10 AUSTRALIAN SKY & TELESCOPE April 2019
ASTRONOMERS ON NASA’STransiting
Exoplanet Survey Satellite (TESS) team
have announced the discovery of eight
confirmed planets, as well as more than
300 exoplanet candidates.
Launched in April 2018, TESS began
science operations last July, searching
for any planets circling 200,000 of the
nearest stars. At press time, the mission
had monitored six sky sectors for 27
days apiece.Thenewfinds,presentedatthe
American Astronomical Society
meetingonJanuary7,useonlythefirst
three months of observations. While
the catalogue scientific paper is still
forthcoming, the team provided details
on three of the smallest confirmed
planets:
Pi Mensae cisasuper-Earthabout
fivetimesEarth’smassthatcirclesits
Sun-like star in six days. A previouslyNASA’s TESS mission announces new planets discovered gas giant accompanies it on a
highly elongated six-year orbit.
LHS 3844 bisahot,slightlymore-
than-Earth-sizeplanetthatcirclesits
red dwarf star in just 11 hours.
HD 21749 b, the newest discovery,
isasub-Neptunethat’sthreetimes
Earth’s girth but 23 times its mass. It’s
denser than Neptune, but not so much
that it’s rocky; astronomers suspect
it has a thick, heavy atmosphere. The
planet is on a 36-day orbit and was
discovered with additional transit data
from ground-based telescopes.
As Principal Investigator George
Ricker (MIT) points out, the spacecraft
is in a stable orbit, its cameras are
performing beautifully, it has oodles
of propellant left, and the only moving
parts are four momentum wheels that
should last decades. As long as the
mission continues to receive funding,
there’snoreasonTESScan’tkeepon
keeping on for at least another decade.
■ MONICA YOUNGmineswhetherit,too,hasbeeninfluenced
bytheputativePlanetX.■MONICA YOUNGM77 supernova discovered
On November 24 the DLT40 survey, conducted
witha0.4-metretelescopeinChile,pickedup
a15.4-magnitudesupernovainM77,abright,
barred spiral galaxy in Cetus. Designated
2018ivc, the new supernova brightened
onlybriefly;interveningdustdimmedand
reddeneditslight.Itfirstappearedasatiny
pinprick of light 8.7 ̋ east and 16.1 ̋ north of
thecentreofthegalaxyalongtheedgeof
thebrightinnerdisk.Spectroscopyrevealed
aTypeIIsupernova,whoseblastsent
debris flying outward at some 13,500 km/s
(48.5 million kph). This is the first recorded
supernova in M77.■BOB KINGWhite dwarfs’ crystal cores
Whitedwarfsfaceacrystallisedfate,
astronomersreportintheJanuary10issueof
Nature.WhentheEuropeanSpaceAgency’s
Gaia satellite revealed precise distances, and
thus luminosities, to 1.7 billion stars last year,it also measured these properties for 200,
whitedwarfs—athousandfoldincrease
compared to what was previously available.
Pier-Emmanuel Tremblay (University of
Warwick, UK) and colleagues placed 15,
of the nearest white dwarfs on a diagram that
plots magnitude against colour, which serves
as a proxy for temperature. The white dwarfs
fall exactly where certain evolutionary models
had predicted. These models suggest that,
as white dwarfs cool, their cores experience
aphasetransition.Whenwhitedwarfsfirst
form,theypacksomuchmatterintososmall
a space that the atomic nuclei join together
into a kind of fluid, while the electrons
become unbound into a gaseous haze. But
once white dwarfs cool below 10 million
degrees, the nuclei fluid solidifies. Moreover,
thenucleireleaseheatastheysettleinto
anorderedstructure,sothecrystallisation
actually delays the white dwarf’s overall
cooling. Cooling resumes once the core is
fully solid. Based on these findings, Tremblay
predicts that the Sun will crystallise, too, in
about10billionyears’time.
■MONICA YOUNGWThe locations of three confirmed small planets are labelled in sections from TESS’s first-light
image.(TheSmallandLargeMagellanicCloudsappearatleftandright,respectively.)LHS 3844 b Pi Mensae cHD 21749 bNASA / MIT / TESSNEWS NOTESMost distant solar system
object discovered
Nicknamed ‘Farout,’ the object provision-
ally designated 2018 VG 18 currently orbits
the Sun somewhere between 115 and 125
astronomical units. That’s more than three
times farther out than Pluto is, on average,
and more distant than any other objects
known. Scott Sheppard and colleagues
discovered the object in November using
the Subaru telescope in Hawai‘i. Gradu-
ate student Will Oldroyd (Northern Arizona
University) joined the team in early Decem-
ber for further observations using one of the
Magellan telescopes in Chile. The additional
images enabled the scientists to measure the
object’s motion against background stars,
giving its distance. The team found Farout as
part of their ongoing search for Planet X, an
as-yet undetected world thought to be shap-
ing the orbits of several distant Solar System
objects. However, depending on the shape
of Farout’s orbit, it could take another one to
three years of observations before the team
nails down its orbital parameters and deter-