Curiosity Has Found The Element Boron On Mars. That’s More Important Than You Might Think

Facebooktwittergoogle_plusredditpinterestlinkedinmail
ChemCam target Catabola is a raised resistant calcium sulfate vein with the highest abundance of boron observed so far. The red outline shows the location of the ChemCam target remote micro images (inset). The remote micro images show the location of each individual ChemCam laser point (red crosshairs) and the B chemistry associated with each point (colored bars). The scale bar is 9.2 mm or about 0.36 inches. Credit JPL-Caltech/MSSS/LANL/CNES-IRAP/William Rapin
Using its laser technology, the Curiosity ChemCam instrument located the highest abundance of boron observed so far on this raised calcium sulfate vein. The red outline shows the location of the ChemCam target remote micro images (inset). The remote micro images show the location of each individual ChemCam laser point (red crosshairs) and the additional chemistry associated with each point (colored bars).  JPL-Caltech/MSSS/LANL/CNES-IRAP/William Rapin

For years, noted chemist and synthetic life researcher Steven Benner has talked about the necessary role of the element boron in the origin of life.

Without boron, he has found, many of the building blocks needed to form the earliest self-replicating ribonucleic acid (RNA) fall apart when they come into contact with water, which is nonetheless needed for the chemistry to succeed. Only in the presence of boron, Benner found and has long argued, can the formation of RNA and later DNA proceed.

Now, to the delight of Benner and many other scientists, the Curiosity team has found boron on Mars.  In fact, as Curiosity climbs the mountain at the center of Gale Crater, the presence of boron has become increasingly pronounced.

And to make the discovery all the more meaningful to Benner, the boron is being found in rock veins.  So it clearly was carried by water into the fractures, and was deposited there some 3.5 billion years ago.

Combined with earlier detections of phosphates, magnesium, peridots, carbon and other essential elements in Gale Crater, Benner told me, “we have found on Mars an environment entirely consistent with a what we consider conducive for the origin of life.

“Is it likely that life arose?  I’d say yes…perhaps even, hell yes.  But it’s also true that an environment conducive to the formation of life isn’t necessarily one conducive to the long-term survival of life.”

The foreground of this scene from the Mastcam on NASA's Curiosity Mars rover shows purple-hued rocks near the rover's late-2016 location. The middle distance includes future destinations for the rover. Variations in color of the rocks hint at the diversity of their composition on lower Mount Sharp. Credits: NASA/JPL-Caltech/MSSS
The foreground of this scene from the Mastcam on NASA’s Curiosity Mars rover shows purplish rocks near the rover’s late-2016 location. The middle distance includes future destinations for the rover. Variations in color of the rocks hint at the diversity of their composition on lower Mount Sharp. NASA/JPL-Caltech/MSSS

Another factor in the Mars-as-habitable story from Benner’s view is that there has never been the kind of water world there that many believe existed on early Earth.

While satellites orbiting Mars and now Curiosity have made it abundantly clear that early Mars also had substantial water in the form of lakes, rivers, streams and perhaps an localized ocean, it was clearly never covered in water.

And that’s good for the origin of life, Benner said.

Steven Benner and his colleagues were the first to synthesize a gene, beginning the field of synthetic biology. He was instrumental in establishing the field of paleogenetics. He founded The Westheimer Institute of Science and Technology (TWIST) and the Foundation For Applied Molecular Evolution.
Steven Benner and his colleagues were the first to synthesize a gene, beginning the field of synthetic biology. He was instrumental in establishing the field of paleogenetics. He founded The Westheimer Institute of Science and Technology (TWIST) and the Foundation For Applied Molecular Evolution.

“We think that a largely arid environment, with water present but not everywhere, is the best one for life to begin.  Mars had that but Earth, well, maybe not so much.  The problem is how to concentrate the makings of RNA, of life, in a vast ocean.  It’s like making a cake in water — all the ingredients will float away.

“But the mineral ensemble they’ve discovered and given us is everything we could have asked for, and it was on a largely dry Mars,” he said.  “So they’ve kicked the ball back to us.  Now we have to go back to our labs to enrich the chemistry around this ensemble of minerals.”

In his labs, Benner has already put together a process — he calls it his discontinuous synthesis model — whereby all the many steps needed to create RNA and therefore life have been demonstrated to be entirely possible.

What’s missing is a continuous model that would show that process at work, starting with a particular atmosphere and particular minerals and ending up with RNA.   That’s something that requires a lot more space and time than any lab experiments would provide.

“This is potentially what Mars provides,” he said,

Benner, it should be said, is not a member of the Curiosity team and doesn’t speak for them.

But his championing of boron as a potentially key element for the origin of life was noted as a guide by one of the Curiosity researchers during a press conference with team members at the American Geophysical Union Dec. 13 in San Francisco.  It was at that gathering that the detection of the first boron on Mars was announced.

