- 4254 - EXOPLANETS - biggest and brightest. - Mirror-like exoplanet that 'shouldn't exist' is the shiniest world ever discovered. A distant planet named “LTT9779 b” reflects 80% of its star's light, making the strange world with metal clouds the biggest known "mirror" in the universe.
------------------------- 4254 - EXOPLANETS - biggest and brightest.
- The bizarre
exoplanet with metallic clouds that rain titanium onto its scalding-hot
interior is the shiniest planet ever discovered. This Neptune-size planet,
which scientists say "shouldn't exist," acts like a giant mirror,
reflecting light back toward its home star, which is positioned unusually close
to the lustrous world.
-
- The exoplanet was
discovered in 2020 by researchers operating NASA's Transiting Exoplanet Survey
Satellite (TESS) spacecraft. The gas giant, which is 260 light-years from
Earth, is five times more massive than our planet and orbits its sun-like star
every 19 hours.
-
- Only 1 in 200
sun-like star systems contains an exoplanet with an orbit that lasts less than
one day on Earth; these worlds are known as ultrashort-period planets. Astronomers have found over 5,000 exoplanets
so far.
-
- Using the European
Space Agency's “Characterising Exoplanet Satellite” (Cheops) spacecraft they
found that the planet's sun-facing side reflects around 80% of the starlight
that hits it, which is the highest albedo, or reflectiveness, of a planet ever
observed.
-
- For context, Earth
only reflects around 30% of the sunlight that hits our planet, despite being
mainly covered by water and having highly reflective polar caps.
-
- The secret to
“LTT9779 b's” high albedo is its metallic clouds, which researchers believe are
made predominantly from silicate, or glass, and titanate, a salt containing
titanium.
-
- When researchers
first discovered the exoplanet, they assumed that its close proximity to its
star would prevent cloud formation because it was too hot for these materials
to condense into a cloud; the planet's atmosphere likely reaches sweltering
temperatures in excess of 3,600 degrees Fahrenheit.
-
- But the planet's
atmosphere likely has such a high abundance of silicate and titanate gases that
they can turn into liquids, similar to how water vapor can form mini-clouds in
a bathroom if you leave the shower running for long enough.
-
- LTT9779 b's
metallic clouds also explain one of the exoplanet's puzzling traits, its size.
Until now, all known ultrashort-period planets are either gas giants that are
much larger than Jupiter or rocky planets no larger than Earth. As a result,
experts had predicted that smaller gas giants like LTT9779 b could not exist so
close to their home star.
-
- It's a planet that
shouldn't exist. We expect planets like
this to have their atmosphere blown away by their star, leaving behind bare
rock, like our planet Mercury.
However, the exoplanet's metallic clouds can help explain its unusual
size.
-
- The clouds reflect
light and stop the planet from getting too hot and evaporating. Meanwhile, being highly metallic makes the
planet and its atmosphere heavy and harder to blow away.
-
- But even with its
shiny shielding, LTT9779 b was most likely larger than Jupiter when it first
formed and has since been eroded over time.
Until now, the shiniest known planet in the universe was Venus, which
bounces back 75% of the sun's light thanks to its highly reflective cloud
layer.
-
- It was once
thought that Venus' clouds contained phosphine, a gas produced by
microorganisms on Earth, which hinted that the planet may harbor
extraterrestrial life. But this controversial idea about Venus’ habitability
was debunked by a 2022 study.
-
- The massive planet
LHS 3154b orbits a star much smaller than Earth's sun, and its discovery could
upend everything we think we know about how solar systems form. Given its large mass, LHS 3154b probably has
a Neptune-like composition. The planet
is 13 times more massive than Earth and its star is 9 times smaller than the
sun.
-
- This ultra-cool
dwarf star, named LHS 3154, lies 51 light-years from our solar system and is
about nine times less massive than our sun. In contrast, its planet,
“LHS3154b”, is 13 times more massive than Earth. That sort of cosmic mismatch
is previously unheard of, the astronomical equivalent of finding a watermelon
on a grapevine.
-
- The astronomers are
using an instrument known as the “Habitable Zone Planet Finder (HPF)” at the
McDonald Observatory in Texas. HPF is designed to detect (relatively) cool
stars like LHS 3154, as the planets orbiting them are more likely to have water
on their surfaces. However, the researchers weren't expecting to find an
oversized planet orbiting one.
-
- While LHS 3154b is
far from the most massive exoplanet discovered so far (that honor likely goes
to the gas giant “HAT-P-67 b”, which has a radius about twice that of Jupiter),
its size relative to its star is record-breaking, and the discovery challenges
the current scientific understanding of how planetary systems form.
-
- When a new star
emerges from a cloud of cosmic dust, the rest of the material in that cloud
becomes a disk around the baby sun. This disk of dust, gas and pebbles then
begins to condense into increasingly large balls of rock, which eventually
snowball into planets.
-
- But LHS 3154b is so
large that researchers think it would require about 10 times the amount of dust
that's estimated to have been present around its newly formed star. Based on
this discrepancy, it seems likely that such systems are extremely rare. The
researchers hope that further analysis will reveal just how the planet got so
big and why its star is so small in
comparison.
-
- This discovery
really drives home the point of just how little we know about the universe.
-
-
December 4, 2023 EXOPLANETS -
biggest and brightest. 4254
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