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Next year there is a plan to send a space telescope to L2 with the main objective being to search for Earth-like planets around Sun-like stars in the habitable
by hajola 2y ago
Next year there is a plan to send a space telescope to L2 with the main objective being to search for Earth-like planets around Sun-like stars in the habitable zone.
Like Kepler and TESS telescopes it will use the transit method to find new exoplanets, but unlike any mission before, it's going to look at the same spot in the sky for over a year. Super excited to see what data it brings back to us.
The telescope is called PLATO ( https://en.wikipedia.org/wiki/PLATO_(spacecraft) https://en.wikipedia.org/wiki/PLATO_(spacecraft) )
I contributed to the project a few years back, very happy to answer any questions.
- fragmede 2y agoWhat was your contribution?
- hajola 2y agoFiguring out the optimal placement of CCDs on Plato's 24(+2) cameras. Due to the way CCDs are fabricated, their properties vary a bit, they are not identical. For example, they can vary how much light they can hold before they become saturated. Given the high cost of fabricating these CCDs, and the fact that for each camera 4 CCDs are used, and all these 4 have to share front-end electronics, it was prudent to optimize their grouping to we maximise the dynamic range we get. More dynamic range means that we can tell more about the planets we find with higher confidence.
- ziddoap 2y ago>CCDs I think this is "Charge-Coupled Device"? "an electronic sensor that converts light to digital signals through charges generated by bouncing photons on a thin silicon wafer" Is that correct? Not familiar with the acronym.
- hajola 2y agoYes that's correct.
- UltraSane 2y agoYes. In telescopes they use high-end CCDs with really big pixels for better light sensitivity and zero dead pixels. This is a picture of the CCD array for the Gaia space observatory that used parallax to measure precise distances and slightly less precise angular velocities of billions of objects http://www.bo.astro.it/~altavilla/FTP/GAIA/IMAGES/The%20complete%20Gaia%20CCD%20array%20(flight%20model).jpg http://www.bo.astro.it/~altavilla/FTP/GAIA/IMAGES/The%20comp...
- fragmede 2y agoThat's awesome! Are the multiple CCDs because you're taking photos in separate colors or something?
- hajola 2y agoGood question. No, these will essentially be black-white "photos". The amount of light is measured. The reason for so many CCDs is so that the field of view would be as large as possible. A larger field of view enables to look at more stars at once. Given that we will be locked into looking at one spot for a whole year, it ups our chances of spotting something cool if we maximise the number of stars we are looking at. However they won't be photos of planets really. It will be countless photos of the same stars over and over again, it's just that sometimes they will be slightly less bright than other times. Directly imaging exoplanets is incredibly difficult, but humans have managed it: https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla...
- byteknight 2y agoDo they move the telescope over the year to account for movement? How is that calculated? Does this change with being closer to planets and their gravitational pull? Asked from a total moron.
- daveguy 2y agoHere is the Wikipedia about Lagrange Points (L2 is one of these): https://en.m.wikipedia.org/wiki/Lagrange_point https://en.m.wikipedia.org/wiki/Lagrange_point The orbital corrections are minimized at L2, because of the relative distance of the moon and other planets vs size. But that is what is accounted for in the corrections. James Webb Telescope is at Sun-Earth L2.
- hajola 2y agoYes, it's something that's referred to as pointing stability. The telescope will have star trackers to precisely know it's relative position - basically you make sure that you see the correct stars from where it is placed on the spacecraft. It will use reaction wheels to make tiny correction's to its position. Imagine you are in a computer chair and trying to spin yourself without feet or hands touching anything, just by twisting your body. Reaction wheels work on the same principle. As Earth completes a year around the Sun, the gravitational pull from other solar system bodies is very minor on PLATO. That said, keeping a spacecraft in L2 is not easy - there is nothing to "orbit".
- UltraSane 2y agoAnd when the reaction wheels get saturated they have to expend propellant to let them spin down. It is a fascinating mechanism.
- jcgrillo 2y agoTo what extent (if any) will this program be impacted if all U.S. federal grant funding is permanently cut? Are there U.S. funded components/researchers involved?
- hajola 2y agoAs far as I know it won't be affected at all, the project is almost fully funded from the European Space Agency. And it will most likely be launched with the European Ariane rocket.
- jcgrillo 2y agoexcellent, thanks.
- bane 2y agoAll the more reason why humanity needs multiple space programs.
- labster 2y agoI’m sure that will come up next year when they privatize NASA.
- DiscourseFan 2y agoYou mean when it gets named as a subdivision of SpaceX?
