NatureVolve

Com­ing soon: A rev­o­lu­tion in the study of ex­o­plan­ets!

- By Matthew Wil­liams - guest writer

For

cen­turies, philoso­phers and schol­ars have won­dered if the stars in the night sky might have their own plan­ets. And yet, it has only been in the past few decades that as­tronomers have been able to find any ex­tra­so­lar plan­ets (aka. ex­o­plan­ets). In fact, it wasn’t un­til 1992 that the first two ex­o­plan­ets were of­fi­cially con­firmed or­bit­ing a pul­sar (PSR B1257+12) 2,300 light-years away.

Since then, thou­sands of ex­o­plan­ets have been de­tected and con­firmed, most of them in just the past decade. All of this is due to a com­bi­na­tion of tech­no­log­i­cal ad­vance­ments, re­fine­ments in ex­o­planet-hunt­ing meth­ods, and im­proved co­or­di­na­tion be­tween ob­ser­va­to­ries world­wide.

In the com­ing years, we can ex­pect many more dis­cov­er­ies as new ob­ser­va­to­ries be­come op­er­a­tional, space tele­scopes are launched, and ma­chine learn­ing and cit­i­zen sci­en­tists get bet­ter at sort­ing through all the data pro­vided. As al­ways, the ul­ti­mate goal is to find plan­ets that are hab­it­able, and maybe even in­hab­ited!

Ex­o­planet-Hunt­ing Tech­niques

So far, most ex­o­plan­ets have been dis­cov­ered us­ing in­di­rect means. Among them, the most pop­u­lar and ef­fec­tive is the Tran­sit Method (aka. Tran­sit Pho­tom­e­try). This con­sists of ob­serv­ing stars for pe­ri­odic dips in bright­ness, which can be the re­sult of a planet pass­ing in front of the star (aka. tran­sit­ing) rel­a­tive to the ob­server.

These dips are used to de­ter­mine the size of the tran­sit­ing planet, as well as its or­bital pe­riod. On rare oc­ca­sions, light pass­ing through the ex­o­planet’s at­mos­phere will pro­vide as­tronomers with spec­tra, which can be used to tell what gases the at­mos­phere is com­posed of.

The sec­ond most pop­u­lar means is the Ra­dial Ve­loc­ity Method (aka. Dop­pler Spec­troscopy). This method con­sists of mea­sur­ing the way a star moves back and forth rel­a­tive to Earth, which in­di­cates that there are grav­i­ta­tional forces act­ing on it - in other words, one or more plan­ets in or­bit. There’s also Grav­i­ta­tional Mi­crolens­ing, which takes ad­van­tage of the ef­fects pre­dicted by Ein­stein’s The­ory of Gen­eral Rel­a­tiv­ity.

In essence, the grav­ity of a star will al­ter the cur­va­ture of space­time around it, which is then used as a “grav­i­ta­tional lens” to en­hance and mag­nify the light of a back­ground star. Over time, dis­tor­tions may oc­cur that could be the re­sult of plan­ets pass­ing through the lens.

Then there’s Di­rect Imag­ing. For this method, as­tronomers de­tect ex­o­plan­ets by look­ing for light re­flected by their at­mos­pheres or sur­faces. The rea­son why this method is so prized is be­cause this light can also be used to ob­tain spec­tra on a planet’s at­mos­phere and/or de­ter­mine what its sur­face might look like (i.e. land­masses, oceans, veg­e­ta­tion, etc.).

Un­for­tu­nately, this tech­nique is used only in rare cases be­cause of the lim­its of our cur­rent tele­scopes. Most of the time, any light re­flected by an ex­o­planet will be eas­ily drowned out by the much brighter light com­ing from its star. Hence, Di­rect Imag­ing has only been pos­si­ble with mas­sive plan­ets (like gas gi­ants) that have wide or­bits.

Mean­while, rocky plan­ets that or­bit closer to their stars (like Earth) can­not be seen be­cause of all the light in­ter­fer­ence. Since it is these plan­ets that as­tronomers and as­tro­bi­ol­o­gists ex­pect to be the most hab­it­able, be­ing forced to study them in­di­rectly is quite lim­it­ing. How­ever, that’s all likely to change in the near fu­ture.

Next-Gen­er­a­tion Ob­ser­va­to­ries

In 2021, af­ter mul­ti­ple de­lays, the James Webb Space Te­le­scope (JWST) will fi­nally be launched. In terms of ex­o­planet stud­ies, the JWST will rely on nextgen­er­a­tion in­frared op­tics to con­duct fol­low-up stud­ies of con­firmed plan­ets. This will al­low it to ob­serve smaller plan­ets that or­bit closer to their stars and de­tect chem­i­cal sig­na­tures in their at­mos­pheres.

