A quick note: if you ask me what #JWST stands for I'll tell you it's the Just Wonderful Space Telescope
Because it launched folded up, #JWST spent the first several weeks verrryyy carefully unfolding itself in space as it traveled to its orbit.
The scariest part was the sunshield tensioning! The sunshield is the pink/grey part and is used to keep the mirrors and instruments nice and cold so we can see the very faint heat from the early universe!
By now you might be wondering: Why is the telescope #gold?
The mirrors are actually made of Beryllium, which is a very strong and lightweight metal, and are coated in a very thin layer of gold. The total amount of gold on #JWST is only about the size of a marble!
Why gold? Gold is VERY efficient at reflecting infrared light! JWST is designed to search for this heat in the early universe
Unlike the #Hubble Space Telescope, #JWST is not orbiting Earth! Because it's designed to look for faint heat in the early universe, it has to be far away so that the Earth's heat doesn't overpower what it's observing!
JWST is orbiting a point in space called L2, a gravitationally stable point nearly a million miles beyond Earth.
In this gif, the sun is at the center, Earth is the large blue dot, and you can see JWST orbiting an empty point in space beyond Earth. This is not to scale!
Did you know that when Hubble launched its primary mirror was made wrong and we had to send a Shuttle mission up to service it and give it glasses? Unfortunately if something goes wrong with #JWST we can't send humans to fix it. #JWST is nearly a million miles away and further than the moon!
Luckily, because JWST needed to be folded up we actually don't have to worry about the mirrors being shaped wrong. Since it's broken into segments, each segment can move on its own to help align the telescope perfectly.
Each segment can move independently so it reflects light perfectly to the secondary mirror and back to the instruments.
So as you may know from my #introduction and bio, I study exoplanets!
These are planets around other stars. One day I'll do a thread about how we find them, but for now I'll talk about how I'll be using #JWST to study their atmospheres!
Recently we just passed over 5,000 discovered exoplanets and the number is growing rapidly! This means we have lots of potential targets for JWST, and it's hard to prioritize our time!
Exoplanets are quite small compared to their stars, so it's really hard to separate their light from the light of their stars. We need BIG telescopes that can capture A LOT of light, and we need their detectors (essentially the camera in their instruments) to be REALLY PRECISE!
One of the ways we'll do that is with a method called "transmission spectroscopy"
For this method, we watch the planet cross between us and its host star, called a transit. The planet blocks out some of the star's light, but some of that star's light also has to travel through the planet's atmosphere before it reaches our telescopes too.
This is convenient for us because the star light will interact with the gases, clouds, etc in the planet's atmosphere, and these things will leave signals in the light we receive from the star!
This cool gif shows what we would see if we could resolve the star and planet system (we actually only see them as a single point of light)
When we split the star light up into it's different color constituents we see that the planet will looks slightly bigger (blocks more starlight) at certain wavelengths of light, so that tells us there must be something in the atmosphere absorbing/blocking light at that specific wavelength.
Now historically we've only been able to use this method to study relatively big planets around small stars. The bigger a planet is relative to its star, the larger percentage of the star light it will block out, making it easier for us to find and measure the planet's contribution to the light we detect.
One of the AMAZING things about #JWST, and why I'm so excited, is that it's big enough that we will be able to study smaller planets! In particular, Earth-sized planets around small stars!
We refer to these measurements in "parts per million", i.e. if we measure one million photons exactly one of them will have been impacted by the planet's atmosphere.
For a hypothetical earth-sized planet around a small star, a biosignature is 10 parts per million
To put into context how hard this is, measuring a biosignature in the atmosphere of this hypothetical #exoplanet is equivalent to finding a SINGLE grain of rice in a 5 lb bag.
All measurements have noise associated with them though - some of it comes from the object itself, and some of it comes from the telescope/instruments/detectors. Unfortunately this means we can't make every measurement we want to because we're limited by how precise our telescopes are. For #JWST, inconveniently we expect that the best precision we will reach is also about 10 parts per million.