Benner said he has been in close touch with the two Curiosity instrument teams involved in the boron research and was most pleased that his own boron work — and that of at least one other researcher — had helped inspire the search for and detection of the element on Mars.  That other researcher, evolutionary biologist James Stephenson, had detected boron in a meteorite from Mars.

Patrick Gasda, a postdoctoral researcher at Los Alamos National Laboratory, is a member of the Chemistry and Camera (ChemCam) instrument team which identified the boron at Gale Crater.  The instrument uses laser technology to identify chemical elements in Martian rocks.

Gasda said at AGU that if the boron they found in calcium sulfate rock veins on Mars behaves there as it does on Earth, then the environment was conducive to life.  The ancient groundwater that formed these veins would have had temperatures in the 0-60 degrees Celsius (32-140 degrees Fahrenheit) range, he said, with a neutral-to-alkaline pH.

While the presence of boron (most likely the mineral form borate, Benner said) has increased as the rover has climbed Mount Sharp, the element still makes up only one-tenth of one percent of the rock composition.  But to stabilize that process of making RNA, that’s enough.

This pair of drawings depicts the same location at Gale Crater on at two points in time: now and billions of years ago. Water moving beneath the ground, as well as water above the surface in ancient rivers and lakes, provided favorable conditions for microbial life, if Mars has ever hosted life. Credits: NASA/JPL-Caltech
A drawing of Gale Crater as it is organized now.  Water moving beneath the ground, as well as water above the surface in ancient rivers and lakes, provided favorable conditions for microbial life, if Mars has ever hosted life. A well-done animation including a second drawing showing conditions 3.5 billion years ago at Gale can be seen here.   It toggles back and forth to show how things have changed.  (NASA/JPL-Caltech)

Benner’s view of Gale Crater and Mars as entirely habitable is not new — the Curiosity team has been saying roughly the same for several years now.  But with four full years on Mars the rover keeps adding to the habitability story, and that was the central message from Curiosity scientists speaking at the AGU press conference.

As the rover examines higher, younger layers, the researchers said they were especially impressed by the complexity of the ancient lake environments at Gale when sediments were being deposited, and also the complexity of the groundwater interactions after the sediments were buried.

“There is so much variability in the composition at different elevations, we’ve hit a jackpot,” said John Grotzinger of Caltech, and formerly the mission scientist for Curiosity.

“A sedimentary basin such as this is a chemical reactor. Elements get rearranged. New minerals form and old ones dissolve. Electrons get redistributed. On Earth, these reactions support life.”

This kind of reactivity occurs on a gradient based on the strength of a chemical at donating or receiving electrons. Transfer of electrons due to this gradient can provide energy for life.

The ChemCam instrument, with its laser zapper, identified the element boron as Curiosity climbs Mount Sharp. (NASA)
An illustration of the ChemCam instrument, with its laser zapper, which identified the element boron as Curiosity climbs Mount Sharp. (NASA)

While habitability is key to Curiosity’s mission on Mars, much additional science is being done  that has different goals or looks more indirectly at the planet’s ancient (or possibly current) ability to support life.  Understanding the ancient environmental history of Gale Crater and Mars is a good example.

For instance, the Curiosity team is now undertaking a drilling campaign in progressively younger rock layers, digging into four sites each spaced about 80 feet (about 25 meters) further uphill.  Changes in which minerals are present and in what percentages they exist give insights into some of that ancient history.

One clue to changing ancient conditions is the presence of the mineral hematite, a form of the omnipresent iron oxide on Mars.  Hematite has replaced magnetite as the dominant iron oxide in rocks Curiosity has drilled recently, compared with the site where Curiosity first found lake bed sediments.

Thomas Bristow of NASA Ames Research Center, who works with the Chemistry and Mineralogy (CheMin) laboratory instrument inside the rover, said Mars is sending a signal. Both forms of iron oxide (hematite and magnetite) were deposited in mudstone in what was once the bottom of a lake, but the increased abundance of hematite higher up Mount Sharp suggests conditions were warmer when it was laid down.  There also was probably more interaction between the atmosphere and the sediments.

On a more technical level, an increase in hematite relative to magnetite also indicates an environmental change towards a stronger tug on the iron oxide electrons, causing a greater degree of oxidation (the loss of electrons) in the iron.  That would likely be caused by changing atmospheric conditions.

It’s all part of putting together the jigsaw puzzle of Mars circa 3.5 billion years ago.

This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover shows an outcrop with finely layered rocks within the "Murray Buttes" region on lower Mount Sharp. (NASA/JPL-Caltech/MSSS)
This view from the Mast Camera (Mastcam) on NASA’s Curiosity Mars rover shows an outcrop with finely layered rocks within the “Murray Buttes” region on lower Mount Sharp. (NASA/JPL-Caltech/MSSS)

Returning to the boron story, Benner said that the discovered presence of all the chemicals his group believes are necessary to ever-so-slowly move from prebiotic chemistry to biology provides an enormous opportunity. Because of plate tectonics on Earth and the omnipresence of biology, the conditions and environments present on early Earth when life first arose were long ago destroyed.

