Italy said that it was the ability to detect subsurface water beneath the ice of Antarctica and Greenland that helped inspire the team to look at Mars.

There are a number of ways to keep water liquid in the deep subsurface even when it is surrounded by ice.  As described by the Italian team and an accompanying Science Perspective article by Anja Diez of the Norwegian Polar Institute, the enormous pressure of the ice lowers the freezing point of water substantially.

Added to that pressure on Mars is the known presence of many salts, that the authors propose mix with the water to form a brine that lowers the freezing point further.

So the conditions are present for additional lakes and streams on Mars.  And according to Flamini, solar system exploration manager for the Italian space agency, the team is confident there are more and some of them larger than the one detected.  Finding them, however, is a difficult process and may be beyond the capabilities of the radar equipment now orbiting Mars.

 

Subsurface lakes and rivers in Antarctica. Now at least one similar lake has been found under the southern polar region of Mars. (NASA/JPL)

The view that subsurface water is present on Mars is hardly new.  Stephen Clifford, for many years a staff scientist at the Lunar and Planetary Institute, even wrote in 1987 that there could be liquid water at the base of the Martian poles due to the kind of high pressure environments he had studied in Greenland and Antarctica.

So you can imagine how gratifying it might be to learn, as he put it “of some evidence that shows that early theoretical work has some actual connection to reality.”

He considers the new findings to be “persuasive, but not definitive” — needing confirmation with other instruments.

Clifford’s wait has been long, indeed.  Many observations by teams using myriad instruments over the years did not produce the results of the Italian team.

Their discovery of liquid water is based on receiving particularly strong radar echoes from the base of the southern polar ice — echoes consistent with the higher radar reflectivity of water (as opposed to ice or rock.)

After analyzing the data in some novels ways and going through the many possible explanations other than the presence of a lake, Orosei said that none fit the results they had.  The explanation, then, was clear:  “We have to conclude there is liquid water on Mars.”

The depth of the lake — the distance from top to bottom — was impossible to measure, though the team concluded it was at least one meter and perhaps in the tens of meters.

Might the lake be a habitable?  Orosei said that because of the high salt levels “this is not a very pleasant environment for life.”

But who knows?  As he pointed out, Lake Vostok and other subglacial Antarctic lake, are known to be home to single-cell organisms that not only survive in their very salty world, but use the salt as part of their essential metabolism.

 

 

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The Mars Water Story Gets Ever More Interesting

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Enchanced-color traverse section of Martian icy scarps in late spring to early summer. Arrows indicate locations where relatively blue material is particularly close to the surface. Image taken by HiRISE camera on Mars Reconnaissance Orbiter. (NASA/JPL/UNIVERSITY OF ARIZONA/USGS )

 

Huge escarpments of quite pure water ice have been found in the Southern Highlands of Mars — accessible enough that astronauts might some day be able to turn the ice into water, hydrogen and oxygen.

Some of these deposits are more than 100 meters thick and begin only a meter or two below the surface.

These are among the conclusion from a new paper in the journal Science that describes these previously unknown water ice reserves.  While Mars scientists have long theorized the presence of subsurface ice under one-third of the planet, and even exposed bits of it with the Phoenix lander, the consensus view was that Martian ice was generally cemented with soil to form a kind of permafrost.

But the “scarp” ice described by Colin Dundas of the U.S. Geological Survey and colleagues is largely water ice without much other material.  This relative purity, along with its accessibility, would make the ice potentially far more useful to future astronauts.

“The ice exposed by the scarps likely originated as snow that transformed into massive ice sheets, now preserved beneath less than 1 to 2 meters of dry and ice-cemented dust or regolith,” the authors write. The shallow depths, the write “make the ice sheets potentially accessible to future exploration.”

 

The bright red regions contain water ice, as determined by measurements by the High-Resolution Imaging Science Experiment (HiRISE) on NASA’s Mars Reconnaissance Oribter. (NASA)

 

The importance is clear:  These sites are “very exciting” for potential human bases as well, says Angel Abbud-Madrid, director of the Center for Space Resources at the Colorado School of Mines in Golden, who led a recent NASA study exploring potential landing sites for astronauts.

Water is a crucial resource for astronauts, because it could be combined with carbon dioxide, the main ingredient in Mars’s atmosphere, to create oxygen to breathe and methane, a rocket propellant. And although researchers suspected the subsurface glaciers existed, they would only be a useful resource if they were no more than a few meters below the surface. The ice cliffs promise abundant, accessible ice, Abbud-Madrid told Science Magazine.

