"Long before it's in the papers"
August 11, 2015


“Fireworks” begin on comet under spacecraft’s watch

Aug. 11, 2015
Courtesy of ESA
and World Science staff

A com­et un­der a space­craft’s close watch is start­ing to give off “fire­works” as its path takes it near the Sun, ac­cord­ing to Eu­ro­pe­an Space Agen­cy sci­ent­ists in charge of the miss­ion.

The sci­en­tists said the craft, Ro­set­ta, has wit­nessed grow­ing ac­ti­vity from Com­et 67P/Chu­ryu­mov–Ge­rasi­men­ko. One out­burst prov­ed so strong, they said, that it even pushed away the in­com­ing so­lar wind, a rapid stream of elec­tric­ally charged part­icles from the Sun that per­vades the So­lar Sys­tem.

July 29 utburst (courtesy ESA)

The com­et reaches “pe­r­i­he­lion” on Thurs­day—the mo­ment in its 6.5-year or­bit when it is clos­est to the Sun. In re­cent months, the in­creas­ing so­lar en­er­gy has been warm­ing the com­et’s fro­zen ices, turn­ing them to gas, which pours out in­to space, drag­ging dust along with it.

The pe­ri­od around pe­r­i­he­li­on draws great sci­en­tif­ic in­ter­est, as the in­tens­ity of the sun­light in­creases and parts of the com­et pre­vi­ously cast in years of dark­ness are flood­ed with sun­light.

The com­et’s gen­er­al ac­ti­vity is ex­pected to peak in the weeks fol­low­ing pe­r­i­he­li­on, much as the hot­test days of sum­mer usu­ally come af­ter the longest days. But sud­den and un­pre­dict­a­ble out­bursts can oc­cur at any time – as al­ready seen.

On July 29, Ro­set­ta ob­served the most dra­mat­ic out­burst yet, reg­is­tered by sev­er­al of its in­stru­ments from their van­tage point 186 km (116 miles) from the com­et. They im­aged the out­burst erupt­ing from the nu­cle­us, or co­re; wit­nessed a change in the struc­ture and make­up of the gas­e­ous cloud or “co­ma” sur­round­ing Ro­set­ta; and de­tected in­creased lev­els of dust im­pacts.

A se­quence of im­ages tak­en by a Ro­set­ta cam­era dubbed OSI­RIS show a je­t-like fea­ture burst­ing out of the side of the com­et’s neck, in a re­gion of the com­et known as Anuket. It was first seen in an im­age tak­en at 1:24 p.m. Green­wich Mean Time, but not in an im­age tak­en 18 min­utes ear­li­er, and has greatly fad­ed in an im­age cap­tured 18 min­utes lat­er. The cam­era team es­ti­mates the ma­te­ri­al in the je­t to be trav­el­ing at least 10 me­ters (yards) per sec­ond, and pe­rhaps much faster.

“This is the bright­est je­t we’ve seen so far,” com­ments Carsten Güt­tler, OSI­RIS team mem­ber at the Max Planck In­sti­tute for So­lar Sys­tem Re­search in Göt­tin­gen, Germany.

“Usu­ally, the je­ts are quite faint com­pared to the nu­cle­us and we need to stretch the con­trast of the im­ages to make them vis­i­ble – but this one is brighter than the nu­cle­us.”

* * *

Send us a comment on this story, or send it to a friend

Sign up for


On Home Page         


  • Plane­tary rings fol­low “beau­tiful” law wher­ever they are

  • Ro­mantic kiss­ing ab­sent from many cul­tures, study finds


  • Study links global warming, war for first time—in Syria

  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find


  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

A comet under a European Space Agency spacecraft’s close scrutiny is waking up with “fireworks” as its path takes it near the Sun, researchers report. Agency scientists said the craft, Rosetta, has witnessed growing activity from Comet 67P/Churyumov–Gerasimenko, with one outburst proving so strong that it even pushed away the incoming solar wind. The comet reaches “perihelion” on Thursday—the moment in its 6.5-year orbit when it is closest to the Sun. In recent months, the increasing solar energy has been warming the comet’s frozen ices, turning them to gas, which pours out into space, dragging dust along with it. The period around perihelion draws great scientific interest, as the intensity of the sunlight increases and parts of the comet previously cast in years of darkness are flooded with sunlight. Although the comet’s general activity is expected to peak in the weeks following perihelion, much as the hottest days of summer usually come after the longest days, sudden and unpredictable outbursts can occur at any time – as already seen earlier in the mission. On July 29, Rosetta observed the most dramatic outburst yet, registered by several of its instruments from their vantage point 186 km (116 miles) from the comet. They imaged the outburst erupting from the nucleus, or core; witnessed a change in the structure and composition of the gaseous coma environment surrounding Rosetta; and detected increased levels of dust impacts. A sequence of images taken by a Rosetta camera dubbed OSIRIS show a jet-like feature bursting out of the side of the comet’s neck, in a region of the comet known as Anuket. It was first seen in an image taken at 1:24 p.m. Greenwich Mean Time, but not in an image taken 18 minutes earlier, and has faded significantly in an image captured 18 minutes later. The camera team estimates the material in the jet to be traveling at least 10 meters (yards) per second, and perhaps much faster. “This is the brightest jet we’ve seen so far,” comments Carsten Güttler, OSIRIS team member at the Max Planck Institute for Solar System Research in Göttingen, Germany. “Usually, the jets are quite faint compared to the nucleus and we need to stretch the contrast of the images to make them visible – but this one is brighter than the nucleus.”