In the 1997 movie "Contact," adapted from Carl Sagan's 1985 novel, the lead character scientist Ellie Arroway (played by actor Jodi Foster) takes a space-alien-built wormhole ride to the star Vega. She emerges inside a snowstorm of debris encircling the star — but no obvious planets are visible.
It looks like the filmmakers got it right.
A team of astronomers at the University of Arizona, Tucson used NASA's
Hubble and James Webb space telescopes for an unprecedented in-depth look at
the nearly 100-billion-mile-diameter debris disk encircling Vega. "Between
the Hubble and Webb telescopes, you get this very clear view of Vega. It's a
mysterious system because it's unlike other circumstellar disks we've looked
at," said Andras Gáspár of the University of Arizona, a member of the
research team. "The Vega disk is smooth, ridiculously smooth."
The big surprise to the research team is that there is no obvious
evidence for one or more large planets plowing through the face-on disk like
snow tractors. "It's making us rethink the range and variety among
exoplanet systems," said Kate Su of the University of Arizona, lead author
of the paper presenting the Webb findings.
[left] A Hubble Space Telescope false-color view of a
100-billion-mile-wide disk of dust around the summer star Vega. Hubble detects
reflected light from dust that is the size of smoke particles largely in a halo
on the periphery of the disk. The disk is very smooth, with no evidence of
embedded large planets. The black spot at the center blocks out the bright glow
of the hot young star.
[right] The James Webb Space Telescope resolves the glow of warm dust in a disk
halo, at 23 billion miles out. The outer disk (analogous to the solar system’s
Kuiper Belt) extends from 7 billion miles to 15 billion miles. The inner disk
extends from the inner edge of the outer disk down to close proximity to the
star. There is a notable dip in surface brightness of the inner disk from
approximately 3.7 to 7.2 billion miles. The black spot at the center is due to
lack of data from saturation.
NASA, ESA, CSA, STScI, S. Wolff (University of
Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)
Webb sees the infrared glow from a disk of particles the size of sand swirling around the sizzling blue-white star that is 40 times brighter than our Sun. Hubble captures an outer halo of this disk, with particles no bigger than the consistency of smoke that are reflecting starlight.
The distribution of dust in the Vega debris disk is layered because the pressure of starlight pushes out the smaller grains faster than larger grains. "Different types of physics will locate different-sized particles at different locations," said Schuyler Wolff of the University of Arizona team, lead author of the paper presenting the Hubble findings. "The fact that we're seeing dust particle sizes sorted out can help us understand the underlying dynamics in circumstellar disks."
The Vega disk does have a subtle gap, around 60 AU (astronomical units) from the star (twice the distance of Neptune from the Sun), but otherwise is very smooth all the way in until it is lost in the glare of the star. This shows that there are no planets down at least to Neptune-mass circulating in large orbits, as in our solar system, say the researchers.
Hubble acquired this image of the circumstellar disk
around the star Vega using the Space Telescope Imaging Spectrograph (STIS).
NASA, ESA, CSA, STScI, S. Wolff (University of
Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)
"We're seeing in detail how
much variety there is among circumstellar disks, and how that variety is tied
into the underlying planetary systems. We’re finding a lot out about the
planetary systems — even when we can’t see what might be hidden planets,"
added Su. "There's still a lot of unknowns in the planet-formation
process, and I think these new observations of Vega are going to help constrain
models of planet formation."
Disk Diversity
Newly forming stars accrete
material from a disk of dust and gas that is the flattened remnant of the cloud
from which they are forming. In the mid-1990s Hubble found disks around many
newly forming stars. The disks are likely sites of planet formation, migration,
and sometimes destruction. Fully matured stars like Vega have dusty disks
enriched by ongoing "bumper car" collisions among orbiting asteroids
and debris from evaporating comets. These are primordial bodies that can
survive up to the present 450-million-year age of Vega (our Sun is
approximately ten times older than Vega). Dust within our solar system (seen as
the Zodiacal light) is also replenished by minor bodies ejecting dust at a rate
of about 10 tons per second. This dust is shoved around by planets. This
provides a strategy for detecting planets around other stars without seeing
them directly – just by witnessing the effects they have on the dust.
"Vega continues to be
unusual," said Wolff. "The architecture of the Vega system is
markedly different from our own solar system where giant planets like Jupiter
and Saturn are keeping the dust from spreading the way it does with Vega."
Webb acquired this image of the circumstellar disk
around the star Vega using the Mid-Infrared Instrument (MIRI).
NASA, ESA, CSA, STScI, S. Wolff (University of
Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)
For comparison, there is a nearby
star, Fomalhaut, which is about the same distance, age and temperature as Vega.
But Fomalhaut's circumstellar architecture is greatly different from Vega's.
Fomalhaut has three nested debris belts.
Planets are suggested as
shepherding bodies around Fomalhaut that gravitationally constrict the dust
into rings, though no planets have been positively identified yet. "Given
the physical similarity between the stars of Vega and Fomalhaut, why does Fomalhaut
seem to have been able to form planets and Vega didn't?" said team member
George Rieke of the University of Arizona, a member of the research team.
"What's the difference? Did the circumstellar environment, or the star
itself, create that difference? What's puzzling is that the same physics is at
work in both," added Wolff.
First Clue to Possible Planetary Construction Yards
Located in the summer constellation
Lyra, Vega is one of the brightest stars in the northern sky. Vega is legendary
because it offered the first evidence for material orbiting a star — presumably
the stuff for making planets — as potential abodes of life. This was first
hypothesized by Immanuel Kant in 1775. But it took over 200 years before the
first observational evidence was collected in 1984. A puzzling excess of
infrared light from warm dust was detected by NASA's IRAS (Infrared Astronomy
Satellite). It was interpreted as a shell or disk of dust extending twice the
orbital radius of Pluto from the star.
In 2005, NASA's infrared Spitzer
Space Telescope mapped out a ring of dust around Vega. This was further confirmed by observations using
submillimeter telescopes including Caltech's Submillimeter Observatory on Mauna
Kea, Hawaii, and also the Atacama Large Millimeter/submillimeter Array (ALMA)
in Chile, and ESA's (European Space Agency's) Herschel Space Telescope, but
none of these telescopes could see much detail. "The Hubble and Webb
observations together provide so much more detail that they are telling us
something completely new about the Vega system that nobody knew before,"
said Rieke.
Two papers (Wolff
et al. and Su et.
al.) from the Arizona team will be
published in The Astrophysical Journal.
The James Webb Space Telescope is
the world's premier space science observatory. Webb is solving mysteries in our
solar system, looking beyond to distant worlds around other stars, and probing
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 CSA (Canadian Space Agency).
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
Source: NASA's Hubble, Webb Probe Surprisingly Smooth Disk Around Vega - NASA Science
