Researchers will use NASA’s upcoming James Webb Space Telescope to study Beta
Pictoris, an intriguing young planetary system that sports at least two
planets, a jumble of smaller, rocky bodies, and a dusty disk. Their goals
include gaining a better understanding of the structures and properties of the
dust to better interpret what is happening in the system. Since it’s only
about 63 light-years away and chock full of dust, it appears bright in
infrared light – and that means there is a lot of information for Webb to
gather.
Beta Pictoris is the target of several planned Webb observing programs,
including one led by Chris Stark of NASA’s Goddard Space Flight Center and
two led by Christine Chen of the Space Telescope Science Institute in
Baltimore, Maryland. Stark’s program will directly image the system after
blocking the light of the star to gather a slew of new details about its
dust. Chen’s programs will gather spectra, which spread light out like a
rainbow to reveal which elements are present. All three observing programs
will add critical details to what’s known about this nearby system.
First, a Review of What We Know
Beta Pictoris has been regularly studied in radio, infrared, and visible
light since the 1980s. The star itself is twice as massive as our Sun and
quite a bit hotter, but also significantly younger. (The Sun is 4.6 billion
years old, but Beta Pictoris is approximately 20 million years old.) At this
stage, the star is stable and hosts at least two planets, which are both far
more massive than Jupiter. But this planetary system is remarkable because
it is where the first exocomets (comets in other systems) were discovered.
There are quite a lot of bodies zipping around this system!
Like our own solar system, Beta Pictoris has a debris disk, which includes
comets, asteroids, rocks of various sizes, and plenty of dust in all shapes
that orbit the star. (A debris disk is far younger and can be more massive
than our solar system’s Kuiper Belt, which begins near Neptune’s orbit and
is where many short-period comets originate.)
This outside ring of dust and debris is also where a lot of activity is
happening. Pebbles and boulders could be colliding and breaking into far
smaller pieces — sending out plenty of dust.
Scrutinizing This Planetary System
Stark’s team will use Webb’s coronagraphs, which block the light of the
star, to observe the faint portions of the debris disk that surround the
entire system. “We know there are two massive planets around Beta Pictoris,
and farther out there is a belt of small bodies that are colliding and
fragmenting,” Stark explained. “But what’s in between? How similar is this
system to our solar system? Can dust and water ice from the outer belt
eventually make its way into the inner region of the system? Those are
details we can help tease out with Webb.”
Webb’s imagery will allow the researchers to study how the small dust grains
interact with planets that are present in that system. Plus, Webb will
detail all the fine dust that streams off these objects, permitting the
researchers to infer the presence of larger rocky bodies and what their
distribution is in the system. They’ll also carefully assess how the dust
scatters light and reabsorbs and reemits light when it’s warm, allowing them
to constrain what the dust is made of. By cataloging the specifics of Beta
Pictoris, the researchers will also assess how similar this system is to our
solar system, helping us understand if the contents of our solar system are
unique.
Isabel Rebollido, a team member and postdoctoral researcher at STScI, is
already building complex models of Beta Pictoris. The first model combines
existing data about the system, including radio, near-infrared,
far-infrared, and visible light from both space- and ground-based
observatories. In time, she will add Webb’s imagery to run a fuller
analysis.
The second model will feature only Webb’s data – and will be the first they
explore. “Is the light Webb will observe symmetrical?” Rebollido asked. “Or
are there ‘bumps’ of light here and there because there is an accumulation
of dust? Webb is far more sensitive than any other space telescope and gives
us a chance to look for this evidence, as well as water vapor where we know
there’s gas.”
Dust as a Decoder Ring
Think of the debris disk of Beta Pictoris as a very busy, elliptical highway
– except one where there aren’t many traffic rules. Collisions between
comets and larger rocks can produce fine dust particles that subsequently
scatter throughout the system.
“After planets, most of the mass in the Beta Pictoris system is thought to
be in smaller planetesimals that we can’t directly observe,” Chen explained.
“Fortunately, we can observe the dust left behind when planetesimals
collide.”
This dust is where Chen’s team will focus its research. What do the smallest
dust grains look like? Are they compact or fluffy? What are they made of?
“We’ll analyze Webb’s spectra to map the locations of dust and gas – and
figure out what their detailed compositions are,” Chen explained. “Dust
grains are ‘fingerprints’ of planetesimals we can’t see directly and can
tell us about what these planetesimals are made of and how they formed.” For
example, are the planetesimals ice-rich like comets in our solar system? Are
there signs of high-speed collisions between rocky planetesimals? Clearly
analyzing if grains in one region are more solid or fluffy than another will
help the researchers understand what is happening to the dust, and map out
the subtle differences in the dust in each region.
“I’m looking forward to analyzing Webb’s data since it will provide
exquisite detail,” added Cicero X. Lu, a team member and a fourth-year Ph.D.
student at Johns Hopkins University in Baltimore. “Webb will allow us to
identify more elements and pinpoint their precise structures.”
In particular, there’s a cloud of carbon monoxide at the edge of the disk
that greatly interests these researchers. It’s asymmetric and has an
irregular, blobby side. One theory is that collisions released dust and gas
from larger, icy bodies to form this cloud. Webb’s spectra will help them
build scenarios that explain its origin.
The Reach of Infrared
These research programs are only possible because Webb has been designed to
provide crisp, high-resolution detail in infrared light. The observatory
specializes in collecting infrared light – which travels through gas and
dust – both with images and spectra. Webb also has another advantage – its
position in space. Webb will not be hindered by Earth’s atmosphere, which
filters out some types of light, including several infrared wavelength
bands. This observatory will allow researchers to gather a more complete
range of infrared light and data about Beta Pictoris for the first time.
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