- yieldcrv 2y agoI love it when the Press Secretary says Doge with a straight face while defending attacks by reporters
- gosub100 2y agoyou mean make it like 10x more efficient and effective? I'm game.
- Rebelgecko 2y agoWhy is it pointing at the same spot for a year ? Is it to get a more exhaustive survey single star or can full of stars? Or does that help it find smaller/further/different planets? And how do they pick where to point at? Is there a way of guessing the likelihood of finding a planet?
- pwatsonwailes 2y agoLight collection. You want to observe one point for a really long time so you get a really good understanding of where the light is coming from, the properties of that light, and its behavioural patterns. A lot of the detection is statistics around signals, so the better (read more thorough and coherent) your data (observations of changes in light), the more confidence you can have in your conclusions around what's causing the changes (planets with different atmospheres, different positions, different sizes and compositions etc...).
- hajola 2y agoGreat questions. > Is it to get a more exhaustive survey single star or can full of stars? PLATO will look at 100k+ stars at once. And for most we will be unlucky to see a transit between PLATO and the star. Geometrically it won't align - imagine the star systems being in different angles from us. To bring an analogue - Take a pack of cards and throw them in the air, and take a quick picture while they are sitll in the air - how many cards will be facing the camera exactly with their edge. For us to spot a transit, the planet has to pass between us and the star. If the orbital plane is not parallel to us, we will miss the transit. So that's one of the reasons why it helps to look at bunch of stars with transit method. We expect that about 1% of the orbital planes will be aligned so that we can get meaningful data. > Or does that help it find smaller/further/different planets? Imagine you are trying to find Earth from another solar system. The longer you look at our Sun the higher the likelihood that Earth will pass between you and the Sun. And once you get lucky, and the Earth transits between you and the Sun, the brightness of the Sun only dips about 0.01%, so that means that in order to find small planets we have to have sensitive instruments and little noise, so that the dip in brightness can be measured. Furthermore, as the planet passes the transit and continues on its orbit, the perceived brightness of the star will increase, due to the planet reflecting some extra light. Measuring that can gives us some rudimentary information about the atmosphere - e.g. if a small planet reflects a lot of light back, maybe it's covered in clouds or snow. > And how do they pick where to point at? There's a whole complicated process to find consensus on where to point. Basically they look at spots that have lots of stars, and they look what type of stars they are. Here the objective is to find planets around Sun-like stars, so they would prioritize fields that have more Sun-like stars. > Is there a way of guessing the likelihood of finding a planet? It seems that some stars are more likely to have planets than others.
- divbzero 2y agoHow far away PLATO will be from the James Webb Space Telescope? How big is the L2 Lagrange point? (i.e., how closely do you need to be for an orbit around L2 to be practical?)
- hajola 2y ago> How big is the L2 Lagrange point? (i.e., how closely do you need to be for an orbit around L2 to be practical?) The L2 point doesn't really have size, and even its location isn't stable. It's a mathematical point, and when we say "orbit around L2" then that is not fully true either. The spacecraft are on what's called "halo orbit" - maybe imagine balancing a steel ball (like from a bearing) on a bottle that's sideways, it's probably easier to roll and balance the ball lenghtways of the bottle, than on rolling it sideways. The best analogy I could come up with. You don't want to be too close to the L2 point, as then the orbit would be very short and less stable, think of it as having a smaller bottle - probably harder to balance the steel ball on a smaller bottle than a big one. > How far away PLATO will be from the James Webb Space Telescope? Probably on the magnitude of hundreds of thousands of kms on average. Interesting question though, hopefully they won't get too close :D
- nick3443 2y agoWhat's the typical time scale for a transit? Also, why use transits instead of the Doppler method? Has this patch of sky been selected based on previous Doppler method star studies? Thanks!
- hajola 2y ago> What's the typical time scale for a transit? Generally measured in hours, or minutes. For example, if we were observing our system with perfect alignment, Earth's transit would be about 12 hours, Jupiter's transit around 29 hours. > Also, why use transits instead of the Doppler method? Quantity. PLATO can observe a sizeable portion of the sky at once, 100k+ of stars. With Doppler method the quantities are smaller + afaik there is a trade-off between number of stars being observed and the velocity we can measure. So to find Earth-like planets around Sun-like stars, we would likely have to go one or a few stars at a time. > Has this patch of sky been selected based on previous Doppler method star studies? I am not actively involved anymore. So I am not sure if they have already picked what part of the sky they PLATO is going to be observing. The previous Doppler method (aka as radial-velocity or rv method) star studies play a role, not only because if there's one planet, there might be more, but also because rv gave information about the star. However, keep in mind that this is to find new exoplanets, less to find out more data about existing ones. Rv will definitely be used along side PLATO, to confirm and gather more information about exoplanets that PLATO finds.
