An Alien View of Earth - How Alien Astronomers Would Know the Earth is Habitable - pt. 2 (Nitrogen)

Imagine for a moment that you are an alien astronomer. You grew up studying astronomy on the fourth planet of a Sun-like star known to us Earthlings as 72 Herculis, 47 light-years away. Your sun (72 Herculis) and your home planet is roughly the same age as the Solar System and Earth.

Your civilization has recently taken a keen interest in discovering other planetary systems and learning more about them after one of your predecessors discovered a gas giant orbiting a nearby neighboring star known to us as Psi Serpentis.

In the years that followed other smaller worlds were found, worlds similar to your own but only the most basic information was known about them: Size, Mass, Orbit and not much else.

Nevertheless these planets tantalized the imagination of your colleagues and the public. Could there be others out there like your civilization, with great observatories and curiosity about the galaxy?

It was determined by your global scientific congress that the search for other worlds like yours would be of the utmost importance and so great space telescopes were placed into orbit around your planet and star.

One was large enough to capture images of planets in nearby star systems out to around 60 light years. The 12 meter space telescope with coronagraph blocked out the light of a dim star in your planet's southern sky and it produced a very interesting image of a planetary system which you were the first to see:



Image: This image is a simulation of what our alien astronomer would see while taking a 40 hour exposure of our inner solar system with the space telescope described above from a planet around 45 light years away. Venus, Earth and Jupiter would be clearly visible. Mars would be too small as would Mercury (which would also be too close to the Sun and thus blocked out due to what is known as the inner working angle.)

Or to put it another way, the image above shows the expected data that our own High Definition Space Telescope (HDST), a 2030s era successor to Hubble, would produce in a 40-hour exposure of a star system 45 light years away in three filters (blue, green, and red).

Three planets in this simulated twin solar system – like Venus, Earth, and Jupiter – are readily detected. The Earth’s blue color is clearly detected. The color of Venus is distorted slightly because the planet is not seen in the reddest image. The image is based on a state-of-the-art design for a high-performance coronagraph (that blocks out starlight) that is compatible for use with a segmented aperture space telescope. Image from- L. Pueyo, M. N’Diaye (STScI).

Continuing with my bit of sci-fi….

In the decade which followed new resources were appropriated to study this and other intriguing systems discovered previously. You have been tasked with the job as principal investigator on a very large array of 15 meter optical/near infrared telescopes flown with precision and linked by laser communications.

This array is capable of imaging details such as landmasses, oceans, large lakes, and clouds even in some circumstances, large moons. Important since you know that the largest of your planets two moons does a great deal to stabilize it from "flipping over".

When turned towards one of the blue planets of that dim yellow star it produced this series images:



A planet similar to your own but with only one large moon.

Earlier, light from the planet revealed hints that it like yours could be alive so with new even more detailed images you and other astronomers immediately began studying the light from the planet in detail and learned that it contained a number of molecules not only friendly to the chemistry of life but also an indicator that life exists on that world:



The following sounds like science fiction but everything you read is known to our own astronomers to be possible. While there is no known planetary system much less civilization on a planet around 72 Herculis there is one on Earth with the capability in the near term to do the above.

The series of images of the Earth and moon were taken during a NASA mission called EPOXI, which repurposed the Deep Impact spacecraft after its primary mission.

It was found by researchers at the University of Washington that the Earth's nitrogen atmosphere could be detected and this was talked about in a recent paper.

FInding nitrogen would be very important in that it can help astronomers to determine whether a distant world's surface pressure is suitable for the existence of liquid water.

Also if we find nitrogen and oxygen in an atmosphere and can measure both with accuracy then we can use the nitrogen detection to rule out other non-biological causes for the oxygen.

Nitrogen is very hard to detect so finding it requires measuring how two nitrogen molecules collide with each other. The paper states this collision pairs create a biosignature we can observe and the team from UW used data from the EPOXI mission to confirm there model.

Nitrogen pairs, written as (N2)2, are visible in a spectrum at shorter wavelengths, giving us another way to look for Earthlike worlds. The paper explains how this works:

A comprehensive study of a planetary atmosphere would require determination of its bulk properties, such as atmospheric mass and composition, which are crucial for ascertaining surface conditions. Because (N2)2 is detectable remotely, it can provide an extra tool for terrestrial planet characterization. For example, the level of (N2)2 absorption could be used as a pressure metric if N2 is the bulk gas, and break degeneracies between the abundance of trace gases and the foreign pressure broadening induced by the bulk atmosphere. If limits can be set on surface pressure, then the surface stability of water may be established if information about surface temperature is available.

