I am by no means an astronomy expert, having only taken 2 semesters in college. But I am an avid follower of news reports that look for signs of life on other planets. Today it was announced that 20 new planets "with the potential for life" have been found. Along with the usual signs (temperature and water) these planets were also cited because one of them has a year of 395 Earth days, a very similar year to our own.

However, I'm always bothered by these reports because they are all predicated on the premise that life on other planets will closely resemble our own. What if life on other planets doesn't need water? What if they are not carbon-based life forms? What if they can live in extremely hot (or extremely cold) temperatures?

It just seems like a massive mistake to (effectively) say, "this planet doesn't look anything like ours, there must be no life there" or to imply that only Earth qualities (or similar) can support life. Are there any fields of astronomy that look beyond the "near-Earth" life comparisons and look for life in other (drastically different) forms?

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    $\begingroup$ Well, we don't have any examples of life as we don't know it, so kinda hard to know what to look for. $\endgroup$
    – zeta-band
    Oct 31, 2017 at 19:16
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    $\begingroup$ 1.) What zeta-band said. 2.) Habitable zones are not a scientific concept 3.) We barely know of water in atmospheres of gas giants outside of the solar system. We know essentially nothing of atmospheres of rocky exoplanets. So don't take those reports seriously. Science reporters want to sell. $\endgroup$ Oct 31, 2017 at 19:30
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    $\begingroup$ Tangentially related question here. I see this claim all the time, that scientists must be missing something because they assume life is like our own. But they do so for good reasons! No offense, but you haven't stumbled on some great revelation hundreds of scientists haven't. $\endgroup$
    – zephyr
    Oct 31, 2017 at 19:43
  • $\begingroup$ You'll also find that no scientist actually says, "no life exists here because its not like Earth" (as you seem to be implying). At most they'll say "life (as we know it) is more likely to exist here because it looks like Earth". $\endgroup$
    – zephyr
    Oct 31, 2017 at 19:49
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    $\begingroup$ Well, what do you suggest? Nobody is assuming that life elsewhere will be similar to life as we know it; they are looking for life that might be like ours, since nobody has a clue how to look for life that isn't like ours. Your last paragraph contains a quote - please attribute it. I have not heard any scientist say such a thing. $\endgroup$
    – ProfRob
    Oct 31, 2017 at 21:40

2 Answers 2


What if we are looking for the wrong signs of life on other planets?

Are there any fields of astronomy that look beyond the "near-Earth" life comparisons and look for life in other (drastically different) forms?


I'm always bothered by these reports because they are all predicated on the premise that life on other planets will closely resemble our own.

Short answer:

It doesn't matter what people think. What matters is what we can observe. Just because they will probably look for life on Earthlike planets first, doesn't mean they won't look elsewhere. The answer will depend on what they find, not what anyone expects to find.

Long answer:

I think there are a lot of good comments below your question, but I want to try to address a few points.

On looking for life.

The scientists that look into space through our biggest telescopes aren't exactly "looking" for life on other planets because life is too hard to see. Mostly, they look at stars. Our best telescopes today can't see exoplanets at all. Exoplanets are detected indirectly by variations in the stars they orbit. If exoplanets are too far away most of the time to even be seen, looking for signs of life on them is obviously out of reach. We're not actively looking for life because we can't. We need much bigger telescopes for that.

So, basically "20 Earthlike planets discovered" is the upper limit of our technology right now. That's today's cutting edge discovery. I understand that it might be boring. I know that they're just adding more planets to the directory, but that's the limit that our best equipment can deliver right now.

Almost nothing is known about all those planets, just the very basics, like how close they are to their star, and about how large they are and sometimes, about how dense they are giving us a limited idea of their composition and if they are hot, cold or perhaps in the Goldilocks zone. If there's only 5 lines of data per exoplanet, the tag-line "Earth-like" often makes the best headline, not because NASA is focused on only Earthlike planets, but because there's not a lot of detail.

It's kind of like "I see a bird, but it's far away and I don't have my binoculars. It's flying south", but I can't see what kind of bird, I can make out the size, to some extent, I can see that there's just one, but I can't make out the shape. So, I write in my bird journal "One largeish bird flying south - too far away to see what kind".

That's basically where we stand with exoplanet observation right now.

This will change some when the James Webb Space Telescope is operating. The JWST should be able to see star-light filtered through some exoplanet atmospheres, which will tell us a whole lot more than we currently know about some of those exoplanets. Information such as how thick an atmosphere and what it's made of will tell us a lot, and give us some information on the climate of the planet. JWST will be a HUGE (all caps for emphasis) step forward in the search for alien life, though it still won't observe life directly, but it will hopefully get a good read on some exoplanet's atmospheres, and from that, deductions can be made, such as abundant oxygen isn't expected without some form of photosynthesis. Oxygen is too reactive to be likely to exist on it's own.

A combination of CH4 and O2 could be especially interesting and one of the first things to look for, but they also have to be careful. There's always the chance of more than one explanation for a planet's atmosphere. We shouldn't expect any kind of guarantee of discovery, but JWST should be an enormous step forward in what we can observe about exoplanets.

On reporting

Scientists in this field, their job is essentially to analyze and report the data. Their job is not, for the most part, to speculate on life but to simply report what can be verified (and today, relatively little other than "I found a planet" can be verified).

