An In­Sight in­side MARS

NASA plans to launch its next mis­sion to Mars this month. El­iz­a­beth Pear­son looks at what In­Sight hopes to un­cover deep be­neath the Mar­tian sur­face

Sky at Night Magazine - - INSIGHT MARS LANDER -

Dozens of ro­botic ex­plor­ers have been sent to Mars over the decades, but so far most of them have done lit­tle more than scratch at the sur­face. NASA’s next mis­sion to the Red Planet, how­ever, will look much deeper into the planet than any of its pre­de­ces­sors. The In­Sight (In­te­rior Ex­plo­ration us­ing Seis­mic In­ves­ti­ga­tions, Geodesy and Heat Trans­port) lan­der is pre­par­ing to hun­ker down on the Mar­tian sur­face, ready to take the planet’s pulse and tem­per­a­ture, and peel back its lay­ers to ex­pose its very core.

The mis­sion is due to launch in early May from Van­den­berg Air Force Base, Cal­i­for­nia, ar­riv­ing at Mars six months later, to send a static lan­der to the sur­face on 26 Novem­ber. How­ever, as this is in the mid­dle of the Mar­tian au­tumn, when dust

storms can sweep across the en­tire planet, the de­scent could be a fraught one. Luck­ily, this isn’t the first time NASA has put down a probe like In­Sight.

“We tried to stick to the de­sign of a pre­vi­ous lan­der, Phoenix, as much as pos­si­ble,” says Suzanne Sm­rekar, Deputy Prin­ci­pal In­ves­ti­ga­tor of In­Sight. “First, we have an aeroshell that will slow us down when we hit the at­mos­phere. Then we have a para­chute to take us most of the way through the at­mos­phere. Fi­nally, for the last lit­tle bit we come down on rock­ets.”

Once it has safely en­dured this land­ing and is on the sur­face, In­Sight will spend the next 10 weeks set­ting it­self up. Its first task will be un­fold­ing its so­lar ar­rays so that it can sup­ply power to the lan­der. Then the mis­sion will look around for the best place to put its fin­gers to the ground, so that it can feel for marsquakes – tremors cre­ated by the shift­ing of in­ter­nal rocks, which ra­di­ate out from deep within the planet.

“Our pri­mary in­stru­ment is a seis­mome­ter, the Seis­mic Ex­per­i­ment for In­te­rior Struc­ture (SEIS),” says Sm­rekar. “It ac­tu­ally has sev­eral short and long pe­riod seis­mome­ters to mea­sure nearby seis­mic waves and those that come from deeper within the planet re­spec­tively. We have three of each so we can tell the direc­tion and ori­en­ta­tion that they are com­ing from.”

Mea­sur­ing marsquakes

These seis­mome­ters are so sen­si­tive that they have to be cov­ered over with a dome that will pro­tect them from tiny shakes caused by wind or ther­mal ex­pan­sion to make them as pre­cise as pos­si­ble. Such

“RISE is track­ing the wob­ble of Mars as it spins on its axis since plan­ets with liq­uid cores wob­ble more” Suzanne Sm­rekar, NASA

ac­cu­racy is vi­tal in marsquake mea­sure­ments to de­tect the tiny changes that oc­cur when a seis­mic wave trav­els be­tween the dif­fer­ent lay­ers in­side the planet – go­ing from the vis­cous fluid of the man­tle to the solid crust, for in­stance. By look­ing for these tiny vari­a­tions, plan­e­tary ge­ol­o­gists will be able to work out the thick­ness and den­sity of each layer, build­ing a map of the world be­neath the Mar­tian sur­face. Gath­er­ing this knowl­edge is the first step to un­der­stand­ing how Mars grew and evolved into the planet we see to­day.

“We’re try­ing to un­der­stand what hap­pens im­me­di­ately af­ter the plan­ets came to­gether. The heat of that ki­netic en­ergy caused the bod­ies to melt and then rel­a­tively rapidly, within 10 mil­lion years, they be­gan to form their ini­tial lay­ers as light stuff floated to the top and heavy stuff sank to the bot­tom form­ing the core, man­tle and crust: a process called dif­fer­en­ti­a­tion,” says Sm­rekar.

Stunted growth

The ex­tent to which a planet dif­fer­en­ti­ates is mostly de­fined by how much heat it has and how hot a planet is mostly de­pends on its size. Small rocky bod­ies, like the Moon, rapidly cool af­ter they form and so never fully dif­fer­en­ti­ate their in­te­rior. Mean­while Earth has kept evolv­ing for bil­lions of years be­cause it’s been kept warm by the de­cay of ra­dioac­tive el­e­ments. As its in­te­rior is molten, the ma­te­rial there can re­dis­tribute it­self in­side the planet. The liq­uid lay­ers also al­low the con­ti­nen­tal plates to move around, chang­ing the to­pog­ra­phy of the sur­face, while liq­uid magma bub­bles up from vol­ca­noes and cov­ers what was there be­fore. The end re­sult is that Earth to­day bears lit­tle re­sem­blance to the planet it was when it first formed bil­lions of years ago. The same pro­cesses are thought to play out on the other, larger ter­res­trial worlds, but Mars has some unique ge­o­log­i­cal qual­i­ties.

