Don’t hold your breath ex­pect­ing space­ships

Mas­sive dis­tances ren­der in­ter­stel­lar travel all but im­pos­si­ble, sci­en­tists say

Ottawa Citizen - - CITY - TOM SPEARS ts­[email protected]­ twit­­pears1

Three cen­turies af­ter his death, Sir Isaac New­ton still keeps us from trav­el­ling to the stars.

Or at least his laws of physics do. Re­mem­ber that big space rock called Ou­mua­mua that flew through our neigh­bour­hood in the sum­mer? As­tronomers nearly didn’t see it; rocks are dark blobs against a black sky, and a tele­scope spot­ted it only as it flew back to­ward the edge of our so­lar sys­tem and pre­sum­ably be­yond.

For a brief mo­ment in early Novem­ber, though, some eggheads at Har­vard Univer­sity saw it speed­ing up when it had no busi­ness speed­ing up and won­dered: What if it’s an alien ship?

Con­sen­sus to­day among peo­ple who study these things: It al­most cer­tainly isn’t. But it got ev­ery­one talk­ing about whether aliens from an­other so­lar sys­tem could fly here — or what it would take for hu­mans to fly to a dis­tant, in­hab­ited planet.

That was New­ton’s time to bring ev­ery­one down to Earth.

We asked some as­tronomers about it.

“We be­lieve that ev­ery star in our galaxy has a plan­e­tary sys­tem,” Paul De­laney of York Univer­sity said. That be­lief is the re­sult of years of ob­ser­va­tions, es­pe­cially by the Ke­pler Space Tele­scope launched in 2009. About 15 to 20 per cent of these have plan­ets that could sup­port life, mean­ing there are tens of bil­lions of Earth-like plan­ets in the Milky Way.

Ge­og­ra­phy gets in the way, though. The prob­lem is all about dis­tance.

There are 11 stars within about 10 light years of Earth. (A light year is the dis­tance light trav­els in one year, or nearly 9.5 tril­lion kilo­me­tres.) The clos­est is more than four light years away, so it’s go­ing to be a long trip.

“At best it’s go­ing to take you years to go be­tween the stars, and that’s if you get up close to the speed of light,” De­laney said. Light trav­els about 300,000 kilo­me­tres ev­ery sec­ond.

What does it take to speed up a space­ship?

“Lots and lots of en­ergy. We’ve got noth­ing even re­motely ca­pa­ble of do­ing that,” he said.

Blame New­ton. First for his first law of mo­tion: Any ob­ject has in­er­tia; it will ac­cel­er­ate only if an ex­ter­nal force acts on it. Add some more New­to­nian physics: The more mass an ob­ject has, the more force is re­quired to speed it up.

Even “space chips,” or wafer-sized space probes weigh­ing a few dozen grams, re­quire more en­ergy than we know how to pro­duce to reach a speed that would carry them to a star in a rea­son­able time.

“And don’t for­get rel­a­tiv­ity,” De­laney said. “The closer you get to the speed of light, the larger is your in­er­tial mass, which means even more en­ergy is re­quired.

“We are re­ally pretty bereft of op­tions (for) big ob­jects be­ing ac­cel­er­ated up to se­ri­ous speed to make them travel in­ter­stel­lar dis­tances.”

Space travel “is not re­ally dif­fi­cult to do if you’re will­ing to wait. If you want to do it in the life­time of a Homo sapi­ens, it’s a lot more dif­fi­cult,” said Seth Shostak, a se­nior as­tronomer with the Search for Ex­trater­res­trial In­tel­li­gence (SETI) in California.

A typ­i­cal NASA Mars probe, if launched from the near­est star, “would take about 75,000 years to get here (and) by that time your own so­ci­ety is prob­a­bly so dif­fer­ent that you have for­got­ten en­tirely about hav­ing done it.”

To send one ship to a nearby star within a cen­tury, “you’re talk­ing about the en­ergy ex­pen­di­ture com­pa­ra­ble to what Canada uses in a few cen­turies.”

Still, De­laney and oth­ers were thrilled to learn about Ou­mua­mua “from the mo­ment you say ‘in­ter­stel­lar vis­i­tor,’ even if it is prob­a­bly a rock.

“All of us have a lit­tle bit of wish­ful think­ing,” De­laney said. But ev­i­dence? Not so far.

Mean­while the big­ger ques­tion for Shostak is: Why would aliens pay at­ten­tion to Earth at all, let alone travel here? “Be­cause, if they are that far away, what do they know about Earth?” Only that we have oxy­gen in our at­mos­phere and, there­fore, life of some sort.

Ra­dio sig­nals — es­pe­cially air­port radar, which is a very good fre­quency for reach­ing into deep space — have been go­ing out for about 70 years. Most of the uni­verse hasn’t re­ceived those sig­nals yet.

Yet Shostak re­mains a be­liever in alien life, some­where.

Cal­cu­lat­ing roughly a tril­lion plan­ets in our galaxy, the Milky Way and a tril­lion other gal­ax­ies, he fig­ures it would take a mir­a­cle for Earth to be the only place with life, and he doesn’t be­lieve in mir­a­cles.

In the mean­time, an as­tronomer at Mas­sachusetts In­sti­tute of Tech­nol­ogy has pro­posed shin­ing a mil­lion-watt laser beam into space as a “porch light” to let ev­ery­one know that Earth is oc­cu­pied.

James Clark fig­ures any­one within 20,000 light years would no­tice.

We are re­ally pretty bereft of op­tions (for) big ob­jects be­ing ac­cel­er­ated up to se­ri­ous speed to make them travel in­ter­stel­lar dis­tances.


This artist’s ren­der­ing shows the in­ter­stel­lar ob­ject named Ou­mua­mua, which some spec­u­lated might be an alien ship when it ex­hib­ited odd move­ment pat­terns in the sum­mer. But sci­en­tists say in­ter­ga­lac­tic travel is ex­tremely un­likely. Dis­tances be­tween stars are too great and our en­ergy sys­tems too weak .

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