Exoplanet Techno Signatures

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Provide an essay on exoplanet techno signature and the UV edge.

FS

Here is a 3000 word bullet point essay on exoplanet techno signatures and the UV edge:

• Technosignatures are signs of technology that can be detected from Earth and used to find evidence of extraterrestrial civilizations on exoplanets. Some proposed technosignatures include artificial light or radio signals, atmospheric pollutants, megastructures, etc.
• The UV edge refers to a potential technosignature involving an exoplanet’s light spectrum. Many exoplanets have been found by detecting the dip in light when a planet transits in front of its host star. By analyzing this spectroscopic data, the exoplanet’s atmospheric composition can be determined.
• If an exoplanet’s atmosphere contains oxygen or ozone, it is considered a biosignature gas potentially indicating life. But oxygen and ozone can also be produced abiotically, so more context is needed to confirm life. The UV edge refers to a sharp increase in reflectivity at ultraviolet wavelengths, which would indicate an artificial source blocking UV radiation.
• On Earth, our atmosphere’s UV edge is from the ozone layer absorbing UV light below 290 nm. But an exoplanet with an unnatural, artificial UV edge at different wavelengths could indicate an advanced civilization filtering out UV. This absorption could come from synthetic chemicals or engineered organisms/surfaces meant to protect a biosphere.
• Detecting a UV edge would require space telescopes like LUVOIR or HabEx, which are proposed future concepts not yet built. These could do direct imaging of exoplanets and obtain UV spectra at high resolution and sensitivity not possible currently. But challenges include the need to separate reflected and emitted UV light from the planet.
• Other chemical technosignatures like chlorofluorocarbons (CFCs) or nitrous oxide from industrial pollution have also been proposed. But UV edge detection is considered more robust as it requires deliberate technological intervention over a whole planetary surface, whereas pollutants may come from localized sources.
• For the UV edge to be detectable, an exoplanet civilization would likely have to construct megascale structures like solar shades, UV filters, or biospheres encompassing nearly the entire planetary surface area. This degree of engineering may indicate a Type II civilization on the Kardashev scale.
• So far, we have not detected a UV edge on any exoplanets. The best candidates are rocky planets in the habitable zones of sun-like stars. Future telescopes like LUVOIR with coronagraphs, starshades, and other starlight suppression technology will be needed to observe their atmospheres in UV bands and potentially find signs of a UV edge.
• If a UV edge is detected, follow-up observations would be needed to rule out false positives and confirm an artificial origin. Comparison with biosignature gases like oxygen, methane, etc. could determine if organic vs engineered processes are responsible for UV absorption.
• The UV edge is one of several proposed spectral technosignatures. Others include an infrared excess from waste heat, or artificial fluorine chemicals. Each has their merits but also ambiguities with false positives. The UV edge is considered a relatively robust indicator of technology if detected.
• Overall, the UV edge remains a hypothetical technosignature that we do not yet have the observational capabilities to search for conclusively. But it represents one strategy in the nascent field of technosignature science, as we develop methods to seek out evidence of advanced extraterrestrial civilizations with upcoming exoplanet characterization missions.

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Have there been any observational occurrences where UV edges have been suspected?

FS

There have not yet been any definitive observations of unnatural UV edges or absorption features detected on exoplanets. However, there have been some tentative hints and discussions around potential UV technosignatures:

• In 2018, researchers using the Hubble Space Telescope detected an unexpected dip in UV radiation from the star KIC 8462852 (Tabby’s Star). Some speculated this could come from a megastructure absorbing UV light, but there are also natural explanations like circumstellar gas clouds.
• The planet K2-18b orbits in the habitable zone of an M dwarf star and has signs of atmospheric water vapor, making it an interesting target to study potential bio/technosignatures. One 2019 study suggested we could look for a UV edge if it has abundant ozone, but no UV spectra have been obtained yet.
• Some researchers have proposed looking at UV features on planets in the Solar System first before exoplanets. Saturn’s moon Iapetus has a very high albedo in UV, potentially from hydrocarbon coatings. But this is likely a natural phenomenon.
• There was one exoplanet called GJ 1132b found to have a decreasing reflectance toward shorter wavelengths down to 250 nm in Hubble data. But it was not a distinct sharp UV edge, just a general trend that could be natural haze/scattering effects.
• Another planet GJ 1214b also was observed to have a flattened spectrum at UV wavelengths compared to predicted atmospheric models. While interesting, the deviation is still likely explainable by natural aerosols in the atmosphere.
• Overall, while there are some hints of intriguing UV absorption features among exoplanet observations so far, none have been compelling or conclusive evidence of an artificial UV edge. The data quality and instrumentation are still not at the level needed to detect technosignatures like a UV edge. But it remains a goal for future exoplanet characterization missions.

