The Origin of Ancient Xenon

I’ve often discussed the origin of various elements and compounds on Earth – most notably the isotopic ratio of water, and what that might tell us about the origin of terrestrial water (1).  Data about this can help provide evidence for the Earth’s early history, and often the data is inconsistent with the general theories of oceanic origin, like the ‘late veneer theory’, for instance, where the bulk of terrestrial waters were supposed to have been supplied by comets.  It turns out that the water was on this planet all along (2,3), raising questions about why the Sun’s heat had not driven this relatively volatile resource away from the primordial Earth during the early history of the solar system.

waterworld

Despite such evidence, the ‘late veneer theory’ continues to hold ground for many scientists, and tends to go unchallenged within the science media.  This is apparent within the following excerpt about a new paper on the mysterious presence of a particular isotope of the noble gas xenon found in ancient terrestrial water encased in rock:

“The scientists have been analysing tiny samples of ancient air trapped in water bubbles found in the mineral, quartz, which dates back more than three billion years. The team found that the air in the rocks is partly made up of an extremely rare form of the chemical element, xenon. It is known as U-Xe and what makes it so rare is that it isn’t usually found on Earth. The component is not present in the Earth’s mantle, nor is it found in meteorites.

“Therefore, the team believe that the U-Xe must have been added to the Earth after a primordial atmosphere had developed. Simply put, comets are the best candidates for carrying the U-Xe to the planet. Co-author, Prof Ray Burgess, from Manchester’s School of Earth and Environmental Sciences explains: “The Earth formed too close to the Sun for volatile elements, such as U-Xe, to easily condense and they would have rapidly boiled off the surface and been lost to space.

“”The reason that oceans and an atmosphere exist at all is because volatiles were still being added after the Earth formed. The puzzle is in identifying where the volatiles came from and what objects carried them to the early Earth. The difficulty is that many of the different volatile ingredients that were originally added have been thoroughly mixed together by geological processes during Earth’s long geological history.”” (4)

asteroid_impact

It turns out that xenon, in general, is mostly absent from the Earth’s atmosphere, particularly compared to other noble gases like argon.  No one knows why.  Perhaps the missing xenon is encapsulated within rocks buried deep within the Earth.  Or perhaps, conversely, it has been driven off the Earth because it is not easily captured by rocks like perovskite (5).  Xenon is missing from Mars, too, which may allude to its propensity for loss from a weak atmosphere.

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Red Giants and Planet Formation

This article will explore the potential for life to develop in the outer planetary systems of red giant stars.  It will then discuss the death-throes of red giant stars, and whether the subsequent outward thrust of stellar material might provide another mechanism for free-floating planets in interstellar space.

Exoplanets have already been found orbiting extremely old stars, one some 11 billion years old (1).  This star, named Kepler-444, makes our own Sun, at a mere 4.6 billion years old, seem like an infant in comparison.  The implication of this is that life could readily have got going early on in the history of the universe, long before the birth of our Sun.  Furthermore, if these exoplanets were to benefit from a relatively stable stellar environment during that long timescale, then the chances of life evolving into higher forms are statistically more probable.  Scale this up across trillions of stars, and the possibilities become clear.

Our own Sun has a shorter lifespan than this.  Its main sequence life is expected to last another 5 billion years, by which point it will have burned up all of its hydrogen fuel.  Then it will swell into a red giant star, before collapsing down into a white dwarf.  For Earth, this post-main sequence (post-MS) phase of the Sun’s life will be pretty disastrous.  The Sun’s expansion to a red giant will swallow the Earth up.  However, a less catastrophic outcome might be expected for planets in the outer solar system, beyond, say, Jupiter.  In fact, their climates might significantly improve – for a while, at least.  The habitable zone of the solar system will expand outwards, along with the expanding star.  Saturn’s largest moon Titan, for instance, might benefit greatly from a far milder climate – as long as it can hang onto its balmy atmosphere in the red heat of the dying Sun.

red_dwarf_landscape

The expansion of habitable zones, as late main sequence stars become hydrogen-starved, offers the potential for life to make a new start in previously frigid environments.  The burning question here is how long these outer planets have to get life going before the red giant then withdraws into its cold white shell.  A study published last year by scientists at the Cornell University’s Carl Sagan Institute attempted to answer this question (2), choosing to examine yellow dwarf stars whose sizes range from half that of the Sun, to approximately twice its mass.  They argue that the larger stars along this sequence could well have larger rocky terrestrial planets in their outer planetary systems than our Sun does (at least, insofar as we know it does!)  This is because the density of materials in their initial proto-planetary disks should be that much greater for larger stars (3).  Larger Earth-like planets in outer regions mean more potential for stable atmospheric conditions during the post-MS period under consideration.  In other words, the growing red giant (which is shedding its mass pretty wildly at this point) would not necessarily blast away an outer planet’s atmosphere if that rocky planet had sufficient gravity to hold onto it.

