New Trans-Neptunian Object may add to Planet Nine Cluster

Astronomers have announced the discovery of the third most distant object in the solar system, designated 2014 UZ224 (1).  At a distance of 91.6AU, it is pipped to the title of ‘most distant solar system object’ by V774104 at 103AU (2), followed by the binary dwarf planet Eris at 96.2AU(3).  The new scattered disk object lies approximately three times the distance of Pluto away, and may be over 1000km in diameter – potentially putting it into the dwarf planet range.  Its 1140 year orbit is notably eccentric, which is becoming more expected than otherwise with this category of trans-Neptunian object.

The find is a fortunate byproduct of the Dark Energy Survey, which seems to be rather good at picking out these dark, distant solar system objects.  It was first spotted in 2014, with follow-up observations which have firmed up its orbital properties, but clearly delayed the announcement of its existence until now.  These follow-up observations were rather scatty over time, and so the Dark Energy team, led by David Gerdes  of the University of Michigan, developed software to establish its orbital properties: Read More…

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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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Three New Objects Extend Hunt for Planet X

The two scientists, Scott Sheppard and Chad Trujillo, who first recognised the clustering of objects thought to reveal the presence of ‘Planet Nine’ (1), have announced the discovery of three new objects.  All three are highly distant objects (2).  Two of them are extended scattered disk objects beyond the traditional Kuiper Belt, and fit reasonably well into the afore-mentioned cluster.  The third, perhaps even more amazingly, is an object whose elongated orbit reaches way out into the distant Oort Cloud of comets, but which also never comes closer than the planet Neptune.   So, this is the first outer Oort cloud object with a perihelion beyond Neptune, designated 2014 FE72.

Here’s how the announcement of these three new objects has been described in a press release from the Carnegie Institution for Science (3), where Scott Sheppard works:

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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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On Proxima b

August 2016 saw the announcement of the discovery of an Earth-like planet orbiting our nearest neighbourhood star – the red dwarf Proxima Centauri.  The official press release was preceded by a leak to the German media from within the team of astronomers.  Here, I tell the story of the rumours of the announcement, and the wider implications of the discovery itself:

Rumours of an Earth-like Planet Orbiting Proxima Centauri

The German magazine Der Spiegel has reported that a major announcement is imminent:  there is an Earth-like planet orbiting the red dwarf star Proxima Centauri; the Sun’s closest stellar neighbour at 4.24 light years distance.

The magazine claims that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory’s reflecting telescope in Chile, based upon a leak from an astrophysicist who has been working with the La Silla team (1).  This alleged discovery is in keeping with the current work being carried out at La Silla, as described in January earlier this year:

“What good news that the Pale Red Dot project is now planning a two-month observing campaign to search for potential Earth-analogs around Proxima Centauri using HARPS, the High Accuracy Radial velocity Planet Searcher spectrograph at the ESO La Silla 3.6m telescope. Nightly monitoring began on January 18th.” (2)

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Going the Wrong Way Round

A new Trans-Neptunian Object has been discovered whose quirkiness is breaking into new territory.  This object, currently named ‘Niku’ after the Chinese adjective for ‘rebellious’, is seriously off-piste and heading in a highly inclined, retrograde motion around the Sun (1).   Does this sound familiar?   The retrograde motion is something which Zecharia Sitchin claimed for the rogue planet Nibiru.  Niku…Nibiru.  It sounds like the team who discovered this object, based at the Harvard-Smithsonian Center for Astrophysics (2), are having a bit of fun with us.  Rest assured, this is not Nibiru, or anything like it.  That said, something in the past interacted with this object to fling it into its strange orbital path, and at the moment the identity of that strongly perturbing influence is a definitive ‘unknown‘.

Additionally, Niku’s discovery has prompted the astrophysics team to consider a new cluster of objects (high inclination TNOs and Centaurs) which appear to share the same orbital plane.  This, in itself, is an unexpected and exciting development.  Could the influencing factor be the mysterious Planet Nine (3)?

“…The new TNO appears to be part of another group orbiting in a highly inclined plane, so [Matthew] Holman’s team tested to see if their objects could also be attributed to the gravitational pull of Planet Nine.  It turns out Niku is too close to the solar system to be within the suggested world’s sphere of influence, so there must be another explanation. The team also tried to see if an undiscovered dwarf planet, perhaps similar to Pluto, could supply an explanation, but didn’t have any luck. “We don’t know the answer,” says Holman.” (1)

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Does Planet Nine Solve the Riddle of the Sun’s Obliquity?

The sizeable tilt of the proposed Planet Nine body could explain other unexplained features of the solar system as well as the observed clustering of extended scattered disk object beyond the Kuiper Belt.  The Caltech astrophysics team who introduced the world to Planet Nine in January (1) think it may also explain the Sun’s six degree tilt with respect to the plane of the ecliptic (2).  In addition, the presence of a distant, sizeable Planet X object, whose closest approach to the Sun is argued to be 250 Astronomical Units away (3), could be affecting the tilt of the entire planetary system orbiting the Sun.

