Is That the Foundation of NASA I Feel Shifting?

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A lunar outpost was an element of the George W. Bush era Vision for Space Exploration, which has been replaced with President Barack Obama’s space policy. The outpost would have been an inhabited facility on the surface of the Moon. At the time it was proposed, NASA was to construct the outpost over the five years between 2019 and 2024. Now the man nominated to be the next NASA administrator, James Bridenstine, is a strong and vocal advocate of building a moon colony.  (NASA)

Reading about some of the views coming from the man recently nominated to become NASA’s Administrator, Rep. James Bridenstine of Oklahoma, I heard the sound of a door closing.

Other doors will surely be opened if he is confirmed by the Senate, but that shutting door happens to be to the gateway to a realm that has engrossed and nurtured me and clearly many millions of Americans.

What is happening, I fear, is that our Golden Age of space science, of exploration for the sake of expanding humanity’s knowledge and wonder, is about to wind down.  The James Webb Space Telescope will (probably) still be launched, and missions to Europa and Mars are on the books.  But to be a Golden Age there must be an on-going vision for the future building on what has been accomplished.

When it comes to space science, that clearly takes strong government support and taxpayer money.  And if what I’m reading is correct, a lot of that future NASA funding for exploring and understanding the grand questions of space science will be going instead to setting up and maintaining that colony on the moon.

And the goals Bridenstine appears to have in mind when he speaks of setting up a moon colony are decidedly military, strategic and commercial.  As when Vice President Mike Pence spoke to NASA workers at the Kennedy Space Center to telegraph the Trump Administration’s space vision, space science is essentially an afterthought.

Media coverage of the Bridenstine selection has tended to focus on the fact that he’s a politician and that he has earlier been quite critical of climate change science.

But what concerns me most are his views about space science in general.  Because with the money and focus a major moon colony project would take, NASA’s space science initiatives run the risk of returning to the back seat they occupied in the agency’s earlier days.

Rep. Jim Bridenstine, R-Okla., addresses the Space Symposium in Colorado Springs in 2016. (Tom Kimmell)

A former jet pilot, director of the Tulsa Air and Space Museum and an early supporter of then candidate Donald Trump, Bridenstine has been clear for a long time about his priorities in space.  I think we have to assume they correspond to the views of those in the White House.

In a speech last year to the Lunar Exploration Group titled This is Our Sputnik Moment,”  he pointed to what he described as a major missed opportunity the mid 1990s “discovery” of water at the poles of the moon by a Defense Department mission.  (It was actually a Navy-NASA mission that first made the detection, and it hinted at the presence of water rather than proving anything. The proof came later via missions by NASA, the Japanese space agency, the Chinese space agency and perhaps most important, the Indian space agency.)

Here are excerpts from the talk he gave, which I am quoting at length to to give a better feel for his mindset and for the kind of change he is proposing.  These are points consistent with talks he has given many times before and are memorialized in his proposed American Space Renaissance Act.   American space activities, he makes clear, should focus first and foremost on cis-lunar space, the area between the moon and Earth.

“This single discovery” of frozen water on the moon, he said, “should have immediately transformed America’s space program. Water ice not only represents a critical in situ resource for life support (air and water); it can be cracked into its components, hydrogen and oxygen, to create the same chemical propellant that powered the Space Shuttle.

“From the discovery of water ice on the moon until this day, the American objective should have been a permanent outpost of rovers and machines at the poles with occasional manned missions for science and maintenance. The purpose of such an outpost should have been to utilize the materials and energy of the moon to drive down the costs and increase the capabilities of cis-lunar space. Let’s talk about why.

“The watershed discovery of lunar ice happened at a time when space was transforming all of our lives, ” he continued. “Today, our very way of life depends on space. We have transformed how we communicate, navigate, produce food and energy, conduct banking, predict weather, perform disaster relieve, provide security, and so much more.

“Each of these market segments continues to grow and improve the human condition on Earth, but a 2013 study by the Inter-Agency Space Debris Coordination Committee determined that the debris population in low earth orbit will continue to grow due to collisions even if nothing new is launched. Catastrophic collisions such as Iridium 33-Cosmos 2251 [which took place in 2009] will occur every five to nine years. Each such collision will create thousands of pieces of debris and result in more collisions.”

