Of White Dwarfs, “Zombie” Stars and Supernovae Explosions

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Artistic view of the aftermath of a supernova explosion, with an unexpected white dwarf remnant. These super-dense but no longer active stars are thought to play a key role in many supernovae explosion. (Copyright Russell Kightley)
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White dwarf stars, the remnant cores of low-mass stars that have exhausted all their nuclear fuel, are among the most dense objects in the sky.
 
Their mass is comparable to that of the sun, while their volume is comparable to that of Earth. Very roughly, this means the average density of matter in a white dwarf would be on the order of 1,000,000 times greater than the average density of the sun.
 
Thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star — a category that includes the sun and over 97% of the other stars in the Milky Way — they are dim objects first identified a century ago but only in the last decade the subject of broad study.
 
In recent years the white dwarfs have become more and more closely associated with supernovae explosions, though the processes involved remained hotly debated.  A team using the Hubble Space Telescope even captured  before and after images of what is hypothesized to be an incomplete white dwarf supernova.  What was left behind has been described by some as a “zombie star.”
 
Now a team of astronomers led by Stephane Vennes of the Czech Academy of Sciences has detected another zombie white dwarf, LP-40-365 , that they put forward as a far-flung remnant of a long-ago supernova explosion.  This is considered important and unusual because it would represent a first detection of such a remnant long after the supernova conflagration.
 
This dynamic is well captured in an animation accompanying the Science paper that describes the possible remnant.  Here’s the animation and a second-by-second description of what is theorized to have occurred:
 
 
00.0 sec: Initial binary star outside the disk of the Milky Way galaxy. A massive white dwarf accreting
material through an accretion disk from its red giant companion star. The stars orbit around the center of
mass of the binary system.
 
14.6 sec: The white dwarf reaches the Chandrasekhar mass limit and explodes as a bright Type Ia
supernova. However, the explosion is not perfect; a fraction of the white dwarf shoots out like a shrapnel to the left. The binary system disrupts.
 
18.0 sec: The supernova explosion again, at an edge – on view. The shrapnel comes at the viewer and passes by.
 
20.0 sec: After passing by, the remnant flies off towards the disk of the Milky Way towards the spiral arm with the Solar System.
 
24.0 sec : The fast moving remnant from the solar neighborhood as it passes by the stars in our galactic arm, including the Sun. The remnant gets in the reach of our telescopes. (Copyright Sardonicus Pax)

 

A supernova — among the most powerful forces in the universe — occurs when there is a change in the core of a star. A change can occur in two different ways, with both resulting in a thermonuclear explosion.

Type Ia supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova.

The second type takes place only in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova.

Type Ia supernovae, which are the result of the complete destruction of the star in a thermonuclear explosion, have a fairly uniform brightness that makes them useful for cosmology. The light emitted by the supernova explosion can be, for a short while at least, as bright as the whole of the Milky Way.

Recently, astronomers have discovered a related form of supernova, called Type Iax, which look like Type Ia, but are much fainter. Type Iax supernovae may be caused by the partial destruction of a white dwarf star in such an explosion. If that interpretation is correct, part of the white dwarf should survive as a leftover object.

And that leftover object is precisely what Vennes et al claim to have found.

They have identified LP 40-365 as an unusual white dwarf with a low mass, high velocity and strange composition of oxygen, sodium and magnesium  – exactly as might be expected for the leftover star from a Type Iax event. Vennes describes the white dwarf remnant his team has detected as a “compact star,” and perhaps the first of its kind in terms of the elements it contains.

The team calculate that the explosion must have occurred between five and 50 million years ago.

 

The two inset images show before-and-after images captured by NASA’s Hubble Space Telescope of Supernova 2012Z in the spiral galaxy NGC 1309, what some call a “zombie star.”. The white X at the top of the main image marks the location of the supernova in the galaxy. A supernova typically obliterates the exploding white dwarf, or dying star.  In 2014, scientists found that this faint supernova may have left behind a surviving portion of the white dwarf star.(NASA,ESA)

In an email exchange, Vennes told me that he has been studying the local white dwarf population for thirty years.

“These compact, dead stars tell us a lot about the “old” Milky Way, how stars were born and how they died,” he wrote.

