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Warm Jupiters not as Lonely as Expected

July 14, 2016

Toron­to, ON – After ana­lyz­ing four years of Kepler space tele­scope obser­va­tions, astronomers from the Uni­ver­si­ty of Toron­to have giv­en us our clear­est under­stand­ing yet of a class of exo­plan­ets called “Warm Jupiters”, show­ing that many have unex­pect­ed plan­e­tary com­pan­ions.

The team’s analy­sis, pub­lished July 10th in the Astro­phys­i­cal Jour­nal, pro­vides strong evi­dence of the exis­tence of two dis­tinct types of Warm Jupiters, each with their own for­ma­tion and dynam­i­cal his­to­ry.

The two types include those that have com­pan­ions and thus, like­ly formed where we find them today; and those with no com­pan­ions that like­ly migrat­ed to their cur­rent posi­tions.

Accord­ing to lead-author Chelsea Huang, a Dun­lap Fel­low at the Dun­lap Insti­tute for Astron­o­my & Astro­physics, Uni­ver­si­ty of Toron­to, “Our find­ings sug­gest that a big frac­tion of Warm Jupiters can­not have migrat­ed to their cur­rent posi­tions dynam­i­cal­ly and that it would be a good idea to con­sid­er more seri­ous­ly that they formed where we find them.”

Warm Jupiters are large, gas-giant exoplanets—planets found around stars oth­er than the Sun. They are com­pa­ra­ble in size to the gas-giants in our Solar Sys­tem. But unlike the Sun’s fam­i­ly of giant plan­ets, Warm Jupiters orbit their par­ent stars at rough­ly the same dis­tance that Mer­cury, Venus and the Earth cir­cle the Sun. They take 10 to two hun­dred days to com­plete a sin­gle orbit.

Because of their prox­im­i­ty to their par­ent stars, they are warmer than our system’s cold gas giants—though not as hot as Hot Jupiters, which are typ­i­cal­ly clos­er to their par­ent stars than Mer­cury.

It has gen­er­al­ly been thought that Warm Jupiters didn’t form where we find them today; they are too close to their par­ent stars to have accu­mu­lat­ed large, gas-giant-like atmos­pheres. So, it appeared like­ly that they formed in the out­er reach­es of their plan­e­tary sys­tems and migrat­ed inward to their cur­rent posi­tions, and might in fact con­tin­ue their inward jour­ney to become Hot Jupiters. On such a migra­tion, the grav­i­ty of any Warm Jupiter would have dis­turbed neigh­bour­ing or com­pan­ion plan­ets, eject­ing them from the sys­tem.

But, instead of find­ing “lone­ly”, com­pan­ion-less Warm Jupiters, the team found that 11 of the 27 tar­gets they stud­ied have com­pan­ions rang­ing in size from Earth-like to Nep­tune-like.

“And when we take into account that there is more analy­sis to come,” says Huang, “the num­ber of Warm Jupiters with small­er neigh­bours may be even high­er. We may find that more than half have com­pan­ions.”

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