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from the there-was-no-life-on-Earth-before-there-was-O2? dept.
The presence of large quantities of oxygen ions may be able to distinguish habitable exoplanets with life from barren exoplanets in the habitable zone (resembling Venus or Mars):
Like Earth, Venus and Mars are small rocky planets; they have permanent atmospheres like Earth, and their atmospheres are exposed to the same solar radiation as Earth's. Data from the Pioneer Venus Orbiter and the Viking descent probe on Mars show that they have very similar ionospheres to each other—which don't contain a lot of atomic O+ ions. Know what else Venus and Mars are missing? Photosynthesis.
[Astronomy PhD candidate Paul] Dalba's contention is that photosynthesis on a planet's surface, which generates a surfeit of molecular oxygen, is the only thing that can account for these atomic O+ ions in a planet's ionosphere. The mere existence of life throws a planet's atmosphere out of chemical balance. O+ would be a neat biomarker because there isn't a numerical cutoff required—just the dominance of O+ among the ionic species in the upper atmosphere would indicate "thriving global biological activity" on the planet below.
Dalba claims that Venus and Mars act as negative controls, demonstrating that planets like Earth but lacking life don't have this O+ layer. Some may think that continuous volcanic activity on the surface could also generate enough oxygen, but Dalba doesn't. Chemistry involving water and UV light [open, DOI: 10.1038/srep13977] [DX] can also release oxygen. But the amount of water on Earth is insufficient to account for the requisite oxygen content, so he thinks that the presence of water on other planets wouldn't make enough oxygen there either.
Atomic oxygen ions as ionospheric biomarkers on exoplanets (DOI: 10.1038/s41550-017-0375-y) (DX)
Related: Nitrogen in Ancient Rocks a Sign of Early Life
Oxygen Ions From Earth Escape to the Moon
Researchers Suffocate Hopes of Life Support in Red Dwarf "Habitable Zones"
Seven Earth-Sized Exoplanets, Including Three Potentially Habitable, Identified Around TRAPPIST-1
Cosmic Methyl Chloride Detection Complicates the Search for Life on Exoplanets
Mars Colonists Could Produce Oxygen by Making a Plasma Out of Atmospheric Carbon Dioxide
Analysis of Microfossils Finds that Microbial Life Existed at Least 3.5 Billion Years Ago
To Detect Life on Other Planets, Look for Methane, Carbon Dioxide, and an Absence of Carbon Monoxide
(Score: 1) by tftp on Sunday February 18 2018, @11:06PM (7 children)
I'm still surprised: why are they searching for Earth-like life? This one went further: he declared that photosynthesis must be one and the only reason for existence of oxygen in atmosphere. He rejected the proposed alternatives only because they do not provide sufficient effect on Earth!
I wouldn't be too surprised if we find out that Earth-like conditions are uncommon. There is no obvious reason why all life should be like ours. Even our own life can change into something else once we reach technological singularity. Or even before - we can have whole cities under the soil of Moon and Mars without polluting their atmosphere with oxygen. Of course, astronomers want to do something, but it would be nice if that "something" is useful.
(Score: 1, Informative) by Anonymous Coward on Sunday February 18 2018, @11:26PM
Because it's the only life we know.
Also, we're not, e.g. SETI is searching for any radio-emissions-using life.
(Score: 3, Insightful) by takyon on Sunday February 18 2018, @11:46PM
We're searching for Earth-like life because it's easier to look for something we can recognize. We already know that it can exist in Earth-like conditions (liquid water, source of heat, etc.).
What these astronomers are doing is useful, because assuming the launch and deployment succeeds, the JWST will be up and running in a year or two, providing better data about exoplanet atmospheres than we've ever had. If we find multiple presumed biomarkers in the atmosphere of a potentially habitable exoplanet, then that will be a good sign that we've found an exoplanet that needs to be studied closely.
Oh, and cities under the soil don't matter because the point is to look for obvious surface microbes or vegetation, which you probably won't find on an exoplanet that looks like Mars today. No underground oceans either because you probably need to drill, or at least land there or sample water plumes to confirm life.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 0) by Anonymous Coward on Sunday February 18 2018, @11:54PM (2 children)
Look at the reaction the human has to other humans of different skin colours.
Do you really think that life-unlike-ours will be classified as life?
(Score: 2, Insightful) by tftp on Monday February 19 2018, @12:08AM
(Score: 5, Insightful) by requerdanos on Monday February 19 2018, @01:10AM
There's a relevant passage from Michael Crichton's 1969 novel "The Andromeda Strain [michaelcrichton.com]":
His commentary through his characters' voices has aged pretty well, considering that it's almost 50 years old.
It has flaws and is imperfect, but so too do our definitions of life have flaws and are imperfect.
Here, they are confronted with the difficult question of whether virii are life, and today we're past virii (without resolution) and now wondering whether prions are life, given that they are just chemicals (until you notice that they know how to operate DNA).
I believe that we will with alien life that misses our definition treat it like we often treat the virus: As a special exception that's definitely life, even though we can't say why, because we know it when we see it. I don't think that while-vs-light brown-vs-dark brown skin will be an issue in that area.
Of course, after the alien life is declared to be "life" or even "sentient life" should the case arise, that doesn't mean that killing them to steal their possessions and sell them to make a fortune, for example, or enslaving them to do man's bidding, will necessarily be automatically illegal nor even automatically condemned. Sigh.
(Score: 5, Insightful) by Arik on Monday February 19 2018, @01:13AM
And, conversely, there's also no obvious a priori reason why our circumstances should be exceptional either.
So it seems like a fine assumption to start from. It points out potentially useful lines of inquiry, and if those turn out to prove it wrong, well, that's how science works.
If laughter is the best medicine, who are the best doctors?
(Score: 2, Insightful) by Anonymous Coward on Monday February 19 2018, @04:19PM
Because it's the only form of life we know. We cannot search for forms of life we don't know since we don't know what to search for. Earth-like life is the only form of life we have a realistic chance to detect.
It's like asking why do you look for a certain information in English-language texts, not in Chinese-language texts (assuming you speak English, but not Chinese)? The answer is not that you'd know in advance that the information cannot be found in Chinese language texts; it may very well be there, and it is entirely possible that it only is found in Chinese-language texts. But searching in Chinese-language texts would be pointless for you, because you couldn't identify the information in those texts anyway, even if it were right under your nose.