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“Rogue” asteroids may be the norm

Jan. 30, 2014
Courtesy of MIT
and World Science staff

“Rogue” as­ter­oids, which in­hab­it parts of the So­lar Sys­tem far from where they formed, may be much more com­mon than once thought, as­tro­no­mers say.

That’s be­cause long ago, “the gi­ant plan­ets shook up the as­ter­oids like flakes in a snow globe,” said Fran­ces­ca De­Meo of the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass., lead au­thor of a pa­per on the find­ings pub­lished this week in the re­search jour­nal Na­ture.

Sci­en­tists of­ten look to as­ter­oids to get an idea of how the early so­lar sys­tem may have formed. These relics of rock and dust rep­re­sent what to­day’s plan­ets may have been like in their in­fan­cies.

In the 1980s, sci­en­tists assumed as­ter­oids that formed near the sun stayed near the sun; those that formed far­ther out stayed on the out­skirts. But in the last dec­ade, as­tro­no­mers have de­tected as­ter­oids with com­po­si­tions un­ex­pected for their loca­t­ions: Those that looked like they formed in warm­er en­vi­ron­ments were found fur­ther out in the so­lar sys­tem, and vi­ce versa. Sci­en­tists thought of them as “rogue” as­ter­oids.

Now, a new map de­vel­oped by re­search­ers from the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy and the Par­is Ob­serv­a­to­ry charts the size, com­po­si­tion, and loca­t­ion of more than 100,000 as­ter­oids through­out the so­lar sys­tem, and in­di­cates that rogue as­ter­oids are com­mon. Par­tic­u­larly in the so­lar sys­tem’s main as­ter­oid belt—be­tween Mars and Ju­pi­ter—the re­search­ers found a com­po­si­tionally di­verse mix of as­ter­oids.

The map sug­gests that the early so­lar sys­tem may have un­der­gone dra­mat­ic changes be­fore the plan­ets as­sumed their cur­rent align­ment, the as­tro­no­mers said. For in­stance, Ju­pi­ter may have drifted clos­er to the sun, drag­ging with it a host of as­ter­oids that orig­i­nally formed in the colder edges of the so­lar sys­tem, be­fore mov­ing back out to its cur­rent po­si­tion. Ju­pi­ter’s migra­t­ion may have sim­ul­ta­ne­ously knocked around more close-in as­ter­oids, scat­ter­ing them out­ward.

“It’s like Ju­pi­ter bowled a strike through the as­ter­oid belt,” said De­Meo, who did much of the map­ping as a post­doc­tor­al re­searcher at MIT. “Ev­ery­thing that was there moves, so you have this melt­ing pot of ma­te­ri­al com­ing from all over the so­lar sys­tem.”

She added that the pin­balling of as­ter­oids may have had big im­pacts—lit­erally. For in­stance, colder as­ter­oids that formed fur­ther out likely con­tained ice. When they wan­dered clos­er, they may have hit Earth, bring­ing wa­ter. “The sto­ry of what the as­ter­oid belt is tell­ing us al­so re­lates to how Earth de­vel­oped wa­ter, and how it stayed in this Gold­i­locks re­gion of hab­it­abil­ity,” where tem­per­a­tures are suit­a­ble for liq­uid wa­ter, she said.


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“Rogue” asteroids, which inhabit parts of the Solar System far from where they formed, may be much more common than once thought, astronomers say. That’s because long ago, “the giant planets shook up the asteroids like flakes in a snow globe,” said Francesca DeMeo of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of a paper on the findings published this week in the research journal Nature. Scientists often look to asteroids to get an idea of how the early solar system may have formed. These relics of rock and dust represent what today’s planets may have been like in their infancies. In the 1980s, scientists’ view of the solar system’s asteroids was essentially static: Asteroids that formed near the sun stayed near the sun; those that formed farther out stayed on the outskirts. But in the last decade, astronomers have detected asteroids with compositions unexpected for their locations: Those that looked like they formed in warmer environments were found further out in the solar system, and vice versa. Scientists thought of them as “rogue” asteroids. Now, a new map developed by researchers from the Massachusetts Institute of Technology and the Paris Observatory charts the size, composition, and location of more than 100,000 asteroids throughout the solar system, and indicates that rogue asteroids are common. Particularly in the solar system’s main asteroid belt — between Mars and Jupiter — the researchers found a compositionally diverse mix of asteroids. The map suggests that the early solar system may have undergone dramatic changes before the planets assumed their current alignment, the astronomers said. For instance, Jupiter may have drifted closer to the sun, dragging with it a host of asteroids that originally formed in the colder edges of the solar system, before moving back out to its current position. Jupiter’s migration may have simultaneously knocked around more close-in asteroids, scattering them outward. “It’s like Jupiter bowled a strike through the asteroid belt,” said Francesca DeMeo, who did much of the mapping as a postdoctoral researcher at MIT. “Everything that was there moves, so you have this melting pot of material coming from all over the solar system.” DeMeo added that the early pinballing of asteroids around the solar system may have had big impacts—literally. For instance, she said, colder asteroids that formed further out likely contained ice. When they wandered closer, they may have hit Earth, bringing water. “The story of what the asteroid belt is telling us also relates to how Earth developed water, and how it stayed in this Goldilocks region of habitability,” where temperatures are suitable for liquid water, she said.