“Tens of thousands of these white dwarfs have been catalogued over this past century, most of them in the last decade, but we keep an eye on outliers, objects that are out of the norm. We look for exceedingly large velocity, peculiar chemical composition or abnormal mass or radii.

Stephane Vennes, a longtime specialist in white dwarf stars at the Czech Academy of Science.

“The strange case of LP40-365 came unexpectedly, but this was a classic case of serendipity in astronomy. Out of hundreds of targets we observed at the telescope, this one was uniquely peculiar. Fortunately, theorists are very imaginative and the model we adopted to interpret the observed properties of this object were only recently published. Our research on this object was certainly inspired and directed by their theory.”

Vennes says the team was surprised to learn that the white dwarf LP40-365 is relatively bright among its peers and that similar objects did not show up in large-scale surveys such as the Sloan Digital Sky Survey.

“This fact has convinced us that many more similarly peculiar white dwarfs await discovery. We should search among fainter, more distant samples of white dwarfs,” he wrote.

And that search can be done by the European Space Agency’s Gaia astrometric space telescope, with follow-up observations at large telescopes such as the European Southern Observatory’s Very Large Telescope and the Gemini observatory in Chile.

“It is also likely that our adopted model involving a subluminous {faint} Type Ia supernova will be modified or even superseded by teams of theorists coming up with new ideas. But we remain confident that these new ideas would still involve a cataclysmic event on the scale of a supernova.”

Here is another animated version of the cataclysm described in the paper: 

An ultra-massive and compact dead star, or white dwarf, (shown as a small white star) is accreeting matter from its giant companion (the larger red star). The material escapes from the giant and forms an accretion disk around the white dwarf.
Once enough material is accreted onto the white dwarf, a violent thermonuclear runaway tears it apart and destroys the entire system. The giant star and the surviving fragment of the white dwarf are flung into space at tremendous speeds. The surviving white dwarf shrapnel hurtles towards our region of the galaxy, where its radiation is detected by ground based telescopes. (Copyright Russell Kightley)

 

A supernova burns for only a short period of time, but it can tell scientists a lot about the universe.

One kind of supernova has shown scientists that we live in an expanding universe, one that is growing at an ever increasing rate.

Scientists also have determined that supernovas play a key role in distributing elements throughout the universe. When the star explodes, it shoots elements and debris into space. Many of the elements we find here on Earth are made in the core of stars.

These elements travel on to form new stars, planets and everything else in the universe — making white dwarfs and supernovae essential to the process that ultimately led to life.

 

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

Primordial Asteroids, And The Stories They Are Telling

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The main asteroid belt of our solar system — with almost two million asteroids a kilometer in diameter orbiting in the region between Mars and Jupiter.  There are billions more that are smaller. New research has identified the “family” of a primordial asteroid or planetesimal, one of the oldest ever detected.

Asteroid, we’ve long been told, started tiny in our protoplanetary disk and only very gradually became more massive through a process of accretion.  They collected dust from the gas cloud that surrounded our new star, and then grew larger through collisions with other growing asteroids.

But in recent years, a new school of thought has proposed a different scenario:  that large clumps of dust and pebbles in the disk could experience gravitational collapse, a binding together of concentrated disk material.

This process would produce a large asteroid (which is sometimes called a planetesimal) relatively quickly, without that long process of accretion.  This theory would solve some of the known problems with the gradual accretion method, though it brings some problems of its own.

Now research just published in the journal Science offers some potentially important support to the gravitational collapse model, while also describing the computational detection of a primordial family of asteroids some 4 billion years old.

Led by Marco Delbo’, an astrophysicist at the University of the Côte d’Azur in Nice, France, the scientists have identified a previously unknown family of darkly colored asteroids that is “the oldest known family in the main belt,” their study concluded.

The family was identified and grouped together by the unusual darkness (low albedo) of its asteroids’ reflective powers, a signature that the object has a high concentrations of carbon-based organic compounds.  This family of asteroids was also less extensively heated — having formed when the sun radiated less energy — and contains more water, making them potential goldmines for understanding the makeup and processes of the early solar system.

