ASTRONEWS
EastSept. 6Sept. 725° north35°
north45°
northSept. 5Sept. 6Sept. 5Sept. 6Sept. 5FAST
FAC T12 ASTRONOMY • SEPTEMBER 2017
THAT’S SO METAL. Hot temperatures on exoplanet HAT-P-7b ionize metals in its atmosphere, tying the planet’s
magnetic field to its winds. This effect allows researchers to study exoplanet magnetic fields.BRIEFCASE
NOT SO DARK
Energetic gamma rays emitted from our galaxy’s
center are often attributed by astronomers to dark
matter. But a recent study has turned up a differ-
ent source: pulsars, the dense spinning cores of
stars sometimes left behind after supernovae. The
study, performed with the Large Area Telescope
on NASA’s Fermi Gamma-ray Space Telescope,
looked at the center of the Milky Way, where
researchers expect dark matter to be abundant.
Instead of the diffuse glow that should be pro-
duced by dark matter interactions, the source of
the gamma rays appears “speckled,” or composed
of many small sources. Pulsars not only make up
the majority of small gamma-ray sources in the
Milky Way, but the characteristics of the gamma
rays coming from the galaxy’s center match those
from other known pulsars as well. That makes it
more likely these objects are largely responsible
for the emission.- SOLAR SYSTEM ANALOGUE
NASA’s Stratospheric Observatory for Infrared
Astronomy (SOFIA) took a closer look at a nearby
planetary system just 10.5 light-years away
around the star Epsilon (ε) Eridani. The star hosts a
Jupiter-sized planet that lies about the same dis-
tance as Jupiter from our Sun, as well as a debris
disk of rock and dust, which is left over after plan-
ets form. Using SOFIA’s instruments, astronomers
were able to determine that Epsilon Eridani’s
debris disk is composed of two distinct asteroid
beltlike rings. This finding also indicates the star
likely hosts a planetary-mass body in its outer
solar system responsible for shaping the second
belt. The results were published in The
Astronomical Journal on April 25.
THAT’S NO STAR
A team of researchers led by Jonathan Gagné of
the Carnegie Institution for Science recently dis-
covered that SIMP J013656.5+093347 (SIMP
for short), once thought to be a nearby brown
dwarf, is in fact much more planet-like than star-
like. Brown dwarfs are too small to support the
hydrogen fusion that defines stars; instead, they
burn deuterium (a hydrogen isotope) briefly, then
cool over time, with temperatures that overlap
those observed in some planets. The team found
that SIMP0136’s mass is roughly 13 times that of
Jupiter, indicating it’s a free-floating planet-like
object associated with a young group of stars
called Carina-Near. — Alison Klesman
E
ver since NASA announced in
February that the TRAPPIST-1 system
has seven planets instead of three, sci-
entists have been interested in learning
more about the unusual system. After fur-
ther research, they have pinned down
orbital details about TRAPPIST-1h, the sys-
tem’s most distant and mysterious planet.
Using data from the
Kepler spacecraft, sci-
entists studying the
exoplanets have con-
firmed that the outer-
most planet, which is
about 6 million miles
(9.6 mi l lion k i lometers)
from TRAPPIST-1,
orbits its host star
every 19 days.
Reviewing data
from the Spitzer Space
Telescope, the team
noticed a predictable
pattern, also called an
orbital resonance,
among the first six
planets in the system. An orbital resonance
occurs when orbiting bodies show a consis-
tent gravitational inf luence on each other,
like how Jupiter’s moon Ganymede orbits
twice in the same length of time Europa
takes to complete four orbits.
Orbital resonances essentially lock
objects into specific periods over time; if anobject in the system is perturbed, the reso-
nance will eventually bring it back into a
stable orbit.
The team calculated six potential reso-
nant periods for TRAPPIST-1h based on
this principle. After gathering more data
with Spitzer and ground-based telescopes,
only one of those potential periods — 19
days — remained
plausible. The other
five would have shown
up clearly in the new
observations.
NASA has kept its
eye on the seven-
planet system, which
orbits the ultracool
dwarf star
TRAPPIST-1, since
December 2016. The
system is anywhere
between 3 billion and
8 billion years old.
Researchers originally
thought that the sys-
tem had three planets,
until Spitzer data recently revealed the four
additional planets.
NASA’s Hubble Space Telescope is look-
ing for more information about the planets’
atmospheres. When the James Webb Space
Telescope launches in October 2018, it will
join the search for information about the
TRAPPIST-1 system. — Nicole KiefertDETAILS ARRIVE ON TRAPPIST-1’S
OUTERMOST PLANET
WHEN THE MOON CAN’T WAIT
light-year
The extent of the jet of energy
launched into space by the
brown dwarf Mayrit 1701117.
ASTRONOMY: ROEN KELLYPINNED DOWN. This artist’s depiction shows
what TRAPPIST-1h, the farthest planet from the
TRAPPIST-1 star, may look like. NASA/JPL-CALTECHMOONDANCE. On average,
the Moon rises about 50
minutes later each night. But
at the Full Moon in September,
the delay shrinks to only
about 30 minutes for those
at mid-northern latitudes.
That’s because our satellite
orbits close to the ecliptic (the
Sun’s path through the sky),
and, on autumn evenings, the
ecliptic makes a shallow angle
to the eastern horizon around
sunset. But the angle changes
depending on latitude, so
those who live farther north
don’t have to wait as long.
This year’s Full Moon arrives
the night of September
5/6 — see how much later it
rises on the following nights.
— Richard TalcottFor those who live
north of the Arctic
Circle, September’s
Moon rises earlier
on successive nights
around its Full phase.