Tuesday, March 12, 2019

What is the James Webb Space Telescope?

 What is the James Webb Space Telescope?

The panels of the JWST being assembled
The James Webb Space Telescope, or JWST is a large infrared telescope that will be launched via an Ariane 5 rocket from French Guiana in 2021. The JWST will be the premier observatory of at least the next decade, allowing astronomers worldwide to see the cosmos like never before. The Webb will study every phase of the universe, including the history ranging from the first light after the Big Bang to the formation of solar systems capable of supporting life on planets like earth to the evolution of our own solar system. The Webb is an international collaboration between NASA, the ESA and the CSA, with the main development occurring at the NASA Goddard Space Flight Center. The Space Telescope Science Institute will operate the Webb after its launch. 
For the first time in history, a mission has been named after a human, James Webb. James Webb ran  NASA from 1961 to 1968 and is more closely associated with the Apollo program than he is science development, but his support of space science may have made him the most inspiring government official of the time. His ability to balance trying to get the first humans to the moon and the improvement of aerospace industries and space science in general made him a legendary NASA figure. His vision went beyond the one-shot beat-the-soviets ideal by  striving to create the basis for longstanding success in the aerospace industry. The naming of the Hubble's successor is apt because under Webb, humans had the first into the landscape of outer space and the first view of how science could be used to further human curiosity. 
Now, moving on to the more modern aspects of the JWST. The Webb will be launched by an Ariane 5 rocket,
Ariane 5 rocket on the ESA launchpad
which is part of the ESA's contribution to the mission. It will be launched from Arianespace's launch complex located near Kourou, French Guiana. Unlike the Hubble, the Webb will not orbit the earth. Instead, it will orbit the sun from point L2, which is around 1 million miles away from the earth. L2 is past earth, 1 million miles farther from the sun than the earth. Part of the reasoning for the pos
ition of L2 is the accessibility to communication. Earth will communicate to the Webb via the Deep Space Network, allowing the telescope to downlink data to the earth at least twice a day. The Webb will take 30 days to reach L2 where it will begin its orbit. Here is a timeline of events after the launch:
  • In the first hour: The ariane rocket will provide thrust for about 8 minutes after which the Webb will separate from the launch vehicle 30 minutes after launch.
  • In the first day: Two hours after launch the high gain antenna will deployed. After 10 and a half hours, the Webb will pass the moon's orbit, being nearly a quarter of the way to L2. 12 hours after the launch, small trajectory correction will be made by onboard rocket engines.
  • In the first week: A second trajectory correction will be made 2.5 days after launch. The sequence of major deployments of the craft will be started after that, beginning with the sunshield pallets followed by the secondary and primary mirrors. 
The Webb is sometimes viewed as the Hubble's replacement, but NASA prefers to call it a successor because the goals of the Webb were created by images from the Hubble. Also, the main difference between the Hubble and the Webb is the way they view the galaxies. The Hubble uses mostly visible and ultraviolet capabilities while the Webb will use infrared wavelengths. Webb also has a much bigger mirror than Hubble, allowing it collect more light which allows it to see farther back into time than Hubble. 
The Webb has 4 main science based themes: first light and reionization, assembly of galaxies, birth of stars and protoplanetary systems, and planets and the origins of life. 
Timeline of events since the big bang
1. First light and reionization. The infrared wavelengths will allow the Webb to see back 13.5 billion years to the formation of the first stars and galaxies. Reionization is the process of early clumps of particles(protons and neutrons) combining into ionized atoms of hydrogen and helium. These atoms attracted electrons, turning them into neutral atoms which allowed light to travel freely for the first time, bringing the universe out of the dark ages. The Webb will address several questions about the early structure of the universe, such as: when and how did reionization occur, what caused this reionization, and what are the first galaxies. In order to answer these questions, the Webb will make ultra deep infrared surveys of the universe. Why is first light important? For at least a hundred million years after the big bang, there was no light in the universe. Once reionization occurred, the universe now had the ability to create stars and solar systems. This era in which this process occured is called the Epoch of Reionization. 

Two combining galaxies
2. Assembly of galaxies. First let's talk about why it's important to understand and learn more about early galaxies. Galaxies are a way to view the organization of matter on a large scale. Sure, scientists can view individual cells under microscopes, but the galaxies give us a blown up picture of what is happening under that microscope. To learn more about the universe, scientists can study how matter is organized now and how that is different from how it was organized a billion years ago. One way we know matter was organized differently in the past is how galaxies have changed. The spiral shaped galaxies we have come to know and love are not formed this way. They have come to be like this due to collisions with other similar sized galaxies after which they merge into one spiral. But if you look at the oldest galaxies, they do not appear this way. Instead, they tend to be small and clumpy with clusters of new stars forming. Why are they like this? This is a question the Webb hopes to answer. Other questions the Webb could answer are How did the first galaxies form, Where did the different varieties come from, How are chemical elements distributed throughout galaxies and How do central black holes influence their host galaxies? To answer these questions, the Webb will observe galaxies far back in time so we will be able to compare today's galaxies to the past and observe the differences. The process of galaxy formation still occurs today, with new galaxies being created and other galaxies colliding and forming bigger galaxies. 