Artist depiction of a dusty disc surrounding a red dwarf.artist rendering of a protoplanetary dust disk, from which asteroid, planetesimals and ultimately planets are formed. NASA/JPL-Caltech/T. Pyle (SSC)

“They are from an original planetesimal and the location of these fragments tell us they are very, very old,” Delbo’ told me.  “So old that the original object is older than the epoch when our giant planets moved to their current locations.”  That would make this ancient asteroid family more than 4 billion years old, formed when the solar system was but 600 million years from inception.

By adding up the masses of the members of the asteroid family, the researchers could also come up with a size for the original planetesimal that gave birth to the asteroid family — at least 35 kilometers wide at its inception.

Some background:

What is termed our “solar nebula” is thought to have been a disk-shaped cloud of gas and dust that remained after the formation of the sun.  Just like a dancer that spins faster as she pulls in her arms, the cloud began to spin as it collapsed. Eventually, the cloud grew hotter and more dense in the center, with a disk of gas and dust surrounding it that was hot near the center but cool at the edges.

Marco Delbo is a researcher at the Italian Istituto Nazionale di Astrofisica (INAF) at present on leave at the Observatoire de la Côte d’Azur in Nice, France, with an External Fellowship of the European Space Agency (ESA).

Since these earliest days of the solar system, a vast collection of dust and later rocks of all shapes and sizes has been circling the sun, especially in the broad expanse of space between Mars and Jupiter.  This is both the material from which planets were formed, and also leftover material from the formation of the solar system.

There are many of these asteroids, or planetesimals, but they don’t carry much mass — all of them together roughly equaling that of our moon.

There are some 130 known “families” of asteroids.  The effort to understand the processes that created the asteroids has been enormously difficult because they have been broken and then broken again and again as they crash into each other.

But that is changing thanks to this discovery of the new family of “dark” asteroids.  Unlike the brighter, highly reflective asteroid families nearby, the population of dark asteroids’ orbits are more spread out, interpreted to mean that more time has passed since the asteroids formed.

Most asteroid families are thought to have formed about 1 billion years ago. By aggregating the sizes of the modern dark asteroids, researchers suggest their original planetesimals formed about 4 billion years ago, making this one of the oldest asteroid families in the main asteroid belt.

The scientists also determined that the dark family’s original planetesimals were no smaller than about 25 miles across.

This provides support for the gravitational collapse hypothesis, originated at Germany’s Max Planck Institute, by suggesting the oldest asteroids started out large, and then became smaller through collisions and other destructive forces happening in the ancient solar system.

The earlier and more conventional theory had the asteroids starting small and getting gradually bigger. This difference in hypotheses has been a hot topic among planetary scientists for nearly a decade.

This image, taken by NASA’s Near Earth Asteroid Rendezvous mission in 2000, shows a close-up view of Eros, an asteroid with an orbit that takes it somewhat close to Earth.  American and Japanese and European missions to study and scoop up material from asteroids are now on their way. The European Space Agency has also undertaken an asteroid landing mission and a joint NASA-ESA asteroid-ramming mission is under consideration. NASA/JHUAPL

These findings are not based on telescope viewing and measuring;  that was all done by NASA’s  Wide-field Infrared Survey Explorer in 2011.  The spacecraft took images of some 750 million objects, including millions of asteroids. 

Delbo’ and his team used computer models to search for groups of related asteroids spread within a V-shaped region. This V pattern is what one would expect from a single object that fragmented into pieces, and the wider the V-shape the older the objects.

Their asteroid family features rocks averaging 7.15 miles in diameter, and are found across the entire inner part of the main asteroid belt. The family has 108 members  and counting, with the largest of which the largest being asteroid 282 Clorinde, which is about 26 wide.

“Each family member drifts away from the center of the family in a way that depends on its size, with small guys drifting faster and further than the larger guys,” Delbo said.  “If you look for correlations of size and distance, you can see the shapes of old families.”

But that wasn’t all.

“By identifying all the families in the main belt, we can figure out which asteroids have been formed by collisions and which might be some of the original members of the asteroid belt,” said Southwest Research Institute astronomer Kevin Walsh, a coauthor of the Science article.

“We identified all known families and their members and discovered a gigantic void in the main belt, populated by only a handful of asteroids. These relics must be part of the original asteroid belt. That is the real prize, to know what the main belt looked like just after it formed.”

