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The search for signs of life on exoplanets at the interface of chemistry and planetary science.

Seager S, Bains W - Sci Adv (2015)

Bottom Line: The discovery of thousands of exoplanets in the last two decades that are so different from planets in our own solar system challenges many areas of traditional planetary science.However, ideas for how to detect signs of life in this mélange of planetary possibilities have lagged, and only in the last few years has modeling how signs of life might appear on genuinely alien worlds begun in earnest.Recent results have shown that the exciting frontier for biosignature gas ideas is not in the study of biology itself, which is inevitably rooted in Earth's geochemical and evolutionary specifics, but in the interface of chemistry and planetary physics.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. ; Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

ABSTRACT
The discovery of thousands of exoplanets in the last two decades that are so different from planets in our own solar system challenges many areas of traditional planetary science. However, ideas for how to detect signs of life in this mélange of planetary possibilities have lagged, and only in the last few years has modeling how signs of life might appear on genuinely alien worlds begun in earnest. Recent results have shown that the exciting frontier for biosignature gas ideas is not in the study of biology itself, which is inevitably rooted in Earth's geochemical and evolutionary specifics, but in the interface of chemistry and planetary physics.

No MeSH data available.


Related in: MedlinePlus

Schematic of a transiting exoplanet.When the planet goes in front of the star as seen from a telescope (a “transit” or “primary eclipse”), the starlight drops in brightness by the planet-to-star area ratio. In addition, the starlight passes through the planet atmosphere and planet atmosphere spectral features are imprinted on the stellar spectrum. This is called transmission spectroscopy. When the planet goes behind the star, the planet disappears and reappears, adding either reflected light or thermal emission to the combined planet-star radiation. This is referred to as secondary eclipse photometry or spectroscopy. Dozens of transiting exoplanet atmospheres have been studied, taking advantage of the fact that the planet and star do not need to be spatially separated as projected on the sky.
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Figure 3: Schematic of a transiting exoplanet.When the planet goes in front of the star as seen from a telescope (a “transit” or “primary eclipse”), the starlight drops in brightness by the planet-to-star area ratio. In addition, the starlight passes through the planet atmosphere and planet atmosphere spectral features are imprinted on the stellar spectrum. This is called transmission spectroscopy. When the planet goes behind the star, the planet disappears and reappears, adding either reflected light or thermal emission to the combined planet-star radiation. This is referred to as secondary eclipse photometry or spectroscopy. Dozens of transiting exoplanet atmospheres have been studied, taking advantage of the fact that the planet and star do not need to be spatially separated as projected on the sky.

Mentions: Now, the field boasts several different atmosphere observation techniques. Most take advantage of transiting planets, using painstaking analysis to extract the spectroscopic signal from the planet’s atmosphere from the combined light of planet-star system without having to spatially separate the dim planet from that of its bright host star (Fig. 3). These include transit transmission spectra (16, 25) and measuring secondary eclipse spectra in thermal emission (17, 18) and reflected light (26, 27). We now turn to nontransiting planets. For those planets with short orbital periods and consequent high orbital velocities, a high spectral dispersion cross-correlation technique has been used to measure atmospheric spectral features, which takes advantage of the planet’s orbital motion (and the consequent Doppler shift in the planetary spectrum compared to the stellar spectrum) and a known template of high spectral resolution molecular lines (28). Reflected light and thermal phase curves also do not require transiting geometry, but for now are limited to planets close to their star that are bright in reflected light or hot thermally. For giant planets orbiting relatively far from their host stars, ground-based telescopes with adaptive optics and careful post-processing techniques have begun to succeed in measuring near-infrared (IR) atmospheric lines (29). Starlight suppression to observe only the planet light is beginning in earnest for giant planets far from the star using large ground-based telescopes (29). An impressive, rapid maturation of data interpretation techniques for atmospheric retrieval (30) has emerged as adaptations and improvements over established solar system planet atmosphere retrieval techniques to take analysis of the exoplanet atmosphere data as far as it can go both for current data sets (31–34) and the exoplanet atmosphere data sets expected in the future.