But on Mars, the apparent absence of those most powerful agents of change means it’s possible to detect, observe and study conditions in a changed but intact world that just might have given rise to life on Mars.  Taken a step further, Mars today could provide new and important insights into how life arose on Earth.

And then there’s the logic of what finding signs of ancient, or perhaps deep-down surviving life on Mars would mean to the larger search for life in the cosmos.

That life exists on one planet among the hundreds of billions we now know are out there suggests that other planets — which we know have many or most of the same basic chemicals as Earth — might have given rise to life as well.

And if two planets in one of those many, many solar system have produced and supported life, then the odds go up dramatically regarding life on other planets.

One planet with life could be an anomaly.  Two nearby planets with life, even if its similar, are a trend.

 

 

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Enceladus and Water Worlds

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Glittering geysers of water ice erupt from Saturn's enigmatic moon Enceladus as seen during a previous flyby. The plumes are backlit by the sun, which is almost directly behind the moon. The moon's dark side that we see here is illuminated by reflected Saturn-shine. Today, the Cassini spacecraft flew right through the plumes in order to let its instruments 'taste' them. Credit: NASA/JPL/SSI/Ugarkovich
Glittering geysers of water ice erupt from Saturn’s enigmatic moon Enceladus as seen during a previous flyby. The plumes are backlit by the sun, which is almost directly behind the moon. The moon’s dark side that we see here is illuminated by reflected Saturn-shine.  Credit: NASA/JPL/SSI/Ugarkovich

As if the prospect of billions of potentially habitable exoplanets wasn’t enough to get people excited, what about all those watery exo-moons too?

The question arises as the Cassini mission makes its final pass near the now famous geysers at the south pole of the moon Enceladus ,scheduled for Saturday.  The plumes are currently in darkness and so it’s a perfect time to tease out a particularly compelling aspect of the Enceladus story:  how hot is the inside of the mini-moon.  Earlier measurements of the water ice spray took place when the sun was on that southern pole, so this will be the first time Cassini can measure precisely how much of the already detected heat comes from the moon’s interior.

The expectation is that much of the heat does indeed come from inside, warmed substantially by tidal forces and perhaps hydrothermal vents that together serve to keep liquid a subsurface ocean all around the moon.  As a result, the evolving scientific view is that tiny Enceladus, one of 63 moons of Saturn, just may have the ingredients and characteristics that put it into an improbable habitable zone.

“Step by step, we’re learning about an environment that seemed impossible not long ago,” said Cassini Mission Scientist Linda Spilker.  “We know that Enceladus has some rocky core, and that it touches the liquid water.  We also know that some of the compounds identified in the geysers can only be formed when rock is in contact with hot water, and that must be happening at the bottom of the moon’s ocean.  All the pieces are coming together to tell us that the moon has an ocean that might be able to support life.”

NASA's Cassini spacecraft captured this view as it neared icy Enceladus for its closest-ever dive past the moon's active south polar region. The view shows heavily cratered northern latitudes at top, transitioning to fractured, wrinkled terrain in the middle and southern latitudes. The wavy boundary of the moon's active south polar region -- Cassini's destination for this flyby -- is visible at bottom, where it disappears into wintry darkness. This view looks towards the Saturn-facing side of Enceladus. North on Enceladus is up and rotated 23 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 28, 2015. The view was acquired at a distance of approximately 60,000 miles (96,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 45 degrees. Image scale is 1,896 feet (578 meters) per pixel.
The Cassini spacecraft, sponsored by NASA, the European Space Agency and the Italian space Agency,  captured this view on Oct. 28 as it neared Enceladus. The wavy boundary of the moon’s active south polar region — Cassini’s destination for this flyby — is visible at bottom. The image was taken in visible light with the Cassini spacecraft narrow-angle camera from approximately 60,000 miles away. (Cassini Imaging Team, SSI, JPL, ESA, NASA)

That a moon might have habitable conditions is not a new idea:  science fiction great Arthur C. Clarke (as well as many scientists and now members of Congress) have pressed for a mission to Jupiter’s moon Europa because its internal ocean has been identified as similarly promising.

But what is so compelling about Enceladus is that its potential habitability pretty much came out of nowhere.  While Europa is the sixth largest moon in the solar system, Enceladus is but 370 miles in diameter.  It is covered in ice, but in 2004 its four parallel “tiger stripe” fractures were discovered, leading to the conclusion that some kind of volcanic action was taken place beneath them.  Spilker was a scientist with the Voyager mission that passed by Saturn in 1980-81 and said that Enceladus was then in relative darkness and made little impression on the team.  “We definitely missed the tiger stripes,” she said.