These primordial objects had to have formed differently from those belonging to the newer families. They were the original inhabitants and were present in the inner asteroid belt before anything else.

ranging from 21 to around 93 miles across, their size matches up with predictions from theoretical models of how large original asteroids might have been 4 billion years ago, when they initially formed.

In other words, their age and size supports the gravitational collapse theory of asteroid formation.

An artist’s concept depicts a distant hypothetical solar system, similar in age to our own. Looking inward from the system’s outer fringes, a ring of dusty debris can be seen, and within it, planets circling a star the size of our Sun. This debris is all that remains of the planet-forming disk from which the planets evolved. Planets are formed when dusty material in a large disk surrounding a young star clumps together. (NASA)

To put these findings into a larger context, I asked Elizabeth Tasker, astrophyscist at the Japan Space Agency and the Earth-Life Science Institute in Tokyo, to explain further.  She is the author of the soon-to-be released book, “The Planet Factory,” which deals extensively with these issues.  First is her take on the logic of gravitational collapse:

“In the gravitational collapse model, the pebbles and small boulders around 1m-ish in size concentrate in one region of the protoplanetary disk. This concentration initially happens because nothing is ever perfectly homogeneous, but it grows because having a group of rocks together helps mitigate the gas drag.

Elizabeth Tasker an associate professor in the Department of Solar System Science at ISAS /JAXA (the Japanese space agency.) Her research focuses on exploring galaxy, star and planet formation using numerical simulations.

This grows until eventually its combined mass is enough that their total gravity finally becomes a big enough force to bind them together into a planetesimal. This doesn’t happen until you have a serious chunk of mass, so the result is always a big planetesimal tens to hundred of kilometers across (about the size of Ceres). A smaller group of rocks wouldn’t have enough total mass to produce the gravitational force needed to collapse.”

And now why the Delbo’ paper is important:

“The formation of our own solar system is the key to understanding the properties of exoplanets around other stars. For example, if we truly want to find another habitable world, we need to understand how the Earth acquired and kept its oceans, developed a protective magnetic field and a sizeable moon, while Venus and Mars did not.

“A problem we face is that the early planet-forming action happened 4.6 billion years ago. We can build models, but how do we tell which one is correct when this all happened so long ago?

“Marco Delbo’ and his team have identified a holy grail; an observational signature that can be used to constrain the myriad of formation ideas we are imaginative enough to create.”

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

Gone Exo-Fishing

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I’m taking a little break alongside the Atlantic but can’t leave exoplanets et al completely behind. 

Water worlds are inferred, or known, to be present and perhaps not uncommon in the galaxy.  And there is reason to conclude that they may have much more water than Earth.  Although 70.8% of all Earth’s surface is covered in water, H2O accounts for just some 0.05% of Earth’s mass.

Some animations and illustrations of what these aquaworlds might look like:

Depiction of a world completely covered with ocean.
(NASA Kepler Mission/Dana Berry)

A 2017 study published in The Monthly Notices of the Royal Astronomical Society suggests that Earth is in a minority when it comes to smaller planets, and that many habitable planets may be greater than 90% ocean. There are worlds where more than 10% of the mass may be water. This may be the case, for example, for all the six innermost planets orbiting the star Kepler-11 (David A. Aguilar (CfA)

 

Watery exoplanet with exo-moon. (Phys.org, CBC11, CC By-SA )

 

Exoplanet scientists have been studying whether the potential glint from a planet would tell them that there is water on the surface. This artist’s concept shows Kepler-62f, an exoplanet in the habitable zone of its host star, which is located about 1,200 light-years from Earth in the constellation Lyra. Researchers think Kepler-62f may be a waterworld. (NASA/Ames/JPL-Caltech)

 

Many waterworlds may be ice covered with a global ocean underneath, like Saturn’s moon Enceladus. NASA’s Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015.
(NASA/JPL-Caltech)

 

Artist rendering of TRAPPIST-1f in the seven-exoplanet Trappist-1 system in constellation Aquarius. The color comes from orbiting a red dwarf star. With added fisherman. (NASA)

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

Has America Really Lost It’s “Lead in Space?”

