text and infographic by Sara Chodoshpale blue
dots in a
haystack
DATASCOPE22 FALL 2019 • POPSCI.COM
1
Confirmed planets
Orbiting bodies dim starlight as
they pass in front of their re-
spective suns, which makes the
fireballs appear to flicker out at
regular intervals from our per-
spective. Astronomers think
they’ve already spotted poten-
tially telltale winks from more
than 8,000 planets but have
confirmed the existence of only
around half that number.
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Habitable-zone planets
Life is a Goldilocks game; too
close to the sun and you roast,
too far and you freeze. A few
dozen worlds seem to spin in an
orbit that’s just right. They could
receive anywhere from half to
double the radiation that ham-
mers Earth and still harbor life,
but factors like how often host
stars spit plasma flares could
eliminate many contenders.2
Rocky planets
Mass really does matter. Rocks
much smaller than ours lack the
gravity to hold an atmosphere, so
liquid surface water won’t stick
around. Anything twice our size or
larger is likely to gather dust, gas,
and ice, creating a barren world
like Jupiter or Neptune. Orbs 0.8
to 1.5 times Earth’s radius can be
both rocky and wet, and we’ve
found around 1,000 of them.4
Earth-like planets
Headlines oft herald worlds as
“Earth-like,” and a couple dozen
could be. But we can’t yet tell
whether bodies in other star sys-
tems share crucial atmospheric
similarities with our home. The
closest of our planetary twins is
Proxima Centauri b, roughly 4
light-years away. Current probes
and scopes can’t gather the intel
we need at that distance—yet.ASTRONOMERS’ CUPS HAVE RUNNETH OVER WITH ALIEN
worlds since NASA launched its (now retired) exoplanet- hunting
Kepler space telescope in 2009. But sussing out which orbiting rocks
could support life as we know it isn’t an exact science; our current
deep-space-searching technology can’t peer closely enough to de-
termine surface and atmospheric compositions on faraway places.
Here’s what experts have managed to work out so far.1342SOURCE:^ NASA^ EXOPLANETARCHIVE,^ COMPOSITE^ PLANET^ DATA