- 4418 - EXOPLANET FOUND - will it host life? Hycean Planet Found? “TOI-270 d”. It may be able to host life even though being outside what scientists consider the regular habitable zone. Exoplanet's thick atmospheres can trap enough heat to keep the oceans warm even though they’re not close to their stars.
------------------------- ?
- The word “hycean” is a portmanteau of
‘hydrogen’ and ‘ocean’ and it describes worlds with surface oceans and thick
hydrogen-rich atmospheres. Scientists think that they may be common around red
dwarfs and that they could be habitable, although any life that exists on a
hycean world would be aquatic.
-
- Because they contain so much water,
scientists think they’re larger than comparable non-hycean planets. Their
larger size makes them easier targets for atmospheric study by the JWST.
-
- The telescope’s ability to characterize
exoplanet atmospheres could be the key to confirming their existence. Using
transmission spectroscopy, the space telescope can watch as starlight travels
through their atmospheres, revealing the presence of certain important
chemicals and even biosignatures.
-
- The exoplanet “TOI-270 d" could be a
hycean world. The JWST has ushered in a
new era in atmospheric characterizations of temperate low-mass exoplanets with
recent detections of carbon-bearing molecules in the candidate Hycean world
“K2-18 b,” .
-
- TOI-270 is an M-dwarf (red dwarf) star
about 73 light-years away. Red dwarfs are known to sometimes flare violently,
ruling out habitability on nearby planets. However, TOI-270 is a quiet star. It
hosts three sub-Neptune planets, and the pair of outermost planets, TOI-270 c
and d, are both candidate hycean worlds. TOI-270 d is considered the strongest
candidate.
-
- TOI-270 d is about 4.2 Earth masses and
measures about 2.1 Earth radii. It takes just over 11 Earth days to complete an orbit, a fact
that aids atmospheric study. The Hubble Space Telescope looked at TOI-270 d
recently, and its observations suggested a hydrogen-rich atmosphere with some
evidence of H2O.
-
- Though scientists still haven’t proven that
hycean worlds exist, they know something about their atmospheric chemistry. On
an ocean world with a thick, hydrogen-rich atmosphere, scientists expect to
find strong signatures of CH4 (methane) and CO2 and no evidence of NH3
(ammonia.) This is what the JWST found at K2-18b, though there is still
uncertainty if that exoplanet is a hycean world.
-
- Every planet is different, but each type
should have things in common. For Hycean worlds, the presence of an ocean below
a thin H2-rich atmosphere may be inferred by an enhancement of CO2, H2O, and/or
CH4, together with a depletion of NH3.
Since TOI-270 d is a candidate hycean world, its spectroscopy should be
similar to other hycean candidates like K2-18b.
-
- In October, 2023, the JWST observed TOI-270
b and d during two transits. The observations amounted to a total exposure time
of 5.3 hours. This rare event allows for transmission spectroscopy of both
planets.
-
- The appearance of CS2 (carbon disulphide)
in TOI-270 d’s atmosphere is intriguing. It’s considered a detectable biomarker
in hycean world atmospheres, as well as in hydrogen-rich atmospheres of rocky
worlds, although the direct sources could also be volcanic or photo-chemical.
-
- The atmospheric spectrum also contains
hints of C2H6 (ethane.) Ethane can be a byproduct of photo-chemical reactions
involving methane and other gases, including biogenic ones. Its presence is
another indication that methane is present.
-
- The abundances of ethane and carbon
disulphide are well above theoretical predictions. All the researchers can conclude is that
TOI-720 d is a candidate hycean world. But while the previous HST observations
that hinted at its status showed the presence of H2O in an H2-rich atmosphere,
the JWST observations provide more depth. The JWST’s more robust detections of
CH4 and CO2, along with its non-detection of NH3, makes it an even stronger
hycean world candidate.
-
-
March 29, 2023 EXOPLANET
FOUND - will it host life? 4418
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--------------------- --- Thursday, April 4, 2024
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