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Register a new userPresence of water on exomoons orbiting free-floating planets: a case study
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Added by
Patricio Javier \\'Avila
Publication date
2021
fields
Physics
and research's language is
English
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A free-floating planet is a planetary-mass object that orbits around a non-stellar massive object (e.g. a brown dwarf) or around the Galactic Center. The presence of exomoons orbiting free-floating planets has been theoretically predicted by several models. Under specific conditions, these moons are able to retain an atmosphere capable of ensuring the long-term thermal stability of liquid water on their surface. We model this environment with a one-dimensional radiative-convective code coupled to a gas-phase chemical network including cosmic rays and ion-neutral reactions. We find that, under specific conditions and assuming stable orbital parameters over time, liquid water can be formed on the surface of the exomoon. The final amount of water for an Earth-mass exomonoon is smaller than the amount of water in Earth oceans, but enough to host the potential development of primordial life. The chemical equilibrium time-scale is controlled by cosmic rays, the main ionization driver in our model of the exomoon atmosphere.
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The mass and distance functions of free-floating planets (FFPs) would give major insights into the formation and evolution of planetary systems, including any systematic differences between those in the disk and bulge. We show that the only way to measure the mass and distance of individual FFPs over a broad range of distances is to observe them simultaneously from two observatories separated by $Dsim {cal O}(0.01,AU)$ (to measure their microlens parallax $pi_{rm E}$) and to focus on the finite-source point-lens (FSPL) events (which yield the Einstein radius $theta_{rm E}$). By combining the existing KMTNet 3-telescope observatory with a 0.3m $4,{rm deg}^2$ telescope at L2, of order 130 such measurements could be made over four years, down to about $Msim 6,M_oplus$ for bulge FFPs and $Msim 0.7,M_oplus$ for disk FFPs. The same experiment would return masses and distances for many bound planetary systems. A more ambitious experiment, with two 0.5m satellites (one at L2 and the other nearer Earth) and similar camera layout but in the infrared, could measure masses and distances of sub-Moon mass objects, and thereby probe (and distinguish between) genuine sub-Moon FFPs and sub-Moon ``dwarf planets in exo-Kuiper Belts and exo-Oort Clouds.
Genomic complexity can be used as a clock with which the moment in which life originated can be measured. Some authors who have studied this problem have come to the conclusion that it is not possible that terrestrial life originated here and that, in reality, life originated giga-years ago, before the solar system existed. If we accept this conclusion there is no other option than to admit that panspermia is something viable.The goal of this study is to propose a viable hypothesis for the transport of SLF from one planetary system to another. During the formation period of a planetary system giant planets can eject planets the size of the Earth, or larger, turning them into free-floating planets in interstellar space. These free-floating planets have also been called free floaters. If a free floater, which has developed life, enters a lifeless planetary system, it can seed the worlds of this system with SLF dragged by the stellar wind from one planet to another or by great impacts on the free planet. To support this hypothesis, I calculate the probability that one free floater reaches the planets zone of a planetary system, and also it was calculated the time it remains within the planetary zone in order to see if there is enough time to seed the host system.The probability of a free floater in the galaxy, within the region of the Sun, entering the planet zone of a system is 2.8x10-4, i.e., that {sim}3 of 10,000 free planets manage to enter some planetary system. At the galactocentric distance from the Sun I calculated that there are 21,495 free floaters floating around the galactic center. Hence, 6 free-floating planets manage to enter in planetary systems every galaxy rotation. Since the galaxy has rotated 54 times since its formation, then, {sim} 324 free floaters have entered some planetary system at the galactocentric distance of the Sun.
Brown dwarfs are essential targets for understanding planetary and sub-stellar atmospheres across a wide range of thermal and chemical conditions. As surveys continue to probe ever deeper, and as observing capabilities continue to improve, the number of known Y dwarfs -- the coldest class of sub-stellar objects, with effective temperatures below about 600 K -- is rapidly growing. Critically, this class of ultra-cool objects has atmospheric conditions that overlap with Solar System worlds and, as a result, tools and ideas developed from studying Earth, Jupiter, Saturn and other nearby worlds are well-suited for application to sub-stellar atmospheres. To that end, we developed a one-dimensional (vertical) atmospheric structure model for ultra-cool objects that includes moist adiabatic convection, as this is an important process for many Solar System planets. Application of this model across a range of effective temperatures (350, 300, 250, 200 K), metallicities ([M/H] of 0.0, 0.5, 0.7, 1.5), and gravities (log $g$ of 4.0, 4.5, 4.7, 5.0) demonstrates strong impacts of water latent heat release on simulated temperature-pressure profiles. At the highest metallicities, water vapor mixing ratios reach an Earth-like 3%, with associated major alterations to the thermal structure in the atmospheric regions where water condenses. Spectroscopic and photometric signatures of metallicity and moist convection should be readily detectable at near- and mid-infrared wavelengths, especially with James Webb Space Telescope observations, and can help indicate the formation history of an object.
The next decade will see two large-scale space-based near-infrared surveys, Euclid and WFIRST. This paper shows that the subtle differences between the filters proposed for these surveys and those from ground-based photometric systems will produce a ground-space colour term that is dependent on water absorption in the spectra of astronomical objects. This colour term can be used to identify free-floating planets in star forming regions, mimicking a successful ground-based technique that uses a filter sensitive to water absorption. This paper shows that this colour term is an effective discriminant between reddened background stars and ultracool dwarfs. This represents just one science justification for a Galactic Plane survey in the event of an extension to the Euclid mission beyond its original timeframe.
Planet formation theories predict the existence of free-floating planets that have been ejected from their parent systems. Although they emit little or no light, they can be detected during gravitational microlensing events. Microlensing events caused by rogue planets are characterized by very short timescales $t_{rm E}$ (typically below two days) and small angular Einstein radii $theta_{rm E}$ (up to several uas). Here we present the discovery and characterization of two ultra-short microlensing events identified in data from the Optical Gravitational Lensing Experiment (OGLE) survey, which may have been caused by free-floating or wide-orbit planets. OGLE-2012-BLG-1323 is one of the shortest events discovered thus far ($t_{rm E}$=0.155 +/- 0.005 d, $theta_{rm E}$=2.37 +/- 0.10 uas) and was caused by an Earth-mass object in the Galactic disk or a Neptune-mass planet in the Galactic bulge. OGLE-2017-BLG-0560 ($t_{rm E}$=0.905 +/- 0.005 d, $theta_{rm E}$=38.7 +/- 1.6 uas) was caused by a Jupiter-mass planet in the Galactic disk or a brown dwarf in the bulge. We rule out stellar companions up to a distance of 6.0 and 3.9 au, respectively. We suggest that the lensing objects, whether located on very wide orbits or free-floating, may originate from the same physical mechanism. Although the sample of ultrashort microlensing events is small, these detections are consistent with low-mass wide-orbit or unbound planets being more common than stars in the Milky Way.
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