Prof Suzie Im­ber on Mer­cury’s mys­ter­ies.

Sky at Night Magazine - - CONTENTS - with As­so­ciate Pro­fes­sor Suzie Im­ber AS­SO­CIATE PRO­FES­SOR SUZIE IM­BER is a space physi­cist at the Uni­ver­sity of Le­ices­ter re­search­ing Mer­cury’s mag­ne­to­sphere via BepiColombo

For many years our at­ten­tion has been grabbed by the rings of Saturn, the ice caps of Mars or Jupiter’s Great Red Spot. Mis­sions to these plan­ets have provided a wealth of in­for­ma­tion about our So­lar Sys­tem. How­ever, there is an anoma­lous planet that con­tin­ues to per­plex sci­en­tists, so much so that we have just launched our sec­ond ded­i­cated mis­sion there this cen­tury: Mer­cury.

Un­der­stand­ing the for­ma­tion and evo­lu­tion of Mer­cury may pro­vide the key to un­lock­ing some of the out­stand­ing mys­ter­ies of our So­lar Sys­tem. It’s so close to the Sun in the sky that the ma­jor­ity of our cur­rent knowl­edge has come from in situ space­craft ob­ser­va­tions. Even get­ting a satel­lite to Mer­cury presents a huge chal­lenge, re­quir­ing a seven-year jour­ney in­cor­po­rat­ing sev­eral fly­bys of Earth, Venus and Mer­cury to slow it down enough to be cap­tured by Mer­cury’s weak grav­i­ta­tional field. And that’s just the first step; the en­vi­ron­ment around Mer­cury presents huge en­gi­neer­ing and op­er­a­tional chal­lenges. Chief among these is the heat: or­bit­ing space­craft must en­dure tem­per­a­ture swings from +450°C to –180°C in pe­ri­ods as short as 30 min­utes, while most of the in­stru­ments on board are de­signed to op­er­ate at room tem­per­a­ture.

Mer­cury is the dens­est planet in the So­lar Sys­tem (ac­count­ing for grav­i­ta­tional com­pres­sion), as its metal-rich core takes up a far greater frac­tional vol­ume of the planet than any other. This could be the re­sult of a huge col­li­sion that re­moved the outer lay­ers of rock, but Mer­cury’s sur­face ap­pears to be rich in the volatile el­e­ments that would be the first to dis­ap­pear as a re­sult of such a col­li­sion. How then – and where – did Mer­cury form?

En­dur­ing a so­lar as­sault

Over the four years it or­bited Mer­cury from 2011-2015, NASA’s MES­SEN­GER space­craft made the re­mark­able dis­cov­ery that Mer­cury’s mag­netic field is off­set to the north of the planet. It also re­vealed tan­ta­lis­ing hints that Mer­cury’s space weather may be fun­da­men­tally dif­fer­ent to Earth’s, be­cause Mer­cury’s gi­ant iron core is fend­ing off the pow­er­ful so­lar wind in the in­ner he­lio­sphere. Can the so­lar wind from the Sun ever scour the sur­face of the planet, and what im­pact would this have on the plan­e­tary at­mos­phere? Are the mysterious X-ray emis­sions on the night side of the planet sim­i­lar to Earth’s aurora, and if so, what can these fea­tures tell us about Mer­cury’s space weather? Also, what ex­actly is the dark ma­te­rial that MES­SEN­GER dis­cov­ered on Mer­cury’s sur­face, and does it play a role in the for­ma­tion of mysterious holes – known as ‘hol­lows’ – on the plan­e­tary sur­face? On 20 Oc­to­ber this year I wit­nessed the launch of the joint Euro­pean-Ja­panese BepiColombo mis­sion, car­ry­ing a suite of in­stru­ments (in­clud­ing one built at Le­ices­ter) to Mer­cury. It’s a pi­o­neer­ing mis­sion com­posed of two space­craft that will travel to­gether un­til they ar­rive at Mer­cury in De­cem­ber 2025, then split apart and or­bit the planet sep­a­rately.

This con­fig­u­ra­tion will en­able some ground-break­ing stud­ies of the sur­face and en­vi­ron­ment, seek­ing to ex­plain Mer­cury’s for­ma­tion, evo­lu­tion and dy­nam­ics, with im­pli­ca­tions for our So­lar Sys­tem and be­yond. It’s a long jour­ney, but I can’t wait to see what dis­cov­er­ies our new mis­sion will bring to light!

BepiColombo launched in Oc­to­ber 2018 and is due to reach Mer­cury in 2025

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