Focus-Science and Technology - - DISCOVERIES -

It’s a space odd­ity for real: as­tronomers have spot­ted an ex­o­planet that wob­bles. The wob­bling could be due to an exomoon – a moon or­bit­ing a planet out­side our So­lar Sys­tem. If con­firmed, it would be the first exomoon to be dis­cov­ered.

Alex Teachey and David Kip­ping of Columbia Uni­ver­sity used NASA’s Hub­ble and Ke­pler space tele­scopes to gather data on what they think is a huge moon – sim­i­lar in di­am­e­ter to Nep­tune – in or­bit around Ke­pler-1625b, a gas gi­ant ex­o­planet 8,000 light-years away.

As­tronomers search for ex­o­plan­ets by watch­ing for the tem­po­rary dim­ming of a star’s light caused by a planet pass­ing in front of it, re­ferred to as a tran­sit. But while ob­serv­ing Ke­pler-1625b (dis­cov­ered in May 2016) they spot­ted some­thing un­usual.

“We saw lit­tle de­vi­a­tions and wob­bles in the light curve that caught our at­ten­tion,” ex­plained Kip­ping.

What they no­ticed was a sec­ond, much smaller dip in the star’s light after the ex­o­planet’s 19hour tran­sit, a dip that would be con­sis­tent with a fol­low­ing moon.

They also no­ticed that Ke­pler-1625b be­gan its tran­sit 1.25 hours ear­lier than ex­pected be­cause it had wob­bled away from its pre­dicted lo­ca­tion. Such a wob­ble could be ex­plained by the pres­ence of an­other body or­bit­ing a com­mon cen­tre of grav­ity.

“A com­pan­ion moon is the sim­plest and most nat­u­ral ex­pla­na­tion for the sec­ond dip in the light curve and the or­bit-tim­ing de­vi­a­tion,” said Teachey. “It was a shock­ing mo­ment to see that light curve, my heart started beat­ing a lit­tle faster and I just kept look­ing at that sig­na­ture. But we knew our job was to keep a level head and test every con­ceiv­able way in which the data could be trick­ing us un­til we were left with no other ex­pla­na­tion.”

De­vi­a­tions in ex­o­planet Ke­pler-1625b’s or­bit hint at the pres­ence of what could be the first known exomoon

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