The space telescope James WebbNASA’s jewel when it comes to astronomical instruments is about to take off, if there are no further delays. This new instrument will not only complement the Hubble Rather, it promises to surpass it, both in terms of the quality of its images and the breadth of the discoveries that derive from them. We answer some of the most common questions about this huge and ambitious project, which is scheduled to launch next Christmas Eve, at one in the afternoon, Spanish peninsular time.
What is ‘James Webb’ going to study?
The telescope James Webb It began to be designed more than twenty years ago to answer a question about the origin of the Universe: How the first stars were born. What happened during that early period, some 13 billion years ago, is still the subject of conjecture. The first stars are believed to have formed in colossal clouds of gas, compacted by the effect of their own gravity. They were huge bodies, perhaps hundreds of times larger than our Sun, with an equally great luminosity. Dozens of projects have been prepared to develop with him. At least two hundred hours are reserved for studying the time when ultraviolet radiation from the first stars ionized the great hydrogen clouds and caused the universe to become transparent. Eight hundred more will go to research on the primordial galaxies, born about a billion years after the Big Bang: the mechanisms and speed of star formation, the movement of gas in these primitive structures and how the first generation of black holes arose whose relationship with the original galaxies remains the subject of speculation. It will also study the possible existence of life on extrasolar planets or exoplanets.
Where will it be located?
In a “halo” orbit, around a place where there is nothing: The Lagrange point 2. There where the attractions of the Sun, the Earth and the centrifugal and Coriolis forces generated by their motion are balanced. It is on the line that joins both bodies, a million and a half kilometers in the opposite direction to the Sun, that is, in the cone of shadow that the Earth projects and well beyond the orbit of the Moon.
As the Earth moves around the Sun, the L2 point always accompanies it opposite the night side. So apart from circling around it, the James Webb will describe a heliocentric orbit, following the movement of our planet on its annual path, yes, always a million and a half kilometers further from the Sun.
Thus, the ‘Webb’ will always be in the shadow of the Earth?
No, for two reasons: First, seen from L2, the Earth’s angular diameter is smaller than that of the Sun and therefore never completely hides it as the Moon does in a total eclipse. In addition, the telescope will not be “stuck” right in L2 but will rotate around it in a very wide ellipse (half a million kilometers in radius). For six months it will move above the ecliptic and for the other six, below. The cone of shadow of the Earth will practically not affect you. In fact, the Webb relies on sunlight to generate its own electrical energy using traditional photoelectric cells.
How long will it take to get to the destination?
One month. It may seem like a long time when we remember that a trip to the Moon was completed in just over three days, but the trip to L2 is all “uphill” against Earth’s gravity. The Webb will leave the Moon behind in just 36 hours, yes, but then it will gradually slow down until it reaches the Lagrange point, already moving at a snail’s pace.
What will you do during the trip?
Deploy. The first thing will be to open your panel of photoelectric cells to have enough energy and the communication antenna with the Earth. After two days of flight, the sunshade opening and tensioning sequence will begin, which will take a whole week.
From the tenth day the optical system will begin to expand. First, the tripod that supports the secondary mirror; later, the two lateral “wings” with which the 18 individual mirrors will complete the main reflector with its spectacular 6.5 meters in diameter.
The rest of the month until reaching L2, the telescope and equipment will gradually cool down in search of their working temperature. But that will still take weeks. Only when they are really cool can you begin your calibration and adjustment.
Why do your mirrors look gold?
Because son of gold. Each one is a hexagon of beryllium covered with a very thin layer of that metal, the best reflector (98%) for infrared radiation. It is about not wasting a single photon that reaches the mirror after having traveled through space for almost the life of the Universe. And – as its designers say – it is also more beautiful that way.
The coating forms a uniform sheet only 700 atoms thick. In total, the entire mirror uses just under 50 grams of gold. At the current price, about 3,000 euros. Naturally, the process of applying it to beryllium was vastly more expensive.
Why beryllium mirrors?
It is a very light metal, it can be machined into rigid structures, and it does not expand slightly under temperature changes. Even so, as it will have to work below 200ºC, once in orbit it will suffer appreciable thermal contractions. When manufacturing it, this factor had to be taken into account and deliberately wrongly shaped so that, once cooled, it presents the correct curvature.
When will we see the first images?
Not before five or six months. That’s how long it will take for the telescope to cool down to its rated temperature and then go through the delicate calibration process. Not only in your mirror but also in the four main instruments that will collect and analyze the light. One of them by itself, the near infrared spectrograph, will be able to study a hundred objects at a time thanks to a network of as many microscopic grids, the size of a hair that are individually opened and closed to let only the light from one source or another. This equipment – a marvel of miniaturization – is one of the two contributions of the European Agency to the instrumentation of the James Webb.
Will they be similar to the photos sent by ‘Hubble’?
Yes, although not entirely. Infrared images are slightly different from visible light. Some very bright stars shine poorly at longer wavelengths, and vice versa. In certain cases, cosmic dust is more transparent and allows you to see stars in formation embedded in large gas clouds that are usually opaque in normal light. For example, in infrared the famous photo of the “pillars of Creation” obtained by Hubble, looks very different with its colossal columns of almost priceless dust.
Will they be color images?
Our eyes cannot see infrared. Also, both Hubble and Webb produce only monochrome photos, obtained through different color filters. The spectacular images we are used to are generated on a computer, combining black and white photographs recorded in different bands, then applying a standard color palette known as the “Hubble palette” to them.
Will you be able to see Mars in more detail?
Mars is not among the priorities of the Webb, perhaps because it shines a lot in the infrared. Other more distant planets such as Uranus or Neptune or the great red spot of Jupiter are better candidates, as long as an astronomer asks for it (and justifies it, of course). Observation time is a rare commodity and is in high demand. The list of targets prepared for the first months of operation focuses more on very distant extragalactic objects, or on one of the thousands of recently discovered exoplanets. For example, the rocky worlds of the TRAPPIST-1 system, similar in size to Earth and only 40 light years from us.
What will its shelf life be?
The telescope is designed to operate for a minimum of five years and is fueled to maintain its orbit for ten years. Now, if we are guided by the experience of Hubble, who has been in space for more than 30 years, it is very likely that the Webb exceed its intended life.
How much has it cost?
The James Webb it probably holds the record for being the longest overdue and most over budget project in NASA history. So much so that it has been on the verge of cancellation more than once. Its launch has taken more than 14 years and the bill amounts to just over 10 billion dollars, including the cost of five years of operation. About twenty times what was originally planned.
To these figures we must add 700 million euros from the European Space Agency, which goes to the Ariane 5 launcher and the two instruments that it has contributed to the project; and another 200 million dollars, corresponding to the equipment contributed by Canada. This places the James Web as one of the most expensive science projects in history, in the same order as Hubble or CERN’s hadron collider.
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