- 3900 - EXOPLANETS - too large for its “sun”? Astronomers have discovered another unusual planetary system consisting of a Jupiter-sized planet orbiting a tiny star that is only four times the size of the solar system gas giant. This "forbidden" configuration of a massive planet orbiting a relatively tiny star which could challenge theories of how gas giant planets form.
-------------- 3900 - EXOPLANETS - too large for its “sun”?
- Astronomers
latest discovery is a an Earth-size body just 72 light-years away from us. “K2-415b”, as the newly discovered world
orbits the nearby red dwarf star K2-415. (March, 2023)
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- While
K2-415b is not the closest known exoplanet to Earth, it is, on a cosmic scale,
one of our close neighbors. The K2-415
system is unique in that K2-415 is one of the coolest, or lowest-mass, stars
known to host an exoplanet.
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- There are
only four stars cooler than K2-415 that are known to host at least one
exoplanet, including the famous TRAPPIST-1, which has seven known exoplanets.
-
- Solar-type
stars are stars akin to our sun. Red dwarf stars , (also known as M-dwarfs),are
far cooler and much smaller. K2-415 is
thought to have a surface temperature of about 5,250 degrees Fahrenheit,
compared to our sun's 9,900 degrees F, with a diameter of 0.2 solar radii and a
mass just 0.16 times that of the sun.
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- K2-415b is
not in the habitable zone of its star.
Habitsble zone is the distance from a star at which liquid water can
exist on a world's surface. This exoplanet is extremely close to K2-415, so
close that it only takes about four Earth days to complete an orbit.
-
- Preliminary
estimates are that it is three times more massive than Earth, despite having a
radius just 1.015 times that of Earth.
So far, only one transiting planet was found in the system, but this
does not necessarily mean the system is a 'single' one. Further radial velocity observations, as
well as photometric monitoring, will be able to constrain the presence of outer
planets in the system.
-
- The
"exoplanet," orbits a red dwarf star designated TOI 5205 that is much
cooler and smaller than the sun. The small size and relatively cool
temperatures of these M-dwarf stars, the most common type of stellar body in
the Milky Way, make them redder than the sun.
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- The host
star is just about four times the size of Jupiter, yet it has somehow managed
to form a Jupiter-sized planet, which is quite surprising!Though gas giants
have been discovered around M dwarf stars before, none of them have been
discovered orbiting such a low mass example of this class of star.
-
- Planets are
created in spinning discs of gas and dust called "protoplanetary
discs" that surround young stars. This material is the remains of the same
matter that collapsed to birth its central star. When dense patches collapse
under their own gravity planet cores are born and they then collect more
material.
-
- Current
planet formation models suggest that to birth a gas giant it takes material
equivalent to 10 times the mass of Earth. This first forms a rocky core and
this core goes on to accumulate gas to form the disc to grow a giant planet.
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- If there
isn't enough rocky material in the disk to form the initial core, then one cannot
form a gas giant planet. And at the end, if the disk evaporates away before the
massive core is formed, then one cannot form a gas giant planet. And yet
TOI-5205b formed despite these guardrails.
-
- To picture
how unbalanced this system is to planetary systems that astronomers expect,
imagine our star the sun squashed down to the size of a grapefruit. That size
reduction would mean the largest gas giant in our solar system, Jupiter, would
be about the size of a garden pea. The TOI-5205 system is more like a pea
orbiting a lemon.
-
- The size
disparity in the size is so great that when TESS used the drop in light caused
by a planet as it passes in front of its star, known as the transit method,
that dip in light was 7% of the star's total light output. That makes the dimming of TOI-5205 by this
Jupiter-sized exoplanet the largest known drop in light caused by an exoplanet
transit.
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- This
extreme dip in light or technically, "large transit depth," could
make the system ideal for follow-up investigations with the James Webb Space
Telescope (JWST). Observations with the
JWST could help determine the composition of TOI-5205 b's atmosphere and may
shed light on the processes that birthed this "forbidden" planet.
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March 3, 2023 EXOPLANETS - too
large for its “sun”? 3900
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--- Sunday, March 5, 2023
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