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PIXL: A New NASA Instrument For Ferreting Out Clues of Ancient Life on Mars

 

Extremely high definition images of the com ponents of rocks and mud as taken by PIXL, the Planetary Instrument for X-ray Lithochemistry .   On the Mars 2020 rover, PIXL  will have significantly greater capabilities than previous similar instruments sent to Mars.  Rather than reporting bulk compositions averaged over several square centimeters, it will identify precisely where in the rock each element resides. With spatial resolution of about 300 micrometers, PIXL will conduct the first ever petrology investigations on Mars, correlating elemental compositions with visible rock textures . (NASA)J

The search for life, or signs of past life beyond Earth is now a central issue in space science, is central to the mission of NASA, and is actually a potentially breakthrough discovery in the making  for humanity.    The scientific stakes could hardly be higher.

But identifying evidence of ancient microbial life – and refuting all reasonable non-biological explanations for that evidence — is stunningly difficult.

As recent wrangling over Earth’s oldest rocks in Greenland has shown, determining the provenance of a deep-time biosignature even here on Earth is extraordinarily difficult. In 2016, scientists reported discovery of 3,700 million yr-old stromatolites in the Isua geological area of Greenland.

Just three years later, a field workshop held at the Isua discovery site brought experts from around the world to examine the intriguing structures and see whether the evidence cleared the very high bar needed to accept a biological interpretation. While the scientists who published the initial discovery held their ground, not one of the other scientists felt convinced by the evidence before them.  Watching and listening as the different scientists presented their cases was a tutorial in the innumerable factors involved in coming to any conclusion.

Now think about trying to wrestle with similar or more complex issues on Mars, of how scientists can reach of level of confidence to report that a sign (or hint) of past life has apparently been found.

As it turns out, the woman who led the Greenland expedition — Abigail Allwood of NASA’s Jet Propulsion Lab — is also one of the key players in the upcoming effort to find biosignatures on Mars.  She is the principal investigator of the Planetary Instrument for X-ray Lithochemistry (PIXL) that will sit on the extendable arm of the rover, and it has capabilities to see in detail the composition of Mars samples as never before.

The instrument has, of course, been rigorously tested to understand what it can and cannot do. … Read more

The Remarkable Race to Find the First Exoplanet, And the Nobel Prize It Produced

Rendering of the planet that started it all — 51 Pegasi b. It is a “hot Jupiter” that, when discovered, broke every astronomical rule regarding where types of planets should be in a solar system. (NASA)

Earlier this week, the two men who detected the first planet outside our solar system that circled a sun-like star won a Nobel Prize in physics.  The discovery heralded the beginning of the exoplanet era — replacing a centuries-old scientific supposition that planets orbited other stars with scientific fact.

The two men are Michel Mayor,  Professor Emeritus at the University of Geneva and Didier Queloz, now of Cambridge University.  There is no Nobel Prize in astronomy and the physics prize has seldom gone to advances in the general field of astronomy and planetary science.  So the selection is all the more impressive.

Mayor and Queloz worked largely unknown as they tried to make their breakthrough, in part because previous efforts to detect exoplanets (planets outside our solar system) orbiting sun-like stars had fallen short, and also because several claimed successes turned out to be unfounded.  Other efforts proved to be quite dangerous:  a Canadian duo used poisonous and corrosive hydrogen flouride vapor in the 1980s as part of their planet-hunting effort.

But since their 1995 discovery opened the floodgates, the field of exoplanet science has exploded.  More than 4,000 exoplanets have been identified and a week seldom goes by without more being announced.  The consensus scientific view is now that billions upon billions of exoplanets exist in our galaxy alone.

While Mayor and Queloz were pioneers for sure, they did not work in a vacuum.  Rather, they were in a race of sorts with an American team that had also been working in similar near anonymity for years to also find an exoplanet.

And so here is a human, rather than a purely scientific, narrative look — reported over the years — into the backdrop to the just announced Nobel Prize.  While Mayor and Queloz were definitely the first to find an exoplanet, they were quite close to being the second.

 

Swiss astronomers Didier Queloz and Michel Mayor are seen here in 2011 in front of the European Southern Observatory’s ’s 3.6-metre telescope at La Silla Observatory in Chile. The telescope hosts the High Accuracy Radial Velocity Planet Searcher (HARPS), one of the world’s leading exoplanet hunters.  After the discovery of 51 Pegasi b, Mayor led the effort to build the HARPS planet-finding spectrometer.