The plumes emerge from the south pole region, not far from the tiger stripe fractures, and appear to come from  near-surface pockets of liquid water. (The oceans of Europa are not nearly as accessible, lying 6 to 20 miles below the icy surface.)  Making Enceladus even more interesting, the 70 geysers spit out organic chemicals known as the building blocks of life along with its water ice.

The chemical composition of the plumes of Enceladus's includes hydrocarbons such as ammonia, methane and formaldehyde in trace amounts similar to the makeup of many comets. (NASA)
The chemical composition of the plumes of Enceladus’s includes hydrocarbons such as ammonia, methane and formaldehyde in trace amounts similar to the makeup of many comets.  The presence of the organic compounds suggests that very interesting chemistry is taking place where the moon’s oceans touch its core. (NASA, ESA)

So Enceladus (and perhaps Europa, too) provide a kind of emerging “proof of concept” that ice-covered water worlds can and do exist elsewhere.  (Jupiter’s giant moons Ganymede and Callisto also have massive ocean, but far below their surfaces and sandwiched between layers of ice.)  In fact, subterranean oceans may be common because, in recent years, scientists have come to understand that water — especially in its vapor and ice stages — is ubiquitous in the solar system, the galaxy and the universe.  Comets, which are generally half water ice and half rock, are one of numerous delivery systems.

And we already have, of course, one good example of what would generally be considered a waterworld without the ice covering — Earth.  But that’s not all, even without leaving our solar system.   We look at planets such as Mars and Venus and now see desiccated landscapes.  Yet it is broadly accepted that Mars once was quite wet on the surface, based on findings from the Curiosity mission and years of satellites imaging, and some have speculated that Venus might once have been wet as well.

So are there many waterworlds or aquaworlds with surface liquid water out there?

“It would be fair to say there is a consensus view that exoplanets and moons with lots of water are all over the place,” said Joel Green, an exoplanet scientist with the Space Telescope Science Institute. “The known presence of so much H2O makes that non-controversial.”

Kepler-62e has been described as being a possible waterworld, with large oceans. UPR Arecibo
Kepler-62e has been described as being a possible waterworld, with large oceans. UPR Arecibo

 

What is indeed controversial is whether any waterworlds, or even potential waterworlds, have been detected. There actually has been wide coverage of waterworld discoveries far, far away,  and even some declared confirmations.  But so far at least, those confirmations have not lasted.  As early as 2004, the Hubble Space Telescope identified the signature of water vapor in the atmosphere of an exoplanet, and similar detections have followed.  But that information and more that scientists have collected and modeled about H2O on exoplanets has never been sufficient to make a confirmation stick.

“It’s a very challenging detection to make, and many don’t think we haven’t gotten there yet,” Green said.  Especially challenging is the detection of liquid water, since it does not show up using optical, infrared, ultraviolet or any other kind of light, and so can’t be identified with a spectroscope. It’s presence can only be inferred based on other conditions.  Water vapor and water ice are, however, detectable via spectroscope.

But waterworld theories abound.  For instance, scientists know that Neptune and Uranus in the outer part of our solar system consist of vast amounts of water ice, and they also know that planets tend to change orbits and sometimes migrate closer to their suns.  Marc Kurchner of NASA’s Goddard Space Flight Center has proposed that if similar planets were to migrate inward in different solar systems, the result could be a very wet planet, with oceans hundreds of miles deep.

There is a general tendency to associate the presence of water with the presence of life, and the ubiquity of water in the galaxies with the likelihood of finding life.   But while life is found everywhere that water exists on Earth, that does not at all mean that the discovery of water elsewhere means life will be present, too.

All it means is that one of many prerequisites for life (as we know it) will have been met. But as Enceladus shows, when water is present, all kinds of interesting things start of happen.

A view of Enceladus’ southern hemisphere in enhanced color (IR-green-UV). The “tiger stripe” fractures, the source of plumes venting gas and dust into space, are prominently visible in the center. {NASA/JPL-Caltech/SSI/Lunar and Planetary Institute, Paul Schenk (LPI, Houston)
A view of Enceladus’ southern hemisphere in enhanced color (IR-green-UV). The “tiger stripe” fractures, the source of plumes venting gas and dust into space, are prominently visible in the center. {NASA/JPL-Caltech/SSI/Lunar and Planetary Institute, Paul Schenk (LPI, Houston)
Facebooktwittergoogle_plusredditpinterestlinkedinmail

Many Worlds, Subterranean Edition

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Scanning electron microscope blue-tinted image of nematode on biofilm, collected from Kopanang mine almost one mile below surface. (Borgonie, ELi)
Scanning electron microscope blue-tinted image of a nematode on biofilm, collected from Kopanang mine almost one mile below surface. (Borgonie, ELi)

One of the richest lines of research for those thinking about life beyond Earth has been the world of microscopic creatures that live in especially extreme and hostile environments here.  The realm of extremophiles has exploded in roughly the period that exoplanet discoveries have exploded, and both serve to significantly change our view of what’s possible in nature writ large.

