Exoplanets and SETI

Exoplanets and SETI

Author:

Wright

Abstract:
The discovery of exoplanets has both focused and expanded the search for extraterrestrial intelligence. The consideration of Earth as an exoplanet, the knowledge of the orbital parameters of individual exoplanets, and our new understanding of the prevalence of exoplanets throughout the galaxy have all altered the search strategies of communication SETI efforts, by inspiring new "Schelling points" (i.e. optimal search strategies for beacons). Future efforts to characterize individual planets photometrically and spectroscopically, with imaging and via transit, will also allow for searches for a variety of technosignatures on their surfaces, in their atmospheres, and in orbit around them. In the near-term, searches for new planetary systems might even turn up free-floating megastructures.

Are Niven Rings Around Pulsars Detectable?

Are the Dyson rings around pulsars detectable?

Authors:

Osmanov

Abstract:
In the previous paper (Osmanov 2016) (henceforth Paper-I) we have extended the idea of Freeman Dyson and have shown that a supercivilization has to use ring-like megastructures around pulsars instead of a spherical shell. In this work we reexamine the same problem in the observational context and we show that facilities of modern IR telescopes (VLTI and WISE) might efficiently monitor the nearby zone of the solar system and search for the IR Dyson-rings up to distances of the order of 0.2kpc, corresponding to the current highest achievable angular resolution, 0.001mas. In this case the total number of pulsars in the observationally reachable area is about 64±21. We show that pulsars from the distance of the order of ∼1kpc are still visible for WISE as point-like sources but in order to confirm that the object is the neutron star, one has to use the UV telescopes, which at this moment cannot provide enough sensitivity.

Transit Detection of a "Starshade" at the Inner Lagrange Point of an Exoplanet

Transit Detection of a "Starshade" at the Inner Lagrange Point of an Exoplanet 

Author:

Gaidos

Abstract: 

All water-covered rocky planets in the inner habitable zones of solar-type stars will inevitably experience a catastrophic runaway climate due to increasing stellar luminosity and limits to outgoing infrared radiation from wet greenhouse atmospheres. Reflectors or scatterers placed near Earth's inner Lagrange point (L1) have been proposed as a 'geo-engineering" solution to anthropogenic climate change and an advanced version of this could modulate incident irradiation over many Gyr or "rescue" a planet from the interior of the habitable zone. The distance of the starshade from the planet that minimizes its mass is 1.6 times the Earth-L1 distance. Such a starshade would have to be similar in size to the planet and the mutual occultations during planetary transits could produce a characteristic maximum at mid-transit in the light-curve. Because of a fortuitous ratio of densities, Earth-size planets around G dwarf stars present the best opportunity to detect such an artifact. The signal would be persistent and is potentially detectable by a future space photometry mission to characterize transiting planets. The signal could be distinguished from natural phenomenon, i.e. starspots or cometary dust clouds, by its shape, persistence, and transmission spectrum.

Detecting a Nicoll-Dyson Beam

Detecting the Ultimate Power in the Universe with LSST

Authors:

Lund

Abstract:
Large time-domain surveys, when of sufficient scale, provide a greatly increased probability of detecting rare and, in many cases, unexpected events. Indeed, it is these unpredicted and previously unobserved objects that can lead to some of the greatest leaps in our understanding of the cosmos. The events that may be monitored include not only those that help contribute to our understanding of sources astrophysical variability, but may also extend to the discovery and characterization of civilizations comprised of other sentient lifeforms in the universe. In this paper we examine if the Large Synoptic Survey Telescope (LSST) will have the ability to detect the immediate and short-term effects of a concave dish composite beam superlaser being fired at an Earth analog from an alien megastructure.

Do not look into laser with remaining civilizaion.

Did a Large Ringed Exoplanet With Trojans dim Tabby's Star?

KIC 8462852: Will the Trojans return in 2021?