It is worth noting that for half of Earth’s history, there was little oxygen in our atmosphere even though life existed for a large part of this time. The researchers argue that given Earth’s example, there may be habitable and inhabited planets without Oxygen (O2) we can detect. Furthermore, atmospheres with low abundances of gases like N2 and argon are more likely to accumulate O2 abiotically, giving us a false positive for life.

So we have a tool which can both point out places of interest and weed out false positives at the same time. Quoting the paper:

A water dominated atmosphere lacks a cold trap, allowing water to more easily diffuse into the stratosphere and become photo-dissociated, leaving free O2 to build up over time. Direct detection of N2 through (N2)2 could rule out abiotic O2 via this mechanism and, in tandem with detection of significant O2 or O3, potentially provide a robust biosignature. Moreover, the simultaneous detection of N2, O2, and a surface ocean would establish the presence of a significant thermodynamic chemical disequilibrium and further constrain the false positive potential.

When the EPOXI data is combined with the UW Virtual Planetary Laboratory modeling it demonstrates that nitrogen collisions that are apparent in our own atmosphere should likewise be apparent in exoplanet studies by future space telescopes like the HDST.

Oops. I forgot to mention.. Here was Pt.1 which I wrote last year. That covered Oxygen and Methane -An Alien View of Earth - How Alien Astronomers Would Know the Earth is Habitable

Absolutely wonderful thread! I hope someone gives you the applause you deserve.

One question, and this may be a dumb one so please forgive me If it is, while we know OUR kind of life produces these results, is it possible that other forms of life would not?

What "other forms" might be able to breathe or produce might widen the field of possibility for life, though certainly not for habitability?

Again, outstanding OP!!

AB

a reply to: JadeStar

This array is capable of imaging details such as landmasses, oceans, large lakes, and clouds even in some circumstances, large moons.

From forty five light years? Thats some imager… Oh, its still "sci fi".

Nice read (I did actually read it). Thanks for putting in the work, Jade Star.

a reply to: AboveBoard

I would also like an answer to your question.

originally posted by: AboveBoard
Absolutely wonderful thread! I hope someone gives you the applause you deserve.

One question, and this may be a dumb one so please forgive me If it is, while we know OUR kind of life produces these results, is it possible that other forms of life would not?

Absolutely.

In fact I posted a thread about efforts to look for other types of what in technical jargon is called "thermodynamic chemical disequilibrium", or to everyone else strong evidence for life on other worlds.

Here was that thread: Scientists Sharpen Skills As They Prepare to Search For and Detect Life *NOT* As We Know It!

Which of course is important because we don't know how common our type of life is so its best to both look for life as we know it and for things which may indicate life that is significantly different.

Of course it is easier to look for what we are most familiar with but that by no means says the search for life is only limited to that. No one involved in it wants to miss out on a potential huge discovery which might change the course of human history.

What "other forms" might be able to breathe or produce might widen the field of possibility for life, though certainly not for habitability?

Well here's an example from within our own Solar System. Scientists are looking into how we could detect life on Saturn's moon Titan. Life there would be based completely different from us and we don't typically view Titan as a habitable place for us but that doesn't mean it isn't a habitable place for other types of life.

From National Geographic: Saturn's Moon Would Host Really, Really, Weird Life

Again, outstanding OP!!

AB

Thank you.

originally posted by: intrptr
a reply to: JadeStar

This array is capable of imaging details such as landmasses, oceans, large lakes, and clouds even in some circumstances, large moons.

From forty five light years? Thats some imager… Oh, its still "sci fi".

Nice read (I did actually read it). Thanks for putting in the work, Jade Star.

You're welcome.

The one which could show the pale blue dot of the Earth (High Definition Space Telescope or LUVIOR Surveryor) will most likely be built in the 2030s.

The one which would image continents and oceans is Sci-Fi for now, but certainly possible and in NASA's 30 year long range roadmap (see below).

They call it the "ExoEarth Mapper" and it is possible with current and near future technology. There's nothing which would prevent us from having such images in most of our lifetimes. (unless you're like over 65 or something).

In fact the first studies into such an imager concluded that around the time I was born. It would just take a commitment to spend the money to build it.

And from this 2013 NASA document: Enduring Quests-Daring Visions - NASA Astrophysics in the Next Three Decades (NASA/JPL) - PDF, Full Text

a reply to: JadeStar

Are we alone? Once we remove the bounds, boundless space becomes possible. If their is no barrier out there, then the Universe goes on forever. If it goes on forever, it has always been there and, if infinite and eternal, then life has had infinite time to develop and spread everywhere it is possible for it to exist. There is surely life out there, most everywhere.

Thats just my tele scopinion.

Double thanks for the bit of info about the deep impact repurposed images of earth. How far was the telescope from earth when it took the moon transit pics?