I was reminded of this with the publication today of a paper on extreme life in the deep mines of South Africa.  This is not a brand new story, but rather significant step forward in a story that has implications galore for the search for life beyond Earth.

The extremophile chronology in South Africa goes like this:

First there was the microbe D. Audaxviator, “the Bold Traveler,” found living in lightless solitude more than two miles down a South African gold mine. Nothing alive had ever been found in rock fractures at that depth before.

Then there was H. Mephisto, the “Worm From Hell,” the first complex, multicellular creature (a type of worm) found living at almost equal depths in the same group of mines.

SEM of critters
Scanning electron miscope images of species of worms and a crustacean from Driefontein and Kopanang mines (Borgonie, ELi)

Now the researchers who made both of those discoveries have discovered a “veritable zoo” of multicellular creatures living in the wet rock fissures of the gold and diamond mines of the Witwaterstrand Basin of South Africa, roughly
a mile below the surface.

The earlier discoveries (reports about them were published in 2006 and 2011) had already changed scientists’ understanding of life in the rocky underworld. They had also given encouragement to those convinced that microbes and maybe multi-celled creatures can survive in fissures deep below the surface  of Mars and other moons and planets. The latest jackpot carries this shift in thinking further.

“It is very crowded in some places down under,” said Gaetan Borgonie of ELi, a Belgian nonprofit that studies extreme life, and of South Africa’s University of the Free State in Bloemfontein.

Borgonie, lead author of a paper about the “veritable zoo,” said that his discovery in 2011 of a new species of nematode at great depth had been dismissed by some as a “freak find.” But now, he said, “the fact that we have found in two mines, in different water, two ecosystems featuring several types of invertebrates hopefully puts that notion to rest as wrong.”

Scientists, including Borgonie (right), deep underground at Northam Platinum mine in South Africa. (Marc Kaufman)
Scientists, including Borgonie (right), deep underground at Northam Platinum mine in South Africa. (Marc Kaufman)

He called the findings, published this week in the online journal Nature Communications, “particularly good news for Martian research. If life ever arose there, these findings suggest it may be more likely to remain alive in the subsurface” where it would be protected from the deadly radiation on the Martian surface.  The same can plausibly be said of faraway exoplanets, too.

Borgonie has been working with Princeton University’s Tullis Onstott, who pioneered the search for extreme life in the South African mines, the deepest man-made cuts in the world.  I had the rather searing (and fascinating) experience of joining Borgonie and some colleagues while researching a book on astrobiology some years ago.

Onstott said the number and variety of creatures – worms in particular – found so deep underground was “just startling.” He said the paper makes clear that previous estimates of the amount of life (biomass) underground and under the bottom of the oceans have been too low. Those estimates have ranged from 20 to 50 percent of the total mass of life on Earth.

There are, of course, extremophiles of all sorts.  Some can withstand intense heat (think the ocean floor Black Smokers and Old Faithful), some live in permanent ice (think Antarctica), some in very salty and very alkaline environments, some up in the atmosphere, some in the presence of intense radiation.

A thermophile, such those living in hot springs like this one from Yellowstone National Park, is an organism that thrives at relatively high temperatures 106 and 252 °F).
A thermophile, such those living in hot springs like this one from Yellowstone National Park, is an organism that thrives at relatively high temperatures 106 and 252 °F).

There’s every reason to think that if a biosignature is ever detected from an exoplanet, it will be from a creature distinctly on the extremophile sideWhile extremophiles are literally everywhere on Earth, it seems worthwhile to probe a little further into the world of deep subterranean life.

The newly-described mile-deep zoo was collected over a two-year period from water that was determined, by carbon dating, to have rained down more than 12,000 years ago. It then made its way deep underground through rock cracks and fissures.  That’s not a particularly long period of time in a Martian or other planetary or lunar context, but the earlier finds involved considerably more longtime residents.

The initial South African extreme extremophile  — the bacterium Desulforudis Audaxviator — came out of boreholes in tunnel walls almost two miles down the Mponeng gold mine.  Onstott’s team determined the new species had lived and evolved at that depth for millions of years (between two and 40 million,) and had been totally cut off for all that time from the sun or anything that it influenced or made possible.

The rod-shaped D. audaxviator was recovered from thousands of liters of water collected deep in the Mponeng Mine in South Africa. (Micrograph by Greg Wanger, J. Craig Venter Institute, and Gordon Southam, University of Western Ontario, used with permission)
The rod-shaped D. audaxviator was recovered from thousands of liters of water collected deep in the Mponeng Mine in South Africa. (Micrograph by Greg Wanger, J. Craig Venter Institute, and Gordon Southam, University of Western Ontario)

 

They also determined that it had survived on chemical food sources that derive from the radioactive decay of minerals in the surrounding rock, and that it lived in an ecosystem of one.  Its genome was sequenced and in 2012 an organism with DNA 99 per cent identical to that of D. audaxviator was found in boreholes more than half a mile deep near Death Valley in eastern California.