With so many satellites and much debris in low-earth orbit, Bridenstine said, it has become increasingly hazardous to send up multi-million and billion-dollar satellites.  One way to limit the congestion, he said, is to make satellites fly higher and live longer, and that means getting them additional fuel to stay on course.  The way to do that, he argues, is to gear up that envisioned water-cracking facility on the moon to produce the hydrogen to refuel satellites.   A potentially reasonable series of points.

Spent space satellites and debris, including that from a Chinese missile fired in 2007 that broke up one of the nation’s older weather satellites, are making low-Earth orbiting more hazardous.  Can hydrogen fuel from cracked water ice on the moon help break the logjam by servicing satellites further from Earth and allowing them to orbit for longer periods of time?  (NASA)

Then comes what would be a real game-changer:

“This is only possible because of all the risk that the government has already retired for these capabilities. Now, the U.S. government should play a part in developing the tools for lunar energy resource development, cis-lunar satellite servicing, and maintenance. The U.S. government must work to retire risk, make the operations routine, and once again empower commercial companies.

In other words, the U.S. government and presumably NASA should do the heavy lifting to create (and fund) this architecture so that commercial companies — among others — can profit from it.

This investment, he said, “has already worked to an extent in low Earth orbit, and now we should apply this model to cis-lunar space. This is not only appropriate for economic development and to improve the human condition on Earth, but to provide for national security, which is now entirely dependent on space-based capabilities. Every domain of warfare today depends on space.

“Once the cis-lunar market develops to service and maintain our traditional space-based military and commercial capabilities, other opportunities will naturally follow. The surface of the moon is composed mainly of oxides of metals: iron, magnesium, aluminum, silicon, titanium and others.

Raw platinum

“While these oxides can be used to produce oxygen for life support and metals for additive manufacturing in situ, they will not likely be exported to earth. However, it is possible, if not likely, that highly valuable platinum group metals are much more available on the moon from astroblemes than they are on earth.

“Such a discovery with cis-lunar transportation capabilities would fundamentally transform American commercial lunar development and could profoundly alter the economic and geopolitical balance of power on Earth. This could explain the Chinese interest in the moon. The question is: What are WE, the United States, doing to make sure the free world participates economically in such a discovery? The U.S. government has a role to play here.

“Competition for locations on the moon (the poles) and resources is inevitable. It must be stated that constitutionally, the U.S. government is required to provide for the common defense. This includes defending American military assets in space AND commercial assets in space, many of which have and will have a dual role of providing commercial and military capabilities. President Kennedy said, ‘Whatever men shall undertake, free men must fully share.’

“The U.S. government must establish a legal framework and be prepared to defend private and corporate rights and obligations all within keeping the Outer Space Treaty. And to enable freedom of action, the United States must have cis-lunar situational awareness, a cis-lunar presence, and eventually must be able to enforce the law through cis-lunar power projection. Cis-lunar development will either take the form of American values with the rule of law, or it will take the form of totalitarian state control. The United States can decide who leads.”

This image of the moon’s north polar region was taken by the Lunar Reconnaissance Orbiter Camera, or LROC. One of the primary scientific objectives of LROC is to identify regions of permanent shadow and near-permanent illumination. Since the start of the mission, LROC has acquired thousands of Wide Angle Camera images approaching the north pole. From these images, scientists produced this mosaic, which is composed of 983 images taken over a one month period during northern summer. This mosaic shows the pole when it is best illuminated, regions that are in shadow are candidates for permanent shadow, and possibly H2O. (NASA/GSFC/Arizona State University)

So this is where a moon colony leads us as viewed by a proponent: to a day when satellites and spacecraft can be fueled with lunar hydrogen while in space, but also with potential turf wars on the moon over the source of that precious hydrogen fuel.  To an expansion of American might and power to meet the perceived need to dominate space between Earth and the moon. And to a desire to exploit the moon for platinum and potentially other riches.

