Mis­sion to mer­cury

The sci­en­tists re­veal how Bepicolombo will crack the So­lar Sys­tem’s small­est planet

All About Space - - Contents - Re­ported by Lee Cavendish

“BepiColombo will be per­fect to fol­low up on MES­SEN­GER”

Mer­cury, the clos­est planet to the Sun, is an un­solved mys­tery that has left many ques­tions swirling around the minds of sci­en­tists. We have re­cently been blessed with many mis­sions ex­plor­ing the outer re­gions of our So­lar Sys­tem, such as NASA’s Juno mis­sion at Jupiter and the New Hori­zons mis­sion to Pluto and the Kuiper Belt, and the NASA/ESA/ASI Cassini-Huy­gens mis­sion to Saturn. How­ever, a mis­sion to the in­ner-most planet poses its own set of chal­lenges and re­wards.

Now, the highly an­tic­i­pated BepiColombo mis­sion, a col­lab­o­ra­tive mis­sion be­tween the ESA and the Ja­pan Aerospace Ex­plo­ration Agency (JAXA), will be launched in or­der to an­swer the most pro­found ques­tions about Mer­cury and our So­lar Sys­tem. Once the BepiColombo stack ar­rives at Mer­cury in late 2025 the stack will split apart and send two or­biters into their own unique or­bit around the planet. The ESA is re­spon­si­ble for the op­er­a­tion of the Mer­cury Plan­e­tary Or­biter (MPO), and JAXA will op­er­ate the Mer­cury Mag­ne­to­spheric Or­biter (MMO, or Mio as named by JAXA).

“MPO and MMO com­ple­ment each other.

While the MPO is more fo­cused on study­ing the planet it­self and its in­te­rior, the MMO is fo­cused

Dr Jo­hannes Benkhoff

on study­ing the plasma, par­ti­cle and mag­netic en­vi­ron­ment around the planet,” ex­plains Benkhoff to All About Space. “There­fore the BepiColombo mis­sion will pro­vide a rare op­por­tu­nity to col­lect multi-point [on two space­craft] mea­sure­ments in a plan­e­tary en­vi­ron­ment.”

This ball of met­als and sil­i­cate ma­te­ri­als has a rel­a­tively tiny ra­dius of only 2,440 kilo­me­tres

(1,516 miles), mak­ing it smaller than the moons Ganymede and Ti­tan of Jupiter and Saturn re­spec­tively. As Mer­cury sits at an av­er­age dis­tance of 58 mil­lion kilo­me­tres (36 mil­lion miles) from the Sun, which is less than 40 per cent of the SunEarth dis­tance, this tiny planet ex­hibits a harsh en­vi­ron­ment due to its close prox­im­ity. The planet faces two dif­fer­ent ex­tremes; day­time tem­per­a­tures can reach a toasty 430 de­grees Cel­sius (806 de­grees Fahrenheit) while night-time tem­per­a­tures, due to Mer­cury's lack of at­mos­phere, can drop to a chilly -180 de­grees Cel­sius (-292 de­grees Fahrenheit), and the Sun pep­pers the sur­face in high-en­ergy par­ti­cles that have enough power to reach the other plan­ets in the So­lar Sys­tem.

An en­vi­ron­ment such as this is not an easy one to ex­pe­ri­ence as a space­craft, let alone sus­tain a work­ing lab­o­ra­tory for a pro­longed time. Only two space­craft have ever vis­ited the planet. Be­tween 1974 and 1975, NASA’s Mariner 10 space­craft flew by Mer­cury three times in or­der to find out about its en­vi­ron­ment, at­mos­phere and sur­face, and it im­aged about 45 per cent of its sur­face.

Fast-for­ward to March 2011 and NASA’s Mer­cury Sur­face, Space En­vi­ron­ment, Geo­chem­istry, and Rang­ing (MES­SEN­GER) space­craft be­came the first space­craft to or­bit Mer­cury, mak­ing un­ri­valled ob­ser­va­tions about ev­ery as­pect of the planet for about four years and one month. Af­ter trav­el­ling over 14 bil­lion kilo­me­tres (8.7 bil­lion miles) and com­plet­ing 4,105 or­bits of Mer­cury, and re­turn­ing over 250,000 im­ages back to Earth in the process, MES­SEN­GER was de­lib­er­ately crashed into the sur­face of Mer­cury on 30 April 2015. The data col­lected from this mis­sion re­shaped our knowl­edge of Mer­cury and the evo­lu­tion of the So­lar Sys­tem, re­veal­ing un­known traits about the planet’s mag­ne­to­sphere, sur­face fea­tures and com­po­si­tion.

Al­though MES­SEN­GER was a pi­o­neer­ing space­craft, it was still lim­ited by its or­bit at the time. “Be­cause of the or­bital lim­i­ta­tion, there is not enough learned from MES­SEN­GER about the south­ern hemi­sphere of the planet” says Fu­ji­moto. “BepiColombo will com­plete the full-hemi­sphere cov­er­age and will set the ground to ob­tain deeper un­der­stand­ing of the is­sues.”

Much like when we look back on any past space­craft, it was also lim­ited by its tech­nolo­gies of the time, as Benkhoff ex­plains: “BepiColombo, with its com­pre­hen­sive in­stru­men­ta­tion, its so­phis­ti­cated ra­dio sci­ence in­stru­ment set, its [ther­mal and] multi-wave­length spec­tral im­agers, not to men­tion its much closer or­bit al­low­ing full global high­res­o­lu­tion cov­er­age, will be per­fect to fol­low up on MES­SEN­GER.”