Rings of heat around a star signifying planetary development
3. Birth of Stars and Protoplanetary Systems. The infrared capabilities of the Webb will allow us to see more stars than we ever have before. The Hubble Telescope is optimized for visible-light detection rather than infrared imaging, which is the main difference from the Webb. The capabilities of the Webb will allow us to study stars as they are forming, and it will be able to image disks of heat around the stars which could indicate the formation of planetary systems. It will also be able to study organic molecules that important for life to develop. The questions the Webb will be gathering data to answer are How do clouds of gas and dust collapse to form stars, Why do most stars form in groups and How do planetary systems form. To answer these questions, we need to be able to see into the dense cloud cores where star formation begins, which Hubble couldn't do. This increased mirror size and infrared wavelengths will give us a view into how our own planetary system formed as well as how early galaxies and star formations came to be.

4. Planets and Origins of Life. One of the main uses of the Webb will be to study exoplanets that we have found. Their atmospheres are of interest to us because if one of these planets has a similar atmosphere to us it could house life. But since the infrared wavelengths of the Webb are not made directly for studying planets, we will have to use other methods, such as the transit method. The transit method means looking for a dimming of the light from a star, which could signify a planet passing between the telescope and the star. Collaboration with ground-based telescopes can help us measure the mass of the planets via the radial velocity technique. This technique involves measuring the stellar wobble produced by the gravitational tug of a planet to find the mass of the planet. The Webb will then do spectroscopy on the atmosphere of that planet. The Webb will also carry coronagraphs to allow direct imaging of exoplanets near bright stars, which are needed because of the light pollution that the star would cause. The questions that the Webb will try to answer include How are the building blocks of planets assembled, How do planets reach their ultimate orbits, How do large planets effect smaller ones, How did life develop on earth and many more planetary questions. The JWST will try to answer some of these by observing life first on our own planet and then looking beyond to the rest of our solar system and exoplanets to try to deduce which planets could have life. 

Now let's get into the instruments that will be used to give us all the data to answer all those detailed, heavy scientific questions. The instruments of the JWST are housed in the ISIM, or Integrated Science Instrument Module, which is one of the three major elements that make up the JWST Observatory flight system. The ISIM is considered the main payload and carries many important objects, such as the NIRCam, NIRSpec, MIRI, and FGS. I'll go more into depth later on these, but for right now let's stick to the ISIM. The ISIM is divided into 3 regions. Region 1 is the cryogenic instrument module which cools the heat detectors of the craft down to 39 Kelvin. This region is necessary so that the spacecraft's own heat doesn't interfere with the infrared light detected from whatever is being imaged. Region 2 is the electrics compartment which provides the mounting surfaces and ambient thermally controlled environment for instrument control electronics. Region 3 is the command and data handling subsystem. It also contains flight software as well as the cryocooler of the MIRI and its control electronics. 
The NIRCam being assembled
NIRSpec design
Let's get back to the fancy abbreviations from above. The NIRCam, or Near Infrared Camera, is Webb's primary camera that covers the wavelength of infrared waves from 0.6 to 5 microns. The NIRCam will detect light from the earliest stars and galaxies, the stars in nearby galaxies as well as stars in the Milky Way and Kuiper Belt objects. NIRCam is also equipped with the previously mentioned coronagraphs, allowing it to take pictures of objects close to a bright central object, like a stellar system. Next up is the NIRSpec, or the Near Infrared Spectrograph, which is a device used to disperse light from an object into a spectrum. The NIRSpec also operates over a wavelength range of 0.6 to 5 microns. Analyzing the spectrum of an object tells us about its physical properties like temperature, mass and chemical composition, and gives us the unique chemical fingerprint of the object. The fingerprint can reveal a wealth of information about physical conditions in the object. Some of the objects that the Webb will study are so dim that the mirror will have to be focused on the for hundreds of hours to gain enough light to form a spectrum, but once this spectrum is built, it has the ability to give us a never-before-seen look at our own planets as well as exoplanets that could have life. However, to increase efficiency, the NIRSpec is programmed to study 100 objects at once, making this spectrograph the first in space with this new technology. Next up is the MIRI which is both a camera and a spectrograph that sees light in the mid range of the electromagnetic spectrum, 5 to 28 microns. The main function of the MIRI will be to provide wide-field, broadband imaging. The last instrument is the FGS, or Fine Guidance Sensor, which will allow the Webb to point precisely so that it can obtain these images that we've been talking about. This instrument will also be used to investigate first light detection, exoplanet detection and characterization, and exoplanet transit spectroscopy. The FGS has a range of 0.8 to 5 microns. 

The James Webb Space Telescope is an extremely exciting amalgamation of new technologies that will facilitate the research of astronomers and scientists worldwide. It will pay homage to its predecessor, the Hubble Space Telescope. This telescope represents the most cutting edge technology couple with the imagination and determination of the human spirit. Exciting stuff.

Thank you for reading this post!



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