 

While tens of thousands or tens of millions of years deep underground is not long in the history of Mars or any other celestial body,  Mars scientists now say that life doesn’t have to dig down too far  — maybe one to three yards — to be largely protected from the killing radiation that began to dominate the Martian surface after much of the the planet’s atmosphere was stripped away.  And if some creatures can migrate miles down, many more might be living meters down on otherwise hostile planetary and lunar surfaces.

Halicephalobus mephisto, the first multicellular organism found far below Earth’s surface, is a ravenous bacteria eater. (Borgonie, University of the Free State)
Halicephalobus mephisto, the first multicellular organism found far below Earth’s surface, is a ravenous bacteria eater. (Borgonie, University of the Free State)

The discovery of H. Mephisto, the “worm from hell,” was as surprising as that of D. Audaxviator because it is multicellular, was found at great depth, and had itself evolved into a unique creature.  The newly reported “zoo” of multicellular animals found at one mile down are little different from species on the surface, so either they arrived much later or they were already adapted in ways that allow them to flourish in such harsh conditions.  Many were found in biofilms, a gauzy collection of microorganisms encased in a protective coating and connected to the rock walls of the boreholes.

Carl Pilcher, director of NASA’s Astrobiology Institute had this to say about the new findings:  “This study shows that Earth’s microscopic and near-microscopic life is amazingly versatile, with organisms including tiny animals able to thrive deep below Earth’s surface.  The subtitle for this paper could be ‘Biofilms can grow anywhere.’ And that should probably be what we are thinking as we explore other planets and delve into their subsurfaces in search of habitable environments.”

These particular deep subterranean creatures are surely not living on other planets.  But as a proof of concept, as it were, the South Africa mines show that extreme life in the deep, rocky subsurface does indeed find a way, and given the slightest chance will create many worlds.

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Counting Our Countless Worlds

Facebooktwittergoogle_plusredditpinterestlinkedinmail
The Milky Way has several hundred billion stars, and many scientists are now convinced it has even more planets and moons. (NASA)
The Milky Way is home to several hundred billion stars, and many scientists are now convinced it has even more planets and moons. (NASA)

Imagine counting all the people who have ever lived on Earth, well over 100 billion of them.

Then imagine counting all the planets now orbiting stars in our Milky Way galaxy , and in particular the ones that are roughly speaking Earth-sized. Not so big that the planet turns into a gas giant, and not so small that it has trouble holding onto an atmosphere.

In the wake of the explosion of discoveries about distant planets and their suns in the last two decades, we can fairly conclude that one number is substantially larger than the other.

Yes, there are many, many billions more planets in our one galaxy than people who have set foot on Earth in all human history. And yes, there are expected to be more planets in distant habitable zones as there are people alive today, a number upwards of 7 billion.

This is for sure a comparison of apples and oranges. But it not only gives a sense of just how commonplace planets are in our galaxy (and no doubt beyond), but also that the population of potentially habitable planets is enormous, too.   “Many Worlds,” indeed.

The populations of exoplanets identified so far, plotted according to the radius of the planet and how many days it takes to orbit. The circles in yellow represent planets found by Kepler, light blue by using ground-based radial velocity, and pink for transiting planets not found by Kepler, and green, purple and red other ground-based methods. (NASA Ames Research Center)
The populations of exoplanets identified so far, plotted according to the radius of the planet and how many days it takes to orbit. The circles in yellow represent planets found by Kepler, light blue by using ground-based radial velocity, and pink for transiting planets not found by Kepler, and green, purple and red other ground-based methods. (NASA Ames Research Center)

It was Ruslan Belikov, an astrophysicist at NASA’s Ames Research Center in Silicon Valley who provided this sense of scale.  The numbers are of great importance to him because he (and others) will be making recommendations about future NASA exoplanet-finding and characterization missions based on the most precise population numbers that NASA and the exoplanet community can provide.

Natalie Batalha, Mission Scientist for the Kepler Space Telescope mission and the person responsible for assessing the planet population out there, sliced it another way. When I asked her if her team and others now expect each star to have a planet orbiting it, she replied: “At least one.”

Kepler-186f was the first rocky planet to be found within the habitable zone -- the region around the host star where the temperature is right for liquid water. This planet is also very close in size to Earth. (NASA Ames/SETI Institute/JPL-Caltech)
Kepler-186f was the first rocky planet to be found within the habitable zone — the region around the host star where the temperature is right for liquid water. This planet is also very close in size to Earth. (NASA Ames/SETI Institute/JPL-Caltech)

I caught up with Belikov, Batalha and several dozen others intimately involved in cataloguing the vast menagerie of exoplanets at a “Hack Event” earlier this month at Ames. The goal of the three-day gathering was to find ways to improve the already high level of reliability and completeness regarding planets identified by Kepler.

