Exoplanets & the Search for Habitable Worlds (Synopsis)

“Hundreds or thousands of years from now, when people look back at our generation, they will remember us for being the first people who found the Earth-like worlds.” -Sara Seager

Just a scant 25 years ago, we had never yet found and confirmed another planet orbiting a star other than our own. Fast forward to the present, and we've not only got thousands, we've found a significant number of rocky planets at the right distance from stars even longer-lived than our Sun for liquid water to suggest that there are literally billions of potentially habitable worlds in our own galaxy.

Image credit: NASA / NSF / Lynette Cook. Via http://www.nasa.gov/topics/universe/features/gliese_581_feature.html. Image credit: NASA / NSF / Lynette Cook. Via http://www.nasa.gov/topics/universe/features/gliese_581_feature.html.

But how do we take that next great leap? How do we go from "potentially habitable" to worlds that are actually inhabited? How do we find them?

The secret lies in directly observing these worlds -- and their atmospheres -- something that NASA's proposed Starshade mission is capable of doing with present technology. And the PI of Starshade, Sara Seager, is speaking this Tuesday at 4:10 PM ET / 1:10 PM PT at Perimeter Institute's conference, Convergence, with an exclusive live-stream and live-blog over at the main Starts With A Bang on Medium!

Image credit: NASA / JPL-Caltech. Image credit: NASA / JPL-Caltech.

Come check it out, and don't miss the live-blog of this amazing talk as it happens.


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What would be the advantage of using such a large diaphragm to block the disc of a distant star compared to that of the likes of SOHO with an occulting disc at focus which is more than capable of hiding SOL without circular diffraction issues? Since any stars being investigated are going to be of such a small angular diameter, is it practical to use a similar method to observe those potential planets?

@ PJ

from what I can gather on wiki, there are several factors. Typical coronagraph (such as on SOHO), as designed to block the main body of the sun in order to view the corona. One thing that happens inevitably, is that you get difraction from the edges of the "shield". Even tough you block the majority of the light source, you still get considerable glare from outside.
Another thing is that the separation between host star and planet is very small, so (as far as I understand) even if you use classical "dark spot" in the focus area, the difraction will interfere with faint light coming from the planet orbiting the star.

Starshade (according to wiki) is designed to work with any space based telescope i.e. hubble or james webb if it flies :) Those telescopes already have regular coronographs in them.. you would manouver starshade in front of the telescope (petals are there instead of just circle to minimize difraction) and point it to where you want to look. So starshade would literaly provide the shade from any incoming light (if I understand correctly, you would point your telescope between the petals thus minimizing difraction) and you would be able to image the exoplanet with much less light pollution.

That's at least my understanding of it :)

here's the whitepaper for starshade.. gives nice technical background


By Sinisa Lazarek (not verified) on 22 Jun 2015 #permalink

Cliff notes version, PJ: Diffraction depends on the size of the obstruction: the narrower the obstruction, the wider the haze.

Thanks, S.L.
that paper cleared up a few points. I do understand the diffraction issues involved. I have several objectives and mirrors under my belt over the past 55years or so. The petals are shaped thus to delineate any circular edge diffraction; being that particular style also decreases any linear diffraction similar to the spikes observed in stellar photos due to the spider in the optical chain . Obviously, the use of existing telescopes precludes the manufacture of specialized 'scopes with diffraction limited optics.
With a target (the shade) some 80,000 km away from the telescope, that makes for a very interesting (and accurate) steering arrangement. Since the intent is to observe several tens of stars, the telescope would be the only moving part of the setup, from what I can determine.
I wonder if this will get off the ground, so to speak, in the next five years. The current technology, according to the noted PDF, is for a period of 10 years; ie. 2010 to 2020. It will be interesting to find out what may be planned after this period.

I would wish Sara Seager and the team all the success in their endeavour. A bold plan to gain more knowlwdge is the only way to go.

@ WOW, #3
Agreed, yet a 50 metre shade at 80,000 km is going to subtend an incredibly small angle for the shadow over that distance. :)

PJ, it doesn't matter the size of the object extended at the objective, it's the size compared to the wavelength.

(Well, not in this discussion does it matter the angular size. It does have an effect, but not to why they chose this size of shade)

The Starshade is a neat idea, but how do you hold the relative position between the Starshade and the space telescope at large distances such as 80,000km? They are both in different orbits around the Sun, and some kind of, eg ion, propulsion is need to counteract the Sun's gentle tidal force, otherwise they would drift out of alignment. How long before it runs out of fuel?

