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Between meetings today I thought I'd talk about #NASA #JWST and all the exciting #science we can expect from it starting in a few months!
(Yes, I made this travel mug ❤️)
#SciComm #Exoplanets #Astronomy #Astrophysics #Telescope #MastodonNewbie
A quick note: if you ask me what #JWST stands for I'll tell you it's the Just Wonderful Space Telescope
https://www.scientificamerican.com/article/nasa-needs-to-rename-the-james-webb-space-telescope/
Fun Fact #1: #JWST is the LARGEST space telescope ever built! It's so big that the mirrors were folded up to fit in the #ESA #Ariane5 #Rocket 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, #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!
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 #JWST isn't serviceable like #Hubble
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.
This is best demonstrated by this #Lego #JWST 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.
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.
One of the most exciting topics for Earth-sized planets that we *can* study with #JWST 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?
@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!
@m7tlg It's a little harder for #JWST to last so long since we don't currently have the capabilities for a crewed or robotic servicing mission. Part of why #Hubble has survived so long is the upgrades!
The nominal lifetime was required to be at least 5 years, but it was fueled for at least 10 years. Most of that fuel was to get it out to L2, but it turns out the #Ariane5 #Rocket provided such a PERFECT launch that it saved JWST lots of fuel, so now the prediction is it has about 20 years!
@_astronoMay I'd never thought of the servicing side of it before, I suppose if #Hubble wasn't in orbit then it might've been a *bit* of a disaster after the initial 'teething' problem!
20 years for the #JWST is still amazing! Means it might still be operational as my toddler (currently obsessed with dinosaurs, rockets and cars - like me!) is at university!
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