Ever see cities at night? is was done ad hoc from the ISS at night. Wonder what the Hubbles capabilities for terrestrial viewing are?

originally posted by: intrptr
a reply to: JadeStar

Are we alone? Once we remove the bounds, boundless space becomes possible. If their is no barrier out there, then the Universe goes on forever. If it goes on forever, it has always been there and, if infinite and eternal, then life has had infinite time to develop and spread everywhere it is possible for it to exist. There is surely life out there, most everywhere.

Thats just my tele scopinion.

Double thanks for the bit of info about the deep impact repurposed images of earth. How far was the telescope from earth when it took the moon transit pics?

Ever see cities at night? is was done ad hoc from the ISS at night. Wonder what the Hubbles capabilities for terrestrial viewing are?

You will be happy to know there have been a number of studies looking at what it would take to detect the equivalent of our city lights on alien worlds out to 100 light years or so.

Here was a 2011 Space.com article on one of them: Alien City Lights Could Signal E.T. Planets - Space.com

Excerpt:

Astronauts in orbit around the Earth often gaze down on a world lit at night by city lights. Now researchers suggest that scientists could detect alien civilizations from similarly bright lights.

Science fiction has long imagined entire planets covered with cities. Examples include galactic capitols such as Coruscant from the "Star Wars" films and Trantor from sci-fi legend Isaac Asimov's "Foundation" books.

Assuming that aliens need light to see at night much as we do, theoretical astrophysicist Abraham Loeb at Harvard University and astronomer Edwin Turner at Princeton University reasoned that extraterrestrial civilizations would switch on city lights during the hours of darkness on their world.

"Both Ed and I were attending a conference in Abu Dhabi about novel ways to detect life, and we had a tour guide on a trip to the nearby emirate of Dubai who bragged that it was so bright at night that you could see it easily from space — that's what gave us the idea," Loeb told Astrobiology Magazine.

On Earth, artificial illumination comes in two forms — thermal, in the form of incandescent light bulbs, and quantum, in the form of fluorescent lights and LEDs. The spectra or combination of colors from this artificial lighting would likely differ from natural sources of light such as volcanoes, and thus might serve as a lamppost that signals the existence of extraterrestrial technology and intelligent life.

More at the link above.

Worth noting that Abraham Loeb is also one of the researchers behind the Mathematic Model of Panspermia I talked about in a thread here yesterday.

Also worth noting is your scenario is the basis for a sci-fi short story I'm writing called "The Neighborhood". The first part of which I posted as a question in the Aliens & UFOs forum on ATS a couple of years ago
You might like to read it.

Astronomers Detect First 'Clear Signs of Civilization' Beyond Earth - How will you react?

a reply to: JadeStar

How would I react?

I was dumbfounded. So were my friends.

Thanks for your time. I enjoyed your other thread, too.

originally posted by: intrptr
a reply to: JadeStar

How would I react?

I was dumbfounded. So were my friends.

Thanks for your time. I enjoyed your other thread, too.

Thanks for bringing up the fascinating possibility/scenario. It's one of my favorite "first contact" scenarios.

some day i hope that some one or some thing comes to this small little planet of houres but i feel that it wont happen in my life time ... but they mite have already have bean hear and we could be the throw back from their visit ....

a reply to: JadeStar

Another great OP JadeStar.

With advanced interferometry and space borne telescopes I hardly think that alien astronomers would be limited to current terrestrial designs.

It is probable that different types of telescopes could attain to planetary scales if the interest was there.

The potential is there to produce better than "Google Earth" resolution images from 60 light years away with technology not far in advance of our own!

Never noticed your threads before JadeStar, but I will make sure to from now on.

You have an ability to write a story while describing something, that added great value to the read

I can tell that your imagination must be vivid with details when you write !!

S&F !!

a reply to: JadeStar

Thanks for that - I will check out both of those links. (And I'm glad I wasn't alone in my question, after all!)

- AB

Wow. So the proposed HDST, if built in the 2030s as planned, will actually be able to visually resolve exoplanets to a degree any average person can view an image captured with it and see a dot!? If so, that's the single most exciting thing I've ever heard, and I move that we accelerate funding for it immediately! That's huge both scientifically and in terms of firing the human imagination.

It seems the biggest hurdle and dissuading threats from what I'm reading are merely 1) cost, and 2) the current inability to repair it once in orbit. But I have a sneaking suspicion the latter won't be an issue within coming years. (I hope.)

Peace.

originally posted by: chr0naut
a reply to: JadeStar

Another great OP JadeStar.

With advanced interferometry and space borne telescopes I hardly think that alien astronomers would be limited to current terrestrial designs.

Correct and star for you.

I only used the alien example to make the research "pop" and so people could see it from a non Earth-centric perspective.