- stouset 2y ago> Earth's transit would be about 12 hours, Jupiter's transit around 29 hours …per year, for Earth; per ~12 years for Jupiter is I think what the GP was asking. This is extremely dependent on the radii of the inner and outer limits of the the habitable zone for any given star, though, as well as the star’s mass.
- nick3443 2y agoBoth are relevant! Thanks!
- 2y ago
- glomgril 2y agoVery cool. Got a silly sci-fi question for you. IIUC, with current technology it would take on the order of tens of thousands of years for a vessel to physically travel to the closest known Earth-like planet (correct me if I'm wrong). So any thoughts on what kinds of hypothetical breakthroughs would be needed to make the trip doable in (say) less than a human lifetime? And related, what do you think about the plausibility of the [Breakthrough Starshot](https://en.wikipedia.org/wiki/Breakthrough_Starshot https://en.wikipedia.org/wiki/Breakthrough_Starshot) initiative? Aware of any alternative approaches?
- BugsJustFindMe 2y agoTime dilation means that the closer you get to the speed of light the less time you experience passing. So even a 12000 year long journey as seen from earth, if moving fast enough, could feel to the travelers like a much shorter amount of time.
- dustingetz 2y agoand in that 10,000 year blink, a civilization progresses from bronze metalworking to digital computers, awaiting our arrival
- galangalalgol 2y agoAnd we don't have to send people, we should do our job as a Von Neumann probe and send frozen rna to distribute across the surface.
- idlewords 2y agoIn space culture this is widely considered a dick move.
- stevenwoo 2y agoYes, but practically with todays technology there is no feasible way of getting to a speed where time dilation matters over that distance, we run out of fuel so we need some external power source like a laser or solar wind that have other issues, iirc one only gets to 2x time dilation at 0.9 c. That’s a lot of acceleration.
- metadat 2y agoL2 as related to space telescopes was a new term to me, and turned out to be utterly fascinating. The Webb orbits the sun and periodically boosts velocity using Earth's gravity: > The James Webb Space Telescope is not in orbit around the Earth, like the Hubble Space Telescope is – it actually orbits the Sun, 1.5 million kilometers (1 million miles) away from the Earth at what is called the second Lagrange point or L2. https://science.nasa.gov/mission/webb/orbit/ https://science.nasa.gov/mission/webb/orbit/
- chuckwfinley 2y agoThe wiki on lagrangian points also has a bunch of useful info on this stuff. Gravity is absolutely incredible https://en.m.wikipedia.org/wiki/Lagrange_point https://en.m.wikipedia.org/wiki/Lagrange_point
- safety1st 2y agoLagrange points are fascinating to me and I feel they are underrepresented in science fiction, compared to how the space age ahead of us may play out. The events of human history on earth have revolved in great part around settling at or controlling strategically advantaged locations, for example any coastline, or a geographic bottleneck for trade and travel (think of Singapore and the Strait of Malacca). A Lagrange point is the simplest space-based analog to this that I know of, if you want to put something in a fixed location relative to other bodies, the Lagrange points are places where you can do it with the highest fuel economy. Then when operating from that position you will have more energy available to do other things, granting you advantage over competitors who are not at the Lagrange point. So whether it's science, research, trade, defense etc. there is a compelling reason to locate things at a Lagrange point, and it seems this is already happening as we have science satellites at L1 and L2 and I believe L3 has been talked about. The Lagrange points are not all created equal in terms of distance to their respective bodies, size, energy required to maintain a position etc. All two body systems have them, so for example the Earth and Moon have a set of Lagrange points that are significant to us. The LPs are what a lot of our space politics and problems may eventually revolve around (quite literally!).
- kosta777 2y agoHi, thanks for answering the questions in this thread, it feels like something out of a sci-fi novel. Do you know of any similar projects that a software engineer could contribute to in their free time? Could be of much smaller scale of course.
- diegof79 2y agoMany thanks! Comments like yours are what I love about HN. How is the spot to analyze during that year of focus determined?
- diegof79 2y agoSorry, I see this was answered in a previous comment: https://news.ycombinator.com/item?id=42855433 https://news.ycombinator.com/item?id=42855433
- floxy 2y agoAnd hopefully some day we'll build a solar-gravitation lens to look at the surface of one of these exoplanets: https://arxiv.org/abs/1802.08421 https://arxiv.org/abs/1802.08421 ...with a very interesting video that someone made on that paper: Someone also made an interesting Youtube video of the concept: https://www.youtube.com/watch?v=NQFqDKRAROI https://www.youtube.com/watch?v=NQFqDKRAROI