The only references I’ve seen from Bridenstine about space science are that a moon colony could be a good refueling and take-off point for travel to deeper space, and the belief that while sending humans to Mars should be a long-range vision, it isn’t going to happen anytime soon.  In fairness, it must be said that Bridenstine has pretty consistently voted in favor of NASA space science projects in the past,  and he has not shown hostility towards planetary or orbiting observatory missions.  But that was before there was a costly moon colony infrastructure to potentially build.

In some ways a NASA U-turn like this was almost inevitable.  The agency that made its historic mark with the Apollo program has been, with limited exceptions, out of the humans-to-space business for years.  Rockets and capsules to change this are on their way, and many possible uses for this very powerful and very costly equipment has been debated for some time.

All the while,  in the place of human exploration of space has been the phenomenal success of the space science program — with its grand observatories like the Hubble (and soon the James Webb Space Telescope), unmanned mission such as Cassini (to Saturn) and Juno (to Jupiter) and New Horizons  (to Pluto,) ground-breaking surveys of the exoplanet world by Kepler, and the now five years of Curiosity roving on Mars.

All have been immensely popular with the public by any measure, and I like to think they helped people understand much better the world in which we live.  But the missions are clearly less appealing to commercial, military and generally strategic forces that seem to want a very different kind of American space program.

Our overall national space effort has always spent more on the military side than the civilian, and NASA has also obviously played a role that is both geopolitically and militarily important.

But at its heart, NASA has for some time been about exploring and better understanding the planets and exoplanets and stars and galaxies of our universe (those Many Worlds,) and thereby enriching, enormously, I believe, life here on Earth.

The cis-lunar vision of Bridenstine and others may fail to get off the drawing boards, rather like the Obama Administration’s plan to capture and pull an asteroid towards Earth where astronauts could learn how to live and work in deep space.

But change is in the air, and the selection of Bridenstine is a pretty clear sign of how and where the winds are blowing.

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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.

Cassini Inside the Rings of Saturn

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Movie produced from images taken while Cassini flew inside the rings of Saturn – a first. (NASA/JPL-Caltech/Space Science Institute)

The triumphant Cassini mission to Saturn will be coming to an end on September 15, when the spacecraft dives into the planet.  Running out of fuel, NASA chose to end the mission that way rather than run the risk of having the vehicle wander and ultimately land on Europa or Enceladus, potentially contaminating two moons very high on the list of possible habitable locales in our solar system.

Both the science and the images coming back from this descent are (and will be) pioneering, as they bring to an end one of the most successful and revelatory missions in NASA history.

As NASA promised, the 22-dive descent has already produced some of the most compelling images of Saturn and its rings.  Most especially, Cassini has delivered the remarkable 21-image video above.  The images were taken over a four minutes period on August 20 using a wide-angle camera.

The spacecraft captured the images from within the gap between the planet and its rings, looking outward as the spacecraft made one of its final dives through the ring-planet gap as part of the finale.

The entirety of the main rings can be seen here, but due to the low viewing angle, the rings appear extremely foreshortened. The perspective shifts from the sunlit side of the rings to the unlit side, where sunlight filters through.

On the sunlit side, the grayish C ring looks larger in the foreground because it is closer; beyond it is the bright B ring and slightly less-bright A ring, with the Cassini Division between them. The F ring is also fairly easy to make out.

 

NASA’s Cassini spacecraft will make 22 orbits of Saturn during its Grand Finale, exploring a totally new region between the planet and its rings. NASA/JPL-Caltech

While the Cassini team has to keep clear of the rings, the spacecraft is expected to get close enough to most likely answer one of the most long-debated questions about Saturn: how old are those grand features, unique in our solar system?

One school of thought says they date from the earliest formation of the planet, some 4.6 billion years ago. In other words, they’ve been there as long as the planet has been there.

But another school says they are a potentially much newer addition. They could potentially be the result of the break-up of a moon (of which Saturn has 53-plus) or a comet, or perhaps of several moons at different times. In this scenario, Saturn may have been ring-less for eons.

