JPL: A Cold, Close Neighbor

[geckzilla]

Cold and Close Celestial Orb (Artist's Concept)
Image credit:
NASA/JPL-Caltech/Penn State University

NASA's Spitzer, WISE Find Sun's Close, Cold Neighbor
NASA's Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescope have discovered what appears to be the coldest "brown dwarf" known -- a dim, star-like body that surprisingly is as frosty as Earth's North Pole.

Images from the space telescopes also pinpointed the object's distance to 7.2 light-years away, earning it the title for fourth closest system to our sun. The closest system, a trio of stars, is Alpha Centauri, at about 4 light-years away.

It's colder than Antarctica. Not really what I think of when I think about stars, but ok.
Read more!

[BDanielMayfield]

Thanks for bringing this new discovery to our attention geckzilla. This certainly sheds light on my interest in how many planets exist, even though this object is referred to as both a “brown dwarf” and a “star-like body” in that article.

Technically I don’t think either expression fits real well. As we know stars shine by sustained nuclear fusion of normal Hydrogen into Helium etc., while the term brown dwarf should, in what I think is an opinion held by many astronomers, be limited to sub-stellar massed objects that can only achieve brief fusion of Deuterium and sometimes Lithium as well. 13 Jupiters is the lower mass cut-off for any fusion to occur at all.

Compare what’s said in the JPL news report with what Wikipedia says:

WISE J085510.83-071442.5 is estimated to be 3 to 10 times the mass of Jupiter. With such a low mass, it could be a gas giant similar to Jupiter that was ejected from its star system. But scientists estimate it is probably a brown dwarf rather than a planet since brown dwarfs are known to be fairly common. If so, it is one of the least massive brown dwarfs known.

Brown dwarfs are substellar objects too low in mass to sustain hydrogen-1 fusion reactions in their cores, unlike main-sequence stars, which can. They occupy the mass range between the heaviest gas giants and the lightest stars, with an upper limit around 75 to 80 Jupiter masses (MJ). Brown dwarfs heavier than about 13 MJ are thought to fuse deuterium and those above ~65 MJ, fuse lithium as well.
…
Currently, the International Astronomical Union considers an object with a mass above the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) to be a brown dwarf, whereas an object under that mass (and orbiting a star or stellar remnant) is considered a planet.

The 13 Jupiter-mass cutoff is a rule of thumb rather than something of precise physical significance. Larger objects will burn most of their deuterium and smaller ones will burn only a little, and the 13 Jupiter mass value is somewhere in between. The amount of deuterium burnt also depends to some extent on the composition of the object, specifically on the amount of helium and deuterium present and on the fraction of heavier elements, which determines the atmospheric opacity and thus the radiative cooling rate.

The Extrasolar Planets Encyclopaedia includes objects up to 25 Jupiter masses, and the Exoplanet Data Explorer up to 24 Jupiter masses.
A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object formed in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but that has a mass below the limiting mass for thermonuclear fusion of deuterium (about 13 Jupiter masses). Some researchers call them free floating planets while others call them planetary-mass brown dwarfs.

Sub-brown dwarfs are formed in the manner of stars, through the collapse of a gas cloud (perhaps with the help of photo-erosion) but there is no consensus amongst astronomers on whether the formation process should be taken into account when classifying an object as a planet. Free-floating sub-brown dwarfs can be observationally indistinguishable from rogue planets that originally formed around a star and were ejected from orbit, and on the other hand a sub-brown dwarf formed free-floating in a star cluster may get captured into orbit around a star. A definition for the term "sub-brown dwarf" was put forward by the IAU Working Group on Extra-Solar Planets (WGESP), which defined it as a free-floating body found in young star clusters below the lower mass cut-off of brown dwarfs.

In my totally unimportant opinion this object is a rouge planet, and I would count it as such, no matter how it formed. And to me the discovery of the first nearby rouge planet is bigger news than the discovery of just another "common" brown dwarf.

Bruce

[geckzilla]

There goes that rogue rouge planet again...

I've looked at enough astronomical objects by now to know that strict categorization of an intermediate object will always fail in some regard by creating an argument that may never be resolved. Personally I am content at simply calling it a brown dwarf and assigning it all stellar and planetary characteristics it has without trying to push it in one direction or another, especially since there are potentially unknowable but important details about such an object.

[Ann]

BDanielMayfield wrote:
In my totally unimportant opinion this object is a rouge planet, and I would count it as such, no matter how it formed.

