How are "earth like" planets identified?

BrokenArrows

How are "earth like" planets identified?

This question has always confused me and i cant seem to find a clear answer online. There is so much spam in the search results when you search for "earth like planet".

We cannot visually see far enough with optical telescopes to see what the planet looks like.

What information do radio telescopes provide that allows them to identify the makeup of the planet?

The closest answer i can find is that they are making assumptions about "earth like" planets based on the size of the sun, size of the planet and the distance from the planet to the sun.

clintondaly

https://en.wikipedia.org/wiki/Circumstellar_habitable_zone

Some light reading for you

Drumpot

Yeh I do wonder about these things sometimes.

Looking lightyears away through space and god knows what sort of molecules that could distort our interpretation of the universe. I know space is a vacuum so it’s kit exactly the same as looking long distances in earth, but there are all sorts of cosmic rays and unknown things that could be giving us completely innacurate details on which we base our understanding.

I’ve oy a passing interest in this sort of stuff so it’s limited to watching cox or “how the universe works” types of information. But they seldom qualify how they interpret what they understand. Cox does explain it somewhat better but even at that I find myself asking things like “they only recently figured out that life can exist on moons in our solar system but are confident speaking of pictures of galaxies far away”.

I mean for all we know the laws of physics in our universe could be very different in others. Colors of other planets far away could be completely different compounds. We really don’t know for sure so it sounds like they say “this is what we know about earth and it’s parts and we will apply it to the universe”.

It’s scary how little factual information we know about our own solar system. Even if you consider how much of the earth we haven’t explored you get an idea of how much we rely and trust theory.

In future years they will look back at some of our theories of today and it will be like us looking back and mocking the age where man thought the earth was flat. Informed theories are still theories that haven’t been proven.

Muppet Man

What blows my mind is that even though they are so far away, we have actually imaged many of them.

https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets

From that article, here is an image of HR8799 - which is 129 light years away...

"HR 8799 is ... located 129 light years (39 parsecs) away from Earth in the constellation of Pegasus. It has roughly 1.5 times the Sun's mass and 4.9 times its luminosity. It is part of a system that also contains a debris disk and at least four massive planets.[6] Those planets, along with Fomalhaut b, were the first extrasolar planets whose orbital motion was confirmed via direct imaging."



The mind blown information doesnt stop there.... all (?) 3,500 exoplanets so far confirmed have been only in our own Milky Way galaxy.... so the probable numbers of planets for all galaxies in the universe is hard to fathom...

This is worth a look: http://www.milkywaygalaxyatlas.com/

clintondaly

http://scaleofuniverse.com/

This also worth looking at ,its the scale of the universe

Click start and wait a second and use mouse wheel to scroll

El Weirdo

Drumpot wrote: »

I mean for all we know the laws of physics in our universe could be very different in others. Colors of other planets far away could be completely different compounds. We really don’t know for sure so it sounds like they say “this is what we know about earth and it’s parts and we will apply it to the universe”.

No one has ever claimed to have found earth-like planets in another universe.

Drumpot

El Weirdo wrote: »

No one has ever claimed to have found earth-like planets in another universe.

I wasn’t trying to suggest that or piss on scientific interpretations of our universe. I find it all fascinating but many people take what is communicated to them as fact. It’s not that it’s being stated as fact but it’s as good as we know at the moment.

Science always challenges and corrects itself but most likely what little we really know or understand about our own solar system will be proven as invalid in future years.

As a species I don’t understand why such small amounts of resources are invested in learning more about our home world or solar system. It’s just mind boggling .

lordlame

Drumpot wrote: »

I wasn’t trying to suggest that or piss on scientific interpretations of our universe. I find it all fascinating but many people take what is communicated to them as fact. It’s not that it’s being stated as fact but it’s as good as we know at the moment.

Science always challenges and corrects itself but most likely what little we really know or understand about our own solar system will be proven as invalid in future years.

As a species I don’t understand why such small amounts of resources are invested in learning more about our home world or solar system. It’s just mind boggling .

Seeing what Kendal / Kim Kardashian has eaten is sadly more appealing to the masses

BrokenArrows

BrokenArrows wrote: »

How are "earth like" planets identified?

This question has always confused me and i cant seem to find a clear answer online. There is so much spam in the search results when you search for "earth like planet".

We cannot visually see far enough with optical telescopes to see what the planet looks like.

What information do radio telescopes provide that allows them to identify the makeup of the planet?

The closest answer i can find is that they are making assumptions about "earth like" planets based on the size of the sun, size of the planet and the distance from the planet to the sun.

There's two main methods for finding Exo-planets.
One is measuring the very slight wobble of a star caused by the pull of the gravity of it's surrounding planets.
The other method is to watch stars for the slight dip in light output when a planet crosses in front of the star from our perspective.

From these methods we can figure out roughly the mass, size and distance from the star of the planets.

An exoplanet is "earth-like" when it's around the same size or mass as earth and/or it's the right distance from it's star that water can possibly exist as a liquid on it's surface.
(Though the definition of "earth-like" is more dependant on what grabs headlines.)