While the discovery adds to the view that Mars is neither bone-dry now nor was earlier in its history, it does not necessarily add to the question of where all the Martian water has gone or how much was originally there.

That’s because the paper describes the huge ice deposits as the result of snowfall over more recent eons that was packed into its current form, rather than water that might have been present during the warmer wetter periods of Mars history. With this in mind, Dundas said in an email that his team’s work does not add to what is known about the early Mars water budget.

As for the age of the water ice, he said “we can’t put an accurate number on it at this time, but the icy units are lightly cratered. Others in the community have proposed snowfall during periods of high axial tilt within the last few million years.”

So the ice is relatively young. But that doesn’t mean it has no story to tell.  Exposed ice, like exposed rock, always has a story to tell.

“We expect the vertical structure of Martian ice-rich deposits to preserve a record of ice deposition and past climate,” the authors write.

The eight scarps studied were steep and faced the poles. All were in the mid-latitudes, and therefore far from the polar ice sheets.

 

The lander Phoenix dug into the soil of the northern polar region and found cemented ice as well as pure ice several inches down. (NASA)

 

NASA has long had a motto for exploring Mars and other sites beyond Earth of “follow the water.”  That has been expanded to “follow the carbon” and “follow the organics,” but the water is still a guidepost of sorts of where life, or its remnants, might be found.  Now with these large and seemingly accessible deposits of water ice, “follow the water” takes on a new meaning for potential future astronauts in search of essential chemical components.

Still, the issue of just how much water there is and has been on Mars is a central to piecing together the planet’s history and how much of the planet might have one day been eminently habitable.

The last decade of Mars exploration and observation has led most Mars scientists to conclude that the planet once had rivers, lakes and possibly a northern ocean. That water is almost entirely (or perhaps entirely) gone from the surface now, and understanding where it went is certainly key to understanding the history of the planet.

While much no doubt escaped to space after the early protective Mars magnetic field and atmosphere largely disappeared, researchers say there remains a lot of Mars water to be accounted for.

An article in the journal Nature last month reported the possibility of large amounts of water mixing with Martian basalts long ago and forming a broadly water-rich crust.  The authors of that paper, led by Jon Wade of Oxford’s Department of Earth Sciences, described modeling that found water on early Mars could be absorbed into spongy rock at a far greater rate than on Earth.

In an accompanying review, geochemist and cosmochemist Tomohiro Usui of the Earth-Life Science Institute (ELSI) in Tokyo, supported the notion, and added another possibility that he has published on as well.

“Ground ice might also account for the missing water reservoir on Mars,” he wrote. “Subsurface radar-sounder measurements have detected an anomaly in an electrical property of rocks in the planet’s northern hemisphere, which implies that massive ice deposits are embedded among or between layers of sediment and volcanic materials at a depth of 60–80 m.”

Usui wrote that the ground-ice model has also been proposed based of analyses of hydrogen isotopes in Martian meteorites and of the shapes and characteristics of craters. Indeed, the crater study indicated that the subsurface water ice has a volume comparable to the size of the ancient oceans.

Where did the large amounts of water once present on Mars go. Some clearly was lost to the atmosphere, but some researchers are convinced that much is underground as ice or incorporated into minerals. (Nature)

 

Dundas agreed that the new paper was a continuation of earlier work, rather than something entirely new. “We’ve known for some time that there is shallow ground ice within a meter of the surface, and there have been recent radar detections of ice sheets tens of meters thick,” he said in his email. “What our work does is provide some three-dimensional information at high resolution that helps tie things together.”

Dundas et al reported that the fractures and steep angles found indicate that the ice is cohesive and strong. What’s more, bands and variations in color suggest that the ice contains distinct layers, which could be used to understand changes in Mars’ climate over time.

Because the ice is only visible where surface soil has been removed, the paper says it is likely that ice near the surface is more extensive than detected in this study.

And that could be very important to astronauts on future missions to Mars.

