- 4448 - EXOPLANETS - can we find them? - The Hubble Space Telescope joins the hunt for newborn exoplanets. James Webb Space Telescope quickly spotted signs of a forming exoplanet, but, not the one that astronomers had expected to see.
------------------------- 4448 - EXOPLANETS - can we find them?
- Astronomers are hunting for planets that
were in the process of forming around infant stars using the JWST. The powerful
space telescope quickly delivered the goods in an unexpected way.
-
- These infant planets take shape in swirling
clumps of gas and dust called protoplanetary disks, gathering more mass as they
do so. Astronomers have imaged many of
these protoplanetary disks, but astronomers have only glimpsed the forming
planets within them a few times to date.
-
- Adding the power of JWST's sensitive
infrared instruments to this quest used to observe the protoplanetary disks “HL
Tau, SAO 206462”, and “MWC 758” revealed unseen interactions between
protoplanetary disks and the envelopes of gas that are closer to the stars that
sit at the heart of these disks.
-
- In every disk observed with high enough
resolution and sensitivity, we have seen large structures like gaps, rings and,
in the case of SAO 206462, spirals. Most
of these structures can be explained by forming planets interacting with the
disk material, but other explanations that do not involve the presence of giant
planets exist.
-
- If we manage to finally see these planets,
we can connect some of the structures with forming companions and relate
formation processes to the properties of other systems at much later stages.
-
- A “protostar” is a stellar body that has
not yet piled on enough mass to trigger the fusion of hydrogen to helium in its
core which is the process that defines a fully fledged main sequence star like
the sun.
-
- In the protoplanetary disk around SAO
206462, the team spotted the signals of a forming planet. It wasn't the planet they were expecting to
see. Several simulations suggest that
the planet should be within the disk, massive, large, hot and bright. But we
didn't find it. This means that either the planet is much colder than we think,
or it may be obscured by some material that prevents us from seeing it.
-
- This isn't the first time that the disk of
SAO 206462 has been brought into focus. Hubble, Alma, and the Very Large
Telescope (VLT) have all studied this protoplanetary disk, with these
observations revealing that it's composed of two strong spirals.
-
- These spirals are likely being created by a
forming planet. Before looking for this planet with JWST, however, the team had
expected to see a gas giant planet made up mostly of helium, like Saturn or
Jupiter.
-
- The problem is, whatever we're trying to
detect is hundreds of thousands, if not millions of times fainter than the
star. That's like trying to detect a
little light bulb next to a lighthouse.
-
- JWST's Near Infrared Camera (NIRCam) allowed
Cugno and colleagues to delve deeper into the disk of SAO 206462 and detect
thermal energy from the planet, some of which is released as material falls
onto it at high speeds.
-
- When material falls onto the planet, it
shocks at the surface and gives off an emission line at specific
wavelengths. A set of narrow-band
filters are used to try to detect this accretion. This has been done before
from the ground at optical wavelengths, but this is the first time it's been
done in the infrared with JWST.
-
- This indicated a planet separated from the
central protostar by around 300 times the distance between Earth and the sun.
Gas giants usually form much closer to their stars than this, with some then
migrating outward after the protoplanetary disk has dissipated.
-
- The NIRCam results ruled out an object in
the disk with a mass greater than 2.2 times the mass of Jupiter. If there is a gas giant carving out the neat
spirals of the protoplanetary disk of SAO 206462, it must be very cold.
-
- The star “HL Tauri” (HL Tau) is an infant
located around 450 light-years from Earth that has been investigated by a wealth of
telescopes. With an estimated age of no
more than 1 million years (compared to our middle-aged 4.6-billion-year-old
sun), HL Tau is the youngest star in the JWST protoplanetary disk
investigation.
-
- "HL Tau” is the youngest system in our
survey and still surrounded by a dense inflow of dust and gas falling onto the
disk. Unfortunately, it obscures any
signals from potential planets.
-
- The they were able to distinguish a feature
called a “proto-stellar envelope” with the JWST. This represents the dense
inflow of dust and gas that is beginning to coalesce around HL Tau. This raw
material is flowing to the star and its disk from the interstellar medium, gas
and dust that exist between stars, and it will eventually serve as the raw
material to birth planets.
-
- The protoplanetary disk of MWC 758 was
examined with the JWST. This is another protoplanetary disk with spiral arms
that could indicate the presence of a massive planet. This possible planet and
any others failed to manifest in the study, but the sensitivity and power of
the JWST did allow them to put constraints on any potential forming planets
within this protoplanetary disk. This included ruling out the possibility that
there are planets on the outskirts of the disk, far from the star MWC 758.
-
- The lack of planets detected in all three
systems tells us that the planets causing the gaps and spiral arms either are
too close to their host stars or too faint to be seen with JWST. It tells us that they're of relatively low
mass, low temperature, enshrouded in dust, or some combination of the three, as
is likely the case in MWC 758."
-
- Investigations like these into the
formation of planets around young stars are vitally important in understanding
how materials are distributed across young systems and how mature gatherings
like the solar system came to be. Only
about 15% of stars like the sun have planets like Jupiter. It's really
important to understand how they form and evolve and to refine our theories.
-
- Some astronomers think that these gas giant
planets regulate the delivery of water to rocky planets forming in the inner
parts of the disks. Thus, this
investigation may ultimately be crucial to understanding how Earth formed and
how it became able to support life.
-
-
April 28, 2023 EXOPLANETS - can
we find them? 4448
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--------------------- --- Sunday, April 28, 2024
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