By Llewelyn Evans (not verified) on 24 Jun 2015 #permalink

@Llewelyn Evans #7

The design specs have yet to be locked in, but the requirements Northrup Grumman is basing their design on specifies 36 months of usable life. With transit times to get the star shade into the proper position for each viewing, the total operational lifetime of the starshade is enough to view 53 pre-specified stars. The design of the starshade would allow to change the predetermined list if something interesting comes up, but essentially we'd get slightly better views of 53 systems for a cost of $1 Billion (before inevitable cost overruns).

What do you expect with private contractors? They get paid extra if they take longer to do it, and their executives can then claim a damn good bonus into the bargain.

It's not like it's that they'll be blamed: just blame gubmint.

Originally I was a big fan of the Exo-S Starshade concept, but that is a horrible ROI and a billion dollars is a lot of money. You could fund a lot of optics and imaging research for $1B and that would net you a lot more than 53 slightly clearer pictures.

To put the expenditure in perspective, the Kepler space telescope which is responsible the overwhelming number of confirmed exoplanets was designed, constructed, launched, and operated for a little more than half that amount. The Starshade isn't even a telescope and won't detect anything on its own.

I am a huge fan of all things space related and exoplanets are a particular favorite, but I really hope the Starshade dies and stays dead. It has already been killed and revived about 3 times.

@ Denier

To put your perspective in perspective:
- The cost of a NASA project is generally spread over years or decades.
- The US military has it's own separate space program with a much larger budget than NASA, with practically no return whatsoever serving the academic/intellectual interests of astronomy.
- The US military, as a whole, spends AT LEAST a billion dollars every 12 hours.

If NASA had the military's budget, we might benefit from a few projects with little immediate ROI. Pure knowledge, whether immediately applicable or not, is a uniquely worthwhile return.

When is humankind ever gonna realize that the status quo of perpetual conflict our species maintains is a shameful mess of waste and stupidity.

In any decent future we will look back at these times as incredibly foolish.

By MandoZink (not verified) on 24 Jun 2015 #permalink

"You could fund a lot of optics and imaging research for $1B and that would net you a lot more than 53 slightly clearer pictures."

Yeah, you'd find fuck all about exoplanets, though.

@Wow #12

Not true. Existing optics systems were already able to directly image exoplanets that orbited their stars at greater than 30 astronomical units. An example of a directly imaged exoplanet in that range is Fomalhaut b imaged by Hubble as far back as 2004. Technology marches on and the Gemini Planet Finder, which already has first light but is still being dialed in, has cut that down to a 5 astronomical unit separation between exoplanet and host star.


There is no reason to believe they won't continue to come up with better sensors, better adaptive optics, and better image processing algorithms. When they do, they drive up to the telescope and upgrade it.

If I had a billion dollars to spend and had to decide between launching the Exo-S Starshade or funding the development of GPI 2.0 and GPI 3.0 and probably even GPI 4.0 and 5.0 ($1B would buy a lot of optics research), there is no question where I'd put my money. But PhD astronomy geeks don't have near the lobbying power of Northrup Grumman so we'll probably end up with the Exo-S Starshade. Those 53 images better be A.....MAZE.....ZING.

"Not true. Existing optics systems were already able to directly image exoplanets that orbited their stars at greater than 30 astronomical units"


Pluto is further than 30AU from our own sun. Yet we weren't able to directly image it with ground based equipment until very recently (with crap imagery).

It doesn't matter how far away the planet is. The size matters.

"An example of a directly imaged exoplanet in that range is Fomalhaut b imaged by Hubble "

You mean the Hubble SPACE TELESCOPE? Oooh, bugger.

That cost a lot. More than a billion,right? So not "image manipulation software" is it.

And why do you think the planet had to be 30AU from the star?

Go on, why?

Is it because there's a bloody bright hot burny thing too close to the planet so it swamps the image entirely?

Now what would happen if you found a method to block out the star's light?

Could you do it in software? Just set all the pixels where the star is to zero?


So what sort of image manipulation would you do?

@Wow #14

Improvements in image analysis algorithms was exactly how Fomalhaut b was imaged. The snapshots were taken by Hubble in 2004 and 2006, but the image of the planet wasn't published until 2012. Back in 2006, the best they could do was see the distribution in the ring debris around Fomalhaut that indicated a large planet. It wasn't until half a decade later that improvements to image analysis showed Fomalhaut b.

Anther problem with the Exo-S Starshade is that you can't 'dif' the images because the spacecraft can't hang around for years and doesn't have enough fuel to get back.

