Jupiter’s Internal Powerhouse and Ultracool Dwarfs

Jupiter, the solar system’s largest planet, is turning out to be as majestic as its ancient name implies.  High definition images taken of its poles, transmitted back to Earth by the space probe Juno, show a vibrant, churning cloudscape which appear to have been artistically generated in oils (1).  The gnarly appearance of the storms and tempests which are woven into this mind-blowingly immense vista seem peaceful enough from space, but the ferocity of their winds can only be imagined.  Although the colours have been enhanced to a certain extent artificially (2), Juno’s imaging equipment has captured the incredibly beautiful blue colours of the polar zones and the immense set of storms swirling within.

(Image credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt/Seán Doran)

These dramatic regions contrast strongly with the generally dull series of beige bands wrapping around the more familiar equatorial region (although Juno has also allowed us to better appreciate the intricate patterns of these banded zones, too) .  These blues are more reminiscent of the ice giants Neptune and Uranus, and perhaps even of Earth – although the constituent gases of the atmospheres of these worlds can differ significantly from Jupiter’s.  which give the clouds.  The different colours and properties of Jupiter’s clouds can be attributed to their constituent gases – mostly hydrogen and helium, but also water, ammonia, methane and sulphur.

It seems to me that the solar system is starting to come to life – not in the way of biological life, although that may yet come to be, but instead in terms of our appreciation of its rich complexity and visuality.  The Pioneer and Voyager space probes provided what were incredible images of the outer solar system planets back in their day.  But limitations in the image-capturing technology also created a sense in those images of dull uniformity.

In the decades before the space-probe images had been sent back from the outer solar system, sci-fi writers, film-makers and scientists had created an amazing array of ideas about what these worlds might be like.  This potential had become ingrained within the public collective consciousness, and to some extent helped drive NASA’s ambitious space programme forward.  This was enhanced by a sense of mystery – and a hope of alien life.  However, the images returning to our television screens in the latter part of the 20th century clearly did not do these worlds justice.  So, although obtaining the planetary images were astonishing achievements in themselves, the disappointing lack of features within them dashed many hopes, and provided the public with a new view of the outer solar system.  Like lifeless Mars and overheated Venus, the outer solar system consisted of a rather mundane set of giant planets distinctly lacking in the vibrant complexity of our own Earth.  Read More…

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Planet Nine and the Nice Model

It looks like it’ll be another long, lonely autumn for Dr Mike Brown on the summit of the Hawaiian dormant volcano Mauna Kea, searching for Planet Nine.  He made use of the 8m Subaru telescope last year, and it looks like he’s back again this year for a second role of the dice (unless he does all this by remote control from Pasadena?).  I can only assume, given the time of the year, that the constellation of Orion remains high on their list of haystacks to search.

A recent article neatly sums up the current state of play with the hunt for Planet Nine (1), bringing together the various anomalies which, together, seem to indicate the presence of an undetected super-Earth some twenty times further away than Pluto (or thereabouts).  Given how much, I’ve written about this materials already, it seems unnecessary to go over the same ground.  I can only hope that this time, Dr Brown and his erstwhile colleague, Dr Batygin, strike lucky.  They have their sceptical detractors, but the case they make for Planet Nine still seems pretty solid, even if the gloss has come off it a bit recently with the additional OSSOS extended scattered disk object discoveries (2).  But there’s nothing on Dr Brown’s Twitterfeed to indicate what his plans are regarding a renewed search for Planet Nine.

Even if the Planet Nine article’s discussion about a new hunt for the celestial needle in the haystack is misplaced, it does make a valid point that super-Earths, if indeed that is what this version of Planet X turns out to be, are common enough as exo-planets, and weirdly absent in  our own planetary backyard.  So a discovery of such an object way beyond Neptune would satisfy the statisticians, as well as get the bubbly flowing at Caltech.  Dr Brown did seem to think that this ‘season’ would be the one.  We await with bated breath…

Meanwhile, the theoretical work around Planet Nine continues, with a new paper written by Konstantin Batygin and Alessandro Morbidelli (3) which sets out the underlying theory to support the result of the 2016 computer simulations which support the existence of Planet Nine (4).  Dr Morbidelli is an Italian astrophysicist, working in the south of France, who is a proponent of the Nice model for solar system evolution (named after the rather wonderful French city where he works).  This model arises from a comparison between our solar system’s dynamics, and those of the many other planetary systems now known to us, many of which seem bizarre and chaotic in comparison to our own.  Thus, the Nice model seeks to blend the kinds of dynamical fluctuations which might occur during the evolution of a star’s planetary system with both the outcomes witnessed in our own solar system, and the more extreme exoplanets observed elsewhere (5).  It invokes significant changes in the positions of the major planets during the history of the solar system, for instance.  These migrations have knock on effects which then drive other disturbances in the status quo of the early solar system, leading to the variations witnessed both here and elsewhere.  For instance, Dr Morbidelli lists one of the several factors which brought about the Nice model:
Read More…

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Planet Nine: Are They Digging in the Wrong Place?