“Using an analytic model for secular interactions between Planet Nine and the remaining giant planets, here we show that a planet with similar parameters can naturally generate the observed obliquity as well as the specific pole position of the sun’s spin axis, from a nearly aligned initial state. Thus, Planet Nine offers a testable explanation for the otherwise mysterious spin-orbit misalignment of the solar system.” (3)

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New Dwarf Planet Sparks Debate about Planet Nine

The family of extended scattered disk objects beyond the classical Kuiper Belt just keeps getting bigger.  The latest addition to this population of objects is a fairly substantial dwarf planet 700km across, currently referred to by the moniker 2015 RR245 (1).  Its elliptical orbit is not absolutely defined as yet, but the best estimates give it an aphelion distance of about 120 Astronomical Units, and a closest approach to the Sun of about 34 AU (2).  The Minor Planet Center describes the object as the 18th largest in the Kuiper Belt, but it is not yet clear what its surface features might include.  2015 RR245 takes approximately 700 years to orbit the Sun.  2015 RR245was discovered by National Research Council of Canada’s Dr J.J. Kavelaars while studying images taken by Canada–France–Hawaii Telescope in Hawaii in September 2015 .

Does this object fit in with Mike Brown’s analysis of the cluster of 6 (now 7) Sednoid objects which he argues (along with his dynamicist colleague Konstantin Batygin) point to the existence of a substantial planet beyond the Kuiper Belt (3)?  Given the vague data regarding the orbit of 2015 RR245, it is perhaps too early to say.  But other scientists are already citing the on-going discoveries of distant objects like 2015 RR245 as reasons to be cautious.  In an informative on-line article, more nuanced than its title suggests, astrophysicist Ethan Siegel notes that the pattern of discovery of objects within and beyond the Kuiper Belt is subject to an observational bias favouring the closest objects.  This means that the unknown populations of objects yet to be discovered may eventually statistically overwhelm the small populations of extended scattered disk objects and Sednoids already discovered.  This, he argues, could bring Brown and Batygin’s analysis of the cluster into question. 

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Interstellar Planet Formation

Continuing the discussion from last month’s blog about planetessimal-building conditions in space beyond the solar system’s heliopause boundary (1).  In my February paper, I discussed anomalous results which had come back from various space probes regarding the influx of large grain interstellar dust into the heliosphere (2).  More on this in a moment.  A correspondent of mine had noted similarities between what I had been writing about and previous work by Paul LaViolette, who had written about the origins of the dust picked up by the Ulysses spacecraft:

“I would suggest that the dust originates from a circumsolar dust sheath that is concentrated toward the plane of the ecliptic in a fashion similar to the disk girdling the star Beta Pictoris and that is co-moving with the Sun. Infrared observations confirm the existence of dust sheaths around other stars in the solar neighborhood, leading to the conclusion that our Solar System is similarly shrouded.” (3)

The 20 million year old star Beta Pictoris provides astronomers with the best example of a gas giant exoplanet found orbiting within an evolving proto-planetary disk, made all the more dramatic by its side-on view and the brightness of scattered light from the revolving disk:

“In 1984 Beta Pictoris was the very first star discovered to host a bright disc of light-scattering circumstellar dust and debris. Ever since then Beta Pictoris has been an object of intensive scrutiny with Hubble and with ground-based telescopes. Hubble spectroscopic observations in 1991 found evidence for extrasolar comets frequently falling into the star.” (4)

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4Mj Dark Star found in Triple Star System

A young ‘Dark Star’, weighing in at 4 Jupiter masses, is one of only a few such exoplanets to have been directly imaged.  It’s also a rather curious object for another reason:  It’s orbiting the main star of a triple star system some 340 light years away, in a dynamical arrangement which lies on the very edge of mathematical possibility (1).  HD131399ab is just 16 million years old, and could be classified as an ultra cool sub-brown dwarf rather than a Jovian class gas giant.  At this youthful age its temperature is about 600 degrees Celsius, allowing it to be directly imaged in infra-red by SPHERE operated by the European Southern Observatory.

The triple star system is indeed curious.  The two minor stars (B and C) orbit the main star A at a distance of about 300 Astronomical Units, all the time twirling around each other at approximately Saturn’s distance from the Sun.  The newly discovered exoplanet, HD131399ab, also orbits around the main star A in a wide orbit “about twice as large as Pluto’s if compared to our solar system, and brings the planet to about one-third of the separation of the stars [B & C] themselves.” (2).  The massive planet’s orbit around its parent star is by far the widest known orbit within a multi-star system.

This graphic shows the orbit of the planet in the HD 131399 system (red line) and the orbits of the stars (blue lines). The planet orbits the brightest star in the system, HD 131399A.

This graphic shows the orbit of the planet in the HD 131399 system (red line) and the orbits of the stars (blue lines). The planet orbits the brightest star in the system, HD 131399A.  Image Credit ESO

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