What would Earth look like to aliens? If they were looking for signs of habitability, what would their observations tell them? It is a fun idea.
The experiment is more than just enjoyable. It is easier to study our planet and how it appears and then use that information to make better decisions.
According to a new study, finding evidence of life on Earth may be dependent on the season aliens are observing.
There is a lot of excitement when you find a potentially habitable planet. The headlines spread like a bug on the internet. We have only a small amount of exoplanets that may be able to support life. There is a long way to go for us.
We need a lot of science and innovative reasoning before we can say yes. The distant planet is warm. There is a new study looking at Earth's appearance through different seasons.
The study is called Earth as an exoplanet. There is a time-variable thermal emission and seasonality of bio-indicators. The author is Jean-Noel Mettler. Mettler is a PhD student in the department of physics at the university.
The history of this type of research goes back to the 70s when the solar system was being explored. Pioneer 10 and 11 flew past some of Earth's siblings. It was the beginning of more detailed analysis of other planets. Scientists learned a lot by measuring the UV and IR.
Today, we are in the time of exoplanets. The same type of observations are being extended to other planets. If there is a Holy Grail in exoplanet science, it is habitability. We want to know if other people live there.
Astronomers are using more powerful instruments to look at distant planets. The same thing would likely happen in another civilization. The study looked at the effect of different observation geometries on the Earth's emission spectrum. The researchers looked at how the seasons affect the spectrum. The strength of bio-indicators, such as N2O, CH4, O3 and CO2, depends on both season and viewing geometry.
The study looked at four different observing geometries, one of which was centred on the north and south poles. NASA's Aqua satellite was used to observe the spectrum with the AtmosphericInfraredSounder.
There is no single sample of Earth's thermal emissions. It is not possible due to the seasonal changes. The strength of biosignature absorption features depends on both season and viewing geometry, according to the paper.
The researchers observed geometry and found that thermal emissions varied a lot. Over the course of time, the variability in readings was greater than above the ocean. The African and North Pole views were based on land mass. The paper concluded that the northern hemisphere pole-on view and the Africa-centered equatorial view show annual variabilities of 22% and 33%, respectively.
Less variability could be achieved by the thermal stability of the oceans. Smaller annual variabilities can be seen in geometries with a high sea fraction, such as the southern hemisphere pole-on and the Pacific-centered, equatorial view.
A living, dynamic planet like Earth can't be characterized by a single thermal emissions spectrum. This study didn't look into clouds or their effect because there's too much going on. Future work is needed to investigate how cloud fraction and cloud seasonality affect the detection and result.
The authors write about the seasonal atmosphere.
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