Here’s How NASA Thinks We’ll Find Aliens

The agency thinks we’ll find life on other planets soon, but we may not be exchanging messages for a while.

We can't phone E.T.'s home just yet, but NASA thinks we may not be far from finding it.
National Journal
Alex Brown
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Alex Brown
July 16, 2014, 1 a.m.

When earth­lings fi­nally dis­cov­er their ali­en neigh­bors, it prob­ably won’t be aboard a warp-speed space­ship or via in­ter­galactic Morse code.

The more likely — and de­cidedly less sexy — scen­ario, sci­ent­ists said at a Monday NASA pan­el, is a gi­ant space-based tele­scope find­ing a plan­et with gases in the at­mo­sphere that in­dic­ate life.

“We are look­ing for bio­lo­gic­al sig­na­tures, gases that are pro­duced by life,” said Sara Seager, a plan­et­ary sci­ent­ist at the Mas­sachu­setts In­sti­tute of Tech­no­logy. “We’re look­ing for whatever’s out there that will be gen­er­at­ing gases in the at­mo­sphere.”

And since our search at the mo­ment ex­tends to about 200 light-years away, it may be a long, long time be­fore we find out what that life looks like.

So where does our search start?

Ac­cord­ing to NASA, we’re well on our way. The agency’s plan in­volves a series of tele­scopes, each big­ger and bet­ter than the last. After one nar­rows down the search, the next will fol­low up with more de­tailed find­ings — un­til even­tu­ally one of them con­firms that we’re not alone.

That all star­ted with the Hubble Space Tele­scope, launched in 1990. It’s been fol­lowed by the Spitzer and Kepler tele­scopes. Their find­ings have helped us learn more about galax­ies, stars, and sol­ar sys­tems — and where we might find “Earth 2.0.”

Thanks to Kepler, we know that our Milky Way galaxy has something like 100 bil­lion plan­ets — know­ledge we didn’t have five years ago. An­oth­er im­port­ant dis­cov­ery? “We ac­tu­ally know now what life might look like,” said Matt Moun­tain, a NASA tele­scope sci­ent­ist. “We know life can im­print it­self on the at­mo­sphere of plan­ets go­ing around oth­er stars. This is what a liv­ing plan­et looks like.”

Es­sen­tially, Kepler has taken a census of nearby stars, giv­ing the next tele­scope a cata­log from which to search. NASA be­lieves 10-20 per­cent of those stars have an Earth-like plan­et in the hab­it­able zone. That’s the area that’s “not too hot, not too cold, just right for life,” Seager said, though there’s some dis­pute over where the bound­ar­ies of that zone start and end.

So what’s the next tele­scope in the queue? That would be TESS, the Trans­it­ing Exo­plan­et Sur­vey Satel­lite, sched­uled to launch in 2017. Its job is to watch about half a mil­lion nearby stars, look­ing for tem­por­ary drops in bright­ness that could in­dic­ate an or­bit­ing plan­et is passing in front. TESS will find about 1,000 stars that will serve as a search list for the next tele­scope in line.

A year later, our best and bright­est hope so far will con­tin­ue the search. The James Webb Space Tele­scope comes in at 6.5 meters, more than twice the size of Hubble. Its 18 hexagon­al mir­rors will give sci­ent­ists a much broad­er view of light wavelengths as they search the sky. “The James Webb Tele­scope will trans­form our view of the uni­verse,” said John Grun­sfeld, a former as­tro­naut and cur­rent mem­ber of NASA’s sci­ence team.

NASA’s team will use the tele­scope to look for signs of life — blue sky, oxy­gen, car­bon di­ox­ide, sul­fur di­ox­ide, plant life, li­quid wa­ter — as the light of a star be­hind a plan­et fil­ters through its at­mo­sphere and ex­poses its char­ac­ter­ist­ics. This is known as trans­it spec­tro­scopy.

It’s still a long shot. “We have to get really lucky,” Seager said. “With the James Webb we have our first chance, our first cap­ab­il­ity, of find­ing life on an­oth­er plan­et. Now nature just has to provide for us.”

