50 ASTRONOMY • MAY 2020
have on Earth. So, mineral specimens
give us a window into faraway worlds
that we will never see up close.
That’s intriguing, because the more
we look around our area of the Milky
Way Galaxy, the more we have discov-
ered that many other planetary systems
exist around nearby stars. Our galaxy
consists of several major parts, but the
most recognizable and distinctive is the
Milky Way’s disk — the brightest portion
where most of the stars, gas, and dust
reside. The Milky Way contains some
400 billion stars spread across this f lat-
tened disk, some 100,000 light-years
across. Our Sun is just one of the roughly
400 billion stars.
We’ve known about our own plan-
etary system since ancient times, of
course, when ancient skywatchers named
the naked-eye planets after gods because
they had the power to move night to
night relative to the fixed stars. We’ve
been all the way through the discovery
of Pluto in 1930 and its demotion to
dwarf planet in 2006, and understand
the huge population of smaller bodies in
our solar system: dwarf planets, Kuiper
Belt objects, comets, and asteroids. They
are almost countless, and many thou-
sands are cataloged and named.
Only in recent times have astrono-
mers had the power to discover planets
orbiting stars other than the Sun.
Technological advances in telescopes and
observing methods brought the first
confirmed discovery of an exoplanet —
shorthand for extrasolar planet — in- As of January 2020, we now know
of about 4,100 exoplanets in more than
3,000 systems, and astronomers have
only reached out to relatively nearby
space in our galaxy.
Because of the difficulty of detecting
planets orbiting stars from enormous
distances, many of these planets are
massive, so-called “hot Jupiters” that are
relatively close to their suns. The most
productive planet-hunting instrument
was the Kepler Space Telescope, which
trailed Earth in its orbit around the Sun
and cataloged exoplanets from 2009
through 2018. This magnificent tele-
scope studied a relatively small area of
sky and found more than 2,600 of the
roughly 4,100 known exoplanets. A
newer telescope, TESS, was launched in
2018 and has begun another epoch of
exoplanet detection.
As we look out into the galaxy
surrounding our solar system, it’s not
surprising to see lots of nearby planetary
systems. Astrophysicists believe that stars
form as cosmic clouds — nebular stellar
nurseries — collapse and stars wink on
inside them. The leftover detritus from
the collapse, swirling slowly around the
infant suns, make a cadre of planets and
smaller bodies surrounding the new star.
And we are only in the pioneering
days of being able to see farther out into
the galactic neighborhood that surrounds
us. Understanding that stars are so
numerous and that planetary systems are
plentiful is exciting. After all, the most
basic driving question everyone would
like to answer is at the foundation of it
all: “Are we alone? Is there other life inA stereo view of the Lagoon Nebula (M8) shows it as bright nebulosity buried within a cave that encloses
a shell of fainter gas and appliqués of dark nebulosity stretching into the foreground.
Rarely do cosmic clouds create letters suspended
in the sky, but such is the case with a pair of dark
nebulae, B142 and B143 in Aquila, which seem to
form a capital letter E. It is nicknamed Barnard’s E
because the nebulae were discovered by
astronomer E.E. Barnard. Set off by a particularly
rich Milky Way star field, this nebula can be
glimpsed in small telescopes on a dark night.
BERNHARD HUBLExploring the world of
nebulae offers an eye-
opening understanding
of the cosmos at large.