Authors:

Ballesteros et al

Abstract:
KIC 8462852 stood out among more than 100,000 stars in the Kepler catalogue because of the strange features of its light curve: a wide and asymmetric dimming taking up to 15 per cent of the total light, together with a period of multiple, narrow dimmings happening approximately 700 days later. Several models have been proposed to account for this abnormal behaviour, most of which require either unlikely causes or a finely-tuned timing. We aim at offering a relatively natural solution, invoking only phenomena that have been previously observed, although perhaps in larger or more massive versions. We model the system using a large, ringed body whose transit produces the first dimming and a swarm of Trojan objects sharing its orbit that causes the second period of multiple dimmings. The resulting orbital period is T≈12 years, with a semi-major axis a≈6 au. Our model allows us to make two straightforward predictions: we expect the passage of a new swarm of Trojans in front of the star starting during the early months of 2021, and a new transit of the main object during the first half of 2023.

Did Tabby's Star Ingest an Exoplanet?

Secular dimming of KIC 8462852 following its consumption of a planet

Authors:

Metzger et al

Abstract:
The Kepler-field star KIC 8462852, an otherwise apparently ordinary F3 main-sequence star, showed several highly unusual dimming events of variable depth and duration. Adding to the mystery was the discovery that KIC 8462852 faded by 14 per cent from 1890 to 1989, as well as by another 3 per cent over the 4 yr Kepler mission. Following an initial suggestion by Wright & Sigurdsson, we propose that the secular dimming behaviour is the result of the inspiral of a planetary body or bodies into KIC 8462852, which took place ∼10–104 yr ago (depending on the planet mass). Gravitational energy released as the body inspirals into the outer layers of the star caused a temporary and unobserved brightening, from which the stellar flux is now returning to the quiescent state. The transient dimming events could then be due to obscuration by planetary debris from an earlier partial disruption of the same inspiralling bodies, or due to evaporation and outgassing from a tidally detached moon system. Alternatively, the dimming events could arise from a large number of comet- or planetesimal-mass bodies placed on to high-eccentricity orbits by the same mechanism (e.g. Lidov–Kozai oscillations due to the outer M-dwarf companion) responsible for driving the more massive planets into KIC 8462852. The required high occurrence rate of KIC 8462852-like systems that have undergone recent major planet inspiral event(s) is the greatest challenge to the model, placing large lower limits on the mass of planetary systems surrounding F stars and/or requiring an unlikely probability to catch KIC 8462852 in its current state.

Sonneberg Plate Photometry for Boyajian's Star in Two Passbands

Sonneberg Plate Photometry for Boyajian's Star in Two Passbands

Authors:

Hippke et al

Abstract:
The F3 main-sequence star KIC 8462852 (Boyajian's Star) showed deep (up to 20%) day-long brightness dips of unknown cause during the four years of the Kepler mission. A 0.164 mag (16%) dimming between 1890 and 1990 was claimed, based on the analysis of photographic plates from the Harvard Observatory. We have gathered an independent set of historic plates from Sonneberg Observatory, Germany, covering the years of 1934–1995. With 861 mag in B, and 397 mag in V, we find the star to be of constant brightness within 0.03 mag per century (3%). Consistent outcomes are found using by-eye estimates of the best 119 plates. Results are supported by data from Sternberg Observatory, Moscow, which show the star as constant between 1895 and 1995. The previously claimed century-long dimming is inconsistent with our results at the $5\sigma $-level, however, the recently reported modest dimming of 3% in the Kepler data is not inconsistent with our data. We find no periodicities or shorter trends within our limits of 5% per five year bin, but note a possible dimming event on 1978 October 24.

How We Will Figure Out What is Happening at Tabby's Star (KIC 8462852)

An interview with Tabetha Boyajian, the Yale astronomer who discovered the flickering star KIC 8462852, better known as Tabby’s Star, or better yet known as the “alien megastructure star”–an object so strange that some scientists openly suggested that it might be obscured by an enormous artificial structure.

link.

A SETI Overview

Academic Bun Fight! Strong Words From Bradley Schaefer OVer Hippke's Paper Refuting the Century Long KIC 8462852 Dimming

A few hours ago, Michael Hippke posted a manuscript to arXiv (http://arxiv.org/abs/1601.07314), and submitted the same manuscript to the Astrophysical Journal Letters (ApJLett). This manuscript claims to have found that the DASCH data produces light curves with secular trends (both systematic dimmings and brightenings) over the century-long records. This same DASCH data (from the collection of archival sky photographs now at Harvard Observatory) was used to recognize a dimming of KIC 8462852 (a.k.a. ‘Tabby’s Star’ or the ‘WTF star’) at an average rate of 0.165±0.013 magnitudes per century from 1890 to 1989.

