Wob­bly planet with strange sea­sons

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

AS­TRONOMERS us­ing data from the plan­ethunt­ing Ke­pler Space Tele­scope have found a wild card of a world: a planet so wob­bly that its “sea­sons” could be in con­stant flux.

This planet, called Ke­pler-413b, is about 2,300 light-years away in the con­stel­la­tion Cygnus, and it or­bits a bi­nary pair of stars that are cir­cling each other. This gas gi­ant weigh­ing roughly 65 Earth masses or­bits ev­ery 66 days, too close to the stars to be hab­it­able.

But here’s the un­usual bit about this planet, de­scribed in an up­com­ing is­sue of the As­tro­phys­i­cal Jour­nal: it’s so wob­bly that its spin axis could vary by as much as 30° over 11 years – a pretty ex­treme swing, given that the Earth, tilted at 23.5°, com­pletes one round of its own “wob­ble” ev­ery 26,000 years.

The team dis­cov­ered this strange sys­tem while look­ing for plan­ets cross­ing in front of bi­nary stars, said lead au­thor Ve­selin Kos­tov, an as­tro­physi­cist with Johns Hop­kins Univer­sity and the Space Tele­scope Sci­ence In­sti­tute in Bal­ti­more.

Nasa’s Ke­pler tele­scope, which was re­tired af­ter it suf­fered a ma­jor in­jury last year, would stare at a patch of sky and wait for a planet to pass in front of a star and block a lit­tle light. When those dips in bright­ness oc­cur a few times at reg­u­lar in­ter­vals, as­tronomers know it must be an or­bit­ing planet.

Ke­pler-413b was any­thing but reg­u­lar. The dips in bright­ness oc­curred in weird fits and starts: three times in the first 180 days, then not at all for the next 800 days, then five more times be­fore it stopped again (and then Ke­pler ceased func­tion­ing).

The sci­en­tists re­alised that the planet’s or­bit was off by 2.5° – it didn’t travel in the same plane as its host stars, a red dwarf and a slightly larger orange dwarf. The sci­en­tists think that, as this un­even pair of stars dance around each other at the cen­tre, their dif­fer­ent grav­i­ta­tional pulls con­stantly warp the planet’s or­bit. It also causes the planet to wob­ble on its axis, like a spin­ning top does (a phe­nom­e­non known as ro­ta­tional pre­ces­sion).

The sea­sons on this gassy planet, such as they are, would be in con­stant flux, Kos­tov said. And this has im­pli­ca­tions for a de­tailed def­i­ni­tion of hab­it­abil­ity. Just be­cause a planet lies in the hab­it­able zone, where liq­uid wa­ter can ex­ist, doesn’t mean it’s an es­pe­cially friendly place to live – par­tic­u­larly if, say, it’s con­stantly swing­ing from hot hu­mid sum­mers to icy win­ters. It’s another fac­tor to con­sider as as­tronomers search for Earth-like ex­o­plan­ets.

“If you have an Earth-sized planet in the hab­it­able zone of a bi­nary star, you have to take into ac­count this pre­ces­sion,” Kos­tov said. “It tells us about the ar­chi­tec­ture of ex­tra­so­lar plan­ets in gen­eral.”

This planet may not be all that un­usual; there could be many more like it. Af­ter all, Ke­pler could only see plan­ets reg­u­larly tran­sit­ing at just the right an­gle; and such wob­bly plan­ets are less likely to cross our line of sight.

“My gut tells me there should be more of them like this,” Kos­tov said. “We just find the ones that are easy to find.” – Los An­ge­les Times / McClatchy-Tri­bune In­for­ma­tion Ser­vices

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