NASA just identified an Earth-like planet. What's next?
July 23, 2015 11:05 AM Subscribe
NASA has identified that Kepler-452b is Earthlike. How do we find out more about Kepler-452b and similar planets?
With New Horizons, we've just seen that even for an object in our Solar System we needed to send a probe directly there to get a real idea of it. Kepler-452b is 1400 light years away, so even if we could accelerate to light speed, sending a probe would take 2800 years to get back to us.
As I understand it, we don't even know the mass of Kepler-452b, much less what elements are in it, much much less what it looks like or if life could be present. We only can detect it because as it passes in front of its star it slightly dims the amount of light reach us.
So, using our current technology and using technology we could feasibly implement in the next thirty or so years, what would be the next step to discover more about this planet and similar planets we discover in the years to come?
With New Horizons, we've just seen that even for an object in our Solar System we needed to send a probe directly there to get a real idea of it. Kepler-452b is 1400 light years away, so even if we could accelerate to light speed, sending a probe would take 2800 years to get back to us.
As I understand it, we don't even know the mass of Kepler-452b, much less what elements are in it, much much less what it looks like or if life could be present. We only can detect it because as it passes in front of its star it slightly dims the amount of light reach us.
So, using our current technology and using technology we could feasibly implement in the next thirty or so years, what would be the next step to discover more about this planet and similar planets we discover in the years to come?
One key will be if the scope gathers enough light and has good enough differentiation to do a spectrum of the planet without interference from the star. Then you look for oxygen lines. If you find them, that means there's life.
But that requires a space-based telescope so that Earth's own atmosphere doesn't get in the way.
(There's no known way for a planet to have substantial oxygen in its atmosphere besides life, so oxygen lines in a spectrum is a smoking gun. But if you don't find oxygen that doesn't mean there isn't any life; there might be life of a different sort entirely, or it could be trapped in deep sea beneath permanent planet-wide ice caps.)
posted by Chocolate Pickle at 1:47 PM on July 23, 2015
But that requires a space-based telescope so that Earth's own atmosphere doesn't get in the way.
(There's no known way for a planet to have substantial oxygen in its atmosphere besides life, so oxygen lines in a spectrum is a smoking gun. But if you don't find oxygen that doesn't mean there isn't any life; there might be life of a different sort entirely, or it could be trapped in deep sea beneath permanent planet-wide ice caps.)
posted by Chocolate Pickle at 1:47 PM on July 23, 2015
Astrobiologists will also use spectroscopy to detect atmospheric pollution. Here's an interesting article about it.
posted by hz37 at 2:05 PM on July 23, 2015
posted by hz37 at 2:05 PM on July 23, 2015
my partner here: "it's going to be the 30m telescope that characterises these. giant gaseous planets we can do now. but these small planets with liitle atmosphere like the earth will need the 30m." (she'a a professional astronomer who's also on various panels related to astronomy funding).
what she's saying is that we'll find out the atmospheric contents with spectroscopy (probably using the star it's orbiting around as a background source and looking at absorption lines).
the "30m" is this thing.
oh,more: "in absorption they use differential spectroscopy. then there's another technique i don't understand. it's more model dependent. something changes and you compare it to models of various molecules. oh, yeah, the effective radius of the planet - it changes depending on the line."
with that i went searching and found this paper which describes the technique.
so basically, what she's saying, if i understand right, is that the obvious technique is to compare spectra from the planet's home star (it's "sun") when it's "alone" and when the planet is in front (at which point its atmosphere absorbs certain frequencies, depending on its composition). that's the differential approach. but it's not very good, so instead they're using models of the planet and calculating an "effective radius" which is easier to measure and gives similar information.
apparently they can correct for the earth's atmospheric absorption (although of course that adds noise too).
ps afaik we have diddly-squat chance of imaging things like this. apart from the resolution needed, they're so close to the (bright) star that they can't be separated.
posted by andrewcooke at 4:40 PM on July 23, 2015 [1 favorite]
what she's saying is that we'll find out the atmospheric contents with spectroscopy (probably using the star it's orbiting around as a background source and looking at absorption lines).
the "30m" is this thing.
oh,more: "in absorption they use differential spectroscopy. then there's another technique i don't understand. it's more model dependent. something changes and you compare it to models of various molecules. oh, yeah, the effective radius of the planet - it changes depending on the line."
with that i went searching and found this paper which describes the technique.
so basically, what she's saying, if i understand right, is that the obvious technique is to compare spectra from the planet's home star (it's "sun") when it's "alone" and when the planet is in front (at which point its atmosphere absorbs certain frequencies, depending on its composition). that's the differential approach. but it's not very good, so instead they're using models of the planet and calculating an "effective radius" which is easier to measure and gives similar information.
apparently they can correct for the earth's atmospheric absorption (although of course that adds noise too).
ps afaik we have diddly-squat chance of imaging things like this. apart from the resolution needed, they're so close to the (bright) star that they can't be separated.
posted by andrewcooke at 4:40 PM on July 23, 2015 [1 favorite]
sorry: when she said "30m" she meant that class of telescope. apparently there are three of them. the GMT (giant magellan), TMT (thirty metre - linked above) and the ELT (extremely large).