By the mid-2020s, the JWST will be joined by the suc­ces­sor to the Hub­ble Space Te­le­scope. Known as the Nancy Grace Ro­man Space Te­le­scope (for­merly the WFIRST), this ob­ser­va­tory will have 100 times the res­o­lu­tion of its pre­de­ces­sor. Com­bined with time­series mi­crolens­ing of the Milky Way’s cen­tral re­gion (the “bulge”), Ro­man will be able to spot ex­o­plan­ets the size of Mer­cury or Mars (“sub-Earths”).

Both ob­ser­va­to­ries will also be equipped with coro­n­a­graphs, a special in­stru­ment that blocks the di­rect light from a star so that nearby ob­jects – like a sys­tem of plan­ets – are vis­i­ble. NASA also has plans for a special class of “qwl­ter” space­ship that will act as a coro­n­a­graph for tele­scopes that don’t have their own.

As part of the pro­posed New Worlds Mis­sion (NWM) project, these plans call for a space­craft equipped with a large “star­shade” to fly ahead of a space te­le­scope. Once in po­si­tion, the NWM space­craft will de­ploy its shade - a flower-shaped struc­ture – to block out the light com­ing from a spe­cific star so the space tele­scopes can get a bet­ter look at its ex­o­plan­ets.

There are also some pow­er­ful ground-based tele­scopes that will be op­er­a­tional by the 2020s. In 2025, the ESO’s Ex­tremely Large Te­le­scope (ELT) will gather light for the first time while the Thirty Me­ter Te­le­scope (TMT) and Gi­ant Mag­el­lan Te­le­scope (GMT) will com­mence ob­ser­va­tions by the mid-2020s and 2029, re­spec­tively.

These tele­scopes have their own coro­n­a­graphs but will also em­ploy what is known as Adap­tive Op­tics (AO). This tech­nique in­volves us­ing com­put­er­con­trolled de­formable mir­rors to cor­rect for dis­tor­tions caused by the Earth’s at­mos­phere in real-time.

“By the end of the decade, as­tronomers could be mak­ing di­rect ob­ser­va­tions of Earth-like ex­o­plan­ets on a reg­u­lar ba­sis.”

Equipped with these in­stru­ments, as­tronomers will have the res­o­lu­tion and sen­si­tiv­ity they need to di­rectly image thou­sands of ex­o­plan­ets and (more im­por­tantly) char­ac­ter­ize them.

From Dis­cov­ery to Char­ac­ter­i­za­tion

In re­cent years, the fo­cus of as­tronomers has slowly shifted away from find­ing ex­o­plan­ets (i.e. dis­cov­ery) to con­duct­ing fol­low-up stud­ies to see if they can sup­port life (i.e. char­ac­ter­i­za­tion). This trend is ex­pected to pick up speed very soon thanks to the afore­men­tioned tele­scopes and more so­phis­ti­cated data-min­ing tech­niques.

By the end of the decade, as­tronomers could be mak­ing di­rect ob­ser­va­tions of Earth-like ex­o­plan­ets on a reg­u­lar ba­sis. These in­clude Prox­ima b, Ross 128 b, Tee­gar­den’s Star b, 82 G. Eri­dani e, and the seven plan­ets of TRAPPIST-1 – po­ten­tially-hab­it­able worlds that are within 40 light-years of Earth.

The data we glean from ob­serv­ing these ex­o­plan­ets will go a long way to­wards help­ing us de­cide which we should be send­ing probes to some­day.

Who knows? Maybe we’ll even de­tect biosig­na­tures on some of these plan­ets (fin­gers crossed!); in the process, solv­ing the mystery of whether or not we’re alone in the Uni­verse at last!

Fur­ther Read­ing...

Ex­o­plan­ets NASA

STSCI sci­ence themes

NASA: Ways to find a planet

ESO: Adap­tive op­tics tech­nol­ogy

SETI: Fu­ture space tele­scopes

Uni­verse To­day: How the next gen­er­a­tion of ground-based su­per tele­scopes will di­rectly ob­serve ex­o­plan­ets

 ??  ?? Right:
Artist’s im­pres­sion of Prox­ima b.
Credit: ESO/M. Korn­messer. Creative Com­mons At­tri­bu­tion 4.0 In­ter­na­tional Li­cense.
Source: Link.
Right: Artist’s im­pres­sion of Prox­ima b. Credit: ESO/M. Korn­messer. Creative Com­mons At­tri­bu­tion 4.0 In­ter­na­tional Li­cense. Source: Link.
 ??  ?? Above: Por­trait of the author, Matthew Wil­liams. Photo credit: C. Jack. All rights re­served.
Above: Por­trait of the author, Matthew Wil­liams. Photo credit: C. Jack. All rights re­served.

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