http://www.skyandtelescope.com.au 23Rogues gallery
Of the 378 stars in the RECONS 10-parsec census, which
ones stand out? Here are five of our most interesting
stellar neighbours:
Epsilon EridaniTodd Henry flags Epsilon Eridani as
being a particularly interestingK-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 billion 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 IndiEpsilon Indi is actually a triple system,
12 light-years away, with aK-type star orbited by a binary
system of brown dwarfs, as well as a giant planet on a
wide orbit.
SCR 1845-6357This 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 675°C. Todd Henry says the
system is one of his favourites, because astronomers can
use it to work out how these different objects evolve.
SiriusThe 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.SEPSILON 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.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%.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. That’s important
because, as TESS’s principal investigator 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
observations 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-metre telescope in space!”
TESS should find 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
first 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). 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
spectral 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!”Looking farther afield
There’s still much work for RECONS to do. The second
data release from the European Space Agency’s astrometric
satellite, 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
NASA / JPL-CALTECH— at least one of the ‘nearby’ objects has already proved to
Inner Solar SystemAsteroid BeltInner Asteroid BeltAsteroid BeltInner Asteroid Belt
Outer Asteroid BeltKuiper BeltComet BeltInner Epsilon
Eridani SystemEpsilon Eridani SystemSolar SystemJupiterEpsilon Eridani bEpsilon Eridani bProposed planetProposed planetJupiterSaturnUranusNeptuneEarthMars