It also provided an opportunity to learn more about how, exactly, these scientists can be so confident about the very large numbers of exoplanets and habitable zone exoplanets they describe. After all, the total number of confirmed exoplanets is a bit under 2,000 – a majority found by Kepler but hundreds of others by pioneering astronomers using ground-based telescopes and very different techniques. Kepler has another 3,000 planet candidates that scientists are in the process of analyzing and most likely confirming, but still. Four thousand is minuscule compared with two hundred billion.

Not everyone completely agrees that we’re ready to estimate such large numbers of exoplanets—suggesting that we need more data before making such important estimates — but the community consensus is that their extrapolations from current data are solid and scientific. And here is why:

The Kepler telescope looks out at a very small portion of the sky with a limited number of stars – about 190,000 of them during its four year survey. And it identifies planets based on the tiny dimming of stars when an object (almost always a planet) crosses between the star and the telescope.

The Kepler telescope looked constantly for four years at almost 200,000 stars in the Cygnus constellation. (Carter Roberts)
The Kepler telescope looked constantly for four years at almost 200,000 stars in the Cygnus & Lyra constellations.  Its lens is always open, by design. (Carter Roberts)

By identifying those 4,000-plus confirmed and candidate planets over four years, Kepler infers the existence of many, many more. As Batalha explained, a transit of the planet is only observable when the orbit is aligned with the telescope, and the probability of that alignment is very small. Kepler scientists refer to this as a “bias” in their observations, and it is one that can be quantified. For example, the probability that an Earth-Sun twin will be aligned in a transiting geometry is just 0.5%. For every one that Kepler detects, there are 200 others that didn’t transit simply because of the orientation of their orbits.

Then there’s the question of faintness and reliability. Kepler is looking out at stars hundreds, sometimes thousands of light years away.  The more distant a star, the fainter it is and the more difficult it is to gather measurements of –and especially dips in — brightness. When it comes to potentially habitable, Earth-sized planets, Batalha said that only 10,000 to 15,000 of the stars observed are bright enough for planets to be detectable even if they do transit the disk of their host star.

Here’s why: Detecting an Earth-sized planet would be roughly equivalent to capturing the image of a gnat as it crosses a car headlight shining one mile away. For a Jupiter-size planet, the bug would grow to only the size of a large beetle.

Add this bias to the earlier one, and you can see how the numbers swell so quickly. And since Kepler’s mission has been to provide a survey of planets in one small region – and not a census – this kind of statistical extrapolation is precisely what the mission is supposed to do.

There are numerous other detecting challenges posed by the dynamics of exoplanets, stars and the great distances. But then there are also innumerable challenges associated with the workings of the 95 megapixel CCD array that is collecting light for Kepler.   “Sensitivity dropouts” caused by those cosmic rays, horizontal “rolling bands” on the CCDs caused by temperature changes in the electronics, “optical ghosts” from binary stars that create false signals of transits on nearby stars — they are some of the many instrument artifacts that can be mistaken as a drop in light coming from a planet. Kepler’s data processing pipeline, much of which has been transferred over to the NASA Ames supercomputer, has the job of sorting all this out.

 

After the CCDs on the Kepler telescope record the light from stars in its viewing field, the data is sent back to Earth and goes through numerous steps before possibly delivering a “Kepler object of interest,” and possibly a planet candidate. Pleiades is the Ames supercomputer. (NASA Ames)
After the CCDs on the Kepler telescope record the light from stars in its viewing field, the data is sent back to Earth and goes through numerous steps before possibly delivering a “Kepler object of interest,” and possibly a planet candidate. Pleiades is the Ames supercomputer. (NASA Ames)

Adding to the challenge, said Jon Jenkins, a Kepler co-investigator at Ames and the science lead for the pipeline development, is that the stars viewed by Kepler turned out to be themselves “noisier” than expected. Stars naturally vary in their overall brightness, and the data processing pipeline had to be upgraded to account for that changeability.  But that stellar noise has played a key role in keeping Kepler from seeing some of the small planet transits that the team hoped to detect.

What the Hack event and other parallel efforts are doing is finding ways to, as Jenkins put it, “dig into the noise…to move towards the hairy edge of what our data can show.” The final goal: “To come up with the newest, best washer we can to clean the data and come out with an improved catalog of sparkling planets.”

All the data that will come from the primary Kepler mission, which came to a halt in the summer of 2013, has been collected and analyzed already on a first round. But now the entire pipeline of data is going to be reprocessed with its many improvements so the researchers can dig deeper into data trove. Batalha said they hope to find planets – especially Earth-sized planets – this way.

