ASTRONEWS
WWW.ASTRONOMY.COM 13Scientists suspect Saturn’s moon
Enceladus has a liquid ocean beneath
its global shell of ice, with volcanism
that drives geyser-like eruptions. But
new research shows the distinct jets
seen shooting up from the surface
might have been an optical illusion,
according to scientists on NASA’s
Cassini mission team. Instead, their
evidence indicates curtain eruptions
occur along massive fractures called
“tiger stripes” on the moon’s south
pole. These eruptions look like jets
in images because the fractures are
squiggly instead of straight.
“The viewing direction plays an
important role in where the phantomjets appear,” says the Planetary
Science Institute’s Joseph Spitale,
who is lead author on the May 7
Nature paper. “If you rotate your per-
spective around Enceladus’ south
pole, such jets would seem to appear
and disappear.”
His group paired Cassini observa-
tions with computer models of how
the curtains would appear and found
such eruptions explain most, but not
all, of the jets observed.Other research summarized in May
by the journal Geochimica et Cosmo-
chimica Acta analyzed the pH of those
plumes and found a salty surprise.
The water packs an ammonia-like
alkaline pH around 11 or 12.
What’s more, Enceladus’ oceans
have the same salt content as Earth’s
but hold higher levels of sodium car-
bonate closer to our planet’s soda
lakes, including Mono Lake in
California. — E. B.QUICK TAKES
GALACTIC DEATH
Astronomers found that most
galaxies die slowly. Instead of
expelling gas and shutting off
star formation all at once, gal-
axies instead steadily eat up
gas until they run out of fuel.- DELTA’S FRIEND
Variable star Delta Cephei,
prototype for a well-known
class of variable stars called
Cepheids, has a smaller com-
panion, undetected for the
230 years astronomers have
studied its partner.
SUPERFLARE STARS
A team of Japanese astrono-
mers found Sun-like stars with
large sunspots that host
superflares, with energies
10–10,000 times greater than
the Sun’s largest flares.
FLUFFY GALAXIES •
Astronomers used the Keck
Observatory in Hawaii to find
“fluffy” galaxies as big as the
Milky Way in size but contain-
ing only 1 percent of the stars
in our galaxy.- WISE FIND
NASA’s WISE telescope discov-
ered a new record-setting
brightest galaxy. Most of the
brightness is probably due to
material lighting up as it falls
into the galaxy’s central super-
massive black hole.
ALMA EYES MIRA
ALMA saw a massive flare on
the well-known red giant star
Mira, which is close enough
for the telescope array to see
surface details.
10,000 TELESCOPES
Jean and Ric Edelman donated
funds for 10,000 Galileoscopes
— small scopes designed for
classroom use — to be distrib-
uted in U.S. schools.
ALIEN MOONS
Scientists announced that
alien moons — larger than
Mars, orbiting planets as large
as Jupiter — might make the
best targets when hunting for
extraterrestrial life.
EUROPAN TOOLS
NASA selected nine out of 33
proposed science instruments
for a mission to explore
Jupiter’s moon Europa, with
an emphasis on habitability.
The mission is scheduled to
launch in the 2020s. — K. H.
ANCIENT MAGNETISM. The recently deceased MESSENGER spacecraft used its last days buzzing Mercury’s surface
to uncover evidence for the planet’s magnetic field arising over 3.7 billion years ago.Curtains of
ice spew from
Enceladus’
salty seas
On May 3, 2014, the intermediate
Palomar Transient Factory (iPTF),
a robotic observatory, spotted a
strong ultraviolet light source from
the vicinity of a galaxy in the Coma
Cluster 300 million light-years away.
Astronomers checked the scope’s
observations and confirmed nothing
was there the previous night. They’d
caught a supernova in action.
For decades, the uniform bright-
ness of type Ia supernovae has earned
these exploding objects an empirical
place as “standard candles” for mea-
suring distances and the speed of cos-
mic expansion. And astronomers know
the process starts when at least one
white dwarf — the core of a dead star
— explodes in a binary system. But
beyond that, type Ia origins remain
mysterious. Does the supernova ignite
as the two stars merge, known as dou-
ble degeneracy? Or is it spawned by a
white dwarf gorging material from a
red giant until the dwarf explodes via
so-called single degeneracy?
In hopes of better understanding,
the iPTF astronomers immediately
enlisted X-ray and ultraviolet instru-
ments on NASA’s Swift space telescope
to watch as the strong ultraviolet sig-
nal rapidly faded. The Las Cumbres
Observatory Global Telescope Network
turned to watch the explosion as well.
“Hot blue supernovae are not sup-
posed to happen in old dead galax-
ies,” says Yi Cao, a graduate student at
the California Institute of Technology
who was first author of the May 21
Nature paper detailing the find.“And yet, as our robotic telescopes
gathered the data, we watched in
amazement as the blue supernova
morphed into a type Ia supernova.”
The team says the find gives evi-
dence for the single-degeneracy
model. They suspect that as the white
dwarf star exploded, the ejecta
slammed into its binary companion
star and heated the surrounding
material. That heat peaks in the UV
and explains the unexpected signal.More importantly, their results show
that type Ia supernovae might have
uniform brightness but likely don’t
share uniform origin stories. Rather
than rule out one theory for another,
astronomers think the discovery indi-
cates both are possible.
“The news is that it seems that
both sets of theoretical models are
right, and there are two very different
kinds of type Ia supernovae,” says
Caltech’s Sterl Phinney. — E. B.Supernova slams star, helps explain standard candles
COURTESY OF DAN KASENNASA/JPL-CALTECH/SSI/PPI
ICY ERUPTIONS. This simulation shows how curtains of fine icy particles could erupt
from fractures in the surface of Saturn’s moon Enceladus and appear as distinct jets.SUPERNOVA SMASHUP. When a white dwarf explodes (brown), the ejecta slams into
its companion star (blue), and the violent collision sends out an ultraviolet pulse.