A good supply of floating planetsis not a surprise, nor even the numbers indicated which may well be quiteconservative. A star mass acts as a hugesponge for dust and material and also inevitably hooks up with at least one gasgiant that then acts as the driver for inner solar system clean up anddevelopment. Outside the influence ofsuch a star mass, we will have gas giants forming that never ignite becausethey are simply too small. The numbersof such objects should be well in excess of actual stars.
It also implies that actualplanets passing through the solar system on an hyperbolic orbit is completelycreditable and even probable. This is avindication of Velikovsky’s ideas relating to a planetary visitation in therecent past, although he was arguing for a capture. A one time pass through would be swift anddisruptive and we do need to model the impact properly because we need tounderstand just how survivable such an event would be.
I make the followingconjecture. The gas giants or at leastthe outer ones are all captured. Jupitermay well be captured also, but also acts as our guardian of the inner solarsystem. Please recall that Jupiter is atthe edge of dynamic instability and will produce earth sized planets whensufficient material is sponged up. It ispossible that Venus is a recent calving of Jupiter as supported by the present circumstantialevidence. This has been discussed inearlier posts.
The sheer volume of planets isnow plausibly confirmed and we can assume that an order of magnitude of smallerplanets also exist that we cannot spot. Howeveron the path to the nearest star, we are still unlikely to run into a planet. There may only be a couple of gas giantsinside a light year or two of Earth and perhaps ten to twenty smaller planetsinside that same envelop. We will haveto go looking for them
Unbound planets could abound in the universe
May 19, 2011
Ten planets that appear to be drifting in interstellar space have been spottedby an international team of astronomers. The planets are so far from any hoststars that they may not orbit a star at all, and could be drifting unboundthrough space. The team believes that such rogue planets could outnumber normalstars almost 2:1 and their existence could confirm computer simulations ofsolar-system formation.
More than 550 planets have so far been found beyond our solar system.The vast majority of these extrasolar planets – or exoplanets – have revealedthemselves by their gravitational influence on their host star, or by the dipin brightness that they cause as they pass in front of their star. However, aclutch of 12 worlds had previously been found by gravitational micro-lensing.
This technique relies on the object of interest passing directlybetween the observer and a more distant background object. The mass of theforeground object acts like a lens and magnifies the light from the objectbeyond. If the foreground object is a star, then any orbiting planet leaves itsown tell-tale fingerprint in the shape of the magnification. However, due tothe need for an exact alignment, fewer than one in a million stars in thecentral part of the Milky Way are micro-lensed at any given time. This is whythe number of exoplanets detected this way is low.
Sifting through 50 million stars
In an attempt to get around this problem the Microlensing Observationsin Astrophysics (MOA) collaboration observes many stars at once. The new rogueplanets were found in MOA observations of 50 million stars within the Milky Waybetween 2006 and 2007.
"Over all the stars observed we are very confident that wewitnessed 474 definite lensing events," lead-author of the study TakahiroSumi, of Osaka University , Japan
The more fleeting the duration of the event, the less massive thelensing object; a duration of less than two days implies the mass of theforeground object to be much less than that of a star. In fact, Sumi believesthe culprits to be planets roughly the mass of Jupiter. What is more, nostars were observed within 10 astronomical units of the lensing objects – oneastronomical unit is the distance between the Sun and the Earth and Saturnorbits at about 9 astronomical units. "There is a possibility thatthese planets do have a host star. However, direct imaging of exoplanets byother teams suggests that such distant planets are very rare," Sumiexplains. "This led us to conclude that the lensing objects are freelyfloating planets, unbound from any star," he adds.
Because they are short-lived events, and the result of chancealignments, Sumi didn't expect to uncover such a high yield of planet-lensingevents with MOA. From statistical analysis of his data he was able toextrapolate a figure for how common these free-floating planets might be."We found that unbound planets, with roughly the mass of Jupiter, shouldbe 1.8 times more common than the stars we observed," Sumi explains.
Scattered into space
The existence of rogue planets isn't completely unexpected: they havebeen predicted from computer models of solar-system formation. "We thinkthey are formed in the same way as other planets but get scattered from thesystem by gravitational interactions between them," says Sumi. JoachimWambsganss, of the University of Heidelberg, Germany, who was not involved inthe work, says that this research quantifies this process for the first time."We just didn't know how often this happened," he said. "Thisresearch gives us an idea," he adds.
Wambsganss went on to describe the research as using a "clear andsolid method", however he thinks some people may not believe the claims ofthe rogue planets' abundance. "They used a very extensive statisticalanalysis, using several different factors, but others may argue with thenumbers they used," he explains. One way of strengthening the research'sclaims will be to use the next stage of data from the MOA experiments."There are three more years of data for 2008–2010 that they can workthrough in the same way. They should find more of these events and this willprovide an even stronger statistical basis for their claims," he says.
The planets are described in Nature 473 349.
MAY 18, 2011
Free-floating planets may be more common in our Galaxy than stars.
BBCNews - Japanese astronomers claim to have found free-floating "planets"which do not seem to orbit a star. They say they have found 10Jupiter-sized objects which they could not connect to anysolar system.They also believe such objects could be as common as stars are throughout theMilky Way. Using a technique called gravitational microlensing, they detected10 Jupiter-mass planets wandering far from light-giving stars. Then theyestimated the total number of such rogue planets,based on detection efficiency, microlensing-event probability and the relativerate of lensing caused by stars or planets. They concluded that there could beas many as 400 billion of these wandering planets, far outnumberingmain-sequence stars such as our Sun
Nature - Unbound or distant planetary mass population detected bygravitational microlensing
Nature - So many lonely planets with no star to guide them
Scattered about the Milky Way are floating, Jupiter-mass objects, which arelikely to be planets wandering around the Galaxy's core instead oforbiting hoststars.But these planets aren't rare occurrences in the interstellar sea: the driftersmight be nearly twice as numerous as the most common stars.
Planetary scientistDavid Stevenson at the California Institute of Technology in Pasadena
Unbound Earth-mass planets might still be capable of carrying liquid water,Stevenson says, even in the frozen reaches of interstellar space – as long asthey have a heat-trapping hydrogen atmosphere. "That can bring the surfacetemperature up to 300 kelvin [about 27 °C]," he says. "And then youcan have oceans."
Since 1995, more than 500 exoplanets have been detected using differenttechniques of which 12 were detected with gravitational microlensing. Most ofthese are gravitationally bound to their host stars. There is some evidence offree-floating planetary-mass objects in young star-forming regions but theseobjects are limited to massive objects of 3 to 15 Jupiter masses with largeuncertainties in photometric mass estimates and their abundance. Here, wereport the discovery of a population of unbound or distant Jupiter-massobjects, which are almost twice as common as main-sequence stars, based on twoyears of gravitational microlensing survey observations towards the GalacticBulge.
These planetary-mass objects have no host stars that can be detectedwithin about ten astronomical units bygravitational microlensing. However, a comparison with constraints from directimaging suggests that most of these planetary-mass objects are not bound to anyhost star. An abrupt change in the mass function at about one Jupiter massfavours the idea that their formation process is different from that of starsand brown dwarfs. They may have formed in proto-planetary disks andsubsequently scattered into unbound or very distant orbits.
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