A new study asks the question : If the Earth were an exoplanet, would aliens be able to tell that there is life on it?

(ORDO NEWS) — What Earth will seem to alien astronomers? What would their observations tell them about the Earth if, like us, they searched the sky for signs of habitability? This is a fun thought experiment.

But it’s more than just fun: it’s educational from a scientific point of view. In many ways, it’s easier to study our planet and what it looks like, and then extrapolate those results as they evolve.

A new study shows that finding evidence of life on Earth may depend on the time of year. are watching.

Nothing in space science generates as much enthusiasm as the search for a potentially habitable planet. Headlines spread like a virus across the Internet, with slight mutations from site to site.

So far, we only have glimpses and hints of exoplanets that could support life. We have a long way to go.

It will take a lot of scientific and innovative reasoning before we get to the point where we can say, “Yes. This distant planet is habitable.”

The new study may be part of getting to that point by studying the appearance of the Earth at different times of the year.

The study is called “Earth as an exoplanet: II. Time-Varying Thermal Radiation of the Earth”. and its atmospheric seasonality of bioindicators”.

It is available from the prepress website arXiv.org and the lead author is Jean-Noel Mettler. Mettler is a doctoral student at the Faculty of Physics at ETH Zurich, studying exoplanets and habitability.

The historical roots of this type of research date back to the [19]70s when spacecraft visited planets in our solar system. System.

Pioneer 10 and 11 (Jupiter and Saturn) and Voyager 1 and 2 (Jupiter, Saturn, Uranus and Neptune) have orbited some of Earth’s siblings.

This was the beginning of a deeper characterization of the Earth. other planets. By measuring ultraviolet and infrared radiation, scientists have learned a lot about the properties of planetary atmospheres, surfaces, and overall energy balance.

But today we live in the age of exoplanet science. We apply the same type of observation to planets that are light years away from us.

The incredible variety of planets we have discovered is interesting in itself, but if exoplanet science is the Holy Grail, it has to be habitable. We want to know if something else lives out there somewhere.

As our technology advances, astronomers have more and more powerful tools to study distant planets. A technological civilization elsewhere in the Milky Way would likely do the same.

This study examines the Earth’s infrared spectrum, the impact of different observing geometries on those spectra, and what the observations would look like to a much larger number of people. remote observer.

The researchers also assessed how the changing seasons affect the spectra. “We learned that there is significant seasonal variability in the Earth’s thermal radiation spectrum, and the strength of the spectral characteristics of bioindicators such as N 2 O, CH 4 , O 3 and CO 2 are highly dependent on both the season and the survey geometry.”

The study looked at four different observing geometries: one each focused on the North and South Poles, one on the African equator, and one on the Pacific equator.

The spectra were observed using the atmospheric infrared probe aboard NASA’s Aqua satellite.

The researchers found that there is no single representative sample of the Earth’s thermal radiation spectrum. Seasonal changes make this impossible.

“Instead,” the paper says, “there is significant seasonal variability in the Earth’s thermal radiation spectrum, and the intensity of biosignature absorption features is highly dependent on both the time of year and survey geometry. ”

The researchers also found that thermal radiation varies greatly depending on the geometry. The variability of readings over land over time was much greater than over the oceans.

The African equatorial view and the view from the north pole were focused on land masses and showed great variability.

“Specifically, the northern hemisphere pole view (NP) and the equatorial view centered on Africa (EqA) showed an annual variability of 33 percent and 22 percent at the Earth’s peak wavelength of ≈10.2 µm, respectively,” the paper says. .

But the thermal stability of the oceans meant less variability. “On the other hand, viewing geometries with high sea proportions such as the Southern Hemisphere Pole (SP) and the Pacific Centered Equatorial View (EqP) shows less annual variability due to the large thermal inertia of the oceans. ”

The general conclusion from this study is that a living, dynamic planet such as the Earth cannot be characterized by a single spectrum of thermal radiation.

There is too much going on here on Earth, and this research hasn’t even delved into the clouds and their impact.

“In the future, it is necessary to study how cloud fraction, cloud seasonality, and their thermodynamic phase properties affect the detection and outcome of atmospheric seasonality,” the authors write.

The authors say some of the variations are subtle and would be difficult to disentangle when observing distant planets. Dirty data can hide them.

“Even for the Earth, and especially for equatorial images, the variations in flux characteristics and extinction strength in disk-integrated data are small, typically ≈ 10 percent. noise in future exoplanet observations will be a problem.”

The complexity of the Earth makes it a challenging target for this type of observation, and the authors acknowledge this.

“This complexity makes it very difficult for remotes to characterize the planetary environment,” they explain.

“Using the Earth as a test bed, we learned that the planet and its characteristics cannot be described by a single thermal radiation spectrum, but can be described by multi-step measurements, preferably in both reflected light and thermal radiation.”

Most of our exoplanet detections are based on multiple transits of these planets in front of their stars. This has its limitations.

The James Webb Space Telescope is aiming to study the spectra of some more powerful exoplanets, so we’re getting closer to the day we need to better understand what we’re seeing.

This study tested a new method for observing exoplanets in the mid-infrared rather than in reflected light.

Despite seasonal fluctuations and observed changes in geometry,”… we found that our result is relatively insensitive to diurnal or seasonal effects, in contrast to the measurement of reflected light.”

Mettler and his colleagues believe their method could provide unique data for reflected-light observations of exoplanets.

“We therefore conclude that the observation of thermally emitted exoplanets can provide unique and additional information needed to characterize terrestrial planets around other stars. .”

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