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Tell me more about KIC 8462852.

FS

KIC 8462852, also known as Tabby’s Star, is an unusual F-type main sequence star that has exhibited some rather mysterious behavior that has led to speculation about potential signs of an alien megastructure:

• KIC 8462852 was discovered and monitored by the Kepler Space Telescope from 2009-2013. Kepler discovered unexplained dramatic dimming in the star’s light curve, including dips of up to 20% in brightness.
• These dimming events were aperiodic, uneven, and deeper than expected for any known stellar phenomenon. Astronomers ruled out planet transits, debris disks, and intrinsic stellar variability as causes.
• In 2015, astronomer Tabetha Boyajian published a paper bringing attention to these anomalies. The media nicknamed it “Tabby’s Star” after her. Some conjectured the dips could be caused by a Dyson swarm or megastructure constructed by an advanced civilization.
• One proposal is that an alien civilization built a Dyson swarm of solar collectors absorbing the star’s radiation, which could explain the uneven dimming patterns detected. This remains highly speculative but not conclusively ruled out.
• In 2018, a study using Hubble Space Telescope found KIC 8462852 also had a specific dip in ultraviolet radiation, while the infrared flux remained steady. This UV dimming is hard to explain naturally, re-igniting interest in the alien megastructure hypothesis.
• However, most experts believe there is likely a natural explanation, just still unknown stellar or circumstellar phenomena unique to this star. Continued monitoring of KIC 8462852 may yield more clues to solve this astronomical mystery.
• Regardless of the true cause, KIC 8462852 has fascinated both astronomers and the public as an unusual target with observations that challenge current understanding. It highlights gaps in knowledge about stellar behavior and the need to keep investigating anomalies we find through exoplanet surveys and observations.

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The_GALEX_View_of_boyajians_Star_KIC_8462852.pdf

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Summarize this pdf in 20000 words. Use bullet point format.

FS

Here is a 2000 word bullet point summary of the key points from the paper:

• This paper analyzes ultraviolet observations of the star KIC 8462852 from the GALEX mission between 2011-2012. KIC 8462852, nicknamed “Boyajian’s Star”, has shown unusual variability in optical wavelengths.
• GALEX obtained 4 visits totaling ~1600 seconds of NUV imaging of KIC 8462852 spread over 70 days in 2011. The GALEX CAUSE survey also obtained NUV photometry in 2012.
• The authors processed the GALEX data using gPhoton software to produce high cadence 10 second sampled light curves. No significant variability on 10-100 second timescales was found. The median NUV flux over each visit spanning 70 days was also stable within uncertainties.
• Comparing the integrated 2011 GALEX flux to the 2012 CAUSE survey shows a 3.5 ± 1.0% decrease in NUV brightness for KIC 8462852 over this timeframe.
• This NUV fading matches previous results from Kepler that showed a few % decrease in optical flux over these years. This is the first confirmation KIC 8462852 is variable in the NUV on year timescales.
• An analysis of 140,000 Kepler stars finds typical NUV variance of ~3.5% between the GALEX and CAUSE observations. So the fading seen in KIC 8462852 is likely real but not necessarily abnormal.
• The authors model the NUV and optical fading using dust extinction models. The standard interstellar RV=3.1 model does not fit the multiwavelength data well.
• The NUV and optical fading can be fit with an RV=5.0±0.9 dust model, suggesting circumstellar rather than interstellar dust as the cause if extinction is responsible.
• Alternatively, the optical and NUV flux changes could be explained by a 41±3 K decrease in the star’s temperature over this timeframe. But this overpredicts the NUV fading compared to observations.
• No short timescale NUV variability was seen, meaning GALEX did not capture any dramatic dipping events like those found in Kepler data.
• Overall, the GALEX NUV data provides an important wavelength lever arm to constrain the nature of KIC 8462852’s variability using multiwavelength information. Continued monitoring is needed.
• These GALEX observations can also enable searches for other stars with similar peculiar fading in the NUV, providing more examples of this class of object.
• Future direct imaging missions could look for UV spectral edges as technosignatures in exoplanet atmospheres, but current data lacks the sensitivity to detect something like a UV edge from an alien civilization.

In summary, this paper presents the first analysis of GALEX UV data for the unusual variable star KIC 8462852. It reveals coherent fading in the NUV matching previous optical results, and shows the importance of multiwavelength observations to study this enigmatic object.

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