The search for signs of life on exoplanets at the interface of chemistry and planetary science.

Seager S, Bains W - Sci Adv (2015)

Schematic of a transiting exoplanet.When the planet goes in front of the star as seen from a telescope (a “transit” or “primary eclipse”), the starlight drops in brightness by the planet-to-star area ratio. In addition, the starlight passes through the planet atmosphere and planet atmosphere spectral features are imprinted on the stellar spectrum. This is called transmission spectroscopy. When the planet goes behind the star, the planet disappears and reappears, adding either reflected light or thermal emission to the combined planet-star radiation. This is referred to as secondary eclipse photometry or spectroscopy. Dozens of transiting exoplanet atmospheres have been studied, taking advantage of the fact that the planet and star do not need to be spatially separated as projected on the sky.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4643826&req=5

Figure 3: Schematic of a transiting exoplanet.When the planet goes in front of the star as seen from a telescope (a “transit” or “primary eclipse”), the starlight drops in brightness by the planet-to-star area ratio. In addition, the starlight passes through the planet atmosphere and planet atmosphere spectral features are imprinted on the stellar spectrum. This is called transmission spectroscopy. When the planet goes behind the star, the planet disappears and reappears, adding either reflected light or thermal emission to the combined planet-star radiation. This is referred to as secondary eclipse photometry or spectroscopy. Dozens of transiting exoplanet atmospheres have been studied, taking advantage of the fact that the planet and star do not need to be spatially separated as projected on the sky.
Mentions: Now, the field boasts several different atmosphere observation techniques. Most take advantage of transiting planets, using painstaking analysis to extract the spectroscopic signal from the planet’s atmosphere from the combined light of planet-star system without having to spatially separate the dim planet from that of its bright host star (Fig. 3). These include transit transmission spectra (16, 25) and measuring secondary eclipse spectra in thermal emission (17, 18) and reflected light (26, 27). We now turn to nontransiting planets. For those planets with short orbital periods and consequent high orbital velocities, a high spectral dispersion cross-correlation technique has been used to measure atmospheric spectral features, which takes advantage of the planet’s orbital motion (and the consequent Doppler shift in the planetary spectrum compared to the stellar spectrum) and a known template of high spectral resolution molecular lines (28). Reflected light and thermal phase curves also do not require transiting geometry, but for now are limited to planets close to their star that are bright in reflected light or hot thermally. For giant planets orbiting relatively far from their host stars, ground-based telescopes with adaptive optics and careful post-processing techniques have begun to succeed in measuring near-infrared (IR) atmospheric lines (29). Starlight suppression to observe only the planet light is beginning in earnest for giant planets far from the star using large ground-based telescopes (29). An impressive, rapid maturation of data interpretation techniques for atmospheric retrieval (30) has emerged as adaptations and improvements over established solar system planet atmosphere retrieval techniques to take analysis of the exoplanet atmosphere data as far as it can go both for current data sets (31–34) and the exoplanet atmosphere data sets expected in the future.

Bottom Line: The discovery of thousands of exoplanets in the last two decades that are so different from planets in our own solar system challenges many areas of traditional planetary science.However, ideas for how to detect signs of life in this mélange of planetary possibilities have lagged, and only in the last few years has modeling how signs of life might appear on genuinely alien worlds begun in earnest.Recent results have shown that the exciting frontier for biosignature gas ideas is not in the study of biology itself, which is inevitably rooted in Earth's geochemical and evolutionary specifics, but in the interface of chemistry and planetary physics.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. ; Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

ABSTRACT
The discovery of thousands of exoplanets in the last two decades that are so different from planets in our own solar system challenges many areas of traditional planetary science. However, ideas for how to detect signs of life in this mélange of planetary possibilities have lagged, and only in the last few years has modeling how signs of life might appear on genuinely alien worlds begun in earnest. Recent results have shown that the exciting frontier for biosignature gas ideas is not in the study of biology itself, which is inevitably rooted in Earth's geochemical and evolutionary specifics, but in the interface of chemistry and planetary physics.

No MeSH data available.


Related in: MedlinePlus