THE HUNT FOR EARTH’S SIS­TER

A search that could make us re­think our place in the Uni­verse

BBC Earth (Asia) - - Front Page -

CHRIST­MAS, 1968. THREE MEN WERE IN OR­BIT AROUND THE MOON, AS FAR AWAY FROM EARTH AS ANY­ONE HAD EVER GONE. THEY THOUGHT THE MAG­NIF­I­CENT DES­O­LA­TION OF THE LU­NAR LAND­SCAPE WAS THE MOST STUN­NING THING THEY WERE

GO­ING TO SEE DUR­ING THEIR MIS­SION. BUT THEY WERE WRONG. On their fourth or­bit, as­tro­naut Bill An­ders saw Earth rise above the Moon’s hori­zon. He pho­tographed the mo­ment and in do­ing so gave the world one of the most iconic images of the space age. This pic­ture of the seem­ingly frag­ile blue planet Earth sub­se­quently be­came a sym­bol to rep­re­sent both the en­vi­ron­men­tal move­ment and the won­ders of space ex­plo­ration. Now, a group of pri­vately funded as­tronomers and en­gi­neers want to recre­ate that act by tak­ing a new pic­ture of another blue planet – one around another star.

BLUE SKY THINK­ING

Dubbed Project Blue, the mis­sion aims to build and launch a space tele­scope with a sin­gle goal in mind: to im­age any plan­ets in the hab­it­able zones of the near­est Sun-like stars. If such plan­ets were Earth-sized with oceans and at­mos­pheres, then they could even “see Blue”, Project Blue’s term for find­ing a po­ten­tially hab­it­able planet.

The mis­sion is the brain­child of the Bold­lyGo In­sti­tute. This not-for-profit or­gan­i­sa­tion was founded by Dr Jon Morse, a for­mer NASA sci­en­tist and White House science ad­vi­sor, to in­ves­ti­gate highly com­pelling sci­en­tific ques­tions us­ing pri­vate money from donors and crowd­fund­ing ini­tia­tives. And there are few ques­tions more com­pelling than whether there are other Earth-like plan­ets around other stars.

The quest to find Earth-ana­logues, as these plan­ets are known, be­gan in earnest in 1995 when a pair of Swiss as­tronomers dis­cov­ered 51 Pe­gasi b – the first ex­tra­so­lar planet (or ex­o­planet) to be found around a Sun-like star. It was the size of Jupiter and not at all Earth-like, but it proved that plan­ets were now in reach of our tech­no­log­i­cal abil­i­ties.

In the decades since, al­most 4,000 other exoplanets have been de­tected but hardly any have had their pic­ture taken. The trou­ble is that plan­ets do not gen­er­ate any of their own light and in­stead sim­ply re­flect their star’s light. This makes them more than a bil­lion times fainter than their par­ent star. Tele­scopes to date have been able to catch a few glimpses of large plan­ets, but plan­ets the size of Earth have re­mained im­pos­si­ble to im­age. In­stead, as­tronomers have used in­di­rect ob­ser­va­tions to in­fer the ex­is­tence of the exoplanets.

Most of the exoplanets found so far were de­tected

“ALTHOUGH SOME

EXOPLANETS GRABBED

HEAD­LINES AROUND THE

WORLD, TO DATE WE

HAVE NOT FOUND A

TRUE EARTH-TWIN”

us­ing NASA’s Ke­pler Space Tele­scope. Ke­pler tracked a star’s bright­ness, look­ing for the dip caused when a planet crossed in front of it. Its in­stru­ments were pre­cise enough that it could see smaller rocky (also called ter­res­trial) plan­ets but none of them have proved to be a twin to Earth. Although some grabbed head­lines around the world for be­ing sim­i­lar, to date we have not found a true Earth-twin in the sense that it is an Earth-sized world in an or­bit the size of Earth’s around a Sun-like star.

