Sky & Telescope - October 2022 - 10

NEWS NOTES
EXOPLANETS
White Dwarf Reveals
Planetary System Chaos
NEW OBSERVATIONS found evidence
of both rocky-metallic and icy worlds
falling onto a white dwarf, indicating
past orbital chaos within the system.
G238-44, a white dwarf 86 lightyears
away, is accreting two very different
kinds of objects simultaneously,
Ted Johnson (University of California,
Los Angeles) told the 240th meeting of
the American Astronomical Society in
Pasadena, California. " This has never
been observed before, " he said.
White dwarfs are the compact cores
of low-mass stars, which first balloon
into red giants - a fate that awaits our
Sun in some 5 billion years - before
blowing off their outer layers in planetary
nebulae. These stars' evolution
can cause them to devour close-in
planets, while the orbits of more distant
worlds become jumbled. Indeed, a third
of white dwarfs have shown signs of
SPACE
Starlink Satellites Are
Brighter Again
UPDATES TO SPACEX'S Starlink satellites
have made them brighter again,
though they are still dimmer than the
original design.
Due to the concerns of the astronomy
community, SpaceX voluntarily
began installing sunshades on their
Starlink satellites two years ago. These
VisorSats were about 1.3 magnitudes
dimmer than the original satellites
(S&T: June 2021, p. 16). But as newer
satellites have shifted to using lasers
rather than radio for communication,
the company has omitted visors from
Starlinks as of late last year.
SpaceX engineer David Goldstein
discussed these changes with the Federation
of Astronomical Societies on
May 7th. He added that the company
has added dielectric mirrors to the
Earth-facing side of the Starlink chassis,
to reflect sunlight away from observers
directly below the spacecraft.
10 OCTOBER 2022 * SKY & TELESCOPE
In this artist's illustration, a
white dwarf star siphons off
debris from shattered objects in
a planetary system.
atmospheric " pollution, " unexpected
amounts of elements heavier than
helium that suggest rocky debris has
rained down onto the stellar core.
But on G238-44, the surface's
chemical composition - as measured
by NASA's Far Ultraviolet Spectroscopic
Explorer, the Keck Telescope in Hawai'i,
and the Hubble Space Telescope -
doesn't match that of any single solar
system object.
According to Johnson, the polluting
material is best described as 1.7 parts
Mercury-like debris - typical rocky
stuff - and one part more similar to
the icy Kuiper Belt objects in the solar
system's outskirts. The findings suggest
I analyzed magnitudes of the new
design, recorded earlier this year by
satellite observer Jay Respler. After
adjusting observed magnitudes for the
satellites' distance from the observer
and angle relative to the Sun, I found
that the new spacecraft are about 60%
brighter than the VisorSats. (And even
the VisorSat design wasn't able to meet
the 7th-magnitude limit astronomers
had recommended to minimize interference
with both research and enjoyment
of the night sky.) However, the new
satellites still represent an improvement
of about 0.8 magnitude compared to the
original design.
In May, SpaceX CEO Elon Musk
spoke of building a new generation of
Starlinks that will be much larger and
heavier than the current model, at
7 meters (23 feet) long and 1¼ tons.
Starlink 2.0 could end up exceeding the
brightness of the current satellites.
In response to the growing number
of satellites in low-Earth orbit, the
International Astronomical Union
(IAU) is establishing a Centre for the
that the star's planetary system had
experienced extreme tumult, which
flung remote icy bodies inward.
Dennis Bodewits (Auburn University),
who was not involved in the study,
found the result intriguing, but suggests
a single, complex object, such as Ceres,
could have polluted the white dwarf.
Johnson agrees it's possible but thinks
the two-body scenario is more likely.
With just one strange white dwarf,
it's difficult to draw definitive conclusions.
Future observations may yield
additional cases. " It's an interesting
find, " says Bodewits, " but I wish there
were more. "
¢GOVERT SCHILLING
-4
-2
4
2
1500 2000 2500 3000 3500 4000
Starlink satellite number
pThe newest Starlink spacecraft (orange dots)
average about 0.5 magnitude brighter than
VisorSats after adjusting for distance and solar
angle. The scatter in the plot comes from variations
in satellite orientation.
Protection of the Dark and Quiet Sky
from Satellite Constellation Interference.
Under the management of astronomers
Piero Benvenuti (IAU), Connie
Walker (NSF's NOIRLab), and Federico
Di Vruno (Square Kilometer Array
Observatory), this center will serve
those seeking to preserve dark skies.
¢ANTHONY MALLAMA
Adjusted visual magnitude
WHITE DWARF: NASA / ESA / JOSEPH OLMSTED (STSCI); MAGNITUDES OF
STARLINK SATELLITES: ANTHONY MALLAMA
Sky & Telescope - October 2022

Table of Contents for the Digital Edition of Sky & Telescope - October 2022
