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New space map reveals “mystery ribbon”

Oct. 15, 2009
Courtesy NASA
and World Science staff

A NASA space­craft has helped sci­en­tists build the first full map of our so­lar sys­tem show­ing its po­si­tion with re­spect to the gal­ax­y—and has al­so turned up a mys­tery, as­tro­nom­ers say.

What researchers de­scribe as a “rib­bon” of highly en­er­get­ic par­t­i­cles at the bound­a­ry of our so­lar sys­tem is caus­ing the puzzle­ment.

An an­i­ma­tion (click to play) show­ing the strip of en­er­get­ic par­t­i­cles. It por­trays how the sky is "flattened" to cre­ate the IBEX maps. (Cred­it: NA­SA/­God­dard SFC)

The map was pro­duced with da­ta from two de­tec­tors on NASA’s In­ter­stel­lar Bound­a­ry Ex­plor­er, or IBEX, space­craft, launched a year ago.

The in­stru­ments meas­ure and count par­t­i­cles known as en­er­get­ic neu­tral atoms. These arise from an ar­ea called the in­ter­stel­lar bound­a­ry. This zone, un­de­tect­a­ble by nor­mal tele­scopes, is where elec­tric­ally charged par­t­i­cles flow­ing from the sun, called the so­lar wind, pass far be­yond the plan­ets and plow in­to the gas and dust of the larg­er gal­axy. 

Af­ter be­ing formed, the en­er­get­ic neu­tral atoms trav­el to­ward the sun at speeds up to 2.4 mil­lion miles (3.9 mil­lion km) per hour or more. 

The new map re­veals the re­gion that sep­a­rates the near­est reaches of our gal­axy, called the lo­cal in­ter­stel­lar me­di­um, from our he­lio­sphere—a pro­tec­tive bub­ble that shields and pro­tects our so­lar sys­tem from most of the dan­ger­ous cos­mic radia­t­ion trav­eling through space. 

“We’re stick­ing our heads out of the sun’s at­mos­phere and be­gin­ning to really un­der­stand our place in the gal­axy,” said Da­vid J. Mc­Co­mas, IBEX prin­ci­pal in­ves­ti­ga­tor and as­sis­tant vi­ce pres­ident of the Space Sci­ence and En­gi­neer­ing Di­vi­sion at South­west Re­search In­sti­tute in San An­to­nio, Tex­as. 

This an­i­ma­tion (click to play) zooms in from a view of the Milky Way Gal­axy to our he­lio­sphere. It sets the scale for our home in the gal­axy. (Cred­it: NA­SA/­God­dard SFC)

One re­sult in par­tic­u­lar was “truly re­mark­able,” he added: “a nar­row rib­bon of bright de­tails or emis­sions not re­sem­bling any of the cur­rent the­o­ret­i­cal mod­els of this re­gion.” 

“We ex­pected to see small, grad­u­al spa­tial varia­t­ions at the in­ter­stel­lar bound­a­ry,” Mc­Co­mas told physicsworld.­com, a web­site of the London-based In­sti­tute of Phys­ics. Sci­en­tists think the find­ing does­n’t fit with the ac­cept­ed mod­el of the he­lio­sphere, thought to be shaped like a com­et by the col­li­sion of the out­go­ing so­lar wind and a great­er “galac­tic wind.”

NASA re­leased the sky map im­age Oct. 15 in con­junc­tion with pub­lica­t­ion of the find­ings in the re­search jour­nal Sci­ence. The IBEX da­ta were com­ple­ment­ed and ex­tend­ed by in­forma­t­ion col­lect­ed us­ing an im­ag­ing in­stru­ment sen­sor on NASA’s Cas­si­ni space­craft.

The sky maps are al­so meant to put ob­serva­t­ions from NASA’s Voy­ag­er space­craft in­to con­text. 

The twin Voy­ag­er crafts, launched in 1977, trav­eled to the out­er so­lar sys­tem to ex­plore Ju­pi­ter, Sat­urn, Ura­nus and Nep­tune. In 2007, Voy­ag­er 2 fol­lowed Voy­ag­er 1 in­to the in­ter­stel­lar bound­a­ry. Both are now in this re­gion where the en­er­get­ic neu­tral atoms orig­i­nate. But the Voy­ag­ers did­n’t de­tect the rib­bon of bright emis­sions. “It’s like hav­ing two weath­er sta­t­ions that miss the big storm that runs be­tween them,” said Er­ic Chris­tian, IBEX dep­u­ty mis­sion sci­ent­ist at NASA’s God­dard Space Flight Cen­ter in Green­belt, Md., which man­ages the craft.

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A NASA spacecraft has helped scientists build the first full map of our solar system showing its position with respect to the galaxy—but it has also turned up a mystery, scientists say. What astronomers describe as a “ribbon” of highly energetic particles at the boundary of our solar system is causing confusion among researchers. The map was produced with data from two detectors on NASA’s Interstellar Boundary Explorer, or IBEX, spacecraft, launched a year ago. The instruments measure and count particles known as energetic neutral atoms. These arise from an area called the interstellar boundary region. This zone, undetectable by normal telescopes, is where electrically charged particles flowing from the sun, called the solar wind, pass far beyond the planets and plow into the gas and dust of the larger galaxy. After being formed, the energetic neutral atoms travel inward toward the sun at speeds up to 2.4 million miles (3.9 million km) per hour or more. The new map reveals the region that separates the nearest reaches of our galaxy, called the local interstellar medium, from our heliosphere—a protective bubble that shields and protects our solar system from most of the dangerous cosmic radiation traveling through space. “We’re sticking our heads out of the sun’s atmosphere and beginning to really understand our place in the galaxy,” said David J. McComas, IBEX principal investigator and assistant vice president of the Space Science and Engineering Division at Southwest Research Institute in San Antonio, Texas. One result in particular was “truly remarkable,” he added: “a narrow ribbon of bright details or emissions not resembling any of the current theoretical models of this region.” “We expected to see small, gradual spatial variations at the interstellar boundary,” McComas told physicsworld.com, a website of the London-based Institute of Physics. Scientists think the finding doesn’t fit with the accepted model of the heliosphere, thought to be shaped like a comet by the collision of the outgoing solar wind and a greater “galactic wind.” NASA released the sky map image Oct. 15 in conjunction with publication of the findings in the research journal Science. The IBEX data were complemented and extended by information collected using an imaging instrument sensor on NASA’s Cassini spacecraft. The sky maps are also meant to put observations from NASA’s Voyager spacecraft into context. The twin Voyager crafts, launched in 1977, traveled to the outer solar system to explore Jupiter, Saturn, Uranus and Neptune. In 2007, Voyager 2 followed Voyager 1 into the interstellar boundary. Both are now in this region where the energetic neutral atoms originate. But the Voyagers didn’t detect the ribbon of bright emissions. “It’s like having two weather stations that miss the big storm that runs between them,” said Eric Christian, the IBEX deputy mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., which manages the craft.