Geckzilla wrote:
Personally I am content at simply calling it a brown dwarf and assigning it all stellar and planetary characteristics it has without trying to push it in one direction or another

Thank you for your informed opinion, geckzilla. Bruce's opinion may be less well informed, but it is humbly and respectfully stated. I find both of your opinions interesting, and since I don't know anything about this cold substellar body, I'll think of it as a probable brown dwarf that just might, who knows, be a rogue planet. Please note that this is just my personal, amateur hypothesis.

Ann

[geckzilla]

I wouldn't say that my opinion is especially informed on the matter of brown dwarfs but I have definitely noticed that there are an awful lot of things that don't fit rigidly into one category or another. Whether it's Pluto, planetary nebulas, or brown dwarfs, there will always be an argument to be made about taxonomy. Most recently, I have discovered there are some extended star clusters around Andromeda which aren't quite globular clusters and aren't quite dwarf ellipsoidal galaxies.

[BDanielMayfield]

There goes that rogue rouge planet again...

Sorry for this and for all the other misspellings I've committed too.

I've looked at enough astronomical objects by now to know that strict categorization of an intermediate object will always fail in some regard by creating an argument that may never be resolved. Personally I am content at simply calling it a brown dwarf and assigning it all stellar and planetary characteristics it has without trying to push it in one direction or another, especially since there are potentially unknowable but important details about such an object."

True, many things span continuums that make classification hard. Contentment is a blessed thing, so I won't push the issue.

[bystander]

First Evidence for Water Ice Clouds Found outside Solar System
Carnegie Institution for Science | 2014 Sep 09

Click to play embedded YouTube video.

A team of scientists led by Carnegie's Jacqueline Faherty has discovered the first evidence of water ice clouds on an object outside of our own Solar System. Water ice clouds exist on our own gas giant planets--Jupiter, Saturn, Uranus, and Neptune--but have not been seen outside of the planets orbiting our Sun until now. Their findings are published today by The Astrophysical Journal Letters and are available here.

At the Las Campanas Observatory in Chile, Faherty, along with a team including Carnegie's Andrew Monson, used the FourStar near infrared camera to detect the coldest brown dwarf ever characterized. Their findings are the result of 151 images taken over three nights and combined. The object, named WISE J085510.83-071442.5, or W0855, was first seen by NASA's Wide-Field Infrared Explorer mission and published earlier this year. But it was not known if it could be detected by Earth-based facilities.

"This was a battle at the telescope to get the detection," said Faherty. ...

Indications of Water Clouds in the Coldest Known Brown Dwarf - Jacqueline K. Faherty et al

• Astrophysical Journal Letters 793(1) L16 (2014 Sep 20) DOI: 10.1088/2041-8205/793/1/L16
  arXiv.org > astro-ph > arXiv:1408.4671 > 20 Aug 2014 (v1), 04 Sep 2014 (v2)

[BDanielMayfield]

Ok, so to many this object is a brown dwarf, but it sure seems like a planet though, doesn't it? It's planetary in every way an object can be planetary except for one: it doesn't currently orbit a star. SInce its mass is well under 13 Jupiters there's no way that fusion ever occurred in its core, therefore it is not very stellar either.

I still wonder why this object doesn't get more fanfare. This is an historic discovery: the first confirmed rogue planet, now known to harbor water ice clouds. Very cool.

Bruce

[rstevenson]

I find that illustration of the object at the end of the video to be highly unlikely, at least through human eyes. I suspect the brown dwarf/rogue planet would look a lot more like this, and only after our eyes had dark adapted...

Rob

[BDanielMayfield]

That's right Rob, it would have to be very dim, out there in the cold darkness of interstellar space. Deep inside it however it must have a hot core, kept warm not by fusion but by fission, the slow release of energy of radioactive elements. After all the heat from gravitational contraction/compression has radiated away radioactive decay would be the only power source left to drive surface weather.

[Nitpicker]

That's right Rob, it would have to be very dim, out there in the cold darkness of interstellar space. Deep inside it however it must have a hot core, kept warm not by fusion but by fission, the slow release of energy of radioactive elements. After all the heat from gravitational contraction/compression has radiated away radioactive decay would be the only power source left to drive surface weather.

Pretty sure it is not fission. You'd need to start with heavy elements like uranium, to get fission.

[Ann]

That's right Rob, it would have to be very dim, out there in the cold darkness of interstellar space. Deep inside it however it must have a hot core, kept warm not by fusion but by fission, the slow release of energy of radioactive elements. After all the heat from gravitational contraction/compression has radiated away radioactive decay would be the only power source left to drive surface weather.

Pretty sure it is not fission. You'd need to start with heavy elements like uranium, to get fission.

Quite so, Nitpicker. But maybe, if this is indeed a rogue planet, it may in fact contain elements like uranium.

