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.
A debris disk, which includes comets, asteroids, rocks of various sizes, and plenty of dust, orbits the star Beta Pictoris, which is blocked at the center of this 2012 image by a coronagraph aboard the Hubble Space Telescope. This is the visible-light view of the system. NASA’s James Webb Space Telescope will view Beta Pictoris in infrared light, both using its coronagraphs and capturing data known as spectra to allow researchers to learn significantly more about the gas and dust in the debris disk, which includes lots of smaller bodies like exocomets. Credits: NASA, ESA, and D. Apai and G. Schneider (University of Arizona)
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.
As a solar system forms,
the young disk is initially bright and thick with dust. Within the first 10
million years or so, gaps appear within the disk as planets form and clear out
paths. In time, this debris disk thins out as gravitational interactions with
planets slowly sweep away the dust. Steady pressure from the starlight and
stellar winds also blow out the dust. After approximately 10 million years,
only a thin ring remains in the outermost reaches of the system, which is known
as a debris disk. Credits: NASA/JPL-Caltech/R. Hurt (SSC/Caltech) Follow link to
download video
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.
These studies will be conducted as part of Webb Guaranteed Time
Observations (GTO) and General Observers (GO) programs. The GTO
programs are led by scientists who helped develop the key hardware and software
components or technical and inter-disciplinary knowledge for the observatory.
GO programs are competitively selected using a dual-anonymous review system,
the same system that is used to allocate time on the Hubble Space Telescope.
The James Webb Space Telescope will be the world's premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
By Claire Blome
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