Largest ever Hubble telescope survey reveals what makes some exoplanets hot

A very interesting paper with 5 questions asked and addressed on these 25 hot jupiters reported. Reference paper, Five Key Exoplanet Questions Answered via the Analysis of 25 Hot-Jupiter Atmospheres in Eclipse,, 25-April-2022.

My observation. The reference paper is very interesting and lists the 25 exoplanets studied. "2. Methodology Our study encompasses data for 25 hot Jupiters observed in eclipse with the HST-WFC3 G141 grism and Spitzer: CoRoT-1 b (CO1), HAT-P-2 b (HP2), HAT-P-7 b (HP7), HAT-P-32 b (HP32), HAT-P-41 b (HP41), HAT-P-70 b (HP70), HD 189733b (HD189), HD 209458b (HD209), KELT-1 b (K1), KELT-7 b (K7), KELT-9 b (K9), Kepler-13 A b (Ke13), TrES-3 b (Tr3), WASP-4 b (W4), WASP-12 b (W12), WASP-18 b (W18), WASP-19 b (W19), WASP-33 b (W33), WASP-43 b (W43), WASP-74 b (W74), WASP-76 b (W76), WASP-77 A b (W77), WASP-79 b (W79), WASP-103 b (W103), and WASP-121 b (W121). For WASP-121 b, we also add the available G102 grism."

I examined CoRot-1 b. Properties for CoRoT-1 b listed,

Using the properties here I calculate P = 1.5163E+00 day. P listed as 1.509 day. In 1 Gyr period, this hot jupiter could complete 2.4089E+11 revolutions or more than 240 billion revolutions around the host star (in its current configuration).

Using a simple model where mass of hot jupiter = 0.5 Mjup, mass of host star = 0.95 Msun, e=0, a=0.05, P=4.1888E+00 day. In 1 Gyr period, 8.7196E+10 revolutions or more than 87 billion revolutions could be completed around a parent star for such a model hot jupiter. Hot jupiters are difficult to explain their origin and the 25 reported in this study, do not have their postulated primordial disc to observe and measure or migrations.

Postulated primordial discs to explain origin of hot jupiters and migration schemes moving them in much closer to parent stars (in some cases many AU distance changes) is not observable. Simulations run, making various input parameter guesses and changes results in a variety of outputs.

Using this exoplanet site, The Extrasolar Planet Encyclopaedia — Catalog Listing (, 5014 exoplanets listed now.

I used SQL and found 953 with semi-major axis < 0.06 au from their parent star. There is potentially a large number of exoplanets moving around their parent stars very close, well inside where Mercury is at in our solar system, and with Jupiter size or more masses.
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The paper asked these 5 questions. "The questions are: (1) Do metal oxides and hydrides cause thermal inversions in exoplanet atmospheres? (2) Are the eclipse spectra of the hottest atmospheres consistent with blackbody curves? (3) What is the dayside–terminator contrast in exoplanet atmospheres? (4) Are metallicity and C/O viable observables to understand planet formation? Hot Jupiters are thought to form via a three-step process (Mizuno 1980; Bodenheimer & Pollack 1986; Ikoma et al. 2000): solid core accretion, runaway gas accretion, and migration. The core accretion is believed to occur in the outer regions of a protoplanetary disk, where the abundance of solid materials leads to the rapid growth of a planetary core before disk gas dispersal...(5) Can refractory elements help us understand exoplanet formation? In addition to the metallicity and C/O, other elemental ratios, such as N/O, S/O (Turrini et al. 2021), or even refractory elements (Lothringer et al. 2021), may help constrain planet formation scenarios. Their potential, however, remains unexplored by observational studies, as their tracers are more difficult to detect. While HST is not particularly sensitive to N- and S-bearing species, refractory elements such as TiO, VO, and FeH have been detected previously in eclipse spectra."
I have more than 5 questions. :)

I'm curious how they can tell that there is an inversion for these hotter planets? What data could reveal the inner atmosphere is actually cooler? This should be interesting to learn.

If the outer layers are that much hotter, then do they act as radiators that prevent the inner layers from getting hot?

Stellar age and metallicity can greatly affect the HZ. So I wonder what equation tweaks are needed to determine their HZ with this information as well. Perhaps none for the high temp ones.

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