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Vice President Mike Pence addresses NASA employees, Thursday, July 6, 2017, at the Vehicle Assembly Building at NASA’s Kennedy Space Center (KSC) in Cape Canaveral, Florida. The Vice President spoke following a tour that highlighted the public-private partnerships at KSC, as both NASA and commercial companies prepare to launch American astronauts in the years ahead.  Pence spoke at length about human space exploration, but very little about NASA space science. (NASA/Aubrey Gemignani)

I was moved to weigh in after reading Vice President Mike Pence’s comments last week down at the Kennedy Space Center — a speech that seemed to minimize NASA’s performance in recent years (decades?) and to propose a return to a kind of Manifest Destiny way of thinking in space.

The speech did not appear to bode well for space science, which has dominated NASA news with many years of exploration into the history and working of the cosmos and solar system, the still little-understood domain of exoplanets, the search for life beyond Earth.

Instead, the speech was very much about human space exploration, with an emphasis on “boots on the ground,” national security, and setting up colonies.

“We will beat back any disadvantage that our lack of attention has placed and America will once again lead in space,” Pence said.

“We will return our nation to the moon, we will go to Mars, and we will still go further to places that our children’s children can only imagine. We will maintain a constant presence in low-Earth orbit, and we’ll develop policies that will carry human space exploration across our solar system and ultimately into the vast expanses. As the president has said, ‘Space is,’ in his words, ‘the next great American frontier.’ And like the pioneers that came before us, we will settle that frontier with American leadership, American courage and American ingenuity.”  (Transcript here.)

Eugene Cernan of Apollo 17, the last team to land on the moon, almost 45 years ago.  (NASA)

That a new president will have a different kind of vision for NASA than his predecessors is hardly surprising.  NASA may play little or no role in a presidential election, but the agency is a kind of treasure trove of high profile possibilities for any incoming administration.

That the Trump administration wants to emphasize human space exploration is also no surprise.  Other than flying up and back to construct and use the International Space Station, and then out to the Hubble Space Telescope for repairs, American astronauts have not been in space since the last Apollo mission in 1972.  It should be said, however, that no other nation has sent astronauts beyond low Earth orbit, either, since then.

Where I found the speech off-base was to talk down the many extraordinary discoveries in recent decades about our planet, the solar system, the galaxy and beyond made during NASA missions and made possible by cutting-edge NASA technology and innovations.

In fact, many scientists, members of Congress and NASA followers would enthusiastically agree that the last few decades have been an absolute Golden Age in space discovery — all of it done without humans in space (except for those Hubble repairs.)

To argue for a more muscular human space program does not have to come with a diminishing of the enormous space science advances of these more recent years;  missions and discoveries that brought to Americans and the world spectacular images and understandings of Mars, of Jupiter and Saturn and their potentially habitable moons, of Pluto, of hot Jupiters, super-Earths and exoplanet habitable zones, and of deep, deep space and time made more comprehensible because of NASA grand observatories.

To say that the United States has given up its “lead in space,” it seems to me, requires a worrisome dismissal of all this and much more.

Selfie of Curiosity rover on sedimentary rock deposited by water in Gale Crater on Mars. (NASA)

Let’s start on Mars.  For the past 20 years, NASA has had one or more rovers exploring the planet.   In all, the agency has successfully landed seven vehicles on the planet — which is the sum total of human machinery that has ever arrived in operational shape on the surface (unless you count the Soviet Mars 3 capsule which landed in 1971 and sent back information for 14 seconds before going silent.)

One of the two rovers now on Mars — Curiosity — has established once and for all time that Mars was entirely habitable in its early life.  It has drilled into the planet numerous times and has tested the samples for essential-for-life carbon organic compounds (which it found.)  It also has detected clear evidence of long-ago and long-standing lakes and rivers.  And it measured radiation levels at the surface over years to help determine how humans might one day survive there.

I think it’s fair to say that Curiosity has advanced an understanding of the history and current realities of Mars more than any other mission, and perhaps more than all the others combined.

Equally important, the almost two-thousand pound rover was delivered to the surface via a new landing technique called the “sky crane.”  If your goal is to some day land a human on Mars, then learning how to deliver larger and larger payloads is essential because a capsule for astronauts would weigh something like 80,000 pounds.

The European Space Agency, as well as the Russians and Chinese, have tried to send landers to Mars in recent years, but with no success.

And as for Curiosity, it has been exploring Mars now for almost five years — well past its nominal mission lifetime.