With a so­phis­ti­cated in­stru­men­tal suite of 16 in­stru­ments and ex­per­i­ments – five on Mio/ MMO and 11 on MPO – in­clud­ing var­i­ous cam­eras, spec­trom­e­ters over a wide range of wave­lengths, par­ti­cle anal­y­sers, a mag­ne­tome­ter, a laser al­time­ter and more, BepiColombo will leave no stone un­turned in the ex­am­i­na­tion of Mer­cury’s mag­ne­to­sphere, ex­o­sphere, sur­face and in­te­rior, along with an ex­per­i­ment to test Ein­stein’s the­ory of gen­eral rel­a­tiv­ity.

The most thought-pro­vok­ing re­sult that MES­SEN­GER pro­vided was the ev­i­dence that Mer­cury’s sur­face is more abun­dant in volatile el­e­ments such as potas­sium and sul­phur, which com­pletely con­tra­dicts the mod­els of Mer­cury’s for­ma­tion, as well as the en­tire So­lar Sys­tem. When MES­SEN­GER mea­sured the ra­tio of potas­sium (the more volatile el­e­ment) to tho­rium (the more sta­ble el­e­ment), they no­ticed that abun­dance of potas­sium was much higher than tho­rium. It was pre­vi­ously thought that potas­sium would have been heated up due to the in­cred­i­bly high tem­per­a­tures and evap­o­rated away. How­ever, the co­pi­ous amounts of potas­sium show the tem­per­a­tures were not as high as first thought.

Pre­vi­ous anal­y­sis of Mer­cury's in­te­rior also showed that the core makes up roughly 85 per cent of the planet's ra­dius. When com­pared to Earth’s core, which makes up only half of our home planet, it is the­o­rised that Mer­cury was once a larger planet that had its outer lay­ers cast off in a de­struc­tive col­li­sion. This is all the­ory how­ever, and with­out in­stru­ments such as the MPO’s Mer­cury Or­biter Ra­dio-sci­ence Ex­per­i­ment (MORE) to fur­ther un­der­stand the planet’s core, and the Spec­trom­e­ters and Im­agers for MPO BepiColombo In­te­grated Ob­ser­va­tory Sys­tem (SIMBIO-SYS), which will an­a­lyse the sur­face com­po­si­tion, the mys­tery of Mer­cury’s evo­lu­tion will re­main ex­tremely blurred.

An­other im­por­tant as­pect of Mer­cury that MES­SEN­GER couldn’t quite an­swer is the state of the planet’s mag­ne­to­sphere – the planet’s self­driven, mag­netic field. Fu­ji­moto says that Mer­cury shouldn’t the­o­ret­i­cally ex­hibit its cur­rent in­trin­sic mag­netic field, as there needs to be some sort of liq­uid or molten in­te­rior pow­er­ing the mag­netic ac­tiv­ity. A planet as small as Mer­cury should have cooled down to its core a while ago and cut off its mag­netic ac­tiv­ity, mak­ing its cur­rent state a keen area of re­search.

“Mio is the space­craft that fo­cuses on this mag­netic-ori­ented sci­ence theme. It will ob­serve the mag­netic field it­self and see how it in­ter­acts with the so­lar wind, the su­per-sonic flow of ionised gas from the Sun,” says Fu­ji­moto. “For this pur­pose, on board Mio are elec­tro­mag­netic field in­stru­ments, plasma par­ti­cle de­tec­tors and an imag­ing de­vice for the thin at­mos­phere that Mer­cury has.”

Ob­ser­va­tions of Mer­cury’s in­te­rior struc­ture, ge­ol­ogy and com­po­si­tion are just some of the as­pects that BepiColombo will ob­serve. In terms of vis­ually in­spect­ing the rocky sur­face, MES­SEN­GER was able to lo­cate a source of wa­ter ice hid­den within the craters at the north pole. With the MPO or­bit more com­pre­hen­sive, the south pole can be scouted for more sources of wa­ter ice.

MES­SEN­GER also im­aged some in­ter­est­ing sur­face fea­tures called ‘hol­lows’ – shal­low, ir­reg­u­lar de­pres­sions on the planet’s sur­face. Along with the ob­served vol­canic fea­tures and ar­eas of a young, un­cratered land, Mer­cury’s sur­face could be much more ac­tive than orig­i­nally thought.

The pre­vi­ous MES­SEN­GER mis­sion raised many ques­tions, and even more ques­tions have come along in re­cent years. With BepiColombo soon to be on its way and sched­uled to ar­rive at Mer­cury in late 2025, the elu­sive na­ture of our most un­known ter­res­trial planet will be placed un­der a mi­cro­scope; this will be an­other step in un­der­stand­ing the his­tory and for­ma­tion of Mer­cury and the in­ner plan­ets, in­clud­ing Earth. “I strongly be­lieve that the in­stru­men­ta­tion of BepiColombo is per­fectly suited to ob­tain our sci­ence goals and to de­liver an­swers to the nec­es­sary and new ques­tions raised by MES­SEN­GER,” con­cludes Benkhoff.

“Be­cause of the or­bital lim­i­ta­tion, there is not enough learned from MES­SEN­GER about the south­ern hemi­sphere”

Dr Fu­ji­moto

MES­SEN­GER’s rev­e­la­tion of small cliff-like land­forms are fea­tures that sci­en­tists be­lieve are ge­o­log­i­cally young

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.