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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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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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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Early Solar System Catastrophism

The two moons of Mars have always presented planetary scientists with something of a mystery. These tiny moons, Phobos and Deimos, whizz around Mars at no great height at all: Phobos whips around the red planet in less than 8 hours, at a height of only 3,700 miles – the closest of any moon to its parent planet. I say ‘parent’ advisedly because a new theory of the origin of these peculiar little moons suggests that they emerged from a major impact between mars and a dwarf planet. It has generally been assumed that they were captured asteroids, but the relative circularity of their orbits argued against such a capture. Work on the possibility of a catastrophic origin was carried out last year by two separate teams of researchers, after decades of battling intense scepticism within the scientific community (1). An important finding of the modelling at that time was that the resultant debris would circulate around the red planet at a relatively low altitude, which is in keeping with the orbits of the two extant moons.
More recently, further computer modelling of various impact scenarios carried out by one of those teams has narrowed down the range of masses of an impactor to about the size of Pluto. The resultant debris field was initially far more extensive than the two moons left today:
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Haystack Latest: The Hunt for Planet Nine Goes On…

Academic papers aimed at further constraining the parameters of the purported ‘Planet Nine’ body continue to emerge from various quarters, many from researchers with long-term interests in outer solar system anomalies. Fairly quickly after Brown and Batygin’s announcement about Planet Nine (1), a paper was published by A. Fienga et al examining the astrometry of Saturn through Cassini’s radio ranging data (2). This work served to constrain the possible locations of Planet Nine, which were wide ranging to say the least. This is because if one can establish the very precise positioning of outer planets over time, then this can provide clues to any slight gravitational effect, or perturbation, the planet might be experiencing from an undiscovered distant substantial Planet X body (3). However, given that Planet Nine is thought to have a highly elliptical orbit, then if it is located at the further end of that ellipse, its effect upon the outer planets gravitationally becomes vanishingly small. It turns out then, as one might predict, that we can rule out its current location being in the nearer half of its elliptical path, according to the Cassini data about Saturn. Which is more or less common sense, anyway.
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