On Wednesday, December 22, the James Webb Infrared Space Telescope (JWST) will be launched from the European spaceport in Kourou (French Guyana ) , after several years plagued by delays, redesigns and even threats of cancellation of funds.
The most expensive and sensitive space observatory in space history has been built thanks to an international consortium involving NASA , the European Space Agency ( ESA ) and the Canadian Space Agency . It will allow the scientific community to see further into the cosmos than ever before, to observe the birth of the first galaxies in the early universe, witness the formation of stars through clouds of dust, and search for signs of life in the atmosphere of planets. extrasolar, among many other things.
The Spanish of Canarian origin Macarena García Marín , an astrophysicist by training, is in charge of the calibration of MIRI , one of the scientific instruments carried by the James Webb. He serves SINC from Baltimore, where he resides as part of the delegation that ESA has sent to the United States to closely monitor the progress made at the space observatory.
It seems that the launch moment has finally arrived, after so many delays …
Finally, finally, on December 22 … There have been delays, but we are here.
The release had been announced on December 18 but then delayed to December 22. What exactly happened?
The telescope is now in Kourou, in French Guiana, at the European Spaceport. It was placed on a platform upright with a series of clamps, and one of them broke and caused a movement, not very abrupt, that sent a vibration throughout the observatory. The four days were to test all the systems and make sure that everything was nominal, all the telemetry was fine. Luckily everything went very well, so … four days late, but we are ready.
Why an infrared telescope? Are there any astronomical mysteries expected to be solved at this wavelength?
I think that in general we always tend to think of optical telescopes. Telescopes like Hubble, which have given all those images of very old galaxies and such. But the limitation of the optician is that, for example, you cannot see behind the dust.
With Webb, in the infrared we will be able to observe the first galaxies, more or less 13.5 billion years ago. Hubble went as far as 12.5 billion years …
You always see those dust clouds that are illuminated, but behind them are stars in formation, protoplanetary discs where planets are formed … There is a lot of activity that cannot be seen in the optical. One of the first advantages is that with infrared you can see behind the dust because the infrared radiation heats the dust and it sends it away, and then it basically becomes transparent.
On the left, the ‘Pillars of Creation’ in visible light, and on the right, in infrared. Note the number of stars that are seen in the infrared. / NASA / ESA.
Another advantage is that you can observe colder objects, for example planets, and also the very distant ones. With Webb, in the infrared we will be able to observe the first galaxies, more or less 13.5 billion years ago. Hubble went as far as 12.5 billion years … The Webb is going to go much further back, at a time in the universe when the first galaxies and stars were forming, and which we have never seen before. I mean, we’re going to explore, let’s say, unknown territory.
But it is known to be there, right?
Yes, yes … It has to be there. We have observed things ‘before’, like for example microwave background radiation, with missions like COBE … Also things after, but we have never observed, say, that moment in the universe.
The JWST is going to be able to analyze exoplanet atmospheres and look for biosignatures. How is it going to do it?
The most powerful technique to study planetary atmospheres is going to be spectroscopy. Basically you have a star, a planet that revolves around the star, so what you do is observe the transit of the planet, with which you obtain spectral data, that is, the light is scattered like a rainbow and you have the information in detail of all biosignatures or, let’s say, the fingerprints of the planet.
First you measure the star with the planet in front, with which you have a combination, and then the star alone, and thus isolate what the planet is. Planetary transits are usually very long observations because you want to add up everything that is the transit of the planet in front of the star and behind it. They are many hours of very very precise observation. That is one of the most powerful tools.
All the instruments are going to be observing exoplanets. In the case of MIRI, which is the instrument I work for, it will observe exoplanets mainly with so-called slitless spectroscopy, which uses a prism to scatter light.
They call James Webb the “successor to Hubble” but in reality he is different, does he come to replace it, or to complement it?
It comes to complement it. It cannot replace it because, as you say, it is different. Hubble was looking at mostly the visible, a little bit of ultraviolet, and a little bit of infrared, but Webb is all infrared, from 0.5 microns to 28 microns. It is also bigger. It is the most sensitive and powerful space telescope that we have ever launched.
Webb is going to detect much fainter objects, much further back in time, and observe them with much better spatial resolution and better detail. It will complement Hubble, but taking everything much further
Webb is going to detect much fainter objects, much further back in time, and observe them with much better spatial resolution and better detail. It’s going to complement Hubble, but taking everything much further, many steps further, which is what you want when you launch something new, of course.
Let’s say it’s like evolving from a camera on a smartphone . Before you had a camera that took photos of “x” quality …
And now you have the ones that have the three cameras that make you these very cool panoramas, yes.
Hubble has been repaired and updated over the years. The Webb, by its characteristics, is tremendously sensitive. If something goes wrong, can repairs be made at the JWST?
No, and there is a fundamental reason: the Hubble were not only repairs, but also change instruments. They removed an old one and put in another new instrument, of a new generation. The Webb was never developed with the concept of repairing it or changing anything because it will be very far away, 1.5 million kilometers from Earth , so sending astronauts at that distance is something that is not possible at this time.
The JWST assembled, with part of the stem folded. Note the size of the telescope compared to the technician on the crane. / NASA / Chris Gunn
Maybe in the future, years from now, something can be designed with the concept of being interchangeable. There are robotic mission ideas that can go to repair things or swap instruments, but Webb is not going to be the case, I think.
Most infrared telescopes, such as ISO, Herschel or Spitzer, have not lasted more than 4 or 5 years in operation. Is that how long the James Webb will also be active, or something else?
On paper, the mission requirement is that it last five years, but we think it will last at least ten, and hopefully many more years. I think a big difference is that Webb doesn’t depend on active cooling, because one of the things about infrared telescopes is that they need to be cold, since they are very sensitive to temperature.