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The Giant Moon That Might Be the Heart of a Jupiter

Artist’s impression of the exomoon candidate Kepler-1625b-i, the planet it is orbiting and the star. (NASA/ESA/L. Hustak, STScI)

“Moons are where planets were in the 1990s,” predicted René Heller from the Max Planck Institute for Solar System Research a few years ago. “We’re on the brink.”

Heller was predicting that we were close to the first discoveries of exomoons: moons that orbit extrasolar planets outside our solar system. When a possible exomoon detection was announced in 2017, Heller’s prediction was proved correct. Not only had we found a candidate moon, but its properties defied our formation theories just as with the discoveries of the first exoplanets.

However, a paper published in Science this month has proposed a method for building this most unusual of moons.

As we move away from the sun, the planets of our solar system become mobbed with moons. How these small worlds formed is attributed to three different processes:

Moons in our solar system are thought to have formed through three different mechanisms (E. Tasker / Many Worlds)

The most extensive moon real estate orbits our gas giants, Jupiter, Saturn, Uranus and Neptune. The majority of these moons are thought to have been born during the planets’ own formation, forming in disks of gas, dust and ice that circled the young worlds. These circumplanetary disks are like miniaturised versions of the protoplanetary disks that circle young stars and give rise to planets.

One exception to this is Neptune’s moon, Triton, which orbits in the opposite direction to the planet’s rotation. This retrograde path would not be expected to arise if Triton has formed out of a circumplanetary disk around Neptune, which always rotate the same direction as the forming planet. Instead, Triton was likely a dwarf planet that was snagged by Neptune’s gravity during a chance encounter.

The capture scenario has also been proposed for the two moons of Mars. The lumpy satellites resemble asteroids and may have been born in the asteroid belt that sits between Mars and Jupiter. However, both moons orbit the red planet in circular orbits that sit in the same plane, pointing to a more disk-like formation method. Although Mars is too small to have had a substantial circumplanetary disk during formation, a giant impact later in its history could have thrown debris into orbit. This debris disk could then have coalesced into the two moons.

Such a violent start to Mars’s moons would mimic the beginnings of our own moon.… Read more

The Planets Too Big for Their Star

Artist rendering of a red dwarf , with three exoplanets orbiting. About 75% of all stars in the sky are the cooler, smaller red dwarfs. (NASA)

Two giant planets have been found orbiting a tiny star, defying our theories for how planets are formed.

To be entirely truthful, there is nothing new in an exoplanet discovery shredding our current ideas about how planets are built. The first extrasolar planets ever discovered orbit a dead star known as a pulsar. Pulsars end their regular starry life in a colossal supernova explosion that should incinerate or eject any orbiting worlds. This discovery was followed a few years later by the first detection of a hot Jupiter; a gas giant planet orbiting its star in just a few days, defying theories that said such planets should form on long orbits where there is more building material to make massive worlds. Exoplanet hunting is a field full of surprises and now, it has one more.

GJ 3512 is a red dwarf star with a luminosity only around a thousandth (0.0016L) of our sun. The small size of these stars makes it easier to detect the presence of a planet, and many of our most famous exoplanet discoveries have been found orbiting red dwarf stars, including Proxima Centauri b and the seven worlds in the TRAPPIST-1 system. But a notable attribute of these systems is that the planets are small. Unlike our own sun which boasts four gas giant worlds, planets around red dwarfs are typically smaller than Neptune.

Artist impression of the seven planets of Trappist-1 that also orbit a red dwarf star. These are small worlds. Jupiter-sized gas giants were not previously thought to form around the small red dwarf stars (NASA/JPL-Caltech).

This preference for downsized worlds is assumed to be due to the protoplanetary disk; the disk of dust and gas that swirls around young stars out of which planets are born. Protoplanetary disks around small stars tend to be low mass and puffy. This limits and spreads out the solid material, making it difficult for a young planet to grow.

Yet the two planets discovered around GJ 3512 are not small.
Led by Juan Carlos Morales at the IEEC Institute of Space Studies of Catalonia, the announcement of the discovery was published in the journal Science today.