“Mars is in this sweet spot: we think it’s in the right place in terms of its size that it never had plate tec­ton­ics, so it still has its ini­tial crust, but it’s big

enough that it has some of the same kinds of lay­ers that we ex­pect in­side of the Earth,” says Sm­rekar.

Al­though Mars started out de­vel­op­ing like a larger rocky planet, it cooled and froze very early in its life­time, halt­ing its growth. As the planet hasn’t changed in bil­lions of years, it now gives ge­ol­o­gists a win­dow into the early years of plan­e­tary for­ma­tion. And the key to un­der­stand­ing why Mars cooled while worlds like Earth didn’t is find­ing out how the Red Planet lost its heat. To do this, In­Sight will de­ploy its sec­ond in­stru­ment, the Heat Flow and Phys­i­cal Prop­er­ties Probe (HP3).

“Most of the planet’s cur­rent heat bud­get comes from the de­cay of ra­dioac­tive el­e­ments: ura­nium, tho­rium, potas­sium. HP3 will help us ex­trap­o­late how much of those el­e­ments Mars had in the past, and how much en­ergy there was to drive things like vol­ca­noes on the sur­face of Mars, and what the sur­face tem­per­a­ture might have been,” says Sm­rekar.

Run­ning on the spot

To take these mea­sure­ments, HP3 will use a heavy probe to ham­mer it­self up to 5m into the ground, pulling a string of tem­per­a­ture sen­sors be­hind it that will mea­sure the heat flow­ing out of the planet. Once ev­ery­thing is in place, the lan­der will cease all fur­ther move­ment so as not to dis­turb the two ex­per­i­ments. For­tu­nately, the fact that the lan­der

is static doesn’t mat­ter – no mat­ter where it comes to rest, it can mea­sure heat flow and keep track of seis­mic sig­nals. The im­mo­bil­ity also ben­e­fits In­Sight’s third and fi­nal main ex­per­i­ment: RISE.

“The Ro­ta­tion and In­te­rior Struc­ture Ex­per­i­ment (RISE) are ra­dios that will com­mu­ni­cate with Earth ev­ery cou­ple of days over Mars’s year, track­ing the place­ment of the lan­der very pre­cisely,” says Sm­rekar. “What we’re re­ally do­ing with them is track­ing the wob­ble of Mars as it spins on its axis, since plan­ets with liq­uid cores wob­ble more than plan­ets with solid cores.”

By mea­sur­ing the wob­ble, plan­e­tary ge­ol­o­gists will be able to de­ter­mine more ac­cu­rately the den­sity and con­sis­tency of each layer, which will help them work out what el­e­ments might make up the planet’s core. By track­ing back, the In­Sight re­searchers will be able to piece to­gether the ge­o­log­i­cal pro­cesses that went into cre­at­ing the rocky world that Mars is to­day, and so how plan­ets such as Earth might have looked be­fore they were trans­formed by bil­lions of years of vol­can­ism and ge­o­log­i­cal de­vel­op­ment.

In­Sight is ex­pected to have fin­ished its ini­tial science goals within one Mar­tian year (which at 687 days is just shy of two Earth years) but the team has built the lan­der to last, and hope­fully In­Sight will con­tinue gath­er­ing data long af­ter its ini­tial run. It might even be able to de­tect the ar­rival of two fel­low Mars ex­plor­ers when they land: both NASA and ESA plan on send­ing rovers to the Red Planet in 2020, dou­bling the num­ber of mo­bile ob­ser­va­to­ries rang­ing across the planet’s sur­face. But for the next two years, In­Sight will take ad­van­tage of the quiet, and sit wait­ing for Mars to shake out its hid­den se­crets.

In­Sight un­folds its so­lar ar­rays for a fi­nal test on 23 Jan­uary 2018 in the Lock­heed Martin clean room in Col­orado

Lay­ers sep­a­rate A NASA artist’s im­pres­sion of how a rocky planet, such as Mars, is formed through pro­cesses known as ac­cre­tion and dif­fer­en­ti­a­tion

Heat builds up

El­e­ments melt

Ma­te­rial ac­cretes

In­Sight will mea­sure seis­mic ac­tiv­ity both near the sur­face and deep in­side the core of Mars us­ing the Seis­mic Ex­per­i­ment for In­te­rior Struc­ture (SEIS)

The land­ing sites of all the suc­cess­ful Mars mis­sions so far, plus the pro­posed equa­to­rial land­ing site for In­Sight

In­Sight will use thrusters to com­plete a des­cent flight plan iden­ti­cal to that of the Phoenix mis­sion be­fore it

In­Sight will ar­rive on Mars packed with all the equip­ment it needs to re­veal the se­crets at the core of the rocky planet ABOUT THE WRITER Dr El­iz­a­beth Pear­son is the news edi­tor at BBC Sky at Night Mag­a­zine and she holds a PhD in ex­tra­galac­tic astronomy

Above right: The tip of the In­Sight drill, which the project’s team has dubbed ‘the mole’

Above left: HP3 was orig­i­nally de­signed to be part of the Ex­oMars mis­sion un­til a re­def­i­ni­tion of its aims re­sulted in the can­cel­la­tion of all its geo­phys­i­cal ex­per­i­ments

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