Magma Oceans with a Steam Atmosphere: Detectability by Future Direct Imaging

We present the thermal evolution and emergent spectra of solidifying terrestrial planets along with the formation of steam atmospheres.

The lifetime of a magma ocean and its spectra through a steam atmosphere depends on the orbital distance of the planet from the host star. For a type-I planet, which is formed beyond a certain critical distance from the host star, the thermal emission declines on a timescale shorter than approximately 106 years. Therefore, young stars should be targets when searching for molten planets in this orbital region. In contrast, a type-II planet, which is formed inside the critical distance, will emit significant thermal radiation from near-infrared atmospheric windows during the entire lifetime of the magma ocean. The Ks and L bands will be favorable for future direct imaging because the planet-to-star contrasts of these bands are higher than approximately 10−7-10−8. Our model predicts that, in the type-II orbital region, molten planets would be present over the main sequence of the G-type host star if the initial bulk content of water exceeds approximately 1 wt%. In visible atmospheric windows, the contrasts of the thermal emission drop below 10−10 in less than 105 years, whereas those of the reflected light remain 10−10 for both types of planets. Since the contrast level is comparable to those of reflected light from Earth-sized planets in the habitable zone, the visible reflected light from molten planets also provides a promising target for direct imaging with future ground- and space-based telescopes.

Lifetime and Spectral Evolution of a Magma Ocean with a Steam Atmosphere: Its Detectability by Future Direct Imaging

Keiko Hamano, Hajime Kawahara, Yutaka Abe, Masanori Onishi, George L. Hashimoto
(Submitted on 13 May 2015)

Comments: 17 pages, 12 figures, 1 table, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1505.03552 [astro-ph.EP) (or arXiv:1505.03552v1 [astro-ph.EP] for this version)
Submission history
From: Keiko Hamano
[v1] Wed, 13 May 2015 21:03:50 GMT (3486kb)
http://arxiv.org/abs/1505.03552

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