This dimming from the DASCH data is just a long-time scale version of the dimming also seen with the Kepler spacecraft, and these dimmings are still a high mystery and a perplexing problem. Hippke is taking his claimed result (that the majority of DASCH light curves have major and widespread calibration errors resulting in apparent secular trends) as then implying that KIC 8462852 does not have any secular trend. This claim is easily proved wrong.

Hippke made two major errors, both of which are beginner’s mistakes, and both of which will erroneously produce apparent dimmings and brightenings when none exist. First, Hippke explicitly includes red-sensitive and yellow-sensitive photographs together with the blue-sensitive photographs. The different colors will produce systematically different brightnesses (magnitudes). The trouble is further that the red and yellow photographs are predominantly at late times in the century-long light curve (in the 1970s and 1980s), so the inclusion of many magnitudes that are systematically high or low only at the end of the century will artificially make the star appear to brighten or dim over the century.

[...]

Perhaps from a journalistic point of view, any ‘stirring of the pot’ is good copy. But from the point of view of science and knowledge, putting up unchecked and false claims is bad all the way around. Science has a great strength of being error-correcting, with the normal procedure now for the DASCH people to put out a full formal refutation of Hippke’s claims, and such will appear in many months. But with the one-day turn-around of arXiv and with fast journalist response, there will be many months where the reputation of DASCH is maligned. So Hippke’s choice of running to reporters before the paper appeared publicly, and disdaining any experienced advice despite being a self-proclaimed “novice”, is not good science.

link.

KIC 8462852 did NOT Fade During the Last 100 Years (hint: calibration is IMPORTANT!)

KIC 8462852 did likely not fade during the last 100 years

Authors:

Hippke et al

Abstract:

A recent analysis found a "completely unprecedented" dimming of 0.165±0.013 magnitudes per century in the F3 main sequence star KIC8462852. This star is interesting, as it shows episodes of day-long dips with up to 20% dimming of unknown origin. We re-analyze the same Harvard archival Johnson B photometry and find comparable dimmings, and structural breaks, for 18 of 28 checked F-dwards (64%) in the Kepler field of view. We conclude that the Harvard plates photometry suffers from imperfect long-term (1890--1989) calibration. The most likely explanation for the century-long dimming of KIC8462852 is thus a data artefact, and it is probably not of astrophysical origin.

KIC 8462852 Needs 648,000 Two Hundred km Comets to Fade as Much as Observed From 1890 to 1989

KIC 8462852 Faded at an Average Rate of 0.165+-0.013 Magnitudes Per Century From 1890 To 1989

Author:

Schafer

Abstract:

The star KIC 8462852 is a completely-ordinary F3 main sequence star, except that the light curve from the Kepler spacecraft shows episodes of unique and inexplicable day-long dips with up to 20% dimming. Here, I provide a light curve of 1232 Johnson B-band magnitudes from 1890 to 1989 taken from archival photographic plates at Harvard. KIC 8462852 displays a highly significant and highly confident secular dimming at an average rate of 0.165+-0.013 magnitudes per century. From the early 1890s to the late 1980s, KIC 8462852 has faded by 0.193+-0.030 mag. This century-long dimming is completely unprecedented for any F-type main sequence star. So the Harvard light curve provides the first confirmation (past the several dips seen in the Kepler light curve alone) that KIC 8462852 has anything unusual going on. The century-long dimming and the day-long dips are both just extreme ends of a spectrum of timescales for unique dimming events, so by Ockham's Razor, all this is produced by one physical mechanism. This one mechanism does not appear as any isolated catastrophic event in the last century, but rather must be some ongoing process with continuous effects. Within the context of dust-occultation models, the century-long dimming trend requires 10^4 to 10^7 times as much dust as for the one deepest Kepler dip. Within the context of the comet-family idea, the century-long dimming trend requires an estimated 648,000 giant comets (each with 200 km diameter) all orchestrated to pass in front of the star within the last century.

