Sky & Telescope - April 2025 - 9

ASTEROID BELT ART: NASA / JPL-CALTECH; ARTIST'S ILLUSTRATION OF NEW PLANET IN
UNIQUE SYSTEM: NASA / JPL-CALTECH / R. HURT, K. MILLER (CALTECH / IPAC)
ASTEROID BELT
New View Shows Surprising
Number of Small Asteroids
A NEW ANALYSIS of archival James
Webb Space Telescope data, published
online December 5th in Nature, reveals
that small asteroids in the main
asteroid belt are more numerous than
thought. The finding could change
calculations of the impact rate on Earth
from such bodies, which range from 10
to 500 meters (30 to 1,600 feet) across.
Larger main-belt asteroids, whose
orbits are between those of Mars and
Jupiter, tend to remain in relatively
stable orbits. However, gravitational
interactions more frequently perturb
smaller objects, which might then
enter the inner solar system to become
potential impactors. The high number
of small objects now found in the main
belt - at least five times more than
expected - could affect calculations of
the frequency of such impacts.
Artem Burdanov (MIT) and colleagues
used a shift-and-stack approach,
EXOPLANETS
Transiting Planet Found
Around Infant Star
PLANETS FORM WITHIN disks of dusty
gas encircling newborn stars - disks
that tend to shield those planets from
view. Now, astronomers have detected a
still-forming planet - thanks, perhaps,
to a stroke of luck that flipped the
obscuring disk out of the way.
The youngest planet previously found
by the transit method (in which a planet
dims its star's light while passing in
front of it) was about 10 million years
old - long enough for most of the dusty
disk to have cleared. The new planet,
found with NASA's Transiting Exoplanet
Survey Satellite (TESS) and cataloged as
IRAS 04125+2902b, is only about 3 million
years old. The discovery is published
in the November 21st Nature.
Until now, it wasn't clear that
planets could form so quickly. While
a handful of such young planets have
been found via other methods, they
pThe young exoplanet TIDYE-1b orbits the
primary star of a wide binary. This illustration
shows the star's planet-forming disk tilted out
of the system's orbital plane.
tend to be far more massive and moving
in wide orbits.
The new planet was only detectable
because its star's large outer dust disk
is oriented almost perpendicularly to a
sparse inner disk in which the newfound
planet orbits. The star is part of a
widely separated binary about 520 lightoften
used to provide images of faint,
fast-moving objects in the solar system.
Usually, this process involves precisely
tracking an object with a known or presumed
orbit; dozens or even hundreds
of digital images added together can
then allow an object to emerge from the
random background noise that changes
from frame to frame.
But without knowing the orbits of
Webb-detected targets (which were
found as foreground objects in archival
images of the TRAPPIST-1 system), the
team used a " brute force " variation on
shift-and-stack, looking in every possible
direction with reasonable velocity
ranges for potential moving targets.
The initial blind search produced
more than 1,000 candidates. Burdanov
and his colleagues then narrowed these
down and confirmed 138 previously
unknown asteroids, as well as eight
known ones. Because the infrared (thermal)
energy emitted per unit surface
area doesn't vary much among objects
in the asteroid belt, the astronomers
could determine the diameters of Webb's
pAs this artist's impression suggests, the
region between Mars and Jupiter appears to
contain far more small asteroids than previously
thought.
discoveries to within 10% to 20%.
These results open the prospect of
mining similar JWST datasets, enabling
an improved census of various asteroid
families. Team member Richard Binzel
(MIT) says, " These asteroid findings
fill an important knowledge gap for
tracing the source of meteorites and
larger potentially hazardous asteroids in
Earth's vicinity. "
¢DAVID L. CHANDLER
years away in Taurus. At first the team
thought that the pull of the companion
star might have warped the disk, but the
secondary star orbits the primary in the
same plane as the newfound planet and
the inner disk. Instead, it's possible that
another star flipped the disk as it passed
close by, says study lead Madyson Barber
(University of North Carolina at Chapel
Hill); however, she adds, " That's not
something we can really test. " Alternatively,
the outer disk may have been
warped due to surrounding gas falling
in along another plane.
TIDYE-1b, as it's also known, is
almost the size of Jupiter and orbits its
star every 8.83 days. Yet it has less than
30% of Jupiter's mass, perhaps having
lost its outer layers in the face of the
young star's winds and radiation. It
might end up as a sub-Neptune, a type
of planet common in the galaxy but
absent in our solar system. Follow-up
observations of this young example may
shed light on these planets' evolution.
¢DAVID L. CHANDLER
sk yand tele scope .o r g * APRIL 2025
9
http://skyandtelescope.org
Sky & Telescope - April 2025

Table of Contents for the Digital Edition of Sky & Telescope - April 2025