This Cassini image of Saturn is the of 21 frames across 7 footprints, filtered in groups of red, green, and blue. The sequence was captured by Cassini over the course of 90-plus minutes on the morning of October 28th. Like many premier images from space, an individual — here Ian Regan — used the public access information and images provided by NASA of all its missions to produce the mosaic. (NASA/JPL-Caltech/Space Science Institute/Ian Regan)

NASA missions to Saturn and Jupiter have sent back images that are startling in their beauty and overflowing in their science.  And they have found unexpected features that could some day lead to a discovery of extraterrestrial life in our solar system.

The most surprising discovery was at Saturn’s moon Enceladus, which turns out to be spewing water vapor into space from its south pole region.  This water contains, among other important compounds, those organic building blocks of life, as well as evidence that the plumes are generated by hydrothermal heating of the ocean under the surface of the moon.

In other words, there is a global ocean on Enceladus and at the bottom of it water and hot rock are in contact and are reacting in a way that, on Earth at least, would provide an environment suitable for life.  And then the moon is spitting out the water to make it quite possible to study that water vapor and whatever might be in it.

If the last decades are a guide, up-close study of these icy moons is a challenge and opportunity that the United States alone — sometimes in collaboration with European partners — has shown the ability and appetite to embrace make happen.

NASA’s Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. (NASA/JPL-Caltech)

The plumes were investigated and even traversed by the Cassini spacecraft, which is a joint NASA-ESA mission.  The primary ESA contribution was the Huygens probe that descended to Titan in 2005.   To people in the space science community, these kind of collaborations — generally with European space agencies — allow for more complex missions and good international relations.

Plumes of water vapor have also been tentatively discovered identified on Jupiter’s moon, Europa.  The data for the discovery came mostly from the Hubble Space Telescope, and is already a part of the previously approved NASA future.  The Europa Clipper is scheduled to launch in the 2020s, to orbit the moon and intensively examine the solar system world believed most likely to contain life.

The plumes would be coming from another large global ocean under a thick shell of ice, a body of water understood to be much older and much bigger than that of Enceladus. Clearly, having some of that H2O available for exploration without going through the thick ice shell would be an enormous obstacle eraser.

A follow-up Europa lander mission has been studied and got favorable reviews from a NASA panel, but was not funded by the Trump Administration.  Several follow-up Enceladus life-detection missions are currently under review.

This very high resolution mosaic image of the Pillars of Creation was taken by the Hubble Space Telescope in 2014 and is a reprise of the iconic image first taken in 1995. The pillars are part of a nebula some 6,500-7000 light-years from Earth, and are immense clouds of gas and dust where stars are born. (NASA)

I think one could make a strong case that the Hubble Space Telescope has been the most transformative, productive and admired piece of space technology ever made.

For more than two decades now it has been the workhorse of the astrophysics, cosmology and exoplanet communities, and has arguably produced more world-class stunning images than Picasso.  In terms of exploring the cosmos and illustrating some of what’s out there, it has no competition.

There is little point to describing its specific accomplishments in terms of discovery because they are so many.  Suffice it to say that a collection of published science papers using Hubble data would be very, very thick.

And because of past NASA, White House and congressional commitment to space science, the over-budget and long behind-schedule James Webb Space Telescope is now on target to launch late next year.  The Webb will potentially be as revelatory as the Hubble, or even more so in terms of understanding the early era of the universe, the nature and origin of ubiquitous dark matter, and the composition of exoplanets.

Preliminary planning for the great observatory for the 2030s is underway now, and nobody knows whether funding for something as ambitious will be available.

The era of directly imaging exoplanets has only just begun, but the science and viewing pleasures to come are appealingly apparent. This evocative movie of four planets more massive than Jupiter orbiting the young star HR 8799 is a composite of sorts, including images taken over seven years at the W.M. Keck observatory in Hawaii. (Jason Wang/University of California, Berkeley and Christian Marois, National Research Council of Canada’s Herzberg Institute of Astrophysics. )

Many of the early exoplanet discoveries were made by astrophysicists at ground-based observatories, and were made by both American, European and Canadian scientists.  NASA’s Spitzer Space Telescope and others played a kind of supporting role for the agency, but that all changed with the launch of NASA’s Kepler Space Telescope.