Ann

[Nitpicker]

That's right Rob, it would have to be very dim, out there in the cold darkness of interstellar space. Deep inside it however it must have a hot core, kept warm not by fusion but by fission, the slow release of energy of radioactive elements. After all the heat from gravitational contraction/compression has radiated away radioactive decay would be the only power source left to drive surface weather.

Pretty sure it is not fission. You'd need to start with heavy elements like uranium, to get fission.

Quite so, Nitpicker. But maybe, if this is indeed a rogue planet, it may in fact contain elements like uranium.

Ann

Okay, but put it this way ... Earth has a certain small mass of uranium, relative to the total mass of Earth. Yet I've never heard anyone suggest with any credibility, that the vast bulk of heat in the Earth's core is/was caused by fission.

[Ann]

Nitpicker wrote:
Earth has a certain small mass of uranium, relative to the total mass of Earth. Yet I've never heard anyone suggest with any credibility, that the vast bulk of heat in the Earth's core is/was caused by fission.

So how can it be that the Earth has remained warm enough for water to be liquid even when the Sun was young and probably released about 20% less energy than today? Of course, a lot of the Earth's inner heat was excess heat from its formation. Still, I find this fact - of the Earth's continued liquid water-friendly temperatures, over billions of years, fascinating.

But if that brown dwarf/rogue planet/whatever is old, then nuclear fission should be totally inadequate to heat it significantly.

Ann

[Nitpicker]

I must admit my opinion on this matter is based purely on what I know about fission. I know very little about the Earth's core (or any other cosmological core). So I did a little Googling, which is always fraught, and found a few random bits and pieces about fission in the Earth's core providing a significant and/or replenishing component of the heat in the Earth's core. Yet I can find nothing too mainstream to back this up, so I'm now wondering if this is a common topic in the realm of pseudoscience. I just don't know.

[Nitpicker]

Whoops. My turn to retract. This article:
http://en.wikipedia.org/wiki/Geothermal_gradient
... would seem to suggest I am quite wrong about the heat sources within the Earth. However, I am less sure that the radioactive decay within the crust and mantle, generating all this heat, is classified as fission. Still, I've learnt something.

[BDanielMayfield]

I must admit my opinion on this matter is based purely on what I know about fission. I know very little about the Earth's core (or any other cosmological core). So I did a little Googling, which is always fraught, and found a few random bits and pieces about fission in the Earth's core providing a significant and/or replenishing component of the heat in the Earth's core. Yet I can find nothing too mainstream to back this up, so I'm now wondering if this is a common topic in the realm of pseudoscience. I just don't know.

There’s nothing pseudoscientific about radioactive decay heating the interiors of Earth and other planets at all Nitpicker. Notice what Wikipedia has to say in its article on “Earth” under the sub-topic “Heat”:

Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).[72] The major heat-producing isotopes in Earth are potassium-40, uranium-238, uranium-235, and thorium-232.[73] At the center, the temperature may be up to 6,000 °C (10,830 °F),[74] and the pressure could reach 360 GPa.[75] Because much of the heat is provided by radioactive decay, scientists believe that early in Earth's history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. This extra heat production, twice present-day at approximately 3 byr,[72] would have increased temperature gradients within Earth, increasing the rates of mantle convection and plate tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today.[76]

The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42 × 1013 W.[78] A portion of the core's thermal energy is transported toward the crust by mantle plumes; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.[79] More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs in the oceans because the crust there is much thinner than that of the continents.[80]

So today after 4.5 billion years of cooling off the heat welling up from the Earth’s interior is mainly from nuclear fission. If this is the case here, wouldn’t it be reasonable to expect this in exoplanets too? (Otherwise you'd have a violation of the Copernican Principle.) Gas giants aren’t made of nothing but gas. They are expected to have rocky cores, and these cores would contain heavy elements, some of which are radioactive and therefore would be a heat source.

Bruce

[BDanielMayfield]

Whoops. My turn to retract. This article:
http://en.wikipedia.org/wiki/Geothermal_gradient
... would seem to suggest I am quite wrong about the heat sources within the Earth. However, I am less sure that the radioactive decay within the crust and mantle, generating all this heat, is classified as fission. Still, I've learnt something.

I was preparing my last comment while you were making yours. The radioactive decay occurs all the way from the Earth's center to the surface, and it is fission when one element splits losing one or more protons, as Uranium does through many steps on its way to becoming stable Lead.

[Nitpicker]

I don't think it is normally considered fission, when only small nucleons are emitted. Fission is the term used when the nucleus is split into "two or more smaller nuclei and other particles". Not that that excuses my being wrong, but the word "fission" certainly appears to have sent me off track!