Theoretical biology is great. Don't get me wrong. It's fun and it's real science, but the majority of telescope observation focuses on observe, analyze and report. That might sound dry, but that's mostly how science works. "20 Earthlike planets found" was impossible 10-15 years ago. It really is cutting edge.

On Theoretical Alien Life:

Scientists, today (Neil deGrass Tyson among them) who would love to get a closer look at some of the Moons of Jupiter and Saturn, because they are thought to hold the best chance of having life beyond Earth in our solar-system. The desire to find alien life, if it's out there, is one of the highest held goals of NASA and Scientists in this field. Nobody's ignoring or dismissing anything. They will likely point JWST towards Earthlike planets first, but that's only natural.

I'd like to also point a basic rule of astronomical observation. "Weird" is actually good. Weird leads to discoveries like dark matter and dark energy. Like the Isaac Asimov "That's funny" quote, finding things they don't expect is often the best find. Scientists love that. If weird atmospheres are found by JWST, it won't matter if they are on Earthlike planets or not. Anything weird or unexpected will be of great interest and closely looked at.

Like those theoretical Alien Mega-structure or Dyson sphere stars (which probably aren't Dyson spheres). I'm highly skeptical that it's aliens, but I'm glad they're looking into it. Anything unexpected is worth studying.

When JWST starts to get better data on atmospheres, then you'll see more interesting headlines than "Earthlike". For now, and for the next year or so, "More Earthlike planets found", is as far as our technology can take us.

Finally, I want to point out that on theoretical biology, there are issues. (The other answer covers this better than I did so I'll abbreviate), but there are reasons to suspect that life might need to be carbon and liquid water based, so planets thought to have liquid water should be the first places to look.

And ultimately, it doesn't matter what people think is out there. What matters is what JWST (and telescopes that follow) will discover. What we know about the Universe is based on what has been observed, not on the various prejudices and assumptions people made. Sometimes what is observed goes against the scientific belief of the day, and that's what's great about science. Evidence trumps belief.

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    $\begingroup$ I also want to mention TESS here. It should be going up next year with JWST to follow in the spring of 2019. Hopefully, TESS will find a half dozen, or better, nearby earth-like planets that are close enough for follow up atmospheric analysis. People forget that telescope time on JWST and other big telescopes is extremely valuable. In other words, JWST needs a good reason to look in a particular place with a relatively large amount of exposure time devoted to this one observation. When the data comes in, scientists will be looking for "out of equilibrium" atmospheres, not just earth-like. $\endgroup$ Nov 6, 2017 at 20:58
  1. We only have a sample of 1 - the Earth - for analysis or proposition of potential life-compatible conditions on other planets.
  2. Only carbon-based life can exist in this universe. Boron and Silicon are the next 2 elements for potential life, and neither have the ability to provide polymeric bonds required for complex biochemical assembly.
  3. Water is essential internally in chemical reaction, cellular construction and metabolism, vital elemental fluidity and other critical cellular operations. No life formation of longer-term survivability is possible without a water source.
  4. There are organisms that can live in environments that are extremely high temp (> 150°C), highly acidic (< pH 1.0), cold temp (<0°C) high pressure (ocean bottom), and other stressful conditions, but there is no evidence that these extremophiles were the first organisms and all evaluations conclude they only survive within their specific environment, not transferrable to other environments.
  5. Carbon-based organisms have fixed limitations on their survivability based on the fossil record and the astrophysics, geology and biology knowledge that exists. These life characteristics place specific limitations and requirements on planets, stars, solar systems and galaxies on many levels and parameters. Elaborate and thorough examination of other potential life compatible extra-stellar bodies is necessary to determine the conditions that may allow life and the nature and specificity of conditions required for life on Earth reveal the levels and type of critical conditions that must be compatible. They are firm and extensive at many levels.
  6. Astrobiology, one of the fastest growing and scientifically lacking areas of science, examines the requirements of exoplanets to support life. The more the requirements are studied, the more the increase of understanding of the high specificity and wide range of life supportive conditions is revealed.
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    $\begingroup$ I don't think the degree of certainty in your answer about water and carbon-based life reflects the knowledge of our time. Only because we don't have other examples of life, we shouldn't rule out exotic form that we simply didn't think of yet. $\endgroup$ Nov 1, 2017 at 15:23
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    $\begingroup$ 4) It is no-where near as simple as this, there is some evidence that Hydrothermal vents may have been the starting place for life (see e.g. New Scientist or Google) - the jury is well and truly out on that question at the moment. $\endgroup$ Nov 2, 2017 at 10:03
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    $\begingroup$ As a chemist I cannot even imagine life if not based on carbon chemistry. Even more if for life we intend forms at least complex as bacteria. $\endgroup$
    – Alchimista
    Nov 2, 2017 at 10:11
  • $\begingroup$ Jonathan - Hydrothermal events are a desperate attempt by naturalists to add credibility and funding to a remote scientific proposition. When you consider the colocation, coincidence concentrations and contamination mitigation requirements for the origin of life, it turns out that only the potential thermal output as a source of energy is the residual attractive factor. Ph, salinity, water surges (when dehydration is considered a critically necessary process) and general flow will put hydrothermal vents to death, eventually. $\endgroup$ Nov 3, 2017 at 4:02
  • $\begingroup$ AtmosphericPrisonEscape - alternate biological bases have been seriously considered such that the characteristics of non-carbon bases are chemically well-known and have been discounted, despite the overly-optimistic hopes of the seekers of extreme lifeforms. $\endgroup$ Nov 3, 2017 at 4:05

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