The team detected these two new worlds using the radial velocity technique which measures the wobble in the position of the star due to the gravitational tug of the orbiting planet.… Read more

On the Ground in Greenland, at the Disputed Ancient Stromatolite Site

Enlarge to full screen on lower right. A pioneering three-dimensional, virtual reality look at a Greenland outcrop earlier described as containing 3.7-billion- year-old stromatolite fossils, which would be the oldest remnant of life on Earth. The video capture, including the drone-assisted overview of the site, is part of a much larger virtual reality effort to document the setting undertaken late in August. As the video focuses in on the scientifically controversial outcrop, cuts are visible in the smooth surfaces that were made by two teams studying the rocks in great detail to determine whether the reported stromatolite fossils are actually present. (Parker Abercrombie, NASA/JPL and Ian Burch, Queensland University of Technology.)

 

Seldom does one rock outcrop get so many visitors in a day, especially when that outcrop is located in rugged, frigid terrain abutting the Greenland Ice Sheet and can be reached only by helicopter.

But this has been a specimen of great importance and notoriety since it appeared from beneath the snow pack some eight years ago. That’s when it was first identified by two startled geologists as something very different from what they had seen in four decades of scouring the geologically revelatory region – the gnarled Isua supercrustal belt – for fossil signs of very early life.

Since that discovery the rock outcrop has been featured in a top journal and later throughout the world as potentially containing the earliest signature of life on Earth – the outlines of half inch to almost two inch-high stromatolite structures between 3.7 and 3.8 billion years old.

The Isua greenstone, or supracrustal belt, which contains some of the oldest known rocks and outcrops in the world, is about 100 miles northeast of the capital, Nuuk.

If Earth could support the life needed to form primitive but hardly uncomplicated stromatolites that close to the initial cooling of the planet, then the emergence of life might not be so excruciatingly complex after all. Maybe if the conditions are at all conducive for life on a planet (early Mars comes quickly to mind) then life will probably appear.

Extraordinary claims in science, however, require extraordinary proof, and inevitably other scientists will want to test the claims.

Within two years of that initial ancient stromatolite splash in a Nature paper (led by veteran geologist Allen Nutman of the University of Wollongong in Australia), the same journal published a study that disputed many of the key observations and conclusions of the once-hailed ancient stromatolite discovery. … Read more

Exploring Early Earth by Using DNA As A Fossil

Betül Kaçar is an assistant professor at the University of Arizona, and a pioneer in the field of paleogenomics — using genetic material to dive back deep into the ancestry of important compounds. (University of Arizona)

Paleontology has for centuries worked to understand the distant past by digging up fossilized remains and analyzing how and why they fit into the evolutionary picture.  The results have been impressive.

But they have been limited.  The evolutionary picture painted relies largely on the discovery of once hard-bodied organisms, with a smattering of iconic finds of soft-bodied creatures.

In recent years, however, a new approach to understanding the biological evolution of life has evolved under the umbrella discipline of paleogenomics.  The emerging field explores ancient life and ancient Earth by focusing on genetic material from ancient organisms preserved in today’s organisms.

These genes can be studied on their own or can be synthetically placed into today’s living organisms to see if, and how, they change behavior.

The goals are ambitious:  To help understand both the early evolution and even the origins of life, as well as to provide a base of knowledge about likely characteristics of potential life on other planets or moons.

“What we do is treat DNA as a fossil, a vehicle to travel back in time,” said Betül Kaçar, an assistant professor at the University of Arizona with more than a decade of experience in the field, often sponsored by the NASA Astrobiology Program and the John Templeton Foundation.  “We build on modern biology, the existing genes, and use what we know from them to construct a molecular tree of life and come up with the ancestral genes of currently existing proteins.”

And then they ask the question of whether and how the expression of those genes — all important biomolecules generally involved in allowing a cell to operate smoothly — has changed over the eons.  It’s a variation on one the basic questions of evolution:  If the film of life were replayed from very early days, would it come out the same?

Cyanobacteria, which was responsible for the build-up of oxygen in the Earth’s atmosphere and the subsequent Great Oxidation Event about 2.5 billion years ago.  Kaçar studies and replaces key enzymes in the cyanobacteria in her effort to learn how those ancestral proteins may have behaved when compared to the same molecules today.