It's possible in the future that super sensitive equipment could detect the individual light from these planets and from that we would be able to tel if there were things like water or oxygen in it's atmosphere. But I don't think anyone's managed this yet.

ps200306

Just to add a little bit to King Mob's excellent answer:

There are a few ways to analyse an exoplanet atmosphere. All of them depend on spectroscopy, breaking down the light from the planet into its constituent frequencies which can tell us what gases are present. Transmission spectroscopy looks at the light of the parent star through planet's atmosphere as it transits the star. Reflection spectroscopy looks at the reflected light of the planet when it is about to disappear behind the star. Emission spectroscopy is possible for planets that are hot enough to emit their own light, generally at infrared wavelengths.

These techniques are all incredibly difficult, but transmission and emission spectrographs have been obtained for a tiny handful of planets, and next generation telescopes will be able to do more. Even more difficult is using planetary spectra to determine temperature, pressure and density of the atmosphere. Those parameters all affect absorption lines in the spectrum, and may be measurable in future.

Right now, habitability is assessed based on a planet's proximity to the star. We can measure both size and mass of the planet so we know its density, and therefore if it is a rocky planet like Earth. We know the temperature and luminosity of the star, so we know what temperature it would be on the planet if it had a suitable atmosphere. For example, without the greenhouse effect of our atmosphere we would have an average surface temperature of -15°C, and no liquid water on the surface. So we have to make assumptions about exoplanets. Future spectroscopy will tell us about their atmospheres and reduce the guesswork.

The real holy grail is not just determining that a planet has the right temperature, density, and atmosphere for habitability, but to actually detect "bio-markers" -- combinations of atmospheric constituents that would indicate life is present. Any given combination of gases and surface elements will react with each other to reach a chemical equilibrium through inorganic processes. A characteristic of life is to drive the chemistry away from equilibrium. For instance, the oxygen in our atmosphere is a bio-marker. Free oxygen in our atmosphere should combine with things like iron in the crust. But our planet rusted billions of years ago until it could take no more, and the oxygen from plant photosynthesis then built up in the atmosphere. Methane from methanogen bacteria would be another tell-tale sign. These markers are indicative, not conclusive. We see methane plumes on Mars but are still unable to say whether it is from organic processes.

ps200306

Probably also should have mentioned that the habitable zone is about more than just temperature. Even within acceptable ranges of temperature, parent star stability is another factor. Stars much bigger than our Sun have stable lifetimes that are much too short for complex life to evolve, as far as we know. But stars that are much smaller tend to produce violent and dangerous flares. Was reminded of that this week when there was a reanalysis of some data from Proxima Centauri which has a "habitable zone" planet. What had been interpreted as an infrared signature of circumstellar dust a few AU from the star turned out to be a transient flare which probably had a violent X-ray component. It's believed that Proxima produces several flares a day and blasts of ionising X-rays a couple of times a week. This is the problem with these very common M-dwarf types: because they are dim, their temperature-determined HZ is very close to the star, but they are also very active which is bad news for anything nearby. Some people doubt whether a planet like Proxima b could retain an atmosphere against such an assault.

ps200306

Just came across several excellent talks/interviews with Dr. Sara Seager from MIT, one of the leading authorities on analysing exoplanet atmospheres. There's some great info on upcoming techniques, from TESS (a satellite to be launched next month) to fleets of tiny cube sats that will be devoted to watching individual stars. What I like about Dr. Seager, apart from her obvious passion for the subject, is she doesn't BS you that we have or will anytime soon detect little green men. It's a sober assessment of what we can and can't do.

The talks are a general one from TEDx, a short interview at MIT, and a longer and much meatier Google Talk.

Rubecula

tac foley

'Only eleven light years from Earth...' Well, that just dandy - we are almost there already, right?

Well, not exactly. Y'see, the fastest interplanetary device is the New Horizons mission to Pluto and the Kuiper belt.

Launched by NASA in 2006, it shot directly to a solar system escape velocity. This consisted of an Earth-relative launch of 16.26 kilometers a second (that's about 36,000 miles per hour), plus a velocity component from Earth's orbital motion (which is 30 km/s tangential to the orbital path). Altogether this set New Horizons barreling off into the solar system with an impressive heliocentric speed of almost 45 km/s or 100,000 miles per hour.

Sounds impressive, right? And, of course, it is.

Here on earth, that is.

Meanwhile, back in the reality of interstellar space, it's hardly moving at all. The nearest star to us - Proxima Centauri - is a 'mere 4.2 LY away [at the moment], but even travelling at 100,000 mph, it would take us 'just' about 30,000 years to get there. That's six times longer than the entire recorded history of the human race.

That doesn't count the extra time it would take to actually slow down after the eventual arrival, nor the fact that by then, Proxima Centauri might not be quite so 'proxima' as it was when when we started off, way back when.

So unless there is a radical breakthrough in transportation, or the discovery of the 'Here/There we are drive', we appear to be stuck just watching.

tac