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Instead of “dark matter,” rogue planets?

May 13, 2012
Courtesy of Springer Science & Business Media
and World Science staff

Weeks af­ter two stud­ies cast doubt on a the­o­ry that a strange “dark mat­ter” ac­counts for vast amounts of ma­te­ri­al in the uni­verse that’s mis­sing, an­oth­er study pro­poses a rad­i­cal new so­lu­tion.

Plan­ets. 

Rogue, free-float­ing, and pos­sibly life-bearing plan­ets could ac­count for much of that “mis­sing mass,” ac­cord­ing to N. Chan­dra Wick­ra­mas­inghe and col­leagues at the Uni­vers­ity of Buck­ing­ham, U.K.

The dark mat­ter the­o­ry that pre­sumably would be pushed aside by their pro­pos­al—should it prove cor­rec­t—was de­vised to ex­plain why about four fifths of the ma­te­ri­al in the cos­mos seems to be mis­sing. This stuff is ap­par­ently de­tect­a­ble through gravita­t­ional ef­fects over huge dis­tances, but is un­seen. 

Through ex­ten­sive cal­cula­t­ions, many as­tro­no­mers have con­clud­ed that the mis­sing ma­te­ri­al should con­sist of enor­mous clouds of some sort of par­t­i­cles, of­ten dubbed cold dark mat­ter. These clouds are sup­posed to en­vel­op and fill ga­lax­ies.

That has been the con­ven­tion­al think­ing in as­tron­o­my, but two stud­ies pub­lished last month raised what their au­thors said were sur­pris­ing and se­ri­ous prob­lems with dark mat­ter the­o­ry. One of the stud­ies found that in our sec­tion of the gal­axy, dark mat­ter is simply no­where to be found, wheth­er through grava­t­ional ef­fects or oth­er­wise.

Wick­ra­mas­inghe, who di­rects the uni­vers­ity’s Buck­ing­ham Cen­tre for As­tro­bi­ol­o­gy, and col­leagues pro­posed their plan­e­tary so­lu­tion to the co­nun­drum on­line May 8 in the re­search jour­nal As­t­ro­phys­ics and Space Sci­ence.

They ar­gue that few hun­dred thou­sand bil­lion free-float­ing, Earth-sized plan­ets may ex­ist in our gal­axy, the Milky Way, and would be among the old­est objects in our uni­verse. What’s more, some of these silent orbs may flit through our so­lar sys­tem or si­m­i­lar ones from time to time, pick­ing up a few stray bits of DNA or liv­ing cells along the way, cre­at­ing new seed­ing sites for life.

Wick­ra­mas­inghe has been a long­time and prom­i­nent pro­po­nent of “pansper­mia,” a the­o­ry pop­u­lar in some cir­cles of as­tro­no­mers hold­ing that life or seeds of it could spread through­out the cos­mos aboard as­ter­oids or through oth­er means. (When in 2008 an In­di­an sci­ent­ist pro­posed that some un­iden­ti­fi­able red cells found in rain could have come from space, many re­search­ers dis­missed his claim, but Wick­ra­mas­inghe leapt to his de­fense.)

While sup­port for pan­sper­mia is un­even among as­tro­no­mers, in­ter­est in search­ing for plan­ets has reached a near fe­ver pitch since 1995, when the first plan­et out­side our so­lar sys­tem was re­ported. All the 750 or so plan­ets re­ported to date or­bit stars, and just a hand­ful have been deemed po­ten­tial can­di­dates for life. 

But the pos­sibil­ity of a much larg­er num­ber of plan­ets was first sug­gested in ear­li­er stud­ies through the ef­fects of “gravita­t­ional lens­ing,” ac­cord­ing to Wick­ra­mas­inghe. This ef­fect oc­curs when an ob­jec­t’s gravita­t­ional field dis­torts im­ages of oth­er ob­jects be­hind it. In this case, the ob­jects in ques­tion are plan­et-sized bod­ies dis­tort­ing the im­ages of dis­tant quasars, enor­mously bright light sources in the very dis­tant uni­verse, Wick­ra­mas­inghe ex­plained. 

Re­cently sev­er­al groups of in­ves­ti­ga­tors have sug­gested that a few bil­lion such ob­jects could ex­ist in the gal­axy. Through new cal­cula­t­ions, Wick­ra­mas­inghe and his team in­creased this grand to­tal to a few hun­dred thou­sand bil­lion, a few thou­sand for every Milky Way star, each world har­bor­ing the leg­a­cy of cos­mic pri­mor­di­al life. Wick­ra­mas­inghe’s group es­ti­mates that a free-float­ing plan­et might vis­it our in­ner So­lar Sytem every 26 mil­lion years. “This pro­cess of­fers a way by which evolved genes from Earth life could be­come dis­persed through the gal­axy,” they wrote.

* * *

Weeks after two studies cast doubt on a theory that a strange “dark matter” accounts for vast amounts of material in the universe that’s missing, another study proposes a radical new solution. Planets. Rogue, free-floating, and possibly life-bearing planets could account for much of that “missing mass,” according to N. Chandra Wickramasinghe and colleagues at the University of Buckingham, U.K. The dark matter theory that presumably would be pushed aside by the new proposal—should it prove correct—was devised to explain why about four fifths of the material in the cosmos seems to be missing. This stuff is apparently detectable through gravitational effects over huge distances, but is unseen. Through extensive calculations, many astronomers have concluded that the missing material should consist of enormous clouds of some sort of particles, often dubbed cold dark matter. These clouds are supposed to envelop and fill galaxies. That has been the conventional thinking in astronomy, but two studies published last month raised what their authors said were surprising and serious problems with dark matter theory. One of the studies found that in our section of the galaxy, dark matter is simply nowhere to be found, whether through gravational effects or otherwise. Wickramasinghe, who directs the university’s Buckingham Centre for Astrobiology, and colleagues proposed their planetary solution to the conundrum online May 8 in the research journal Astrophysics and Space Science. They argue that few hundred thousand billion free-floating, Earth-sized planets may exist in our galaxy, the Milky Way. These life-bearing planets originated in the first few million years of our universe. What’s more, some of these planets may cross through our solar system or similar ones from time to time, picking up a few stray bits of DNA or living cells along the way, creating new seeding sites for life. Wickramasinghe has been a longtime and prominent proponent of “panspermia,” a theory popular in some circles of astronomers holding that life or seeds of it could spread throughout the cosmos aboard asteroids or through other means. (When in 2008 an Indian scientist proposed that some unidentifiable red cells found in rain could have come from space, many researchers dismissed his claim, but Wickramasinghe leapt to his defense.) While support for panspermia is uneven among astronomers, interest in searching for planets has reached a near fever pitch since 1995, when the first planet outside our solar system was reported. The 750 or so detections of exoplanets are all of planets orbiting stars, and very few, if any, have been deemed potential candidates for life. But t possibility of a much larger number of planets was first suggested in earlier studies through the effects of “gravitational lensing,” according to Wickramasinghe. This effect occurs when an object’s gravitational field distorts images of other objects behind it. In this case, the objects in question are planet-sized bodies distorting the images of distant quasars, enormously bright light sources in the very distant universe, Wickramasinghe explained. Recently several groups of investigators have suggested that a few billion such objects could exist in the galaxy. Through new calculations, Wickramasinghe and his team increased this grand total to a few hundred thousand billion, a few thousand for every Milky Way star, each world harboring the legacy of cosmic primordial life. Wickramasinghe’s group estimates that a free-floating planet might visit our inner Solar Sytem every 26 million years. “This process offers a way by which evolved genes from Earth life could become dispersed through the galaxy,” they wrote.