This means every measurement will have *at least* a 10 parts per million error bar on it
So if we find a hypothetical earth-sized planet around a small star with 10 part per million signal sizes, we will still have an error of 10 parts per million on that.
Meaning it's still going to be *really hard* to find biosignatures with #JWST at any high level of significance. The best we'll probably be able to say is that *maybe* this planet has signs of it be habitable.
@_astronoMay it was unfolding *before* reaching its orbit? 😮 I thought it had to be locked in orbit before initiating the unfolding sequence.
@ilyess Yes! It started unfolding only hours after launch! Most things were unfolded within a couple weeks. The instruments couldn't turn on until the sunshield was unfolded and things got cold enough!
@_astronoMay I actually had the choice between two PhDs back when I finished my master's in Computational Physics. The one I did not end up doing was in Comparative Planetology, and I sort of regret not doing it because it is the coolest name ever!
It was in geophyiscs, and involved simulating the mantle of exoplanets and compare it to our own.
@_astronoMay Well, it's the PhD I did *not* pick, so I honestly don't know that much. I ended up in Plasma Wakefield physics instead, which is a subfield of High Energy Physics 😊
@_astronoMay I still regret a bit not going in the Astrophysics direction. In one course I took, we wrote code to find large exoplanets by analysing the Doppler shift of the hydrogen line in stars light, and I remember it was a lot of fun.
@_astronoMay Do you think potentially habitable planets will be common or is it more likely to be a rare occurrence?
@_astronoMay My favorite target would be Beta Canum Venaticorum. Sadly, no planetary companion has been discovered yet.
@_astronoMay how do you measure the different wavelengths? Is it multiple exposures through different filters, or is there some magic you do on a single exposure, like an infrared Fourier transform?
@silvermoon82 Some instruments use filters and do multiple exposures, but for exoplanets we use things like prisms to break up all the light so we get all the wavelengths simultaneously!
@noleli the blur on the planet is it's atmosphere looking bigger and smaller due to it absorbing more or less stellar light, the blur on the star is this thing called limb darkening where the edges of a star look darker because of the geometry causing us to see down to different depths in the star
@Timo_Micro Unfortunately probably not, even if multiple stars with planets fell in our field of view we have to observe them at very specific points in their orbit to find their signals, so it would be hard to find a time we could do both. Each star also requires different length exposures so we get enough light, and two stars in the same field of view might require two very different length exposures
@_astronoMay that's a shame considering how sought-after time on the major telescopes must be. I hadn't at all thought about exposure times being different for objects with different luminosity, thanks for pointing that out!
@_astronoMay dang your followers exploded from yesterday, how do I become as cool as an astrophysicist
@shipp I don't know where all these people are coming from but I'm happy to have them here! Excited to share space with everyone!
But if you're serious about asking how to become an astrophysicist I'd be happy to answer questions!
@_astronoMay I'm super interested in reading about it but my brain is not smart enough for that haha. I mostly get my info from pbs spacetime anyways, which is probably beginner level stuff.
@_astronoMay Any idea when we’ll get meaningful data from the JWST? I can’t wait to see what we’ll find in the deep space.
@ilyess Yes!!! Commissioning/testing will end near the end of June and data will start being taken in July! The first data I'll have access to through program I'm involved with gets taken July 10th, but it'll take us at least a few weeks to analyze the data before we can say anything publicly about what we find! Expect some BIG press releases later this summer/early fall from lots of science teams!
@_astronoMay Really impressive, thank you for giving us an inside view. You did a very good job in explaining all those facts and especially the gifs were helpful. I really liked the one with the May scale. ☺️ Love to read more soon, greetings from Germany! ✌🏼
@_astronoMay I was biting my nails while it was unfolding. I went full pessimist, expecting to see news of some catastrophic failure. So incredibly happy that it's out there and working 😁
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