As far as the unrealized improvements to optics and image analysis that I think have the most potential are in Doppler Spectroscopy. In a nutshell, bodies moving away from us or toward us ever so slightly redshift or blueshift the light we see. Being that exoplanets are usually moving toward us or away from us at a different rate then their host star, you can use the redshift variance to tease planets out of star glare.

"Improvements in image analysis algorithms was exactly how Fomalhaut b was imaged. "

Gosh Do you feel like telling me how the sky is blue, the water is quite wet and bears do indeed shit in the forests of the world?

Listen, when you have a point, I'll accept it, but I read your post and it contained nothing other than wishful thinking and baseless assertion.

Oh, a few semiscience claims that don't hold up to the conversation (IOW a "LOOK! SQUIRREL!!!!") too. And a willing ignorance of what your claims are saying.

@Wow #16: "Listen, when you have a point, I’ll accept it." I find that extremely difficult to believe. Once you've descended to your usual obscenities and juvenile name-calling, you neither listen to nor accept anything anyone has to say. You've demonstrated this far too many times, with readers who do _not_ deserve the trolling you heap upon them, for your statement to be credible in any way.

"but I read your post and it contained nothing other than wishful thinking and baseless assertion." Unlike yours? Every one of Denier's points in this particular discussion is quite defensible. If you don't have the expertise to understand how improvements to both hardware and software can dramatically affect observations, then you aren't competent to reject his/her statements out of hand. All you're doing is demonstrating the same close-minded willful ignorance which our dear friend See Noknowledge shows.

By MIchael Kelsey (not verified) on 27 Jun 2015 #permalink

"@Wow #16: “Listen, when you have a point, I’ll accept it.” I find that extremely difficult to believe."

'sokay, Mike. You don't have to. You can even find it so and not feel the need to inform me of it beforehand!

"Every one of Denier’s points in this particular discussion is quite defensible"

No, it wasn't.

But if you feel they are, go ahead: wow me, as it is termed.

Or do you wish to claim it but not go and provide evidence this is a conclusion based on your own logical process?

Oh, by the way, the only difference between my "juvenile name-calling" and that post is that you made slurs without appending a name to me to give them.

IOW no fucking difference.

"If you don’t have the expertise to understand how improvements to both hardware and software can dramatically affect observations"

If you can find out how you come to a conclusion I don't understand, please supply it. Or keep with the character assassination.

If you can find out how Deniers' post indicates what improvements can be done to the HST by "doppler spectroscopy" to improve images and create a direct image of a planet, feel free.

NOTE: I did have to check to see whether he meant Doppler Beam Sharpening (as I knew it at the time) had been changed to some other name, but no, it's still DBS:


Which could improve the ability of a platform to create a better image than the aperture would otherwise allow (maybe into the near IR, but probably not, even today).

If you can demonstrate how spending on image enhancements could create direct images of planets from ground telescopes (which would be the only way NOT to spend a billion getting new planetary images), feel free to show me where they exist in Deniers' points.

I think the problem is you have a raging hatred of the way I do things.

And I couldn't give a shitted fig for your rage.

Live with it, or leave. It's supposed to be painless. I suspect it may be incorrect on that score, however.

Aye, I know what it is and what it does.

Question: what does it have to do with observing habitable planets? Or spending a billion on it to mean we don't have to spend a billion on this project?

Something nobody yet has explained.

It was not directed at you in particular, rather, at the sandbaggers who do not often comment without bearing torches.
As far as observing goes, the technology is still useful to help locate potential targets for further & in-depth studies. I see something similar to starshade being used in the future as a follow-up to drill down into exo's, hopefully to increase the odds in favor of finding ET.

OK, Fair enough, PJ. I have several lurkers popping out because they want me banned. So I presumed the worst. Which isn't very nice of me.

You're correct that we need to know where to look out of billions of possibilities (exaggerated for literary purposes). It doesn't stop the need for something like this project to do the actual investigation.

It's not like we can only let NASA do one thing at a time.

If anyone else out there can make a stab at making deniers points that they think are valid and shouldn't be "crassly dismissed", they know how to submit.

Actually, we'd want no ET for at least one place. Somewhere to bugger off to. If there's already an ET, we'd not be able morally allowed to land there.

So a planet without a large moon would be better. It can be terraformed quicker than evolution would make large living organisms, so wouldn't be taking up a niche for other life. And we'd be able to weather major upheaval (such as dramatic polar shifts), whilst natural evolution would have to restart. So we'd not be taking up a space that would be occupied by a future race.

Agreed. With testing of atmosphere and other useful elements for our form of life, at such a distance, there is no chance of interference if another life form is occupying that planet. (Starts to sound a little star trekky) ;)