The reason I picked 72 Herculis as home for our alien astronomer is because the star is very similar to our sun and about the same age so their planet would be roughly the same age as Earth and the assumption is that evolution took roughly the same amount of time to come up with astronomers so their technology is roughly at our level in my story.

We should be able to get images like this one of of any Earthlike planets around nearby stars before 2050 (if money/resources are invested into the telescopes to do so):




BTW: Most stars are a lot older than our Sun so it would be quite likely that if there are curious aliens they'd have much better interferometers and other technology to observe the Earth from afar as you stated. That's why I gave you the star.

So in short I used a bit of sci fi about an alien species roughly at our technological level to illustrate what we will be able to do in the near future. If we actually were to have contact with aliens it's far more likely they'd be a lot more technologically advanced than us because most star systems are billions of years older than our solar system. 72 Herculis is the exception not the rule.

That said, it's thought that habitable planets may be abundant with one team of researchers model which would seem to indicate that each star system produces on average two habitable planets.

Of course habitable planet in this case can mean anything from the frigid "Class hp" planets like recent Mars to the boiling "Class T" or "Class hT" planets like Venus. But it also encompasses the lovely and intriguing Class M planets like our own Earth.



They are sure to be out there, it's just a matter of learning that's what they are. We've got plenty of candidates though:

It is probable that different types of telescopes could attain to planetary scales if the interest was there.

Exactly. Or even larger than planetary scale. There is an excellent article about this type of "hyper-telescope" which could see details on a planet's surface down to the size of a small car (a Honda Accord in his example).

That article is entitled: Forget Space Travel, Build this Telescope!

Could we construct such a telescope ... ever?

Here's what it takes: Let's assume that all the alien worlds you wish to view up close and personal are no more than 100 light-years away. That might sound pretty cramped to astronomy nerds, but there are probably several hundred thousand planets within that distance - enough to gratify even the most spirited voyeur.

At 100 light-years, something the size of a Honda Accord -- which I propose as a standard imaging test object -- subtends an angle of a half-trillionth of a second of arc. In case that number doesn't speak to you, it's roughly the apparent size of a cell nucleus on Pluto, as viewed from Earth.

You will not be stunned to hear that resolving something that minuscule requires a telescope with a honking size. At ordinary optical wavelengths, "honking" works out to a mirror 100 million miles across. You could nicely fit a reflector that large between the orbits of Mercury and Mars. Big, yes, but it would permit you to examine exoplanets in incredible detail.

So while that large a telescope daunting for us right now It might not be for us in 500 or 1,000 years. And certainly would be childs play for us in a million years.

And of course smaller, planetary sized interferometers already exist at radio wavelengths. An optical one in space would not be able to see Honda Accords but it would be able to see large lakes, mountain ranges, perhaps even "urban" mega regions on the night side.

The potential is there to produce better than "Google Earth" resolution images from 60 light years away with technology not far in advance of our own!

It is. That's one thing I was hoping to illustrate with this and other threads. We stand at the door step of a great age of discovery. Not necessarily by daring astronauts flying sleek sci fi style starships but by daring astronomers, biologists, physicists and others pushing the boundaries of what we can learn about any potential neighbors without even physically leaving the solar system.

originally posted by: tempestking
some day i hope that some one or some thing comes to this small little planet of houres but i feel that it wont happen in my life time ... but they mite have already have bean hear and we could be the throw back from their visit ....

I used to hope someone would come to our planet but given what I've seen of the ignorance, hatred and fear of just other human beings who are slightly different from each other I'm not so sure that would be a good thing.

On one hand such an event would have the potential to unite humanity but on the other hand humanity's ego is very fragile.

How the average person would deal with something vastly superior in intellect but also vastly different in terms of appearance is an interesting question.

originally posted by: sn0rch
Never noticed your threads before JadeStar, but I will make sure to from now on.

If you do so, maybe just stick to the ones in this and the Aliens & UFOs forum?

You have an ability to write a story while describing something, that added great value to the read

I do want to try my hand at writing sci fi shorts. I have one I am working on which I might debut in the ATS writing forum. I am a huge sci fi fan and I think most scientists you come across are or at the least will tell you that they have been influenced by it. Also some scientists such as Carl Sagan and Ursula Le Guin have written science fiction.

Charlie Jane Anders is my mentor with regards to creative writing in sci fi. I look up to her and love io9.com.

I can tell that your imagination must be vivid with details when you write !!

It always has been.

I think it is important to link current scientific research with science fiction because it helps people understand it better or see its value.

After all, most of the technology we have and things we know about the universe now were once science fiction. Our future starts today. It always has.

S&F !!

thank you.

originally posted by: AboveBoard
a reply to: JadeStar

Thanks for that - I will check out both of those links. (And I'm glad I wasn't alone in my question, after all!)

- AB

It was a great question and one of great interest to a lot of people so you are certainly not alone.