As luck would have it though, the near­est star sys­tem to the Sun con­tains two stars that could be ex­tremely re­ward­ing places to look.

PLANET HUNT

Al­pha Centauri is made up of three stars in mu­tual or­bit around each other. One of these, known as Prox­ima Centauri, is a red dwarf star and there­fore con­sid­er­ably smaller and cooler than the Sun. Of the oth­ers, Al­pha Centauri B is sim­i­lar to the Sun and Al­pha Centauri A is vir­tu­ally iden­ti­cal. These are the stars that Project Blue will tar­get.

Ex­ist­ing stud­ies of these two stars show that large plan­ets like Jupiter are not present. So if there are plan­ets there, all they can be are Earth-sized worlds in Earth-like or­bits. “That’s what we are go­ing to test,” says Morse.

The project pro­poses a small space tele­scope. Its mir­ror is just 0.5 me­tres in di­am­e­ter, which makes it about half the size of Ke­pler. Yet this should be big enough for Project Blue to take di­rect pic­tures of any plan­ets as they move around their star be­cause the space­craft will use an in­stru­ment called a coro­n­a­graph. It will block out the light from the cen­tral star, al­low­ing the much fainter planet to be seen.

Don’t ex­pect any­thing spec­tac­u­lar, though. Any planet will ap­pear as noth­ing more than a sin­gle pixel of light, sim­i­lar to the im­age of Earth cap­tured in 1990 by the Voy­ager 1 space­craft from a dis­tance of four bil­lion miles. De­spite its lack of aes­thetic beauty, it would al­low sci­en­tists ac­cess to un­prece­dented in­for­ma­tion about the planet.

“Mon­i­tor­ing the bright­ness and the colour of plan­ets over time is what al­lows you to make maps of the sur­face,” says Dr Mar­garet Turn­bull of the Carl Sa­gan Cen­ter for Re­search at The SETI In­sti­tute, Cal­i­for­nia, and a mem­ber of the Project Blue team. “Are there oceans? Are there con­ti­nents? Are there cloud pat­terns? Weather pat­terns? Sea­sons? If there are, all of those things should be re­flected – lit­er­ally – in the colour data and in the bright­ness of the planet over time.”

Earth, for ex­am­ple, looks bluer when we are look­ing at an ocean than at a con­ti­nent, and it is brighter when we are look­ing at Antarc­tica.

TELE­SCOPE TECH

The sim­plic­ity with which the mis­sion can be stated be­lies the tech­ni­cal chal­lenge. No one has yet flown a coro­n­a­graph de­signed for tak­ing pic­tures of Earth-like plan­ets. Project Blue is work­ing closely with NASA, which is plan­ning a much larger mis­sion called WFIRST (the Wide-Field In­frared Sur­vey Tele­scope). It is de­signed to have the sen­si­tiv­ity of the Hub­ble Space Tele­scope but with a field of view 100 times the size and will in­clude a coro­n­a­graph that Turn­bull has been work­ing on. Project Blue will use a lot of the ideas and tech­nol­ogy be­ing de­vel­oped for WFIRST to pro­vide an or­bital test of how to use such an in­stru­ment to de­tect plan­ets. This is why it is so im­por­tant to de­vote the whole mis­sion to ex­plor­ing just one star sys­tem.

Scan this QR Code forthe au­dio reader

EARTHRISETaken on Christ­mas Eve by the crew of Apollo 8, Earthrise was the first time a hu­man had seen Earth rise from be­hind the hori­zon of the Moon. A sub­se­quent mis­sion,Apollo 10, took a video of the Earthrise.

ABOVE:Project Blue (left) will be launched into low-Earth or­bit and will pho­to­graph plan­ets in the Al­pha Centauri sys­tem. It will use a lot of tech­nol­ogy be­ing de­vel­oped for NASA’s much larger WFIRST mis­sion (right)

Newspapers in English

Newspapers from Singapore

© PressReader. All rights reserved.