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More Dark Stars than Stars in Milky Way

For some time, astrophysicists have argued over how many Dark Stars there might be in the galaxy, with varying opinions.  (Note that astronomers use several different names for these objects: sub-brown dwarfs, Y Dwarfs, ‘planemos’).  In this short article, I argue that new evidence presented about the stellar populations of open star clusters point towards there being more Dark Stars than stars in our galaxy.

When I use the term ‘Dark Star’ in my book (1) and internet articles, I’m generally referring to gas giant planets/ultra-cool dwarf stars which are several times more massive than Jupiter, up to perhaps ~13 times as massive (at this point, the gas giant begins to burn deuterium and is reclassified as a brown dwarf).  Most examples of these objects (perhaps more than a few million years old) are essentially dark.  By contrast, very young examples light up more brightly, because they still retain some heat from their formation.  It’s a curious quirk of nature that these sub-brown dwarfs are actually smaller in size than Jupiter, despite being heavier.  Because these objects are so small, and so dim, they are extraordinarily difficult to observe.  Some have been found, but they are usually either extremely young (and therefore still burning brightly), or are exoplanets discovered orbiting parent stars (and so detectable through gravitational ‘wobble’ effects, or other means of finding massive exoplanets).

It has been my contention for some time that the populations of these objects are significantly underestimated.  It is recognised generally that these ultra-cool dwarf stars may be free-floating objects in inter-stellar space, often as a result of having been ejected from young star systems as the fledgling planets in those systems jostle for position.  Opinions about their numbers vary greatly among astrophysicists.  There may be twice as many of these objects as stars, according to studies involving gravitational microlensing surveys of the galactic bulge (2).  Other studies conflict with this conclusion, arguing that there may be as few as 1 object of 5-15 MJup size per 20-50 stars in a cluster (3).  This discrepancy is important because the difference is perhaps as high as two orders of magnitude, and this ultimately affects our understanding of how many free-floating Dark Stars we can expect to find out there.

Their mass, lying between that of Jupiter and the deuterium-burning limit at about 13 MJup (4) seems to single Dark Stars out as rather special objects:

“An abrupt change in the mass function at about a Jupiter mass favours the idea that their formation process is different from that of stars and brown dwarfs. They may have formed in proto-planetary disks and subsequently scattered into unbound or very distant orbits.” (2)

Therefore, if the number of free-floating sub-brown dwarfs (also sometimes known as “planemos”) is on the high end of expectation, then it means that there are also likely to be far more of these objects in wide, distant orbits around their parent stars.  This, in turn, increases the likelihood of there being a similar Dark Star object (or more) in our own immediate solar neighbourhood.  Read More…

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Seven Planets Found in Red Dwarf System

NASA made a big announcement this week about new exoplanets found orbiting the dwarf star TRAPPIST-1 some 39 light years away.  I’ve discussed this particular dwarf star system before (1), as it was already known to have three terrestrial planets in attendance orbiting very close to this cool, fairly dim star (2,3).  The dwarf star is approximately one tenth the size of the Sun, and it’s mass places it on the border between a brown dwarf and a red dwarf star.  Unusually for a star this small, TRAPPIST-1 has a high metallicity, which actually exceeds that of the Sun (4).

Now, an international team of astronomers, using the Belgian TRAPPIST telescope in Chile and the Spitzer infra-red space telescope, have released details about a further four terrestrial planets in this mini-star system, three of which (e, f and g) are located within it’s habitable zone, where temperatures favour the presence of liquid water (5):

“Researchers led by Michaël Gillon, of the University of Liège in Belgium, have been studying the infrared light emitted by this miniature star and have detected drops in luminosity characteristic of transits, i.e. the passage of astronomical bodies moving across its face.  As early as 2015, the first three planets (dubbed b, c and d) had been identified.  Tracking the system using TRAPPIST and the space telescope Spitzer, the team was then able to identify four others planets (e, f, g and h) in 2016.  Based on the frequency of these transits and the degree of reduction in luminosity of the star, they have demonstrated that these seven planets are all comparable in size to Earth (to within 15%), and orbit very close to their star.” (6)

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Radio Bursts from Space

I recently reviewed a book about Carl Sagan’s interest in ancient aliens, written by Donald Zygutis (1).  Early on in his illustrious career, Sagan expressed scepticism about seeking E.T. life using radio telescopes, instead advocating a search through historical accounts and myths to determine whether our planet had been visited (2).  He argued that in a standard galaxy there are so many stars/planets etc, that all you’d need to do is point the radio receiver at any given galactic source beyond the Milky Way, and alien radio signals should come screaming out at you.

