- 4182 - EARTH AND VENUS - can we tell the difference? As of this October, 2023, astronomers have discovered 5,506 exoplanets orbiting other stars. If we find a near Earth look alike in the exoplanet discoveries could we tell the difference between and Exo-Earth and and Exo-Venus?
------------- 4182 - EARTH AND VENUS - can we tell the difference?
- That number of
5,506 exo-planet discoveries is growing daily, and astronomers are hoping,
among other things, to find Earth-like worlds. But will we know one when we see
it? How might we be able to tell an Earth-like garden from a Venus-like
pressure cooker from upwards of 40 light years away?
-
- Researchers have
found that there are indeed telltale signatures that should help us parse the
exoVenuses from exoEarths – but there is a catch.
-
- The researchers
placed six Earth-like planets and six Venus-like planets 40 light years away,
each with varying levels of carbon dioxide (CO2), cloud cover, and haze in
their atmospheres. The simulated planets orbited around a star identical to
“TRAPPIST - 1”.
-
- TRAPPIST-1 is one
of the most promising systems discovered so far in which astronomers hope to
find an exoEarth. It features a dim red dwarf star (making observing its planets
an easier task than it would be around a bright yellow star like our Sun). The
system has seven rocky worlds, three or four of which might lie within the
star’s habitable zone. James Webb telescope
has already observed the innermost two planets, and found them to be
barren rocks more akin to Mercury than to Earth or Venus.
-
- The orbits of the
test planets were placed right on the ‘runaway greenhouse boundary’: the
distance from the star where it’s possible for the same planetary catastrophe
that turned Venus into a hellscape to occur.
The authors aimed a simulated JWST at the planets, matching the
capabilities of the real telescope’s NIRCSpec instrument, which observes the
wavelengths of light coming from distant worlds.
-
- Different
compounds in the atmosphere show up as peaks, patterns, and spikes in the
spectra, allowing researchers to see what chemical compounds are present. But, the data isn’t always clear-cut.
Spectral signatures for some molecules hide the signatures of others, or mimic
them, making it difficult to know for sure what we’re looking at.
-
- Venus-like clouds
and hazes may prevent the detection of molecular species, or an atmosphere at
all. But that doesn’t mean impossible,
and the model was intended to help determine what astronomers should be looking
for. Here’s what they found:
-
- First, if you want
to determine whether a planet has an atmosphere at all, regardless of whether
it is Earth-like or Venus-like, the best bet is to look for Carbon Dioxide
(CO2). It has an easily detectable signal, and remains visible for both planets
with clear skies and those with haze and clouds.
-
- But CO2 is less
useful for distinguishing between Earths and Venuses, because the signature of
CO2 overlaps with both water and methane, confusing the data. There is only one
spectral feature that clearly shows up on a Venus-like planet and not on an
Earth-like one: Sulfur Dioxide (SO2). SO2 reacts with water vapor, so if it is
present, it would rule out a wet Earth-like planet and confirm a dry Venus-like
one.
-
- In the real world,
Venus actually doesn’t have much SO2. UV radiation from the Sun has stripped it
away. Around a TRAPPIST-1-like red
dwarf, SO2 would last much longer, making the detection of SO2 possible in that
scenario.
-
- The reduced UV
output from TRAPPIST-1 allows SO2 to have an extended lifetime in the exoVenus
atmosphere, which enhances the possibility of the SO2 being detectable.
-
- As for an
Earth-like planet, the best signature to look for is methane. There are
absorption features of methane that don’t show up on Venus, and can be clearly
distinguished from CO2. Furthermore, if methane is accompanied by oxygen, it
may be evidence of life.
-
- The researchers
also estimated how much observing time would be required for JWST to see each
of the different chemical signatures, and confirmed that it’s doable within a
reasonable time frame.
-
- It will likely be
easier to confirm an exoEarth than it will be to confirm an exoVenus. Like always in astronomy and science, we need
more data.
-
-
October 10, 2023 EARTH
AND VENUS - can
we tell the difference? 4182
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