The Case for the Carl Sagan Space Telescope

Some astronomers are building a case to launch a space telescope in honor of Carl Sagan

Published on 16th Nov, 2019

Hello Space Fans and welcome to another edition of Space Fan News. In this episode, some astronomers, a former astronaut, the current director of the Space Telescope Science Institute as well as the wife of Carl Sagan himself, got together and wrote a white paper that makes the case for a telescope, named after the famous astronomer Carl Sagan, that will look for and directly image planets like Earth around other stars. If you are a professional astronomer or care about the future of research in space astronomy, as most of us Space Fans are, then the next year or so promises to be rather exciting. Anyone who’s followed this channel for any length of time knows about a very important thing that happens every ten years in professional astronomy: the Astronomy Decadal Survey; a once-in-a-decade astronomy nerd-fest where decisions on what the next generation of astronomers will be able to undertake, what questions to ask and of those questions, which one are within our grasp to definitively answer. As part of this survey, which they’ve been doing since 1964, several teams of scientists create elaborate proposals submitted to the National Academy of Sciences for missions they would like to see built that would answer some of the more exciting questions in astronomy and cosmology. These proposals are submitted and reviewed by a NAS panel that will select and prioritize these missions. At the end, a report is written and submitted to the community and government agencies spelling out clearly and precisely what astronomers in the field think are the most important questions facing astronomy and which of the proposed missions are best able to answer them. But the big winner will be the top priority endorsed by the survey and that one usually gets for sure built. NASA for one, pays very close attention to these priorities. Last time it was WFIRST that won and it’s being built now. Before that it was JWST, and way back when, Hubble won the blue ribbon. So you can see that this event is a big deal if you care about the direction and priority of astronomy research. So here we are at the end of 2019 and 2020 looms a couple of months away. Now leading up to this moment, over the past two years, I’ve held hangouts (twice!) with four of the biggest contenders for the top spot in the decadal survey and I’ve put links in the description box if you want to learn more, I’ve also made many shorter videos on some of these as well. The four biggest missions vying for attention is: LUVIOR, HABEx, the Lynx X-Ray Telescope and the Origins Space Telescope. The first two LUVIOR and HABEx are especially interesting because they are concerned with looking for and characterizing habitable Earth-like planets, they want to find out how many planets like Earth are actually out there, not just the one about the size of Earth, but ones that are like Earth. I don’t think anyone would be surprised to learn that the question of life in the universe is among our most important and astronomers are slavering to get an answer to at least some of these questions that we have only begun to get some tantalizing answers for. I mean, we now know there are other planets around other stars in our galaxy and our kids are the first generation to grow up knowing this amazing fact. But we need actual evidence that there are not only other planets, but that some of these planets are just like ours, with surface oceans and atmospheres with carbon dioxide and maybe even plants and animals. These are burning issues that we’d all love more evidence for. Which brings me to the Carl Sagan Observatory, or the Carl Sagan Space Telescope. I was reading a very interesting white paper written by some amazing people in the field: Heidi Hammel from AURA, John Grunsfeld an astronaut who repaired Hubble for the last time, Ken Sembach Director of the Space Telescope Science Institute and even Ann Druyan the wife of Carl Sagan, and many others. They were making the case that in order to find other planets like ours, we need the capability to directly image exoplanets around other stars. This telescope would be specially suited to its task. The Sagan Observatory would be a 12-meter class space telescope, that’s 40 feet for us Americans. Here’s what it looks like compared to Hubble and JWST. As you can see, it’s a whopper, way bigger than JWST. The white paper went on to explain what else this telescope would need: it would need to provide reflected light spectroscopy of dozens of planets around nearby stars. This is measuring, not the light from the star, but the reflected light of the star from the planet! As you can imagine, this is a tall order but the spectra from this light will tell us whether there is water there, in what form, whether there are any biosignatures that would signal plant life and what the compounds in the atmosphere of the planet would be. A 12-meter telescope will be large to enough to enable direct imaging of planets in solar systems like our own. It would need some mechanism to block out the light from the star, like a coronagraph or a starshade to get higher contrast observations. Using such a system, Hammel et al, estimates that for the likely fraction of earth-like planets in a habitable zone, say n sub earth to be between 0.05 and 0.2, the Sagan Observatory would have the capability to characterize dozens of earth-like planets. Here’s a simulated image of what the 12 meter optical component of the Sagan Observatory would see around a nearby G star. If this were our solar system the Sagan could see Venus, Earth, Mars, Jupiter and Saturn. Along with, and this is important, the spectra of the reflected light from the planets themselves. Here is an example of the resolution improvement of a 12-meter class system compared to Hubble. From this image you can see the limitations of a 2.4 meter telescope and why all future scopes are so big. What matters now is providing observations that answer some of the most pressing questions in astronomy, is resolution. So the white paper concludes with this: “We assert that Astro2020” that’s the name of the upcoming decadal survey, “should endorse the idea of accomplishing the longstanding decadal and scientifically-compelling goal of finding the signature of life on another world. We also encourage Astro2020 to recognize that to do so requires high resolution, high sensitivity UV/Optical capability.” They also propose putting it out to the L2 point where everything else is going these days. So as I was reading this, I kept thinking, well just pick LUVIOR, why make the case for a special telescope designed for this? To review for those who didn’t watch my hangouts on this, LUVIOR is a proposed 15 meter telescope, bigger than the Sagan Observatory, and would be designed for use with a coronagraph, a starshade or both but it is pretty flexible. This would have more than enough resolution and would include a high definition imager that could image from the near-UV to the near-IR with enough wavelength range to make the observations required. It also has a multi-object spectrograph and a UV spectro-polarimeter so based on what I know about LUVIOR, it’s a pretty good bet it can make the observations advocated by the authors of the Sagan Observatory white paper. HABex on the other hand is a much smaller telescope, proposed to be between 4 and 8 meters but reading their final proposal it looks like they settled on 4m, and it would require both a coronagraph and a starshade to work. At that diameter, direct imaging of Earth-sized planets would be a challenge but it does have a spectrograph and an imager to make the observations. So maybe these guys are trying to split the difference and make a 12-meter space telescope that can do most things LUVIOR can do but more specialized towards characterizing Earth like planets, I dunno. Either way, I’d love to see this thing get built. I’m not sure what the final cost estimates are for LUVIOR but this paper estimates that the Sagan Observatory would be somewhere in the Great Observatories cost range of 10 billion dollars. I know we’ve been here done that with JWST, so it will no doubt cost more, a lot more. But one thing I thought was interesting was this quote supplied in the paper from Dennis Overbye of the NY Times who was covering a talk at the Hayden Planetarium about the Sagan Observatory:

I used to think $10 billion was a lot of money before TARP, the Troubled Asset Relief Program, the $700 billion bailout that saved the banks in 2008... Compared with this, the science budget is chump change, lunch money at a place like Goldman Sachs. But if you think this is not a bargain, you need look only as far as your pocket...all that NASA money — whether for planetary probes or space station trips — is spent on Earth, on things that we like to say we want more of: high technology, education, a more skilled work force, jobs, pride in American and human innovation, not to mention greater cosmic awareness, a dose of perspective on our situation here among the stars. Even if we never discover even a single microbe anywhere else, the money spent on the search for life out there will make life better for those of us stuck here on Earth .
I wish I had said that. Anyway, what’s next is everybody just submitted their final proposals and the National Academy of Science with a final report with recommendations and priorities listed will be made available in late 2020. Well that’s it for this episode Space Fans, thanks to all Deep Astronomy Patreon Patrons who every month contribute to these videos. Also Christmas is coming up and if you’re thinking of getting a loved one an astronomy gift, you can support Deep Astronomy by clicking on my affiliate link below to OPT Telescopes, any purchase there helps support our work here. Thanks to all of you for watching and as always, Keep Looking Up! Read the white paper here: Watch Future in Space Hangout on LUVIOR: Future in Space HabEx Hangout: Join our Chat on Discord here: Like this content? Please consider becoming a patron: Follow DeepAstronomy on Twitter: @DeepAstronomy Like DeepAstronomy on Facebook: