Mis­sion pro­file hayabusa-2

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The mis­sion to as­teroid Ryugu re­veals the lat­est images

This in­no­va­tive mis­sion will visit the dis­tant as­teroid Ryugu and col­lect pieces of it to an­swer some of the So­lar Sys­tem’s most press­ing ques­tions “Sam­pling sur­face ma­te­rial is the most chal­leng­ing task”

Pro­fes­sor Sei-ichiro Watan­abe

The suc­ces­sor to Hayabusa is cur­rently in the depths of the So­lar Sys­tem spy­ing on an­other as­teroid, with plans to steal a sam­ple away for Earth-based anal­y­sis. Both Hayabusa mis­sions had a com­mon goal: to un­der­stand these an­cient time cap­sules that are dot­ted through­out the So­lar Sys­tem. How­ever, the Ja­pan Aero­space Ex­plo­ration Agency (JAXA) wanted to sam­ple an­other type of as­teroid for its sec­ond at­tempt to fur­ther un­der­stand their dif­fer­ences.

As­ter­oids were formed along with the plan­ets over 4 bil­lion years ago, and since then they have been float­ing around space, or­bit­ing the Sun. Hid­den within these frozen pieces of rock are the early chap­ters of the story of the So­lar Sys­tem. How­ever, as­ter­oids are not as black and white as thought by some; there are many types of as­ter­oids that ex­hibit dif­fer­ent fea­tures. Hayabusa vis­ited the small near-Earth as­teroid 25143 Itokawa in 2005, and suc­cess­fully re­turned sam­ples of the S-type (siliceoustype), 540-me­tre (1,772-foot) rock (at its long­est di­men­sion).

On 3 De­cem­ber 2014 Hayabusa2 was suc­cess­fully launched on board the H-IIA launch ve­hi­cle from the Tane­gashima Space Cen­ter in Mi­na­mi­tane, Ja­pan. This up­dated ver­sion of Hayabusa in­cludes ex­cit­ing new fea­tures and landers. On­board in­stru­ments in­clude op­ti­cal nav­i­ga­tion cam­eras, a near-in­frared cam­era and a ther­ma­l­in­frared cam­era, but there are also de­ploy­able pay­loads. Where Hayabusa only had the MI­cro-Nano Ex­per­i­men­tal Robot Ve­hi­cle for the As­teroid (MIN­ERVA) mini­lan­der, which un­for­tu­nately did not go to plan due to a er­ror in de­ploy­ment, Hayabusa2 has three rovers and one main lan­der. MIN­ERVA-II-1 and MIN­ERVA-II-2 were de­signed to hop along the sur­face to con­duct probes. The Mo­bile As­teroid Sur­face Scout (MAS­COT) lan­der will use four in­ter­nal in­stru­ments to ex­am­ine the sur­face up close while jump­ing from one spot to the next.

So what as­teroid did JAXA choose, hav­ing al­ready sam­pled an S-type as­teroid. “The pri­mary ob­jec­tive of Hayabusa2 is to elu­ci­date the for­ma­tion, dy­nam­i­cal and ma­te­rial evo­lu­tion and im­pact his­tory of a car­bona­ceous [C-type] as­teroid,” says Watan­abe. A C-type as­teroid is a more prim­i­tive as­teroid com­pared to an S-type, so astronomers are hop­ing to delve deeper into the past.

“We can un­der­stand the evo­lu­tion of build­ing blocks of plan­ets [plan­etes­i­mals] around the ‘snow line’ – the bound­ary be­tween the in­ner and outer So­lar Sys­tem,” says Watan­abe. “We can also iden­tify pos­si­ble sources of water and or­ganic ma­te­ri­als de­liv­ered to the early Earth.”

The cho­sen des­ti­na­tion was 162173 Ryugu. Not much was known about the as­teroid un­til Hayabusa2’s ar­rival on 27 June 2018. Be­fore Hayabusa2’s eyes, Ryugu be­gan to take shape. The most strik­ing thing is the al­most di­a­mond-like shape to it, with a mean di­am­e­ter of al­most one kilo­me­tre (0.6 miles). Sci­en­tists also no­ticed that its sur­face shares some sim­i­lar­i­ties with Itokawa in that there are many boul­ders and a grooved ter­rain. What’s more no­tice­able about Ryugu though is that there are more no­tice­able im­pact fea­tures – dents in the sur­face.

In Septem­ber and early Oc­to­ber 2018 the Hayabusa2 team de­cided to re­lease the rovers and landers. The two MIN­ERVA-II-1 rovers, Rover-1A and Rover-1B, were the first to touch down on the mys­te­ri­ous as­teroid, skim­ming across the sur­face and pro­vid­ing some mag­nif­i­cent images as they did so. The next to fol­low was the MAS­COT lan­der, which was de­ployed in the open­ing days of Oc­to­ber 2018. In the clos­ing days of Oc­to­ber the mis­sion will be­gin its most ex­hil­a­rat­ing feat of sci­en­tific and en­gi­neer­ing bril­liance as Hayabusa2 con­ducts its first touch­down onto Ryugu and col­lects its first sam­ple of in­ter­stel­lar rock.

“Sam­pling sur­face ma­te­rial of the tar­get as­teroid is the most im­por­tant and chal­leng­ing task for the Hayabusa2 mis­sion. A sam­pler horn is ex­tended be­neath the space­craft to con­duct sur­face ma­te­ri­als to a sam­ple catcher in­side the main body of Hayabusa2,” ex­plains Watan­abe. “The sam­pling will be per­formed within a few sec­onds, dur­ing which only the flex­i­ble sam­pler horn touches the as­teroid’s sur­face, be­fore the fir­ing of the thrusters for as­cent. Ex­actly speak­ing, the se­quence is not a land­ing but a touch-and-go, and we call it a ‘touch­down’.”

Af­ter two touch­downs Hayabusa2 will re­lease its im­pactor be­tween March and April 2019. Its ar­ti­fi­cial sur­face-de­stroyer will plunge into Ryugu, un­mask­ing rock that hasn’t been ex­posed to space in bil­lions of years.

Af­ter this im­pact Hayabusa2 will col­lect its third and fi­nal sam­ple, af­ter which the re­main­ing MIN­ERVA-II-2 rovers will be de­ployed. This con­cludes Hayabusa2’s stay at Ryugu, and in late 2019 the craft will head back to Earth with a stock­ing not full of coal, but rare as­teroid sam­ples to help ex­plain how our So­lar Sys­tem evolved.

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