Sky and Telescope - September 2018 - 11

The team's simulations show that the
orbits of smaller bodies
revolve more quickly
around the Sun than
NEW RESEARCH
those of larger bodies,
PRESENTED at the
catching up like the
American Astronomiminute hand of a clock
cal Society meeting in
p Artist's concept of Sedna, the
catches up to the hour
Denver suggests that
largest known trans-Neptunian obhand. When that hapinteractions between
ject, whose orbit is "detached" from
Neptune's gravitational influence.
pens, the larger body
small objects in the
feels the combined
outer solar system -
gravity of the small TNOs piling up
rather than a hypothetical "Planet X"
behind it, ultimately pushing it out to a
- could be the reason some of these
more distant and more circular orbit.
far-ﬂung objects follow odd trajectories.
"This could be a really big deal,"
These detached objects are members
says Hal Levison (Southwest Research
of the larger family of trans-Neptunian
Institute), though he's reserving judgobjects (TNOs), bodies that orbit
ment until he sees the published paper
beyond Neptune's orbit. But unlike
(currently in preparation).
most TNOs, detached objects orbit far
One of Planet X's main proponents,
beyond Neptune's gravitational inﬂuastronomer Mike Brown (Caltech),
ence. Sedna, discovered in 2003, is
agrees that the new work could explain
one of the most famous (and distant)
how the orbits become detached from
examples. Yet even though these bodies
Neptune's gravitational inﬂuence, but
move beyond the gravitational effect of
he doesn't think it rules out the existhe inner eight planets, their trajectories share similarities that seem to point tence of Planet X. Other characteristics,
such as how the orbits line up with one
to a common but unknown inﬂuence,
dubbed Planet X (S&T: Oct. 2017, p. 16). another and their tilt with respect to
the planets' orbital plane, remain unexBut a group led by Ann-Marie Madigan and Jacob Fleisig (both at University plained. Nevertheless, ﬁndings like this
may put a bit more pressure on those
of Colorado, Boulder) have found an
looking for Planet X.
alternative cause: the combined gravitational pull of the whole TNO family.
■ JAVIER BARBUZANO
SOLAR SYSTEM

No Planet X in
the Kuiper Belt?

Dust Storm on
Mars; Opportunity
Hunkers Down
Just as the Red Planet began to inch into
the evening sky in late May, ahead of its
closest opposition since 2003, a swath
of bright orange dust clouds covered the dark albedo feature
Mare Acidalium. Within days,
NASA's Mars Reconnaissance Orbiter watched the
dust move south and expand
to cover almost half the planet
by June 11th. In addition to
obscuring albedo features normally
visible from Earth, the thick dust blocked
the solar panels of the 14-year-old Opportunity rover, preventing its batteries
from charging. While NASA engineers
received a transmission from Opportunity on June 10th, the rover has since
fallen silent, indicating that it has entered
low-power mode. In this mode, only the
mission clock runs, periodically waking
the computer to check power levels. The
concern is whether the batteries can outlast the storm. Curiosity, which roves in
the opposite hemisphere, has also seen
an increase in dust, but that won't affect
its radioactive power supply. As of June
21st, amateur images have shown previously obscured features, so the storm
may now be subsiding. See the storm's
progress at https://is.gd/duststorm.
■ BOB KING
p The dust storm on Mars as seen on June
16, 2018.

IN BRIEF

SEDN A: N ASA / JPL- CA LTECH; DUST STOR M: SE A N
WA LK ER / S&T

Globular Clusters Get a
Face-lift
Globular clusters hold the key to understanding our galaxy's earliest years.
For a long time, globular clusters were
thought to be among the earliest objects
to form in our galaxy - a beautiful (and
typical) example is Messier 4, whose
age researchers had pegged at roughly
13 billion years old. Now, a new study by
Elizabeth Stanway (University of Warwick, UK) and JJ Eldridge (University of
Auckland, New Zealand) has given these
ancient beauties a face-lift. Previous
studies had often compared the collective colors of stars in a globular cluster to
models of stellar populations with known
ages and compositions. Stanway and

Eldridge instead compared colors to a new
computational model called Binary Population
and Spectral Synthesis, which takes paired
stars into account. They found they were able
to reproduce globular clusters' colors using
far younger stars. Stanway and Eldridge find
that globular clusters previously found to be
between 10 billion and 14 billion years old
are more likely to be between 5 billion and
8 billion years old. The results, which appear
in the Monthly Notices of the Royal Astronomical Society, could affect astronomers'
understanding of galaxy evolution.
■ MONICA YOUNG

Curiosity Rover Is Drilling
Again
After an 18-month hiatus, NASA's Curiosity
resumed drilling and sampling rocks in May
using a new technique known as percussive

drilling, which allows Curiosity to keep its drill
feed permanently extended. Curiosity had
obtained 15 samples on Mars before issues
began cropping up with the balky drill feed
in October 2016, which led to a temporary
suspension of drilling operations. Engineers
worked on the solution for more than a year,
testing the new method in March. On May
20th the rover successfully drilled a hole
2 inches (50 millimeters) deep into a rock
named Duluth, which is located near Vera
Rubin Ridge in Gale Crater. While this first
attempt experienced difficulty delivering the
drilled sample into the rover for processing,
a second attempt on May 31st successfully
transferred the rock powder to the rover's
mineralogy lab.
■ DAVID DICKINSON
sk yandtelescope.com * S E P TE M B E R 2 018

https://www.is.gd/duststorm http://www.skyandtelescope.com

Sky and Telescope - September 2018

Table of Contents for the Digital Edition of Sky and Telescope - September 2018