planemos

[alokmohan]

Anew type of objescts discoveredMini planetary systems may orbit cosmic objects that are 100 times smaller than our Sun, research suggests. <br />Discs of gas and dust, the ingredients needed to create such systems, have been seen circling these relatively small objects, dubbed "planemos". <br /><br />If the discs were capable of evolving larger aggregations of material, it would blur the definition of the word "planet", scientists said. <br /><br />The work was presented at the American Astronomical Society meeting in Canada. <br /><br />Cosmic newborns <br /><br />The study is based on observations from European Southern Observatory (ESO) telescopes. It looked at a number of recently identified planemos (an unofficial term sometimes used to describe planetary mass objects). <br /><br />Located about 450 light-years away in a star-forming region, four of the objects are just a few million years old, making them cosmic "newborns". They have masses between five and 15 times that of Jupiter. <br /><br />But unlike Jupiter, these objects are floating through space without an accompanying star. <br /><br />Infrared emission reveals the planemos are circled by dusty discs, which scientists believe could evolve into planets, comets and asteroids over time, in much the same way our own Solar System's planets are believed to have formed billions of years ago. <br /><br />"Now that we know of these planetary mass objects with their own little infant planetary systems, the definition of the word 'planet' has blurred even more," said astronomer Ray Jayawardhana, from the University of Toronto, Canada, and lead author of the study. <br /><br />"In a way, the new discoveries are not too surprising - after all, Jupiter must have been born with its own disc, out of which its bigger moons formed." <br /><br />Beyond imagination <br /><br />In separate study, researchers revealed that a companion body to a young brown dwarf (a failed star), designated 2M1207 and located 170 light-years away, was also surr

 

[doubletruncation]

This is quite a neat result that the sub-brown-dwarf free-floating objects have disks! I don't particularly care for the term "planemo" however <img src="/images/icons/smile.gif" /> - too many terms and too much emphasis on supposed "debates" about how to slice up a distribution into categories. It seems likely that they are the small-size tail of the distribution of objects that form like stars do, so I think calling them brown-dwarfs works just fine. <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

But they have no star around which they revolve.IN FACT THEIR DISC MAY MAKE PLANETS IN FUTURE.There is no paralell.They are like brown dwarfs.Who knows if brown dwarfs have planets.

 

[qso1]

doubletruncation:<br />I don't particularly care for the term "planemo".<br /><br />Me:<br />I think I'd have called them "Planimoids"! <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[doubletruncation]

<font color="yellow">Who knows if brown dwarfs have planets.</font><br /><br />I don't see why they wouldn't - brown dwarfs have been found with debris disks as well. (see for example http://arxiv.org/abs/astro-ph/0511807 ). I really think they are a lot like small brown dwarfs, primarily because they don't orbit a star. I don't think the fact that they have debris disks is particularly surprising if they form the way stars do. (Also note that jupiter itself probably had a debris disk from whence formed Ganymede, Calisto, Europa and Io). The only reason they would not be called brown dwarfs is because they're not big enough to sustain deuterium fusion. But is that really an important distinction? I'm not so sure - the difference would be that the brown dwarfs would take a little longer to cool off at first. Is that a big enough difference to warrant a completely different term like "planemo" (or planimoid <img src="/images/icons/smile.gif" />)? <br /><br />(Whoops - I just realized that the above link is for a "planet-mass" brown dwarf disk. They have been found though around regular brown dwarfs as well - <br />http://www.ifa.hawaii.edu/~mliu/Research/bd_disks/bd_disks.html<br />and theoretical calculations suggest that planets can form in these disks http://www.sciencemag.org/cgi/content/short/310/5749/834 ). <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

What is a Brown Dwarf <br /><br />When we look up into the sky at night and see the stars it is not obvious at first glance which of the points of light we see are stars and which are planets. It is only after close examination with various instruments such as telescopes and spectroscopes that we can see that there are some bodies which shine by reflected light (planets), and some bodies which shine by their own light (stars). What is it that underlies this difference between stars and planets? A star forms when a cloud of gas contracts under its gravitational attraction, heating up as it does so. Eventually the temperature rises sufficiently for nuclear fusion to take place in the centre, this generates energy, and thus it can start shining under its own power. A planet forms by a different process: The small particles of dust, which are left over after the formation of the star, collide and sometimes stick together forming larger clumps. These clumps in turn collide to form larger clumps, the process continuing until most of the dust is used up. The result is a relatively cold body which is not sufficiently hot or heavy to produce its own light. <br /><br />So where do Brown Dwarfs come into the picture? If, for some reason, insufficient gas is available to form a star, then the body will not be able to increase its mass and temperature sufficiently to be able to sustain hydrogen fusion. The resulting object is what is meant by a Brown dwarf: <br /><br />Unfortunately this makes it difficult to recognise an Brown Dwarf simply by looking at it - we need to know its history as well - how did it form? However, by the time we find a candidate Brown Dwarf it is too late to see how it formed, so we need some other method of distinguishing a Brown Dwarf from a large planet. What would such a "failed star" be like? <br /><br />At the moment there seems to be no clear cut way of determining if an object is a large planet or a small Brown Dwarf. Some people have suggested a mass li