That’s where things get tricky. It’s really hard to get a good look at plan­ets, which are around 10 bil­lion times faint­er than the stars they circle. And even though our galaxy has an abund­ance of Earth-like plan­ets (the “holy grail” of our ali­en search, as Grun­sfeld put it, though not the only can­did­ates for sup­port­ing life), we don’t know how dif­fi­cult it is for life to get a foothold. In oth­er words, we could find many Earth twins be­fore we dis­cov­er one with any­body home.

And even the James Webb can only see so much. It will prob­ably take an­oth­er gen­er­a­tion or two of satel­lites be­fore our odds really start to go up. The is­sue is size. “You need big­ger tele­scopes, you need more col­lect­ing area,” said Dave Galla­gh­er, who works in NASA’s Jet Propul­sion Labor­at­ory. “You’ve gotta get big­ger.”

But it’s not just as simple as scal­ing up. Big­ger satel­lites need big­ger rock­ets, and even then the tele­scopes are nowhere close to fit­ting in a des­ig­nated pay­load area. The 6.5-meter James Webb, once de­ployed, will have to go through a com­plex un­fold­ing pro­cess be­fore it reaches its full size. Sol­ar pan­els splay out from the sides, cables pull out a five-lay­er sun­shield in­to place, and the fol­ded-back mir­rors come to­geth­er. It’s es­sen­tially like build­ing a ship in a bottle, then re­mov­ing it in space. “This is what it takes to get a big tele­scope in­to a not-big-enough rock­et,” said John Math­er, Webb’s seni­or pro­ject sci­ent­ist.

Big­ger rock­ets, like the gi­ant Space Launch Sys­tem, will help fu­ture pay­loads get to space. And the next planned mis­sion after the James Webb Tele­scope, an in­frared tele­scope in 2024, will meas­ure only 2.4 meters. Be­cause the bright­ness of stars tends to make their plan­ets in­vis­ible, these mis­sions will only be able to ob­serve plan­ets much lar­ger than Earth or­bit­ing stars much smal­ler than the sun. “Some­how we need to block out that star­light,” Seager said.

To have a real shot, sci­ent­ists say we’ll even­tu­ally need a tele­scope that meas­ures 16 or 20 meters. Moun­tain showed a graph­ic dis­play­ing the num­ber of nearby, po­ten­tially hab­it­able plan­ets the James Webb Tele­scope is cap­able of view­ing. The screen showed only a hand­ful. “How lucky do we feel?” he asked. “With a 20-meter tele­scope, we can see hun­dreds of Earth-like plan­ets around oth­er stars. That’s what it takes to find life.”

The large tele­scope is part of the New Worlds Mis­sion. This plan in­volves a sep­ar­ate satel­lite with fol­dout petals tens of meters in dia­met­er, much like the shape of a sun­flower. That shape is spe­cific­ally de­signed to dif­fract stars’ rays and let only plan­ets’ light through. That satel­lite, known as a star­shade, would sep­ar­ate from the tele­scope and fly tens of thou­sands of kilo­met­ers away. Then the tele­scope would point at it, us­ing the star­shade as a fil­ter to bet­ter cap­ture im­ages from plan­ets.

The star­shade/gi­ant satel­lite plan is still in the works, and for now, sci­ent­ists are ex­cited about the res­ults they plan to get from the James Webb Tele­scope. And wheth­er it’s Webb or a suc­cessor that first finds an in­hab­ited plan­et, they’re con­fid­ent that mo­ment will come. “It’s highly im­prob­able in the lim­it­less vast­ness of the uni­verse that we hu­mans stand alone,” said NASA Ad­min­is­trat­or Charles Bolden. “I find it hard to be­lieve that we’re in this world alone.”

Moun­tain put it in more ro­mantic terms. “Just ima­gine the mo­ment when we find po­ten­tial sig­na­tures of life,” he said. “Ima­gine the mo­ment when the world wakes up and the hu­man race real­izes that its long loneli­ness in time and space may be over — the pos­sib­il­ity we’re no longer alone in the uni­verse.”

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