From 2009 to today, the Kepler has identified more than 4,000 exoplanet candidates with more than 2,400 confirmed planets, many of which are rocky like Earth.  Of roughly 50 near-Earth size habitable zone candidates detected by Kepler, more than 30 have been verified.

The census provided by Kepler, which looked fixedly at only one small part of the deep sky for four years until mechanical, led to the consensus conclusion that the Milky Way alone is home to billions of planets and that many of them are rocky and in the habitable zone of their host stars.

In other words, Kepler made enormous progress in defining the population of exoplanets likely to exist out there — a wild menagerie of objects  very different from what might have been expected, and in systems very different as well.

Two additional NASA observatories designed to detect and study exoplanets are scheduled to launch in the next decade.

A NASA rendering of a possible moon colony, along the lines of the International Space Station. It was proposed in 2006 by President George W. Bush.) NASA

Given the number of references to our moon in Pence’s Kennedy Space Station speech — and the enormous costs of the also often referenced humans-to-Mars idea — my bet is that moon landings and perhaps a “colony” will be the Administration’s human space exploration project of choice.

I say this because it is achievable, with NASA rockets and capsules under construction and the fast-growing capabilities of commercial space competitors.  We have, after all, proven that astronauts can land and survive on the moon, and a return there would be much less expensive than sending a human to Mars and back.  (I’m also skeptical that such a trip to Mars will be technically feasible any time in the foreseeable future, though I know that others strongly disagree.)

As readers of Many Worlds may remember, I’m a fan of a human spaceflight project championed by former astronaut and head of NASA’s Science Directorate John Grunsfeld to assemble a huge observatory in space designed to seriously look for life around distant stars.  This plan is innovative, would give NASA and astronauts an opportunity learn how to live and work in deep space, and would provide another science gem.  It would indeed show American space leadership.

But here is why I think a moon colony is going to be the choice:  Russia, China and the Europeans have all announced tentative plans to build moon colonies in the next decade or two.  So for primarily strategic, competitive and national security reasons, it seems likely that this kind of “new frontier” is what the administration has in mind.

After all, Pence also said in his speech at the KSC that “Under President Donald Trump, American security will be as dominant in the heavens as we are here on Earth.”  (An apparent reference to both NASA and the military space program, which is significantly better funded than NASA.)

Setting up an American moon colony would be very costly in dollars, time and focus, but it’s not necessarily a bad thing.  Given that a pie can be sliced just so many ways, however, it’s pretty clear that a major moon colony project would end up taking a significant amount of funding away from space science missions.

Returning to the moon and even setting up a colony is not, however, an example of American leadership.  Rather, it would constitute a decision for the United States and NASA to, in effect, follow the pack.

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

Certain Big, Charged Molecules Are Universal to Life on Earth. Can They Help Detect It In The Far Solar System?

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This article of mine, slightly tweaked for Many Worlds, first appeared today (July 6)  in Astrobiology Magazine,  www.astrobio.net

NASA’s Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. The spacecraft did not have instruments that could detect life, but missions competing for NASA New Frontiers funding will — raising the thorny question of how life might be detected. (NASA/JPL-Caltech)

As NASA inches closer to launching new missions to the Solar System’s outer moons in search of life, scientists are renewing their focus on developing a set of universal characteristics of life that can be measured.

There is much debate about what might be considered a clear sign of life, in part, because there are so many definitions separating the animate from the inanimate.

NASA’s prospective missions to promising spots on Europa, Enceladus and Titan have their individual approaches to detecting life, but one respected voice in the field says there is a better way that’s far less prone to false positives.

Noted chemist and astrobiologist Steven Benner says life’s signature is not necessarily found in the presence of particular elements and compounds, nor in its effects on the surrounding environment, and is certainly not something visible to the naked eye (or even a sophisticated camera).

Rather, life can be viewed as a structure, a molecular backbone that Benner and his group, Foundation for Applied Molecular Evolution (FfAME), have identified as the common inheritance of all living things. Its central function is to enable what origin-of-life scientists generally see as an essential dynamic in the onset of life and its increased complexity and spread: Darwinian evolution via transfer of information, mutation and the transfer of those mutations.

“What we’re looking for is a universal molecular bio-signature, and it does exist in water,” says Benner. “You want a genetic molecule that can change physical conditions without changing physical properties — like DNA and RNA can do.”