Optical SETI Observations of the Anomalous Star KIC 8462852

Optical SETI Observations of the Anomalous Star KIC 8462852

Authors:

Schuetz et al

Abstract:

To explore the hypothesis that KIC 8462852's aperiodic dimming is caused by artificial megastructures in orbit (Wright et al. 2015), rather than a natural cause such as cometary fragments in a highly elliptical orbit (Marengo et al. 2015), we searched for electromagnetic signals from KIC 8462852 indicative of extraterrestrial intelligence. The primary observations were in the visible optical regime using the Boquete Optical SETI Observatory in Panama. In addition, as a preparatory exercise for the possible future detection of a candidate signal (Heidmann 1991), three of six observing runs simultaneously searched radio frequencies at the Allen Telescope Array in California. No periodic optical signals greater than 67 photons/m2 within a time frame of 25 ns were seen. This limit corresponds to isotropic optical pulses of 8E22 joules. If, however, any inhabitants of KIC 8462852 were targeting our solar system (Shostak & Villard 2004), the required energy would be reduced greatly. The limits on narrowband radio signals were 180 - 300 Jy Hz at 1 and 8 GHz, respectively, corresponding to a transmitter with an effective isotropic radiated power of 4E15 W (and 7E15 W) at the distance of KIC 8462852. While these powers requirements are high, even modest targeting could - just as for optical signals - lower these numbers substantially.

SETI Radio Check of KIC 8462852 Gives Initial Negative Results

Radio SETI Observations of the Anomalous Star KIC 8462852

Authors:

Harp et al

Abstract:

We report on a search for the presence of signals from extraterrestrial intelligence in the direction of the star system KIC 8462852. Observations were made at radio frequencies between 1-10 GHz using the Allen Telescope Array. No narrowband radio signals were found at a level of 180-300 Jy in a 1 Hz channel, or wideband signals above 100 Jy in a 100 kHz channel.

KIC 8462852 is an Excellent SETI Target

The Ĝ Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures

Authors:

Wright et al

Abstract:

Arnold (2005), Forgan (2013), and Korpela et al. (2015) noted that planet-sized artificial structures could be discovered with Kepler as they transit their host star. We present a general discussion of transiting megastructures, and enumerate ten potential ways their anomalous silhouettes, orbits, and transmission properties would distinguish them from exoplanets. We also enumerate the natural sources of such signatures.

Several anomalous objects, such as KIC 12557548 and CoRoT-29, have variability in depth consistent with Arnold's prediction and/or an asymmetric shape consistent with Forgan's model. Since well motivated physical models have so far provided natural explanations for these signals, the ETI hypothesis is not warranted for these objects, but they still serve as useful examples of how nonstandard transit signatures might be identified and interpreted in a SETI context. Boyajian et al. 2015 recently announced KIC 8462852, an object with a bizarre light curve consistent with a "swarm" of megastructures. We suggest this is an outstanding SETI target.

We develop the normalized information content statistic M to quantify the information content in a signal embedded in a discrete series of bounded measurements, such as variable transit depths, and show that it can be used to distinguish among constant sources, interstellar beacons, and naturally stochastic or artificial, information-rich signals. We apply this formalism to KIC 12557548 and a specific form of beacon suggested by Arnold to illustrate its utility.

Hunting for Macro-artefacts (Dyson Spheres, etc) for SETI

Reconsidering macro-artefacts in SETI searches

Author:

Jones

Abstract:

The observation of macro-artefacts at interstellar distances offers an alternative search paradigm to SETI programs such as radio astronomy and laser detection. Potential artefacts range from space infrastructure deployed by advanced technological civilizations to deliberate attempts to use artefacts as signals and biomarkers of intelligent life. Passive observations of macro-artefacts could overcome problems with active transmission messaging such as temporal and spatial constraints.

Artefacts could be detected without being spatially resolved by telescopes. Spectral analyses could yield evidence of disruption of the natural electromagnetic spectra of stars by artefacts. Some artefacts could generate diffraction and interference patterns uncharacteristic of natural phenomena. Thus, detecting macro-artefacts is potentially feasible with current astronomical infrastructure.

The construction of large macro-artefacts could be achieved with technological and industrial capabilities that are roughly equivalent to present-day Earth. Thus, the accessibility of macro-artefacts for both transmission and reception can be reconsidered as potentially equivalent to conventional SETI strategies.