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Two Tempting Reprise Missions: Explore Titan or Bring Back a Piece of A Comet

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Dragonfly is a quadcopter lander that would take advantage of the environment on Titan to fly to multiple locations, some hundreds of miles apart, to sample materials and determine the composition of the surface.  A central goal would be to analyze Titan’s organic chemistry and assess its habitability. (NASA)

Unmanned missions to planets and moons and asteroids in our solar system have been some of NASA’s most successful efforts in recent years, with completed or on-going ventures to Mars, Saturn, Jupiter, the asteroid Bennu, our moon, Pluto, Mercury and bodies around them all.   On deck are a funded mission to Europa, another to Mars and one to the unique metal asteroid 16 Psyche orbiting the sun between Mars and Jupiter.

We are now closer to adding another New Frontiers class destination to that list, and NASA announced this week that it will be to either Saturn’s moon Titan or to the comet 67P/Churyumov-Gerasimenko.

After assessing 12 possible New Frontiers proposals, these two made the cut and will receive $4 million each to further advance their proposed science and technology. One of them will be selected in spring of 2019 for launch in the mid 2020s.

With the announcement, associate administrator for NASA’s Science Mission Directorate Thomas Zurbuchen described the upcoming choice as between two “tantalizing investigations that seek to answer some of the biggest questions in our solar system today.”

Those questions would be:  How did water and other compounds essential for life arrive on Earth?  Comets carry ancient samples of both, and so can potentially provide answers.

And with its large inventories of nitrogen, methane and other organic compounds, is Titan potentially habitable?  Then there’s the added and very intriguing prospect of visiting the methane lakes of that frigid moon.

The CAESAR mission would return to the nucleus of  comet explored by the European Space Agency’s Rosetta mission, and its lander Philae.  (NASA)

Both destinations selected have actually been visited before.

The European Space Agency’s Rosetta mission orbited the comet 67P/Churyumov-Gerasimenko comet for two years and deployed a lander, which did touch down but sent back data for only intermittently for several days.

And the NASA’s Cassini-Huygens mission to Saturn passed by Titan regularly during its decade exploring that system, and the ESA’s Huygens probe did land on Titan and sent back information for a short time.

So both Rosetta and Cassini-Huygens began the process of understanding these distant and potentially revelatory destinations, and now NASA is looking to take it further.

The Titan “Dragonfly” mission, for instance, would feature a “quadcopter” or “rotorcraft” — a vehicle that is part helicopter and part drone.  It’s designed to hop hundreds of miles around the moon to sample what has already been determined to be a surface with many organic compounds and liquid methane lakes.

Those already identified hydrocarbon seas may contain amino acids and other interesting molecules, making Titan a test bed of sorts on how life arose on Earth. With spectrometers, drills, and cameras, Dragonfly would split its mission between science in the air and on the ground.

Although frigid, Titan is otherwise now known to be a relatively benign place, and the rotorcraft could potentially survive for several years. That could give the team time to “evaluate how far prebiotic chemistry has progressed in an environment where we know we have the ingredients for life,” said lead investigator Elizabeth Turtle from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.

“Titan is a unique ocean world, with lakes and rivers of liquid methane flowing across its surface,” she said.  But it is also very cold. Average surface temperatures are -290 degrees Fahrenheit,  so any potential lifeforms would face some major challenges.

A methane lake near the northern pole of Saturn’s moon, Titan. The image was taken using radar on the Cassini spacecraft. NASA/JPL-Caltech

The comet mission CAESAR (Comet Astrobiology Exploration SAmple Return) will take a very different route than Rosetta did and will use different propulsion that will get the spacecraft to the comet in four years.  The plan is to then perform a “touch and go” maneuver with an extended arm to pick up 100 grams of precious Rosetta material from the nucleus.

And then unlike with Rosetta, the plan is to cache the sample and bring it back to Earth for intensive study.

By returning to 67P/Churyumov-Gerasimenko, a body mapped in detail by Rosetta, the mission is “able to design our spacecraft specifically for the conditions we know,” said Steven Squyres of Cornell University, principal investigator for the mission.

During a news conference, Squyres said that “comets are among the most scientifically important objects in the solar system, but they’re also among the most poorly understood.

“They’re the most primitive building blocks of planets; they contain materials that date from the very earliest moments of solar system formation and even before. Comets were a source of water for the Earth’s oceans, and critically they were a source of organic molecules that contributed to the origin of life.”

Squyres told me after the announcement that the CAESAR instruments will allow for more precise measurements than from Rosetta, and that a successful sample return could potentially change our understanding of the Earth’s history substantially.  He said the sample collection would also importantly include gases.

NASA has already succeeded with comet sample return — the Stardust mission to fly through the plume of comet Wild-2.  It did gather some dust, but it didn’t land on the nucleus like Rosetta did and CAESAR would.