Steven Benner, director of the Foundation for Applied Molecular Evolution or FfAME. (SETI)

Looking for DNA or RNA on an icy moon, or elsewhere would presuppose life like our own — and life that has already done quite a bit of evolving.

A more general approach is to find a linear polymer (a large molecule, or macromolecule, composed of many repeated subunits, of which DNA and RNA are types) with an electrical charge. That, he said, is a structure that is universal to life, and it can be detected.

As described in a recent paper that Benner’s group published in the journal Astrobiology: “the only molecular systems able to support Darwinian information are linear polymers that have a repeating backbone charge. These are called ‘polyelectrolytes.’

“These data suggest that polyelectrolytes will be the genetic molecules in all life, no matter what its origin and no matter what the direction or tempo of its natural history, as long as it lives in water.”

Through years of experimentation, Benner and others have found that electric charges in these crucial polymers, or “backbones,” of life have to repeat. If they are a mixture of positive and negative charges, then the ability to pass on changing information without the structure itself changing is lost.

And as a result, Benner says, detecting these charged, linear and repeating large molecules is potentially quite possible on Europa or Enceladus or wherever water is found. All you have to do is expose those charged and repeating molecular structures to an instrument with the opposite charge and measure the reaction.

Polyelectrolytes are long-chain, molecular semiconductors, whose backbones contain electrons. The structure and composition of the polyelectrolytes confers an ability to transfer electric charge and the energy of electronic excited states over distance. (Azyner Group, UCSC)

James Green, director of NASA’s Planetary Sciences division, sees values in this approach.

“Benner’s polyelectrolyte study is fascinating to me since it provides our scientists another critical discussion point about finding life with some small number of experiments,” he says.

“Finding life is very high bar to cross; it has to metabolize, reproduce, and evolve — all of which I can’t develop an experiment to measure on another planet or moon. If it doesn’t talk or move in front of the camera we are left with developing a very challenging set of instruments that can only measure attributes. So polyelectrolytes are one more to consider.”

Benner has been describing his universal molecular bio-signature to leaders of the groups competing for New Frontiers missions, which fill the gap between smaller Discovery missions and large flagship planetary missions. It’s taken a while but due to his efforts over several years, he notes that interest seems to be growing in incorporating his findings.

Astrobiologist Chris McKay at NASA’s Ames Research Center.  (IDG News Service)

In particular, Chris McKay, a prominent astrobiologist at NASA’s Ames Research Center and a member of one of the New Frontiers Enceladus proposal teams, says he thinks there is merit to Benner’s idea.

“The really interesting aspect of this suggestion is that new technologies are now available for sequencing DNA that can be generalized to read any linear molecule,” McKay writes in an email.

In other words, they can detect any polyelectrolytes.

Other teams are confident that their own kinds of life detection instruments can do the job. Morgan Cable, deputy project scientist of the Enceladus Life Finder proposal, she says her team has great confidence in its four-pronged approach.   A motto of the mission on some of its written material is: “If Encedadus has life, we will find it.”

Morgan Cable, deputy project scientist for the proposed Enceladus Life Finder.

The package includes instruments like mass spectrometers able to detect large molecules associated with life; measurements of energy gradients that allow life to be nourished; detection of isotopic signatures associated with life; and identification of long carbon chains that serve as membranes to house the components of a cell.

“Not one but all four indicators have to point to life to make a potential detection,” Cable says.

NASA is winnowing down 12 proposals by late this year, so, Benner’s ideas could play a role later in the process as well. NASA’s goal is to select its next New Frontiers mission in about two years, with launch in the mid-2020s.

The Europa Clipper orbiter mission is tentatively scheduled to launch in 2022, but its companion lander has been scrubbed for now by the Trump administration.

Nonetheless, NASA put out a call last month for instruments that might one day sample the ice of Europa. Benner is once more hoping that his theory of polyelectrolytes as the key to identifying life in water or ice will be considered and embraced.

These composite images show a suspected plume of material erupting two years apart from the same location on Jupiter’s icy moon Europa. Both plumes, photographed in UV light by Hubble, were seen in silhouette as the moon passed in front of Jupiter.  Europa is a major focus of the search for life beyond Earth. (NASA/ESA/STScI/USGS)
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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.