[also, why not credit her - paulina lira]
posted by andrewcooke at 4:48 PM on July 23, 2015
[also, why not credit her - paulina lira]
posted by andrewcooke at 4:48 PM on July 23, 2015
That's really clever. But it means you can only take that measurement during a window of a few seconds once per year of the target planet, and then only if it's in the scope's night sky at that moment.
So even after an appropriate giant scope gets built, it might be 5 or 10 earth years before it could be checked, or even longer if we're unlucky.
posted by Chocolate Pickle at 6:53 PM on July 23, 2015
So even after an appropriate giant scope gets built, it might be 5 or 10 earth years before it could be checked, or even longer if we're unlucky.
posted by Chocolate Pickle at 6:53 PM on July 23, 2015
Best answer: Hiya, professional astronomer who was on the NASA Kepler science team here at your service :D
The above answers are all pretty good! Here's my additional $0.02:
As pointed out above, the next aim is to get a spectrum of a small (Earth-ish size) exoplanet so that we can characterize the composition of its atmosphere. The goal is to look for so-called "biomarkers" or "biosignatures"-- not just oxygen or pollution, but the particular mix of chemical compounds in the atmosphere that might indicate the presence of life. The biosignatures you look for can depend on the kind of planet, as well as the kind of star it orbits-- in some cases, there can be potential gotchas where in some systems, regular ol' non-life planet processes can mimic some biosignatures. What biosignatures to look for and how to detect them is a big focus of theoretical research right now.
There are a couple of ways to get a planet's spectrum: one is to observe transiting systems (where the planet passes in front of its parent star) and take a spectrum when the planet is transiting. While the rocky/solid part of the planet is opaque, the atmosphere is not-- so the starlight shines through it before reaching your telescope. When it does, the atmosphere of the planet absorbs some energies of light depending on its composition, imprinting a chemical fingerprint of its makeup in the light you receive. Unfortunately this is a difficult measurement to make-- it's only been done for a few planets so far. To make matters worse, sometimes nature conspires against us and the planet's atmosphere is hazy-- so we don't actually get much of a signal from its atmosphere at all and it just looks gray and featureless. Very annoying!
Also mentioned above are the efforts to directly detect planets by blocking out the light from the central star, either using an instrument called a coronograph (basically a little thing that blocks the starlight and is right next to the telescope and camera itself), or a new concept called a starshade, which is a crazy giant gold sunflower-looking thing that flies in formation with the telescope at a great distance (go look up starshade on YouTube, it's pretty sweet). If you can detect the planet's light directly, you can take a direct spectrum of the planet-- which gives you another way of getting at its composition.
A few other ideas are floating out there-- e.g. to look at the polarized (scattered) light from planets, which is linked to the actual make up of the surface (e.g. oceans, vegetation, deserts etc etc) and potentially provides much more detailed information, but that's even harder to do. Someone above mentioned pollution, an additional thing we could find is an actual intentional or non-intentional broadcast signal, either in radio or visible wavelengths (it's a longshot, but hey then you know there's technologically advanced life!).
SO, all of this is to say that in the immediate future, you're going to hear a lot of exoplanet news from two missions: TESS, and JWST. TESS is a similar instrument to Kepler-- it is designed to find exoplanets that transit their parent star by measuring the brightness of stars and looking for those little dips in the light as the planet blocks them briefly. The thing that is different about TESS is that it will be searching around some of the brightest and nearest stars, so it will really be finding our neighboring planetary systems. The practical motivation there is that these systems will be the easiest to observe with JWST (mentioned above), which is capable of getting the spectra of planets using that transit technique I discussed earlier. The reason we can't do that kind of observation for most of the Kepler planets is that they are distant and therefore relatively faint, so it's just too hard to get enough signal. Kepler was always intended to be a statistical mission-- it told us that small, rocky planets are the most common kind of planet out there, but it was never meant to find the ones we could chase down with these other techniques.
The other mission concepts mentioned above by others and myself are currently under study-- it does indeed take time to design and competitively select the best mission for the job, let alone to actually build and launch it! Just part of making sure your tax dollars are going to work in the best possible way :)
Hope this clears some stuff up! Sorry for not embedding links to the stuff I mentioned above, but I'm actually supposed to be doing some astronomy right now-- just couldn't resist chiming in! Also I'll be on Twitter tomorrow afternoon if anyone wants to ask me more about this stuff (my handle is the same as my AskMeFi name) but not until the current Extremely Pressing Astronomy Task gets finished :)
posted by shaka_lulu at 7:15 PM on July 23, 2015 [15 favorites]
The above answers are all pretty good! Here's my additional $0.02:
As pointed out above, the next aim is to get a spectrum of a small (Earth-ish size) exoplanet so that we can characterize the composition of its atmosphere. The goal is to look for so-called "biomarkers" or "biosignatures"-- not just oxygen or pollution, but the particular mix of chemical compounds in the atmosphere that might indicate the presence of life. The biosignatures you look for can depend on the kind of planet, as well as the kind of star it orbits-- in some cases, there can be potential gotchas where in some systems, regular ol' non-life planet processes can mimic some biosignatures. What biosignatures to look for and how to detect them is a big focus of theoretical research right now.
There are a couple of ways to get a planet's spectrum: one is to observe transiting systems (where the planet passes in front of its parent star) and take a spectrum when the planet is transiting. While the rocky/solid part of the planet is opaque, the atmosphere is not-- so the starlight shines through it before reaching your telescope. When it does, the atmosphere of the planet absorbs some energies of light depending on its composition, imprinting a chemical fingerprint of its makeup in the light you receive. Unfortunately this is a difficult measurement to make-- it's only been done for a few planets so far. To make matters worse, sometimes nature conspires against us and the planet's atmosphere is hazy-- so we don't actually get much of a signal from its atmosphere at all and it just looks gray and featureless. Very annoying!
Also mentioned above are the efforts to directly detect planets by blocking out the light from the central star, either using an instrument called a coronograph (basically a little thing that blocks the starlight and is right next to the telescope and camera itself), or a new concept called a starshade, which is a crazy giant gold sunflower-looking thing that flies in formation with the telescope at a great distance (go look up starshade on YouTube, it's pretty sweet). If you can detect the planet's light directly, you can take a direct spectrum of the planet-- which gives you another way of getting at its composition.
A few other ideas are floating out there-- e.g. to look at the polarized (scattered) light from planets, which is linked to the actual make up of the surface (e.g. oceans, vegetation, deserts etc etc) and potentially provides much more detailed information, but that's even harder to do. Someone above mentioned pollution, an additional thing we could find is an actual intentional or non-intentional broadcast signal, either in radio or visible wavelengths (it's a longshot, but hey then you know there's technologically advanced life!).
SO, all of this is to say that in the immediate future, you're going to hear a lot of exoplanet news from two missions: TESS, and JWST. TESS is a similar instrument to Kepler-- it is designed to find exoplanets that transit their parent star by measuring the brightness of stars and looking for those little dips in the light as the planet blocks them briefly. The thing that is different about TESS is that it will be searching around some of the brightest and nearest stars, so it will really be finding our neighboring planetary systems. The practical motivation there is that these systems will be the easiest to observe with JWST (mentioned above), which is capable of getting the spectra of planets using that transit technique I discussed earlier. The reason we can't do that kind of observation for most of the Kepler planets is that they are distant and therefore relatively faint, so it's just too hard to get enough signal. Kepler was always intended to be a statistical mission-- it told us that small, rocky planets are the most common kind of planet out there, but it was never meant to find the ones we could chase down with these other techniques.
The other mission concepts mentioned above by others and myself are currently under study-- it does indeed take time to design and competitively select the best mission for the job, let alone to actually build and launch it! Just part of making sure your tax dollars are going to work in the best possible way :)
Hope this clears some stuff up! Sorry for not embedding links to the stuff I mentioned above, but I'm actually supposed to be doing some astronomy right now-- just couldn't resist chiming in! Also I'll be on Twitter tomorrow afternoon if anyone wants to ask me more about this stuff (my handle is the same as my AskMeFi name) but not until the current Extremely Pressing Astronomy Task gets finished :)
posted by shaka_lulu at 7:15 PM on July 23, 2015 [15 favorites]
Looking at spectral lines can also give you information about the mass of the planet. A star's surface radiates a continuous spectrum (no lines), and the gasses in it's atmosphere absorb specific colors, leaving lines in that rainbow. (A spectrometer is basically a kind of fancy prism that splits a star's light into a rainbow + a microscope so you can measure specific colors/lines in detail.) One of the things you can learn is how fast a star is rotating by its spectal lines being smeared out and fuzzy. This is because half of the star is rotating toward you and half is rotating away from you, which blue- and red-shifts it's spectal lines, respectively, and it's fuzzy/smeared because this happens at a range of speeds across the star (the poles aren't moving towards/away from you, but the equator is).
A similar technique was used to find the first extrasolar planets, by looking for a continuous 'wobble' in these lines over time as the planet pulls the star around in a circle, red-shifting and blue-shifting the lines repeatedly. These movements are VERY tiny (and require lots of computer processing to remove the fact that the earth is moving around the sun at the same time the observations are made, and also other gravitational effects happening locally, mainly the pull of Jupiter. The technology that does this is pretty sweet...it can detect movements of a star as small as around 3 meters per second, or a slow jog O.O). This technique works best on very large planets that are very close to their star (very close=short period of orbit, very large=big movements), so the first extrasolar planets found were these so-called "hot Jupiters", which was itself a very surprising discovery as until then it was thought that gas giants could only form further out (as in our own system) because ices stick together better than rock, forming bigger cores quickly that are big enough to hold onto hydrogen (the most common element in the universe) and swelling up quickly after that.
This technique can give you a range on the mass of the planet because of how much it drags the star around, but not super-specifically as you can only see the motion along line-of-sight and not tell how much the orbit is angled towards us (i.e. if the system is perpendicular (a circle) you won't see any motion in it's spectral lines, and edge on (a line) then you see all the motion.) If it passes in front of it's star (like the Kepler observations) then you know you're looking at it edge on and can nail down the mass of the planet much more precisely.
posted by sexyrobot at 11:03 AM on July 24, 2015
A similar technique was used to find the first extrasolar planets, by looking for a continuous 'wobble' in these lines over time as the planet pulls the star around in a circle, red-shifting and blue-shifting the lines repeatedly. These movements are VERY tiny (and require lots of computer processing to remove the fact that the earth is moving around the sun at the same time the observations are made, and also other gravitational effects happening locally, mainly the pull of Jupiter. The technology that does this is pretty sweet...it can detect movements of a star as small as around 3 meters per second, or a slow jog O.O). This technique works best on very large planets that are very close to their star (very close=short period of orbit, very large=big movements), so the first extrasolar planets found were these so-called "hot Jupiters", which was itself a very surprising discovery as until then it was thought that gas giants could only form further out (as in our own system) because ices stick together better than rock, forming bigger cores quickly that are big enough to hold onto hydrogen (the most common element in the universe) and swelling up quickly after that.
This technique can give you a range on the mass of the planet because of how much it drags the star around, but not super-specifically as you can only see the motion along line-of-sight and not tell how much the orbit is angled towards us (i.e. if the system is perpendicular (a circle) you won't see any motion in it's spectral lines, and edge on (a line) then you see all the motion.) If it passes in front of it's star (like the Kepler observations) then you know you're looking at it edge on and can nail down the mass of the planet much more precisely.
posted by sexyrobot at 11:03 AM on July 24, 2015
So, using our current technology and using technology we could feasibly implement in the next thirty or so years, what would be the next step to discover more about this planet and similar planets we discover in the years to come?
As shaka_lulu describes above, transit spectroscopy and direct imaging are the immediate future of exoplanet atmospheric characterization, and we'll start seeing many more results from these in the next decade as new instruments and facilities ramp up. If you want to push out beyond that timescale, though, a number of astronomers were tasked with putting together a thirty-year roadmap for NASA[PDF] in 2013. It's not a short read (100+ pages) nor limited to exoplanets, but it's the best source if you want to see exoplanet astronomers saying what they'd really like have in the future. (Spoiler: lots of interferometers---they can resolve closely spaced objects not reachable by other techniques.)
posted by Upton O'Good at 1:27 AM on July 27, 2015
As shaka_lulu describes above, transit spectroscopy and direct imaging are the immediate future of exoplanet atmospheric characterization, and we'll start seeing many more results from these in the next decade as new instruments and facilities ramp up. If you want to push out beyond that timescale, though, a number of astronomers were tasked with putting together a thirty-year roadmap for NASA[PDF] in 2013. It's not a short read (100+ pages) nor limited to exoplanets, but it's the best source if you want to see exoplanet astronomers saying what they'd really like have in the future. (Spoiler: lots of interferometers---they can resolve closely spaced objects not reachable by other techniques.)
posted by Upton O'Good at 1:27 AM on July 27, 2015
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In the longer term, well, there are always proposals for more sensitive telescopes, some of which would be useful for characterizing exoplanets. For example, there is a proposal for a space telescope, ATLAST that might be able to measure the contents of an exoplanet's atmosphere (among many other stunning observations). There is also a proposal called the New Worlds Mission which would build an occulter in space that would block out a star's light so that a telescope (like JWST or ATLAST) could more easily observe the fainter objects orbiting that star. If Hubble and JWST are any indication, building them would be subject to many technical and political delays, so they would probably just fit into your thirty-year time frame.
posted by ddbeck at 12:01 PM on July 23, 2015