A known sub-brown dwarf, which had previously been thought to float on its own through interstellar space, has now been allotted a parent star by sharp-eyed astronomers (1). The two are separated by about 7000 Astronomical Units. As a result, the sub-brown dwarf’s ultra-wide orbit around this parent star takes a colossal 900,000 years, making this the widest orbit yet discovered between planet and star. The sub-brown dwarf 2MASS J2126, which lies about 104 light years away, is thought to be about fifteen Jupiter masses, and is relatively young at somewhere between 10 and 45 million years old (2).
At this kind of age, an object of this size is still burning up some nuclear fuel, and gives out its own light. Ultra-cool dwarfs like 2MASS J2126 eventually ‘go out’, becoming much darker planets – more like a smaller, smouldering equivalent of Jupiter. These older objects are what I call Dark Stars, and they become extremely difficult to spot. Certainly, at 7000 AU distance, it would reflect back only the tiniest amount of light from its parent star. So, given how these objects emit their own light for only a tiny fraction of their full lifetimes (and they would easily outlive our constantly-burning Sun), then we can extrapolate from this chance finding that there are potentially a huge number of Dark Stars in wide orbits awaiting discovery around stars.
Astronomers remain puzzled by how such an orbit might have come about, and how it might be sustainable:
“”Compared to beta Pictoris b [one of the first exoplanets to be directly imaged], 2MASS J2126 is more than 700 times further away from its host star,” says Simon Murphy of the Australian National University. “But how such a wide planetary system forms and survives remains an open question.”” (3)
This has always been an argument set out against a Nemesis/Tyche/massive Planet X object in our own solar system, as such a concept does not fit well with currently understood models of solar system formation. But as more evidence comes forward that these types of exoplanets are actually common, as I believe them to be, then the old models of planetary system formation will simply need updating.
27th January 2016
1) N. Deacon et al “A nearby young M dwarf with a wide, possibly planetary-mass companion” Mon. Not. R. Astron. Soc. 000, 1–18 (2013)http://www.ras.org.uk/images/stories/press/Exoplanets/young_planet_paper.v2.pdf
2) David Szondy “Planet with 900,000-year orbit lies a staggering 1 trillion kilometers from its sun” 25th January 2016 http://www.gizmag.com/planet-one-trillion-kilometer-orbit/41488/ with thanks to Mark
3) Astronomy Now “A lonely planet and its distant star” 26th January 2016 https://astronomynow.com/2016/01/26/a-lonely-planet-and-its-distant-star/