You want to measure very cold things, so the telescope itself, and the instruments have to be cold. And if the fact of being cold depends on a huge tank that has a cryogenic gas, then when that gas is spent, it heats up.
On paper, the mission requirement is that it last five years, but we think it will last at least ten, and hopefully many more years.
The James Webb has a hood , which is the size of a tennis court, which produces passive cooling , and the near-infrared instruments, which are NIRcam , NIRspec and NIRISS, are cooled by just the hood. In the case of MIRI , as you can see in the mid-infrared, it has to be even colder, so we have a cryogenic system that is a closed circuit, like a refrigerator at home. It has a gas in it, but it does not need to be fed any more. It can be cold for many, many years.
What will limit life is the fuel to stay in orbit. The James Webb will do it around Lagrange point 2, which is a semi-stable orbit. It is a very good place to put a telescope, but it needs to make small corrections, and it has fuel for it. When it wears out, and we are no longer able to correct it, then little by little it will go out of orbit and be lost.
Too bad to talk about the end before the beginning …
[Laughs] It’s actually a mission requirement: vacate orbit when it’s done.
For other telescopes to arrive, right?
Exactly, so you can put more.
Of the four JWST instruments you have said that three operate in the near infrared, and MIRI – which you are working on – in the mid infrared. What is the difference, what does each one contribute?
One is called the NIRISS FGS ( Fine Guidance Sensor ) . The NIRISS part is a scientific instrument that has a camera, slitless spectroscopy and also a very interesting observation mode which is interferometry . It has a mask that blocks several of the mirror segments, so you can make interferometric observations and have a lot of spatial resolution. Regarding FGS, it is the cartographic guidance system that tells us where we are in the sky and has a series of maps to guide us.
Another very important near-infrared instrument is NIRCam , which is a dual camera . It is the workhorse for all the mirror segments to work in phase , that is, instead of seeing 18 points [through the 18 hexagonal mirrors of the telescope] when looking at a star, you want to see only one, and that it is perfect. NIRCam is the primary instrument to do that, and it’s double just in case something happens to one of the cameras, the other works. It also has the advantage that you can use both cameras to do science.
In addition to the cameras, it also has spectroscopy without slit and coronography , which consists of simulating an eclipse: you block the light source, like a star –or also the center of a galaxy–, and thus see the planets around. 
On the ‘hot’ side, the on-board computer, the solar panel and the gyros. On the ‘cold’ side, the scientific instruments. / NASA / STScI
Then there is the third one from the near infrared, which is a European instrument , NIRspec , that does spectroscopy only. One of the coolest devices you have is a Micro Shutter Array, which is an array of a quarter of a million tiny windows that can be opened and closed to view many objects at the same time. You can log 100 or more, which is pretty powerful in that regard.
And then MIRI , it’s the only mid-infrared instrument. It’s like three instruments in one: it has imaging, coronography, and two types of spectroscopy.
Once the JWST is in space, what happens to the teams and people who have been in charge of the design and implementation of the instrumentation? Are you still attached to the mission?
After the launch, yes, because the next six months are very busy. The first month is the trip to the point of Lagrange 2 , and during that journey the entire deployment of the telescope, the parasol, the mirrors is carried out … Several weeks ago NASA took a video on YouTube called “29 days on the edge of the abyss”. You’ve seen?
Yes, with the whole arrival process and how it unfolds …
Of course, all the teams that have been in charge of the design are very involved in this phase. The instruments must be turned on, and make sure that they work well etc. etc. So the first six months everyone is very involved and very invested. After that half a year, the phase of scientific operations begins.
At that point, many people who have been part of the design and implementation team move on to other missions. And then people like me will continue to be involved in all that is data processing, calibration and supporting the scientists who are using the instruments.
What is ESA’s participation in this project, both from the global budget and from a scientific and technological point of view? Is it expected to obtain scientific-technological benefits for Europe from the collaboration?
The global budget has been approximately 10 billion dollars . I do not know exactly what the proportion of each of the agencies is, but what I can tell you is that the ESA contributes with the NIRspec instrument, 50% of MIRI (the optical part, everything that is the filter wheel, the spectrograph …), with the whole launch system (the Ariane 5 rocket , the ground repairs and what we’re doing now, basically) and also with personnel.
Everything that is the first year of observations has already been approved, the programs are already designed and revised
There is a commitment between ESA and NASA to have about 15 people displaced to Baltimore, which is why I am here, to help with everything that is development of pre-launch operations, commissioning , which are those six months after launch , and then with all normal science operations.
Then what we guarantee is that the European scientific community receives at least 15% of the observatory’s time . In fact, in the first batch of proposals, I think the scientific community got more than that, but 15% is guaranteed.
In other words, observation proposals have already been approved …
Yes Yes. Everything that is the first year of observations has already been approved, the programs have already been designed, revised … Although later there may be small changes, of course. You may think that an instrument is going to be able to detect galaxies this faint, or that it is going to be this sensitive, and then you discover that it is even more so. Then these small modifications will be incorporated six months before executing the observations.
Speaking of the future, and although this one has not yet been launched, are there already plans to send a telescope even more powerful than the JWST into space?
The Luvoir . It will operate in the ultraviolet, although also part in the optical, and it will be larger than the Webb. I do not know if the details of its design have been closed, but a little will take advantage of the technologies that have been used in Webb (segmented, sunshade, deployments …). All these missions take many, many years, from when you start discussing them until they become reality.
For example, with Webb, the first discussions were before Hubble was launched, which is 25 or 30 years . With the Luvoir we hope that it is not so much and that all the knowledge developed in the Webb can be used. But yes, it will be bigger, more powerful and quite impressive, really.