Media Releases

Newly discovered celestial object defies categories

January 8, 2014

Scientists asking if it is a new kind of planet or a rare kind of failed star

TORONTO, ON – An object dis­cov­ered by astro­physi­cists at the Uni­ver­si­ty of Toron­to (U of T) near­ly 500 light years away from the Sun may chal­lenge tra­di­tion­al under­stand­ings about how plan­ets and stars form.

The object is locat­ed near and like­ly orbit­ing a very young star about 440 light years away from the Sun, and is lead­ing astro­physi­cists to believe that there is not an easy-to-define line between what is and is not a plan­et.

“We have very detailed mea­sure­ments of this object span­ning sev­en years, even a spec­trum reveal­ing its grav­i­ty, tem­per­a­ture, and mol­e­c­u­lar com­po­si­tion. Still, we can’t yet deter­mine whether it is a plan­et or a failed star – what we call a ‘brown dwarf’. Depend­ing on what mea­sure­ment you con­sid­er, the answer could be either,” said Thayne Cur­rie, a post-doc­tor­al fel­low in U of T’s Depart­ment of Astron­o­my & Astro­physics and lead author of a report on the dis­cov­ery pub­lished this week in Astro­phys­i­cal Jour­nal Let­ters.

Named ROXs 42Bb for it’s prox­im­i­ty to the star ROXs 42B, the object is approx­i­mate­ly nine times the mass of Jupiter, below the lim­it most astronomers use to sep­a­rate plan­ets from brown dwarfs, which are more mas­sive. How­ev­er, it is locat­ed 30 times fur­ther away from the star than Jupiter is from the Sun.

“This sit­u­a­tion is a lit­tle bit dif­fer­ent than decid­ing if Plu­to is a plan­et. For Plu­to, it is whether an object of such low mass amongst a group of sim­i­lar objects is a plan­et,” said Cur­rie. “Here, it is whether an object so mas­sive yet so far from its host star is a plan­et. If so, how did it form?”

Most astronomers believe that gas giant plan­ets like Jupiter and Sat­urn formed by core accre­tion, where­by the plan­ets form from a sol­id core that then accretes a mas­sive gaseous enve­lope. Core accre­tion oper­ates most effi­cient­ly clos­er to the par­ent star due to the length of time required to first form the core.

An alter­nate the­o­ry pro­posed for form­ing gas giant plan­ets is disk insta­bil­i­ty – a process by which a frag­ment of a disk gas sur­round­ing a young star direct­ly col­laps­es under its own grav­i­ty into a plan­et. This mech­a­nism works best far­ther away from the par­ent star.

Of the dozen or so oth­er young objects with mass­es of plan­ets observed by Cur­rie and oth­er astronomers, some have plan­et-to-star mass ratios less than about 10 times that Jupiter and are locat­ed with­in about 15 times Jupiter’s sep­a­ra­tion from the Sun. Oth­ers have much high­er mass ratios and/or are locat­ed more than 50 times Jupiter’s orbital sep­a­ra­tion, prop­er­ties that are sim­i­lar to much more mas­sive objects wide­ly accept­ed to not be plan­ets. The first group would be plan­ets formed by core accre­tion, and the sec­ond group prob­a­bly formed just like stars and brown dwarfs. In between these two pop­u­la­tions is a big gap sep­a­rat­ing true plan­ets from oth­er objects.

Cur­rie says that the new object starts to blur this dis­tinc­tion between plan­ets and brown dwarfs, and may lie with­in and begin to fill the gap. “It’s very hard to under­stand how this object formed like Jupiter did. How­ev­er, it’s also too low mass to be a typ­i­cal brown dwarf; disk insta­bil­i­ty might just work at its dis­tance from the star. It may rep­re­sent a new class of plan­ets or it may just be a very rare, very low-mass brown dwarf formed like oth­er stars and brown dwarfs: a ‘plan­et mass’ brown dwarf.”

“Regard­less, it should spur new research in plan­et and star for­ma­tion the­o­ries, and serve as a cru­cial ref­er­ence point with which to under­stand the prop­er­ties of young plan­ets at sim­i­lar tem­per­a­tures, mass­es and ages,” Cur­rie said.

The dis­cov­ery is report­ed in a study titled “Direct imag­ing and spec­troscopy of a can­di­date com­pan­ion below/near the deu­teri­um-burn­ing lim­it in the young bina­ry star sys­tem, ROXs 42B” which can also be viewed on at Cur­rie will present these and oth­er find­ings at the annu­al meet­ing of the Amer­i­can Astro­nom­i­cal Soci­ety in Wash­ing­ton, DC this week.

The obser­va­tion­al data used for the dis­cov­ery was obtained using the Keck and Sub­aru tele­scopes on Mau­na Kea, Hawaii, and the tele­scopes of the Euro­pean South­ern Obser­va­to­ry in Chile. The inter­na­tion­al research team includes sci­en­tists from: the Space Tele­scope Sci­ence Insti­tute in Bal­ti­more, MD; the Uni­ver­si­ty of Mon­tre­al; the Uni­ver­si­ty of Hyo­go in Kobe, Japan; the Uni­ver­si­tats-Stern­warte Munchen and the Lud­wig-Max­i­m­il­ians-Uni­ver­si­tat, Munchen, Ger­many, and Uni­ver­si­ty of Hawaii.

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Note to media: Vis­it for images and illus­tra­tions describ­ing ROXs 42Bb.

For more infor­ma­tion, con­tact:

Thayne Cur­rie
Depart­ment of Astron­o­my & Astro­physics
Uni­ver­si­ty of Toron­to
Cell: 857–998-9771

Sean Bet­tam
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to
Tel: 416–946-7950