sagan

They generally don’t, of course, which led Sagan to the early logical conclusion that SETI’s search with radio telescopes was bound to fail.  However, this approach became the only game in town, with serious funding at its disposal, and Sagan fell into line behind it – supporting this doomed search for E.T. radio signals ostensibly from stars within out galactic neighbourhood.

vla_nm

Decades on, and SETI has come up with little of any merit.  The odd interesting blip, sure, but nothing demonstrably repetitive, or intelligent.  Other searches have also come up empty-handed, including an extensive search for highly advanced galactic civilisations using infra-red (3), based upon the theories of the physicist Freeman Dyson.  Looking for an infra-red signature from other galaxies seems like a bit of a stretch to me.  Sagan’s initial premise about radio waves emanating from other distant galaxies is more plausible.  By staring at the tiny amount of our sky that any given distant galaxy occupies, radio telescopes can cover a lot of possible stars in a very small space.  If any of them contain radio-emitting alien species, shouting for attention, then we should pick them up one would have thought.  Read More…

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Life in the Clouds

I’ve spent many years extolling the virtues of life on a cold brown dwarf moon.  Similar to the Galilean moons of Jupiter, a moon orbiting a sub-brown dwarf would be warmed internally by the tidal forces generated by its proximity to such a powerful gravitational force.  Additionally, the sub-brown dwarf itself might provide some local heating, or at least an abundance of charged-particle strewn local magnetic fields to energise the sub-stellar environment.  So, a habitable environment on a moon seems a likely scenario.  If a cold, dark sub-brown dwarf were to be found orbiting the Sun at a great distance, then it neatly provides the grounding for extraterrestrial life on our doorstep (1).

This seems to me to be the simplest scenario for life in a sub-brown dwarf system.  There are complexities – tidally-locked moons (2), lack of light, and so on.  But the basics are there.

lifeinclouds

Another exotic possibility is that the sub-brown dwarf itself might harbour life.  The complex cloud systems in these failed stars can contain layers which are at room temperature, and abundant in water and other chemical goodies which could form the building blocks of life.  A team of astronomers from Edinburgh University have been considering this very point, wondering whether very simple life might be able to get going in the clouds of a cold brown dwarf (3).  This life might arise in two ways – either somehow evolving from scratch in the cloud environment, or originally being seeded into it by an impacting asteroid or comet.  Either way, conditions for life might be good, except for the lack of a solid surface to dwell on:

Floating out by themselves in the Milky Way galaxy are perhaps a billion cold brown dwarfs, objects many times as massive as Jupiter but not big enough to ignite as a star. According to a new study, layers of their upper atmospheres sit at temperatures and pressures resembling those on Earth, and could host microbes that surf on thermal updrafts...Observations of cold brown dwarf atmospheres reveal most of the ingredients Earth life depends on: carbon, hydrogen, nitrogen, and oxygen, though perhaps not phosphorous. (4)

These ideas build upon work done by the late, great Carl Sagan (with his Cornell colleague E. E. Salpeter) on the potential for life in the clouds of the gas giant Jupiter, first considered back in the 1970s (5).  They envisioned giant ‘floaters’ filled with hydrogen bobbing through the Jovian atmosphere, tiny ‘sinkers’ and self-propelled ‘hunters’ which had evolved from the lazy floaters (6).  All very speculative, but presented in Dr Sagan’s inimitably compelling fashion.  Read More…

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Down a Dusty Lane

Picking up on the mystery of how a massive Planet X could form beyond the outer confines of the Sun’s magnetic environment, as per my previous posts on the accretion of dust beyond the heliopause (1,2) and an exploratory scientific paper I published earlier in the year (3).  I’m searching for evidence, or at least some educated guesswork, about whether interstellar medium beyond the heliosphere of stars might be sufficient over time to build up substantial, gaseous planets loosely bound to their parent star systems.  Such planets might, I suggest, accumulate dust clouds and rings around them, undisrupted by the action of the solar wind trapped within the inner magnetic sphere of the solar system.

bd_snowdisk

Even though this kind of accumulation could be gradually taking place over billions of years, creating a meaningful adjustment to the mass of a substantial planet over these kinds of time periods, it doesn’t seem likely that this kind of effect could take place if our current interstellar environment is anything to go by (although the unexpected presence of interstellar ‘fluff’ beyond the heliopause, described by NASA (4), and the intrusion of large grain particles into the outer solar system (5) do offer some evidence of what could be ‘out there’).

Last month, I looked at evidence of massive stars being aided in their development by the dumping of immense quantities of neighbouring nebula material onto them (6).  I wondered whether a similar mechanism might also be happening in interstellar space at the planetary level, based upon globular frameworks of nebula materials (like gigantic molecular clouds, and the like).

