Do people like threads here? I guess we'll find out!

Between meetings today I thought I'd talk about and all the exciting we can expect from it starting in a few months!

(Yes, I made this travel mug ❤️)

Fun Fact #1: is the LARGEST space telescope ever built! It's so big that the mirrors were folded up to fit in the that launched it last Christmas

(Yes, this diagram of me standing next to the Hubble and JWST mirrors is to scale!)

Because it launched folded up, 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 ?

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 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 Space Telescope, 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!

Now while the benefits of being so far away from Earth allow us to look even further back into the earliest parts of the universe, it also means that isn't serviceable like

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 we can't send humans to fix it. 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.

This is best demonstrated by this model that was submitted to lego ideas and is currently under review!

Each segment can move independently so it reflects light perfectly to the secondary mirror and back to the instruments.

(taking a break for some meetings! I'll be back with more after lunch!)

I'm back with more facts! Let's see... what should we talk about now? I'll switch to the I'll be using for, but let me know if you have any other questions about the telescope itself!


So as you may know from my 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 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!

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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.

Laboratory studies tell us exactly what colors/wavelengths of light things like water absorb, so we can use that information to back out what must be in the planet's atmosphere to explain the absorption we see!

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 , 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 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 , 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 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.

Now, I know a lot of people get really sad when I tell them we probably won't be finding definitive signs of life with - BUT I'm here to tell you that there is still A LOT of REALLY COOL we can learn about Earth-sized exoplanets (and larger ones too!) with

One of the most exciting topics for Earth-sized planets that we *can* study with is answering the question "which planets have atmospheres and why?"

In our Solar System we have Venus, Earth, and Mars and they're all *very* different worlds! Why did Venus undergo runaway greenhouse but Earth didn't? How can we differentiate between and Earth-like and Venus-like exoplanets? And what about exoplanets like Mars that have effectively no atmosphere?

A great system we'll be studying a lot with is called TRAPPIST-1.

It's a system with 7 planets, all of them roughly Earth-sized orbiting a very small star.

3 of them are probably in their star's habitable zone, which is actually *much* closer to the star than it is in our Solar System because of how small and cool the TRAPPIST-1 star is

This is great! This means we have one system that should have all experienced a very similar history that we can study and help us understand why certain planets turn out the way they do.

But there are LOTS of other planets out there as well! I have another set of meetings I have to hop off too, but I'll be back later with more facts!

@_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.

@veronica ooh exoplanet interiors is SUPER cool! I'd love to hear more about it!

@_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 Thanks for the great thread! Mastodon needs more astrophysicists on it 😁

@ansuz yes! There are so many great exoplanet travel posters out of JPL and NASA! I have many of them printed :)

@_astronoMay okay, totally cool. I actually knew most of this already except the error bars and the size of the mirrors. Fantastic information!

@_astronoMay Hi Erin!

Thank you for so many #space #facts in this wonderful thread! I'd love reading more from you!

@_astronoMay which type of star is at the center? I wonder if it's very dense to hold all the other objects within its gravitational well

@astromecanik It's an M-dwarf, actually about the same radius as Jupiter! Not particularly extra dense, things are just able to be in stable orbits much closer to the star because it's smaller.

@_astronoMay is this named after Belgian Trappist ales such as Affligem?

@CORTES2J there is a backronym for TRAPPIST (Transiting Planets and Planetesimals Small Telescope) but I believe it was made up specifically to reference the Belgian beer ☺️

@CORTES2J @_astronoMay As a Belgian, I also immediately thought of this, haha

@jns @CORTES2J @_astronoMay Yup, TRAPPIST is controlled by University of Liège in Belgium, who actually also takes part in SPECULOOS, which is another belgian specialty, as I learned today as I was checking. Because why not? They had to work a bit more to make a backronym of the later though.

@_astronoMay - Is there a tool with which we can determine if an exoplanet has a magnetic field or not?
A method to estimate the age of the star might be useful too.

@fdfolson magnetic fields on exoplanets are hard to detect! I won't pretend to be an expert on searching for them, but hopefully some of the people I know who are working on them will migrate over to mastodon and can share about their work

@_astronoMay Do you think potentially habitable planets will be common or is it more likely to be a rare occurrence?

@David_Kelly_SF That's a hard question and an ongoing topic of research! We call it "eta earth", the average number of earth-like planets in the habitable zone per star.

Unfortunately many of our detection techniques are biased to finding large planets right now, but we're starting to find more and more small planets! Right now though we only know what size a planet is and if it's in the habitable zone, it'll be a while before we know enough about the atmosphere to say if they're habitable!

@David_Kelly_SF Related, I have a public talk about the difference between the terms "habitable zone", "habitable", and "inhabited" and one day I'll talk about that and what they really mean here!

@_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!

@_astronoMay and how the amount of blur (presumably diffusion?) changes! So cool!

@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

@_astronoMay @astromecanik that’s crazy awesome! I’m barely starting to scratch the surface, doing some stellar spectroscopy (100% noob level)

@astromecanik spectroscopy is so fun! but maybe I'm biased because I absolutely love rainbows 🌈

@_astronoMay considering the field of view of #JWST, would it be possible to observe / research multiple #exoplanet atmospheres at once? Or do you get a spectrum of the entire field of view at once?

@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

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