One of the key techniques to measure the performance of Kepler’s analysis pipeline is to inject fake transit signals into the data and see if it picks up their presence. As Batalha explained, this provides another way to gauge the biases in the system, its efficiency at detecting the planets that it could and should see. “If we inject 100 fake things into the pipeline and find 90 of them, that’s means we’re 90 percent complete.” She said the number would then be worked into the calculations of how many planets are out there, and how many of certain sizes will be caught and missed.

Natalie Batalha is the Chief Scientist for the Kepler mission, while announcing the discovery of Kepler’s first rocky planet, Kepler-10b, in January 2011.

So the Hack Event, which brought together astrophysicists, planetary scientists and computer hakers, was designed to come up with ways to improve Kepler’s completeness (seeing everything there to be seen) and reliability (the likelihood that the signal comes from a planet and not an instrument artifact or non-planetary phenomena in space). By computing both the completeness and reliability, scientists are confident that they can eliminate the observation biases and transform the discovery catalog into a directory of actual planets.

This is one of the key accomplishments of the Kepler mission – making it scientifically possible to say that there are billions and billions of planets out there. What’s more, the increased power of Kepler allowed for the discovery of smaller planets, which are now known to make up the bulk of the exoplanets. And while the number of Earth-sized planets detected in that habitable zone is small – around thirty – that’s still quite a remarkable feat. And remember, Kepler is looking at but one small sliver of the sky.

The twelve exoplanets detected so far closest to Earth in size, lined up with the type of stars they orbit. (NASA Ames)
The twelve exoplanets detected and confirmed so far closest to Earth in size, lined up with the type of stars they orbit. (NASA Ames)

Why does it matter how many exoplanets are out there, how many are rocky and Earth-sized, and how many within habitable zones? The last twenty years of exoplanet hunting, after all, has made clear that there are an essentially infinite number of them in the universe, and untold billions in our galaxy.

The answer lies in the insatiable human desire to know more about the world writ large, and how and why different stars have very different solar systems. But more immediately, there’s the need to know how to best design and operate future planet-finding missions. If the goal is to learn how to characterize exoplanets – identify components of their atmospheres, learn about their weather, their surfaces and maybe their cores – then scientists and engineers need to know a lot more about where planets generally, and some specifically, can be found. And those planet demographics just might open some surprising possibilities.

For instance, Belikov and his Ames colleague Eduardo Bendek have proposed a NASA “small explorer” (under $175 million) mission to launch a 30-to-45 centimeter mirror designed to look for Earth-sized planets only at our nearest stellar neighbor, Alpha Centauri. That’s as small a telescope as you can buy off-the-shelf.

Alpha Centauri is the closest star system to our Solar System at about 4.37 lightyears away. (NASA/Hubble Space Telescope)
Alpha Centauri is the closest star system to our Solar System at about 4.37 lightyears away. (NASA/Hubble Space Telescope)

Alpha Centauri is a two-star system, and until recently researchers doubted that binaries like it would have orbiting planets. But Kepler and other planet hunters have found that planets are relatively common around binaries, making Alpha Centauri a better target than earlier imagined.

To make it a truly viable project, ACESat – the Alpha Centauri Exoplanet Satellite – requires something else: a scientifically sound estimate of the likelihood that any star in our galaxy would have an Earth-sized planet in its system. Estimates so far have ranged from 10 percent to 50 percent, but Belikov said newer data is encouraging.

“If that number becomes more firm and approaches 50 percent, then an Alpha Centauri-only mission makes a great deal of sense,” he said. “For a small investment, we could have a real possibility of detecting a planet very close by.”

Intriguing, and an insight into how new space missions are designed based on the science already completed. Both NASA and the European Space Agency have plans to launch three significant exoplanet missions within the decade, and the powerful James Webb Space Telescope will launch in 2018 with some known and undoubtedly some not yet understood capabilities for exoplanet discovery. And perhaps most important, NASA is about to study how a potential mission in the 2030s could be designed with the specific purpose of directly imaging exoplanets – the gold standard for the field. All are being designed based on current exoplanet understandings, including the abundance calculations enabled by the Kepler mission’s observations.

Almost 2,000 exoplanets have now been identified, more than half by Kepler. Another 3,000 exoplanet candidates await confirmation. (NASA Ames)
Almost 2,000 exoplanets have now been detected and confirmed, more than half by Kepler. Another 3,000 exoplanet candidates await confirmation. (NASA Ames)

Future posts will dig deeper into a fair number of the subjects raised here, but for now this much is clear: Our galaxy has many billions of planets, and the process of detecting them is robust and on-going, the process of characterizing them has begun, and all the signs point towards the presence of enormous numbers of planets in habitable zones that, in the biggest picture at least, could possibly support life.

Facebooktwittergoogle_plusredditpinterestlinkedinmail