As Curt Niebur, lead program scientist at NASA headquarters for the Cassini mission, explained it, the key to dating the rings is a close view of, essentially, how dirty they are. Because small meteorites and dust are a ubiquitous feature of space, the rings would have significantly more mass if they have been there 4.6 billion years. But if they are determined to be relatively clean, then the age is likely younger, and perhaps much younger.

“Space is a very dirty place, with dust and micro-meteorites hitting everything. Over significant time scales this stuff coats things. So if the rings the rings are old, we should find very dirty ice. If there is little covering of the ice, then the rings must be young. We may well be coming to the end of a great debate.”

 

Cassini gazes across the icy rings of Saturn toward the icy moon Tethys, whose night side is illuminated by Saturnshine, or sunlight reflected by the planet. Tethys was on the far side of Saturn with respect to Cassini here; an observer looking upward from the moon’s surface toward Cassini would see Saturn’s illuminated disk filling the sky. Tethys was brightened by a factor of two in this image to increase its visibility. A sliver of the moon’s sunlit northern hemisphere is seen at top. A bright wedge of Saturn’s sunlit side is seen at lower left. (NASA/JPL-Caltech/Space Science Institute)

A corollary of the question of the age of Saturn’s rings is, naturally, how stable they are.

If they turn out to be as old as the planet, then they are certainly very stable.  But if they are not old then it is entirely plausible that they could be a passing phenomenon and will some day disappear — to perhaps re-appear after another moon is shattered or comet arrives.

Another way of looking at the rings is that they may well have been formed at different times.

As project scientist Linda Spilker explained in an email, Cassini’s measurements of the mass of the rings will be key.  “More massive rings could be as old as Saturn itself while less massive rings must be young.  Perhaps a moon or comet got too close and was torn apart by Saturn’s gravity.”

The voyage between the rings will also potentially provide some new insights into the workings of the disks present at the formation of all solar systems.

“The rings can teach us about the physics of disks, which are huge rings floating majestically and with synchronicity  around the new sun,” Niebur said.  “That said, the rings of Saturn have a very active regime, with particles and meteorites and micrometeorites smacking into each other.  It’s an amazing environment and has direct relevance to the nebular model of planetary formation.”

The view above was acquired at a distance of approximately 750,000 miles (1.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 140 degrees. . The distance to Tethys was about 930,000 miles (1.5 million kilometers).

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA and the imaging operations center is based at the Space Science Institute in Boulder, Colorado.

 

Polar region of Saturn, with tumultuous cloud pattern. A bizarre six-sided feature encircling the north pole of Saturn was identified earlier using the visual and infrared mapping spectrometer on NASA’s Cassini spacecraft.(NASA/JPL-Caltech/Space Science Institute)

Among the areas of greatest interest during the final descent are the turbulent clouds on the North Pole of Saturn.  Cassini captured this view of the pole on April 26, 2017 – the day it began its grand finale — as it approached the planet for its first dive through the gap between the planet and its rings.

Although the pole is still bathed in sunlight at present, northern summer solstice on Saturn occurred on May 24, 2017, bringing the maximum solar illumination to the north polar region. Now the Sun begins its slow descent in the northern sky, which eventually will plunge the north pole into Earth-years of darkness. Cassini’s long mission at Saturn enabled the spacecraft to see the Sun rise over the north, revealing that region in great detail for the first time.

This view looks toward the sunlit side of the rings from about 44 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

Saturn boasts some unique features in its atmosphere. When the Voyager missions traveled to the planet in the early 1980s, it imaged a hexagon-shaped cloud formation near the north pole.

Twenty-five years later, infrared images taken by Cassini revealed the storm was still spinning, powered by jet streams that push it to speeds of about 220 mph (100 meters per second). At 15,000 miles (25,000 km) across, the long-lasting storm could easily contain an Earth or two.

The recent view was obtained at a distance of approximately 166,000 miles (267,000 kilometers) from Saturn.

But because Saturn is a gas giant and has no defined surface per se, it’s difficult to describe exactly how far from the planet Cassini might be traveling at any given time.

On the final orbit, Cassini will plunge into Saturn’s atmosphere, sending back new and unique science to the very end. After losing contact with Earth, the spacecraft will burn up like a meteor, becoming part of the planet itself.

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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.

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.