Sky and Telescope - March 2016 - 11

SOLAR SYSTEM I Most Distant Object Found

S&T: GREGG DINDERMAN, SOURCE: SCOTT S. SHEPPARD /
CARNEGIE INSTITUTION FOR SCIENCE

During November's meeting of the
American Astronomical Society's Division for Planetary Sciences, Scott Sheppard (Carnegie Institution for Science)
announced that he, Chad Trujillo (Gemini
Observatory), and David Tholen (University of Hawai'i ) have spotted something
farther from the Sun than any other
known object in the solar system. This
body, designated V774104 for now, lies 103
astronomical units (15.4 billion km) away
in the direction of west-central Pisces.
The object turned up in a pair of
images taken October 13, 2015, with
Japan's 8.2-meter Subaru Telescope, as
part of the largest, deepest survey to date
for distant denizens of the Kuiper Belt.
"We detect the motion of solar system
objects by parallax and not by the actual
movement of the object," Sheppard
explains. An object around 100 a.u. away
will shift about 1.3 arcseconds per hour

due to Earth's motion, he says, so it's easily detected in a few hours.
V774104 is so far away that it will take
another year of study to determine its
orbit. "All we really know is the distance,"
Sheppard admits. Given its 24th-magnitude brightness and assuming that its
surface is 15% reflective, the object might
be 500 km (300 miles) across, or about a
sixth the Moon's size.
Dynamicists will be eager to learn
what kind of orbit V774104 occupies. A
highly eccentric track would mean that
it periodically swings much closer to the
Sun. That's the case with Eris, which
likely got flung into its nearly 600-yearlong orbit after a gravitational encounter
with Neptune eons ago.
But if the orbit is more circular, or if
V774104 is near perihelion in an eccentric
path, then it's completely unaffected by
the massive planets - and that will cause
dynamicists to question how it got out
there. Two other distant objects, 90377
Sedna and 2012 VP113, are also in orbital
limbo. Possible causes run the gamut
from gravitational stirring of the distant
Oort Cloud by a close-passing star to the
presence of an undiscovered, massive
planet far beyond the orbit of Neptune.
Or they might be the first-found members of the inner Oort Cloud.

IN BRIEF
Dwarf Galaxies Discovered. Using
the 570-megapixel Dark Energy Camera
at Cerro Tololo Inter-American Observatory in Chile, Roberto Muñoz (Pontifical
Catholic University of Chile) and colleagues have detected 158 dwarf galaxies swarming in the center of the Fornax
galaxy cluster. These objects have
incredibly low surface brightnesses, up
to 100 times fainter even than the dim,
nearby dwarf galaxy Leo I. Surveys such
as this one are uncovering the expected
small, dim dwarfs that simulations predicted but that have long been "missing"
in observations. The team reports the
finds in the November 1st Astrophysical
Journal Letters.
■ MONICA YOUNG

The little moon Phobos is doomed. It whips around Mars in just 7.7 hours, compared
with the 24.7 hours that Mars takes to rotate, and thanks to a teensy tidal interaction that its
gravity creates in the Martian interior, the moon is slowly moving closer to the planet. This
arrangement can't last: dynamicists predict that Phobos should drop into the Martian atmosphere in perhaps 20 to 40 million years.
Exactly what will take place and when depends on the moon's interior structure, but in
December's Nature Geoscience researchers Benjamin Black and Tushar Mittal (University of
California, Berkeley) conclude that Phobos won't simply plunge intact into Mars. Instead, it's
more likely that the moon's dusty, outer layer will be stripped away first, creating a temporary
ring that might linger around Mars for 1 to 100 million years. Meanwhile, the solid chunks of
Phobos will meet a quicker end, striking the planet's surface and creating a series of oblique
craters around its equator.

Extragalactic Gamma Rays. NASA's
Fermi Gamma-ray Space Telescope has
discovered that most of the highest
energy photons in the Large Magellanic
Cloud come from two pulsars. Astronomers already knew about the pulsars,
J0540-6919 and J0537-6910, but this is
the first time they've been able to pinpoint them as gamma-ray sources and
the first time they've detected pulsars
outside the Milky Way at these wavelengths. J0540 is the most luminous
gamma-ray pulsar ever observed - more
than 20 times brighter than the pulsar
powering the Crab Nebula, which had
been the champion. But J0537's gamma
rays don't show a pulse. Why these three
young pulsars look so different remains
unclear, Pierrick Martin (Institute for
Research in Astrophysics and Planetology, France) and others report in the
November 13th Science. It's also strange
that the two pulsars produce 85% of the
dwarf galaxy's gamma rays, given that
astronomers thought these photons
would come from relativistic charged
particles swarming the burgeoning starforming region in which the pulsars sit.
Watch a video exploring the team's result
at http://is.gd/lmcpulsars.

■ J. KELLY BEATTY

■ CAMILLE M. CARLISLE

V774104

Sedna
2012 VP113

Neptune's
orbit
Sun

Kuiper Belt

50 a.u.

■ J. KELLY BEATTY

Beyond its distance and brightness, astronomers know little about the distant object V774104.
Within a year, they hope to determine the characteristics of its orbit.

MARS I Phobos: Future Ring Around the Red Planet?


http://www.is.gd/lmcpulsars

Sky and Telescope - March 2016

Table of Contents for the Digital Edition of Sky and Telescope - March 2016

Contents
Sky and Telescope - March 2016 - Cover1
Sky and Telescope - March 2016 - Cover2
Sky and Telescope - March 2016 - 1
Sky and Telescope - March 2016 - Contents
Sky and Telescope - March 2016 - 3
Sky and Telescope - March 2016 - A
Sky and Telescope - March 2016 - B
Sky and Telescope - March 2016 - 4
Sky and Telescope - March 2016 - 5
Sky and Telescope - March 2016 - 6
Sky and Telescope - March 2016 - 7
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