The possibility of such research — of taking what is existing today and reconstructing ancient sequences from it — was first proposed by Emile Zuckerkandl, a biologist known for his work in the 1960s with Linus Pauling on the hypothesis of the “molecular clock.”… Read more

A Unique Science Expedition to Greenland

Greenland from above, where the ice sheet is melting to form lakes and to expose rocks not visible for millennia. @Susan Oliver

It is my very good fortune to report that I have just arrived in Greenland for quite a scientific adventure.
 
Over the next days, a group of scientists (along with me and NASA videographer Mike Toillion) will be traveling to the site of the stromatolite that might, or might not, be the oldest remains of life on Earth.  In a 2016 Nature paper, it was described as having been fossilized about 3.7 billion years ago.
 
Another Nature paper two years later challenged the biological origins of the “fossil,” and the debate has been pretty vigorous since.

Vigorously debated putative stromatolite from the Isua Peninsula, Greenland.

We’ll be helicoptering about 100 miles northeast of the capital Nuuk to get to the Isua peninsula, where the oldest (or almost the oldest, depending on who you choose to follow) rock formations on Earth can be found. Three days and two nights on the ice, or what we hope is still ice. And then a day or more of scientific debate.

I will be writing about this and more (some folks involved the Mars 2020 mission will also be testing instruments at the site) for Many Worlds in the days and weeks ahead.

To me this is an important story not only because of the possible age of the stromatolite find.  If confirmed, it would move back the presence of identified life on Earth by 200 million years.

It is also important because of the fact that scientists with different views on this important issue have traveled thousands of miles to go to the site together and try to reach a consensus—or at least to vigorously argue their cases.  Doesn’t often happen in such high profile science.

Greenstone Belt formations on the Isua Peninsula where our team will be headed.

 
Greenland has, of course, been in the news of late for reasons ranging  worrisome purchase offers to far more worrisome warming.  Remarkable are the “moulin” — which drain the water running on the ice sheet and send it down thousands of feet to the water or land below. 
Kind of a ice black hole.

A “moulin” in Greenland that acts as a very deep drain for water melting on the ice sheet.

Now it’s in my news because, well, I’m here in Greenland, to learn, to report back, and to take in everything this spectacular place has to offer.
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Searching for the Edge of Habitability

Topographical map of Venus by NASA’s Magellan spacecraft (1990 – 1994). Color indicates height. (NASA/JPL/USGS)

How many habitable worlds like our own could exist around other stars? Since the discovery of the first exoplanets, the answer to this question has seemed tantalizingly close. But to estimate the number of Earths, we first need to understand how our planet could have gone catastrophically awry.

In other words, we need to return to Venus.

We have now discovered over 4000 planets beyond our solar system. Approximately one-third of these worlds are Earth-sized and likely to have rocky surfaces not crushed under deep atmospheres. The next step is to discover how many of these support temperate landscapes versus ones unsuitable for life.

The Earth’s habitability is often ascribed to the level of sunlight we receive. We orbit in the so-called ‘habitable zone’ where our planet’s geological cycle can adjust the level of carbon dioxide in our atmosphere to keep our seas liquid. In a closer orbit to the sun, this cycle could not operate fast enough to keep the Earth cool. Our seas would evaporate and our atmosphere fill with carbon dioxide, sending the planet temperature into an upwards spiral known as a runaway greenhouse.

If our solar system had just one Earth-sized planet, this would suggest we could simply count-up similar sized planets in the habitable zones around other stars. This would then be our set of the most likely habitable worlds.

However, this idea is shredded in a new paper posted this month to be published in the Journal of Geophysical Research: Planets. Led by Stephen Kane from the University of California, Riverside, the paper is authored by many of the top planetary scientists we have met before in this column.

Their message is simple: our sun is orbited by two Earth-sized planets but only one is habitable. To identify habitable planets around other stars, we need to explain why the Earth and Venus evolved so differently. And the data suggests this is not just a climate catastrophe.

