Just how old is Jupiter?

Sci­en­tists use me­te­orites to show that Jupiter is al­most as old as the so­lar sys­tem.

The Star Malaysia - Star2 - - Science - By AMINA KHAN

JUPITER may have been a very early bloomer, gain­ing sig­nif­i­cant mass within the first mil­lion years of the so­lar sys­tem’s birth, ac­cord­ing to a new anal­y­sis of me­te­orite frag­ments.

The find­ings, de­scribed in the jour­nal PNAS, could shed light on the early dy­nam­ics of gas gi­ant plan­ets in our so­lar sys­tem and be­yond – and could help ex­plain Earth’s devel­op­ment too.

Jupiter, king of the plan­e­tary pan­theon, is the lo­cal heavy­weight of our heav­ens; it tips the scale at about 318 Earth masses, dwarf­ing even Saturn (com­ing in at 95 Earths). Jupiter ac­tu­ally holds about 2.5 times as much mass as all other seven plan­ets com­bined – and so its pow­er­ful grav­i­ta­tional tug has pro­foundly shaped the ar­chi­tec­ture of our so­lar sys­tem.

Know­ing ex­actly when Jupiter first formed, then, will help clar­ify ex­actly how Jupiter be­gan to help carve the tu­mul­tuous disc of de­bris around our young star into the sta­ble sys­tem we see to­day. But get­ting a bead on when that hap­pened has long eluded sci­en­tists – though Nasa’s Juno space­craft is try­ing to get a han­dle on that and other ques­tions.

Lead au­thor Thomas S. Krui­jer of the Lawrence Liver­more Na­tional Lab­o­ra­tory stum­bled across a clue as to Jupiter’s age. While work­ing at the Univer­sity of Muen­ster, the cos­mo­chemist and his col­leagues no­ticed that there seemed to be a strange pat­tern among the iron me­te­orites they were study­ing: There seemed to be two dif­fer­ent groups of me­te­orites, one of which had a dis­tinct iso­topic sig­na­ture.

Many of the atoms, in­clud­ing iron, molyb­de­num and tung­sten, were heav­ier ver­sions weighed down by ex­tra neu­trons. Those iso­topes were prob­a­bly cre­ated dur­ing a pow­er­ful su­per­nova ex­plo­sion, and their com­po­si­tion serves as a fin­ger­print of that par­tic­u­lar star’s death.

That’s no great sur­prise; su­per­novas served as a forge for heav­ier el­e­ments that could not be made in the hearts of liv­ing stars. Those heavy el­e­ments went on to seed other stars and fold into their plan­ets and as­ter­oids, in­clud­ing the chunks that fell to Earth as me­te­orites. As sci­en­tist Carl Sa­gan wrote, “We are made of star-stuff.”

In the so­lar sys­tem, much of the de­bris from many dif­fer­ent nearby stel­lar ex­plo­sions should have mixed to­gether, re­sult­ing in a more or less ho­mo­ge­neous soup. And they had – ex­cept for this one par­tic­u­lar group of me­te­orites that seemed to have held on to its orig­i­nal iso­topic fin­ger­print. It was al­most as if the two pop­u­la­tions had been sep­a­rated for a long time and not al­lowed to mix.

“The only mech­a­nism or way to do this is to have a gas gi­ant in be­tween them,” Krui­jer said. “Be­cause only such a body is large enough to sep­a­rate such large reser­voirs.”

The sci­en­tists think Jupiter’s mas­sive body acted like a block­ade, keep­ing the new su­per­nova ma­te­rial from in­ter­act­ing with the well mixed de­bris far­ther in. And by analysing the tung­sten and molyb­de­num iso­topes within the me­te­orites, they could work back to when that sep­a­ra­tion be­tween the two pop­u­la­tions may have hap­pened sur­pris­ingly soon af­ter the birth of the so­lar sys­tem around 4.6 bil­lion years ago.

If they’re right – and much more work needs to be done to con­firm this – Jupiter may have grown to about 20 Earth masses in those first one mil­lion years of the so­lar sys­tem’s for­ma­tion, Krui­jer said. The gas gi­ant would have hogged much of the in­com­ing ma­te­rial that came within its grav­i­ta­tional in­flu­ence, starv­ing the rocky in­ner plan­ets (Mer­cury, Venus, Earth, Mars) and stunt­ing their growth. Jupiter’s early growth might also ex­plain why there are no su­perEarths in our sys­tem, even though they seem to be plen­ti­ful around other stars.

For us, that’s prob­a­bly a good thing, Krui­jer pointed out. Af­ter all, had Earth been al­lowed to ac­cu­mu­late more mass, it may have de­vel­oped into a su­per Earth, with higher grav­ity and a thicker at­mos­phere, and would prob­a­bly have been a far less invit­ing home for life to emerge.

“In a way we should be thank­ful to Jupiter,” he said.

— TNS

Jupiter as seen by the Hub­ble Space Tele­scope. A new study uses me­te­orites to de­ter­mine that within one mil­lion years of the so­lar sys­tem’s for­ma­tion, Jupiter was al­ready 20 times big­ger than Earth is to­day.

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