Astronomy - February 2014

28 ASTRONOMY t FEBRUARY 2014

Alien life

C

ould the brighter inhabitants of

our galaxy be hunkered down

around its dimmer stars? Smile

if you must, but small stars may

mark the best neighborhoods to

search for savvy species. Of course, this

conjecture is at loggerheads with conven-

tional wisdom. For more than 50 years,

astronomers embarking on the search for

extraterrestrial intelligence (SETI) have

slewed their radio antennas mostly toward

Sun-like stars. This choice was more than

just mindless nepotism: The usual assump-

tion of SETI practitioners is that if a neigh-

borhood around a G-type star befits us, it

also will befit the aliens.

But other stellar locales are closer, more

plentiful, and frankly better bets for hous-

ing clever beings: the dim bulbs of the cos-

mos known as red dwarfs.

Plenty of habitats

If you look at the night sky from a dark site,

you’ll behold hundreds of stars even before

you set up your telescope. A nice view for

sure, but this horde isn’t representative of

most stars, any more than a grove of red-

woods represents most trees. The majority

of the prominent naked-eye stars are giants

or supergiants. The latter are 10 or more

times the mass of the Sun and considerably

brighter, which is why we can see them so

well from Earth.

These hefty stars are exceptionally vis-

ible because brightness and mass don’t scale

linearly. Multiply a star’s mass by just 10,

and the intrinsic brightness — the luminos-

ity — goes up by a factor of 3,000. This is

why supergiants are celestial superstars,

dominating the night sky despite their rar-

ity (fewer than 0.2 percent of all stars are

SETI researchers have set their sights

on red dwarfs in hopes of making a big

discovery. by Seth Shostak

Searching for

SMART LIFE

around

SMALL STARS

Seth Shostak is a senior astronomer at the SETI

Institute in Mountain View, California, and the

author of three books about SETI.

This artist’s impression shows the

red dwarf sunset from the surface

of rocky planet Gliese 667Cc, which

orbits a red dwarf. Tens of billions

of planets like this one likely sur-

round small, dim, but perfectly

life-friendly stars. ESO/L. CALÇADA