My first Magazine Sky & Telescope - 01.2019 | Page 41

There’s still much work for RECONS to do. The second data
release from the European Space Agency’s astrometric satel-
lite, Gaia, provided a huge amount of data to churn through.
“It will take us quite a bit more time to sort through the
1,722 objects reported to be within 10 parsecs,” says Henry,
who reckons that three-quarters of them will turn out to be
false positives. That’s a surprising number, but the objects are
exceptionally faint, leading to high levels of uncertainty in
the distance measurements, he explains — at least one of the
“nearby” objects has already proved to be a galaxy. Once the
Solar System
Asteroid Belt
Inner Asteroid Belt
Inner Asteroid Belt
Kuiper Belt
Epsilon Eridani System
Outer Asteroid Belt
Comet Belt
Rogues Gallery
Of the 378 stars in the RECONS 10-parsec census, which
ones stand out? Here are five of our most interesting stel-
lar neighbors:
Epsilon Eridani Todd Henry flags Epsilon Eridani as
being a particularly interesting K-type star. Just 10.5 light-
years away, it is a young replica of what our own solar
system may have looked like when it was less than a bil-
lion years old. It’s known to have at least one giant planet
as well as two dust belts and a comet belt, which could
be home to asteroids or comet-like icy bodies.
Epsilon Indi Epsilon Indi is actually a triple system,
12 light-years away, with a K-type star orbited by a binary
system of brown dwarfs, as well as a giant planet on a
wide orbit.
SCR 1845-6357 This binary system 12.6 light-years away
comprises a red dwarf with about 8% the mass of the Sun
and a brown dwarf with 50 times the mass of Jupiter and
a temperature of about 950K (675°C). Todd Henry says the
system is one of his favorites, because astronomers can
use it to explore how these different objects evolve.
Sirius The famous Dog Star might be the brightest star
in the sky, but it also hosts a white dwarf, the closest to
us at 8.6 light-years. The white dwarf is the remnant of a
star that was five times more massive than the Sun, while
Sirius itself is twice as massive as the Sun.
Ross 128 At 11 light-years away, this red dwarf star is the
11th-closest system to the solar system. It was considered
a fairly unremarkable star with only the odd flare to speak
of, until astronomers discovered a potentially habitable
planet orbiting it in 2017.
p EPSILON ERIDANI Only 800 million years old, Epsilon Eri has
two dusty belts and an outer cold belt, reminiscent of the belts in our
solar system. Astronomers have discovered one Jupiter-mass planet
and suspect there might be two more farther out that carve the edges
of the outer belts.
sk yandtele scope.com • JA N UA RY 2 019
Looking Farther Afi eld
Inner Epsilon
Eridani System
That will now be the task of NASA’s Transiting Exoplanet
Survey Satellite (TESS), which launched in April 2018 and is
going to focus on the 200,000 nearest stars (S&T: Mar. 2018,
p. 22). That’s important because, as TESS’s principal investi-
gator George Ricker (Massachusetts Institute of Technology)
points out, they’re close enough for instruments such as the
upcoming James Webb Space Telescope to perform follow-up
studies to look at atmospheric compositions.
“There’s some pretty demanding but conclusive observa-
tions that can be made with the Webb telescope” on the
TESS targets, he says. “But if you were to only have the Kepler
objects, it would take a 65-meter telescope in space!”
TESS should fi nd several dozen new Earth-size rocky
exoplanets, many of them within 50 pc of our solar system.
However, it has already been beaten in the race to discover
a planet around the nearest star to the Sun, the red dwarf
Proxima Centauri (Alpha Cen C).
It took more than 20 years following the discovery of the
fi rst exoplanets for astronomers to identify a planet orbiting
Proxima Cen. The world, Proxima Cen b, was discovered in
2016 by astronomers led by Guillem Anglada-Escudé (Queen
Mary University of London; S&T: Dec. 2016, p. 10). Now
they are embarking on the Red Dots campaign to search for
planets around not just Proxima but also two other nearby
M dwarfs, Barnard’s Star and Ross 154. The three stars were
chosen because they can be observed together on the same
nights. In the future, the campaign will look at other nearby
M dwarfs, such as Wolf 359.
The Alpha Cen system is a prime example of how much
we still don’t know about the nearest stars. “Have you ever
looked at the fundamental measurements we have for Alpha
Centauri A or B?” asks Tabetha Boyajian (Louisiana State
University). “For Alpha Centauri A, the literature lists spec-
tral types ranging from F8 to G5, and temperatures range
from 5519 to 5939 kelvin. Magnitudes are all over the place,
too. It’s just sad!”
Asteroid Belt
NASA’s Kepler Space Telescope has taught us
that, on average, there is at least one planet
for every star. But only 28 of the closest 317
known star systems (including the Sun’s) are
known to have planets — that’s less than 9%.
Inner Solar System
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