Sample return is clearly a high priority for NASA and other space agencies.  The NASA 2020 mission to Mars is designed to collect and cache rock samples for later return, and two other sample return missions are underway.  Both are to asteroids, with one launched last year by NASA and the other by the Japanese space agency JAXA in 2014.

The nucleus of the 67P/Churyumov-Gerasimenko comet, where the CAESAR mission hopes to be headed in the 2020s. (ESA)

What “Dragonfly” would return is data about a moon shrouded in haze and unlike any other body in our solar system.

When the Huygen’s probe descended to the moon in early 2005, planetary scientists weren’t sure if the moon’s surface was covered in oceans methane and ethane.  So Huygens was designed to float if solid ground wasn’t to be found.

As the lander sailed through the haze it took hundreds of aerial images that showed an alien but strikingly Earth-like landscape of mountains, dry floodplains and what appeared to be river deltas. Huygens did land on something solid, though liquid methane flowed nearby and the Huygens cameras could see intricate channels cutting into the surface.

When Huygens touched down, it did so with a soft thud and a short slide across the frozen surface. Later analysis of the lander’s telemetry showed that Huygens sank around 4.7 inches into the surface on first contact, bounced and slid before coming to a stop.

This knowledge made possible a Titan project with a lander that can jump from one spot to another quite far away.  Those methane lakes, it is now understood, are largely found near the northern pole, and so floatation equipment is no longer necessary.

The Huygens descent to the surface of Titan, as recorded in 2005.  (ESA/NASA)

Squyres, a professor of physical science at Cornell University, is also principal investigator for the long-lasting Mars exploration rovers, one of which operated successfully for 8 years and the other –Opportunity — is still exploring Mars 13 years after landing.

He told me that his long years heading the Mars rover mission had convinced him that his greatest satisfaction in science comes from identifying a plausible space project, putting together a team of scientists, engineers and managers who can plausibly pull it off, and then work nonstop for years putting together a proposal to get it selected and funded. His team now numbers about 150 people and will soon grow much larger.

It was that sense of “shared struggle,” he said, that gave him enormous satisfaction. That came, of course, with a happy ending in several competitions, but he said he also knows the disappointment of not being selected for others.

Two other missions were selected for additional, though limited, funding under the New Frontiers program.  One is headed by NASA Ames Research Center astrobiologist Chris McKay and will be funded to develop “cost-effective techniques that limit spacecraft contamination and thereby enable life detection measurements on cost-capped missions.”

The larger mission his team proposed would go to the water vapor plume spurting out of Saturn’s moon Enceladus, with the goal of searching for signs of life.

The two projects selected were no doubt something of a disappointment to researchers who have longed for NASA to return to Venus.  As the study of exoplanets progresses, one of the key questions facing scientists is why Earth and Venus evolved so differently.  Both are within our sun’s habitable zone, but Venus experienced a runaway greenhouse effect that parched the surface and pushed surface temperatures to a led-melting 870 degrees F.

Three of the proposed New Frontiers missions were to Venus but, as in other recent competitions, none were selected by NASA.  One of the Venus proposals, led by Goddard’s Lori Glaze, was selected for further technology development.

Venus hasn’t been visited by a NASA spacecraft in decades, leading to hopes that one of the New Frontiers finalists would be a mission there. But it was not to be. ESA operated the Venus Express mission orbiting the planet from 2006 to 2014 and the Japanese Space Agency has a probe (Akatsuki) here now. (NASA)

Also noticeably absent among the finalists was any pr0ject going to the moon, especially since the Trump administration has made a lunar colony a priority.  Apparently a New Frontiers mission is not what the administration has in mind.

New Frontiers initiative is the largest NASA planetary exploration program open to outside competition and leadership.  But NASA does set the priorities, as put forward by the planetary science and astrobiology communities.

Previous spacecraft launched under New Frontiers include New Horizons, which surveyed Pluto and is now due to visit MU69, an icy object in the farthest reaches of the solar system; Juno, now in orbit around Jupiter; and OSIRIS-REx, launched last year, which will collect samples from an asteroid and return them to Earth.

Since the New Frontiers program began at the beginning of the century, NASA has selected two missions for each decade, making them the most frequent of the major agency missions.  Costs are capped at $1 billion — with $850 million for the mission and $150 million for the launch.  So far, the money has been demonstrably well spent.

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