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Could Subaru Spot Nibiru?

Almost nine months after the release of their paper about the likely existence of Planet Nine (1), Drs Mike Brown and Konstantin Batygin have secured a sizeable chunk of valuable time on the Subaru telescope, based in Hawaii. If they’re right about where it is, and luck is on their side, then they may detect the elusive planet within weeks. Brown and Batygin think they’ve narrowed it down to roughly 2,000 square degrees of sky near Orion, which will take approximately 20 nights of telescope time to cover with the powerful 8.2-meter optical-infrared Subaru telescope at the summit of Maunakea, Hawaii, which is operated by the National Astronomical Observatory of Japan (2).  Mike Brown is quite gung-ho about it, as can be gleaned from these extracts from a recent interview with the L.A. Times:
“”We are on the telescope at the end of September for six nights. We need about 20 nights on the telescope to survey the region where we think we need to look. It’s pretty close to the constellation Orion…We’re waiting for another couple of weeks before it’s up high enough in the sky that we can start observing it and then we’re going to start systematically sweeping that area until we find it.

“”It makes me think of the solar system differently than I did before. There’s the inner solar system, and now we are some of the only people in the world who consider everything from Neptune interior to be the inner solar system, which seems a little crazy.”” (3)

An Artist's impression of Planet Nine. Image credit: Caltech/R. Hurt (IPAC)

An Artist’s impression of Planet Nine. Image credit: Caltech/R. Hurt (IPAC)

Let’s hope they’re on the money. They have quite a lot to say about some of the correspondence that comes their way from members of what might loosely be termed ‘the Planet X community’.

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Sub-Brown Dwarfs Hiding in Plain Sight

Not so long ago, brown dwarfs (failed stars caught in an awkward in-betweener zone between stars and planets) were hypothetical bodies.  Their low stellar masses allow for only a very short period of light-emission in their early years, after which they cool and darken considerably.

[A] brown dwarf has too little mass to ignite the thermonuclear reactions by which ordinary stars shine.  However, it emits heat released by its slow gravitational contraction and shines with a reddish colour, albeit much less brightly than a star.” (1)

It was recognised early on that if they existed at all, they would be very difficult to spot – and so it proved.  In recent years, the ability to detect these objects has improved considerably, including more effective infra-red sky surveys.  As they have become more common, the frontier of sub-stellar bodies has dropped in mass into the ultra-cool stellar bodies known as sub-brown dwarfs – many of which would equally properly be designated as rogue gas giant planets.  These objects tend to have masses below 13 times that of Jupiter (13Mj) (2).  These objects have always interested me greatly, and very early on in my own research efforts I was advocating the potential importance of sub-brown dwarfs in the hunt for additional planets orbiting our own Sun at great distances (3).  I used the term ‘Dark Star’ to describe these ultra-cool objects; a term suggested by a friend of mine.  Some can be found orbiting stars (usually beyond 50AU) while others are free-floating entities in their own right.

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Complex Brown Dwarf Systems ‘Baffle’ Astronomers

A couple of brown dwarfs have been discovered in a close binary system some 240 light years away, whose two stars circle each other at a distance of about 19AU, similar to that of Uranus around the Sun.   The two new exoplanets orbit close to the primary Sun-like star HD 87646 (1).  These two sub-stellar companions are HD 87646b, which is a minimum 12MJupiter sub-brown dwarf (a ‘hot Jupiter’-type exoplanet) orbiting every 13 days just 0.117AU from the star (2); and  HD 87646c, which is a 57MJupiter brown dwarf circling the star every 673 days (1).  The orbital eccentricity of the brown dwarf is greater than that of the inner sub-brown dwarf, which is in keeping with other observations of brown dwarfs orbiting stars.

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Image Credit: Janella Williams, Penn State University

The international team that discovered this remarkable system is perplexed as to how it might have come about:

“Given the fact that HD 87646 is the first known system to have two massive substellar objects orbiting a star in a close binary and the masses of the two objects are close to the minimum masses for burning deuterium and hydrogen, these peculiarities raise questions about the system’s formation and evolution.

“”The large masses of these two substellar objects suggest that they could be formed as stars with their binary hosts: a large molecular cloud collapsed and fragmented into four pieces; the larger two successfully became stars and formed the HD 87646 binary, and the other smaller ones failed to form stars and became the substellar objects in this system. This scenario might be relevant for the binary stars but seems problematic for the two substellar objects on orbits within one AU because it is unclear whether fragmentation on such a small scale can occur,” the paper reads (1)

“Other hypothesis offered by the scientists is that the two newly discovered giant objects were formed like giant planet in a protoplanetary disk around HD 87646A. However, they added that such massive disks are rare in close binaries, and further investigation is needed to confirm this explanation.” (3)

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