Orbiting beyond the inner edge of the habitable zone, Venus does appear at first to be a runaway Earth. The planet’s atmosphere is 96.5% carbon dioxide, smothering the surface to escalate temperatures to a staggering 863°F (462°C). Images from NASA’s Pioneer Venus mission in the late 1970s revealed a surface of highlands and lowlands that resembled the continents of Earth. This is all consistent with a picture of an Earth-like planet with a runaway greenhouse atmosphere.… Read more

“Agnostic Biosignatures,” And the Path to Life as We Don’t Know It

Most research into signs of life in our solar system or on distant planets uses life on Earth as a starting point. But now NASA has begun a major project to explore the potential signs of life very different from what we have on Earth.  For example, groups of molecules, like those above, can be analyzed for complexity, regardless of their specific chemical constituents.  ( Brittany Klein/Goddard Space Flight Center)

Biosignatures – evidence that says or suggests that life has been present – are often very hard to find and interpret.

Scientists examining fossilized life on Earth can generally reach some sort of agreement about what is before them, but what about the soft-bodied or even single-celled organisms that were the sum total of life on Earth for much of the planet’s history as a living domain? Scientific disagreements are common.

Now think of trying to determine whether a particular outline on an ancient Martian rock, or a geochemical or surface anomaly on that rock, is a sign of life. Or perhaps an unexpected abundance of a particular compound in one of the water vapor plumes coming out of the moons Europa or Enceladus. Or a peculiar chemical imbalance in the atmosphere of a distant exoplanet as measured in the spectral signature collected via telescope.

These are long-standing issues and challenges, but they have taken on a greater urgency of late as NASA missions  (and those of other space agencies around the world) are being designed to actively look for signs of extraterrestrial life – most likely very simple life – past or present.

And that combination of increased urgency and great difficulty has given rise to at least one new way of thinking about those potential signs of life. Scientists call them “agnostic biosignatures” and they do not presuppose any particular biochemistry.

“The more we explore the solar system and distant exoplanets, the more we find worlds that are really foreign,”  said Sarah Stewart Johnson, at an assistant professor at Georgetown University and principal investigator of the newly-formed Laboratory for Agnostic Biosignatures (LAB).  The LAB team won a five-year, $7 million grant last year from NASA’s Astrobiology Program.

“So our goal is to go beyond our current understandings and find ways to explore the world of life as we don’t know it,” she told me.  “That might mean thinking about a spectrum of how ‘alive’ something might be… And we’re embracing uncertainty, looking as much for biohints as biosignatures.”… Read more

Exoplanets Discoveries Flood in From TESS

NASA’s Transiting Exoplanet Survey Satellite (TESS) has hundreds of “objects of interest” waiting to be confirmed as planets in the data from the space telescope’s four cameras.  These three were the first confirmed TESS discoveries, identified last year during its first three months of observing. By the time the mission is done, TESS’s wide-field cameras will have covered the whole sky in search of transiting exoplanets around 200,000 of the nearest (and brightest) stars. (NASA / MIT / TESS)

The newest space telescope in the sky — NASA’s Transiting Exoplanet Survey Satellite, TESS — has been searching for exoplanets for less than a year, but already it has quite a collection to its name.

The TESS mission is to find relatively nearby planets orbiting bright and stable suns, and so expectations were high from the onset about the discovery of important new planets and solar systems.  At a meeting this week at the Massachusetts Institute of Technology devoted to TESS  results,  principal investigator George Ricker pronounced the early verdict.

The space telescope, he said,  “has far exceeded our most optimistic hopes.”  The count is up to 21 new planets and 850 additional  candidate worlds waiting to be confirmed.

Equally or perhaps more important is that the planets and solar systems being discovered promise important results.  They have not yet included any Earth-sized rocky planet in a sun’s habitable zone — what is generally considered the most likely, though hardly the only, kind of planet to harbor life — but they did include planets that offer a great deal when it comes to atmospheres and how they can be investigated.

This infographic illustrates key features of the TOI 270 system, located about 73 light-years away in the southern constellation Pictor. The three known planets were discovered by NASA’s Transiting Exoplanet Survey Satellite through periodic dips in starlight caused by each orbiting world. Insets show information about the planets, including their relative sizes, and how they compare to Earth. Temperatures given for TOI 270’s planets are equilibrium temperatures, (NASA’s Goddard Space Flight Center/Scott Wiessinger)

One of the newest three-planet system is called TOI-270, and it’s about 75 light years from Earth. The star at the center of the system is a red dwarf, a bit less than half the size of the sun.

Despite its small size, it’s brighter than most of the nearby stars we know host planets. And it’s stable, making its solar system especially valuable.

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