As of October 2023, astronomers have discovered 5,506 exoplanets orbiting other stars. This number is growing every day, and astronomers hope to find Earth-like worlds, among other things. But do we know someone when we see one? How can we tell the difference between an Earth-like garden and a Venus-like pressure cooker 40 light years away? Can JWST rise to the challenge?

In a previously published article on the server arXivFour researchers used the simulation to test the space telescope. They found that there are indeed distinctive signatures that will help us distinguish exoVenus from exoEarths, but there’s a catch (we’ll come back to this).

This simulation worked like this: The researchers placed six Earth-like planets and six Venus-like planets, each with different levels of carbon dioxide (CO), 40 light-years away.₂), cloud cover and haze in their atmosphere. The simulated planets orbited a star similar to TRAPPIST-1.

In the real world, TRAPPIST-1 is one of the most promising systems yet discovered, where astronomers hope to find an outer Earth. It shows a faint red dwarf (making its planets easier to observe than around a bright yellow star like our Sun). The system has seven rocky worlds, three or four of which may be located in the star’s habitable zone. JWST has already observed two inner planets and found them to be barren rocks more similar to Mercury than Earth or Venus.

During the simulations, the orbits of the test planets were placed precisely at the “runaway edge of the greenhouse”: the distance from the star where the same planetary catastrophe that turned Venus into hell was possible.

The authors aimed the JWST simulation at planets that matched the capabilities of the real telescope’s NIRCSpec instrument, which observes wavelengths of light from distant worlds. Different compounds in the atmosphere appear as peaks, patterns, and bursts in the spectrum, allowing researchers to see which chemical compounds are present.

But the data is not always definitive. The spectral signatures of some molecules mask or mimic the signatures of others, making it difficult to be sure what we are looking at.

“Venus clouds and fog may hinder detection of molecular species or the atmosphere in general,” the authors write.

But that doesn’t mean it’s impossible, and this model will help define what astronomers should be looking for. Here’s what they found:

First, if you want to determine whether a planet has an atmosphere and is similar to Earth or Venus, your best bet is to look for carbon dioxide (CO2). It has a signal that is easy to detect and remains visible for both clear skies and hazy and cloudy planets.

But CO₂ Less useful in distinguishing Earth and Venus due to CO properties₂ It overlaps with both water and methane, which confuses the data. There is only one spectral feature that clearly shows up on a Venus-like planet rather than an Earth-like planet: sulfur dioxide (SO₂). FOR THIS REASON₂ it reacts with water vapor, thus ruling out a wet Earth-like planet if present and confirming a dry Venus-like planet.

That’s the point. There aren’t that many SOs on Venus in the real world₂. The sun’s UV radiation destroyed it. But there is still hope. Around a red dwarf similar to TRAPPIST-1, SO₂ will exist for much longer, making SO detection possible₂ in such a scenario.

“TRAPPIST-1’s reduced UV radiation allows SO₂ exoVenus has a longer lifetime in its atmosphere, making it more likely to detect SO₂“, the authors claim.

The best trace to look for for an Earth-like planet is methane. It has methane absorption properties not seen on Venus and clearly distinguishable from CO2.₂. Additionally, if methane is accompanied by oxygen, this could be evidence of life.

The researchers also estimated how long the observation would take for JWST to see each of the different chemical signatures and confirmed that this was possible within a reasonable amount of time. What is the biggest takeaway from these new models? “Confirming an exoEarth would likely be easier than confirming an exoVenus,” the authors conclude. Source