Last month, scientists working on the Outer Solar System Origins Survey (OSSOS) published a large dataset of new Kuiper Belt Objects, including several new extended scattered disk objects discovered way beyond the main belt (1).  These four new distant objects seemed to have a more random set of properties, when compared to the rather more neat array of objects which had previously been constituted the Planet Nine cluster.  This led to scepticism among the OSSOS scientific team that there was any real evidence for Planet Nine.  Instead, they argued, the perceived patterns of these distant objects might be a function of observational bias (2).

Whilst reporting on these new discoveries and their potential implications, I predicted that the debate was about to hot up, bringing forth a new series of Planet X-related articles and papers (3).  Indeed, leading outer solar system scientists were publishing related materials in quick succession (4,5), each finding new correlations and patterns which might indicate the presence of an unseen perturbing influence.

planetnineaw

Now, Caltech’s Konstantin Batygin has published an article analysing the impact of the discovery of these new extended scattered disk objects on the potential for a Planet Nine body.  The short conclusion he draws is that although the objects are, on the face of it, randomly distributed, their property set is largely consistent with Caltech’s original thesis (6).  They are either anti-aligned to the purported Planet Nine body (as the original cluster is thought to be), or aligned with it in a meta-stable array.

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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)

Read More…

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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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Recent updates on the Search for Planet Nine

It’s a year since proposed the existence of Planet Nine (1).  Despite the fact that its discovery remains elusive, there have been a great many academic papers written on the subject, and no shortage of serious researchers underpinning the theoretical concepts supporting its existence.  Many have sought evidence in the solar system which indirectly points to the perturbing influence of this mysterious world; others have provided data which have helped to constrain the parameters of its orbit (by effectively demonstrating where it could NOT be).  Throughout 2016, I have been highlighting these developments on the Dark Star Blog.

RedPlanetX_1

At the close of 2016, two further papers were published about Planet Nine.  The first of these delves more deeply into the possibility that Planet Nine (Brown’s new name for Planet X, which seems to have caught on among astronomers keen to distance this serious search from, well, the mythological planet Nibiru) has a resonance relationship with some of the objects beyond the Edgeworth-Kuiper Belt which it is perturbing.  These kinds of resonance relationships are not unusual in planetary orbital dynamics, so such a suggestion is not that odd, even given the eccentricities of the bodies involved here.  The new research, from the University of California, Santa Cruz, bolsters the case for this kind of pattern applying to Planet Nine’s orbit:

“We extend these investigations by exploring the suggestion of Malhotra et al. (2016) (2) that Planet Nine is in small integer ratio mean-motion resonances (MMRs) with several of the most distant KBOs. We show that the observed KBO semi-major axes present a set of commensurabilities with an unseen planet at ~654 AU (P~16,725 yr) that has a greater than 98% chance of stemming from a sequence of MMRs rather than from a random distribution.” (3)

Their randomised ‘Monte Carlo’ calculations provide a best fit with a planet of between 6 and 12 Earth masses, whose eccentric orbit is inclined to the ecliptic by about 30 degrees.  They are unable to point to a specific area of the sky to search, but provide a broad-brush region which they favour as most probable.  Dr Millholland has also helpfully provided a 3D manipulable 3D figure of the cluster of extended scattered disk objects allegedly affected by the purported Planet Nine, alongside their extrapolated orbit for it (4).  Read More…

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The Galactic Core Spits out Dark Stars

A new theory about planet formation has posited that stars, placed under inordinate stress, could break apart catastrophically, flinging their smouldering remains out into the void at tumultuous speeds.  It would take quite a force to render stars apart in this way.  The supermassive black hole which lies at the centre of the galaxy creates just such an impression.  Wayward stars drifting inexorably into the depths of its immense gravitational well would not fare well, during what are termed Tidal Disruption Events (1,2).

tidal_disruption

Researchers from Harvard University (namely, undergraduate Eden Girma and James Guillochon, an Einstein fellow at the Harvard-Smithsonian Center for Astrophysics), have conducted computer simulations to model what happens to this streaming material, and the results are quite extraordinary:

Every few thousand years, an unlucky star wanders too close to the black hole at the center of the Milky Way. The black hole’s powerful gravity rips the star apart, sending a long streamer of gas whipping outward. That would seem to be the end of the story, but it’s not.  New research shows that not only can the gas gather itself into planet-size objects, but those objects then are flung throughout the galaxy in a game of cosmic “spitball.”” (3)

Read More…

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Cryovolcanoes on Ceres 

It’s been a little while since the Dawn probe imaged those mysterious ‘lights’ in the craters of the dwarf planet Ceres (1).  On first impression, these seem to be impact marks where brighter materials lying below the surface were exposed following meteoritic bombardment.  But they are uncommonly bright for an asteroid, so speculation about the nature of the materials involved has been rife in the planetary science community, and what it could mean for how the dwarf planet formed in the first place (2).  The bright spots, now widely thought to be salt deposits, have recently even been given names:

“The two most famous bright spots on Ceres have been given names. These once-mysterious spots are now thought by most scientists to be salt deposits. They’re now called Cerealia Facula (for the brighter of the two spots) and Vinalia Faculae (for the cluster of less reflective spots to the east). Both names are related to ancient Roman festivals.” (3)

ceres_lights

But that’s not the only mystery on Ceres.  There is a growing consensus that there may be geophysical processes going on that are relatively recent (at least in terms of geological time periods): Read More…

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